445 Stroker Build Help

[Thumperbird]

Hello everyone, new to forum, building a 445 stroker and need compression/cam specification advice.
Will use SCAT crank, H beam rods, pistons ?, hydraulic roller cam spec.?
So far, in addition to my own homework, I have engaged several of the well known builders in the US, some frequent this site.  I have gotten a fairly wide range of input on compression target and cam specifications, trying to triangulate on the best approach for my application.  At the end of the day I prefer to know what the lobe profile is specifically so that future changes can be a derivative of my starting point.  Below please find the desired outcome and target automobile setup so far, hoping and looking for feedback anyone is willing to share in collaboration on my project, thank you for your time.

Goal:
500+HP, 500 TQ, all in by 5500 rpm, pump premium, edgy but not too crazy rough idle is good, reasonable idle rpm, reasonably smooth cruiser but of course when I stomp on it from a stop or rolling start I want to get a heavy car up and going quickly with great low end throttle response.  If it pulls hard to 80 mph I will be happy, will likely not see the strip.

Car so far:
1965 Thunderbird (4500 pounds)
390 to be bored 0.030” over and stroked to make a 445
Edelbrock aluminum heads, 72cc (will receive at least port match to intake and exhaust)
Will deck the block to maximize quench
Edelbrock RPM Air Gap dual quad intake
BJ/BK carbs (custom 1” rise/run offset spacers to enable mounting (forward) on Edelbrock manifold, adds open plenum volume just above manifold carb flanges)
Another 1” of 4 hole spacer to set hood scoop height correctly (adds some more plenum volume)
½” nitrous plates (wet)
MSD 6AL ignition and distributor
Harland Sharp roller rockers
Morel lifters
Carter fuel pump
Melling oil pump
FPA headers (will be 2.5” true dual exhaust)
100 to 200 HP nitrous capability (not to really influence design other than H rods maybe)
Broader wide ratio C6 (very firm shifting) with 2600 to 3000RPM stall convertor
Quick Performance 3.5 ratio True Trac (with wide ratio trans. 1st gear is 3.8:1, 2nd 3.6)
27” tires
Electric vacuum pump (not too worried about engine vacuum)

What do you guys think for compression target?  Flat top or dished pistons?
Cam specification, lift, duration, lobe profile, LSA, IDL, dual profile?
Specific part # recommendations welcome as well.

Thanks all!

[Drew Pojedinec]

Danny finally get those spacers turned out?  sweeeeeet

I am interested to see you fit that intake and a 1inch spacer under a tbird hood

[chilly460]

I'd stick to around 9.5:1 compression since you're not looking to wring every bit of power out of the combo, and that should keep things more forgiving as far as detonation for a street car.  That would necessitate a dished piston.  HP goals look attainable but would be helped quite a bit by at least some bowl cleanup and valve job on those Edelbrocks. 

[scott foxwell]

Thumperbird...sent you a message.

[cammerfe]

I'd stick to around 9.5:1 compression since you're not looking to wring every bit of power out of the combo, and that should keep things more forgiving as far as detonation for a street car.  That would necessitate a dished piston.  HP goals look attainable but would be helped quite a bit by at least some bowl cleanup and valve job on those Edelbrocks.

I'd agree if the OP were to be using iron heads. The aluminum heads should be forgiving enough to not cause any problems, due to the extra heat conduction of the aluminum. (I'm basing this comment on the gas available in the Detroit Metro area. 93 ROM is available and even 94 is easily enough found. Just takes a little looking.

KS

[chilly460]

Has anyone ever done a good test to prove or debunk the "rule of thumb" that aluminum heads can handle more compression?  I just don't see it, once the chamber is heated, wouldn't it be controlled by transfer to the coolant? How much cooler is the aluminum chamber and how does that transfer to pre-ignition tolerance?  I know this is one of those "universal" truths that gets thrown around, but many of these have been debunked over time.  Not saying it's not true if people have experience with a good apples to apples comparison, but my suspicion is this tolerance for higher compression is a trend towards aluminum heads being somewhat more modern with a better chamber, and generally being on high performance rebuilds with larger cams and attention to quench that makes them less prone to detonate. 

Not what I'd call "definitive" as it's not in a vehicle, but one article that looks at the subject

http://www.hotrod.com/articles/ccrp-0602-iron-versus-aluminum-cylinder-heads-test/

[Thumperbird]

Thanks all. 
Carb. spacers are my own design.
Hood has a hole, scoop sits above, just for fun.
Anyone else have some more specifics on cam #'s and compression?
Leaning towards at least 10:1 for compression, I can find 93 octane.
One of my bigger concerns is extra plenum volume due o spacers, how do I make this behave like regular RPM dual plane at lower rpm's?
Thanks.

[scott foxwell]

Thanks all. 
Carb. spacers are my own design.
Hood has a hole, scoop sits above, just for fun.
Anyone else have some more specifics on cam #'s and compression?
Leaning towards at least 10:1 for compression, I can find 93 octane.
One of my bigger concerns is extra plenum volume due o spacers, how do I make this behave like regular RPM dual plane at lower rpm's?
Thanks.

Plenum volume won't hurt anything and even though you're technically adding volume, it's not in an area that's going to make a lot of difference, especially on a dual plane.

[scott foxwell]

Has anyone ever done a good test to prove or debunk the "rule of thumb" that aluminum heads can handle more compression?  I just don't see it, once the chamber is heated, wouldn't it be controlled by transfer to the coolant? How much cooler is the aluminum chamber and how does that transfer to pre-ignition tolerance?  I know this is one of those "universal" truths that gets thrown around, but many of these have been debunked over time.  Not saying it's not true if people have experience with a good apples to apples comparison, but my suspicion is this tolerance for higher compression is a trend towards aluminum heads being somewhat more modern with a better chamber, and generally being on high performance rebuilds with larger cams and attention to quench that makes them less prone to detonate. 

Not what I'd call "definitive" as it's not in a vehicle, but one article that looks at the subject

http://www.hotrod.com/articles/ccrp-0602-iron-versus-aluminum-cylinder-heads-test/

The biggest advantage aluminum heads usually have is the chamber is a more modern, more efficienet design. Alum does help with reducing hot spots, but that's a pre-ignition thing, not detonation. Two different animals. Apples to apples as far as chamber design and shape, aluminum heads are really not any less prone to detonation because they're aluminum.

[My427stang]

I'll throw in on this build, as it is pretty close to the approach I took with my 445 truck, minus the juice (although the truck has swallowed plenty in my early years)

I'll speak to the gorilla in the room first, 200 hp of nitrous is a lot, I am not sure I'd feed it that much, but if you do, you likely need a dedicated fuel supply, an ability to retard the timing, and keep in mind, you are seriously pushing the limits of a 390 block, it may split or crack.  I have run bottles and bottles of nitrous through stock block 351s and 390s in younger days at the 100-150 hp range, but that much is pretty serious unless you 2 stage it, keep timing early and fuel plentiful, and even with that, I am not confident those cylinders or the mains will hold their shape if you really put that much juice on top of a 500+ hp build. Just sayin, and I used to love the stuff....

For the rest of the build, the plan looks good for a street 445 and should be faster than that bird should go, I'd say in the low-mid 230's for intake duration, more on the exhaust, especially if there will be spray.  On FEs, we have found a little lazier ramp does good, even when magazines say they dont   I think a hyd roller with 290 intake/300+ degrees exhaust duration is reasonable and will tolerate a little more compression, you'd have to look at intake centers, but my guess is you can go pretty early if you stay around 10-10.25:1.  It'll be real strong, REAL strong and a common 110 LSA would have about 75 degrees of overlap should have some nice chop.  If you want to spend more money, spend it on the heads, that's where the power is.....

FYI It's not far from my combo in the truck but I have a little more head, but maybe less intake with a ported RPM and a 1000 Holley. 

What I really do NOT like is the combination of the low first gear and the loose converter, I'd stay under 2800 with a reputable converter company that builds it for YOUR combo, because it's heavy and torquey which will drive a bargain converter higher and this build doesn't need it  PLUS your wide ratio tranny is likely too deep, 3.5 X 3.8 = 13.3, too much, especially with the multiplication of the converter.  I would run a stock gear set unless you are running 30 inch tall tires.

Good luck, certainly sounds like a crazy bird!

[Thumperbird]

Thanks for "throw in", much appreciated, making a spreadsheet to compile input on cam and compression.
I was not very clear on the trans. in my post, C6 first gear standard ratio is 2.45, the wide ratio first gear is 2.75 so I just added the .3 uptick to the 3.5 rear to get to 3.8 effective ratio.  The idea is that it will still go down the highway at a reasonable RPM since 3rd is 1:1 with 3.5 rear end.  Broader new what the build was when he spec'd the tranny, I will ask him for more details.
Will take it easy on the nitrous, it is mostly just for fun, I can set a shot as low as 75 per plate I think.
Since two carbs and two plates, is the nitrous shot HP additive?
New brake components all around and dual master cylinder so should be able to stop it.
Thanks again to all and keep the info. coming please!

[Drew Pojedinec]

Carb. spacers are my own design.
Hood has a hole, scoop sits above, just for fun.

sweet.  I'm dying to see pictures of this when it's all done.  Sounds super cool.  Good luck

[blykins]

13.5:1 compression, 270/280 @ .050", 106 LSA, .800" lift. 

[Drew Pojedinec]

13.5:1 compression, 270/280 @ .050", 106 LSA, .800" lift.

idle like a taxi cab......

[jayb]

LOL

I'd be looking at about 10.5:1 static, and pick a cam to give about 8.35:1 dynamic.  Then get the heads ported, shoot for around 300 cfm at 0.700" lift.  No way you'll get an honest 500 HP out of that engine with unported heads and a flat tappet cam around 230-235@0.050".  Not that it wouldn't run well like that, but you won't make your horsepower goal.  Torque goal you could make that way, though.  Here's a link to the 390 stroker I did for Car Craft several years back; it made 500/500, but the cam was 260@0.050":

http://www.fepower.net/Articles/CCFE.pdf

The two nitrous plates will be additive.  I agree with Ross, I wouldn't go any more than 75HP per plate...

[scott foxwell]

You should be able to make 500hp in your sleep with this combination. That's a whopping 1.1 hp/ci.

[blykins]

I've done some 500 hp 445 Edelbrock combos with hydraulic rollers.   They barely squeak by 500 and have a ton of torque, but they get there. 

[Rory428]

Between the stroker crank and use of nitrous, I would also be concerned about the 390 block staying together. Back in 1988-89, I had a stock stroke 390 in my Fairmont, with a C6 (no transbrake then). It had iron CJ heads, a solid flat tappet cam, and ran 11.4s @ 118 MPH at 3200 lbs. After a while, I added a NOS "Cheater" adjustable nitrous kit, starting at 125 HP jets.Picked the car up pretty good, 10.6s at 128 MPH, but like many with power adders, since it was so easy, I installed the 175 HP jets. That picked up the performance to a best of 10.28 ay 132 MPH, but by August of 1989 the D4 "105" block had had enough, and tore all the main webbing out between the cam and crankshaft bores. 3 of the main caps split thru the center, and the crankshaft broke into 5 chunks, but all the LeMans rods, although badly bent, were still bolted to the crank journals. Nothing quite like sliding around at 130 MPH, with you own oil and coolant under the slicks! That was the end of the "blue bottle" for me!!

[cammerfe]

Has anyone ever done a good test to prove or debunk the "rule of thumb" that aluminum heads can handle more compression?  I just don't see it, once the chamber is heated, wouldn't it be controlled by transfer to the coolant? How much cooler is the aluminum chamber and how does that transfer to pre-ignition tolerance?  I know this is one of those "universal" truths that gets thrown around, but many of these have been debunked over time.  Not saying it's not true if people have experience with a good apples to apples comparison, but my suspicion is this tolerance for higher compression is a trend towards aluminum heads being somewhat more modern with a better chamber, and generally being on high performance rebuilds with larger cams and attention to quench that makes them less prone to detonate. 

Not what I'd call "definitive" as it's not in a vehicle, but one article that looks at the subject

http://www.hotrod.com/articles/ccrp-0602-iron-versus-aluminum-cylinder-heads-test/

Not definitive, but a check on thermal conductivity tables seems to show aluminum (Depending on alloy) as having a TC rating of around 250 and iron (again depending on exact composition) of having about 80.

It stands to reason, to me, that such a difference in ability to conduct heat away from the maelstrom going on in a combustion chamber might well make it more forgiving of other factors. 

KS

[Barry_R]

I look at this stuff as a risk versus reward question.

Its a 4500 (?) pound car with freeway gears.  Personally I would also vote for a compression ratio under the 10:1 value.  Even with all the DCR numbers and camshaft you will at some point in the power band (torque peak), have a high compression engine and will create some serious cylinder pressure.  You will never notice the 25 horsepower you will lose running n/a down the road.  But you will certainly notice the need for spiking the fuel if anything is less than 100% perfect on your tune up.  If you had a 2800 pound Mustang with a 4 speed and 3.91 gears the answer would be different.

I have probably pushed more nitrous through an FE than most folks, and I also had a sizable collection of split blocks and cylinders to show for the effort.  If you keep the nitrous at a modest level it will be OK.  It will also more than make up for the 25HP compression reduction.  And - if you are anything like I was - you may as well start planning for the next build because once you experience the power of the first hit of spray you re going to turn up the wick.

[blykins]

My previous post about the 13:1 compression was tongue-in-cheek of course.  I spent a great amount of time with the OP last week, tossing 9-10 emails back and forth explaining various camshaft terms, specs, lobe designs, compression ratio tactics, etc.   I suppose he didn't really like what I had to say since he is here asking for advice.  I'm happy to see Barry echoing some of the points that I had made in the emails. 

I don't think it would be best to ride the fence of either "SCR" or "DCR" with such a heavy car and a high gear.   The gain in horsepower is going to be negligible but can be a big deal if the tune isn't right.  Craving for every last pony in situations like these is really futile.   I too second the motion for a low compression ratio, somewhere around the 10-10.25 mark would be sufficient based on past experiences.  It wouldn't hurt my feelings if it ended up under 10; again, a 1/4 point isn't going to make the difference between a tow truck engine or a race car engine, and we are only looking at around 2cc difference in part volumes to swing that direction.

A hydraulic roller camshaft is going to be the best route.  With a hydraulic roller in the FE, you have to keep your eyes on a few different things at the same time:  a heavy valvetrain, like what you would have with a 3/8" stem out-of-the-box Edelbrock head, is going to want a less aggressive cam lobe.   A less aggressive lobe is going to have a longer advertised duration, which will help in the compression ratio arena.  Basically a win/win in this situation, especially when we're rolling the cam ahead to help with extra plenum volume.

If the OP is looking for individual part numbers for specs, he will find very quickly that a lot of this stuff is custom, and it takes some "figurin" to determine the numbers.  Lobe numbers will only be able to be determined by guys who work with custom camshafts on a regular basis.  Otherwise, you'll get a lot of the "I'd use the XR282HR"....Not a lot of guys are used to working with individual camshaft specs.

The nitrous oxide is another area that needs addressed heavily I think.  I think a lot of guys think that “it’s only 500 hp” but the internet is so full of bench racing that not a lot of guys know what a true 500 hp engine feels like.  It will move a heavy car along very nicely.  I think the nitrous deal is a good way to split that block in half. 

All fun stuff....

[Thumperbird]

Brent:
Certainly was not implying I did not like what you had to say and I hope others continue to chime in with their thoughts on this for a while longer here, please don't shy away.
As stated in original post, given lots of variation in recommendations, I was opening it up to a wider audience, and too that end, I am getting a little more comfortable with settling in on a design as planned.
As an automation equipment guy, when I don't have full understanding, especially in the case of very dynamic systems, I collect data so I can make the most informed decision possible.  Since physical prototyping and testing is prohibative I have to rely on published artiles and others experience to educate me.

For you guys that are builders and suppliers, of course you don't want me coming back at you with a problem so I suspect you remain a bit on the conservative side, of course you would.  Do I want to specify a turd, of course not, but some of the car build sport/fun lies in the edginess of the whole thing. (for a thunderbird)  At the end of the day, if there is secret sauce, yes I would kind of like to know what it is so I can be more independant down the road.

As for the nitrous aspect, I get the message, I will dial it back and if it is used it would be couple second shots at most anyways.  I fully understand there will be tuning all around, suspension issues, you name it, I just want to get off to a good start with a solid foundation and not leave too much on the table even though I want to get in it and go on a nice summer day.
Thanks for your time Brent and thanks all for your input.

[blykins]

Brent:
Certainly was not implying I did not like what you had to say and I hope others continue to chime in with their thoughts on this for a while longer here, please don't shy away.
As stated in original post, given lots of variation in recommendations, I was opening it up to a wider audience, and too that end, I am getting a little more comfortable with settling in on a design as planned.
As an automation equipment guy, when I don't have full understanding, especially in the case of very dynamic systems, I collect data so I can make the most informed decision possible.  Since physical prototyping and testing is prohibative I have to rely on published artiles and others experience to educate me.

For you guys that are builders and suppliers, of course you don't want me coming back at you with a problem so I suspect you remain a bit on the conservative side, of course you would.  Do I want to specify a turd, of course not, but some of the car build sport/fun lies in the edginess of the whole thing. (for a thunderbird)  At the end of the day, if there is secret sauce, yes I would kind of like to know what it is so I can be more independant down the road.

As for the nitrous aspect, I get the message, I will dial it back and if it is used it would be couple second shots at most anyways.  I fully understand there will be tuning all around, suspension issues, you name it, I just want to get off to a good start with a solid foundation and not leave too much on the table even though I want to get in it and go on a nice summer day.
Thanks for your time Brent and thanks all for your input.

We tend to keep the secret sauce stuff to ourselves.  :-)

[My427stang]

This is a neat discussion.  I'd say this first, 500 shouldn't be hard to hit IMHO.   I am not sure why Jay's old magazine builds fought that number, but as Scott said, that's 1.12 hp per cid.  Not unreasonable, even in a tight spaced wedge like an FE, but with the cylinder head as picked, as posted, it makes it harder

That's why I think what continues to be missing here is real cylinder head discussion.  Edels are decent for a cost effective build, but on the street I like to consider 2.0 X intake flow as the max a tight bore spacing wedge like an FE will pull.  That's if everything is well matched. With a 260 cfm head, it's tough to be in the low 500s unless it's matched perfectlyl.  That's a probably conservative number as some people can show 2.2 or so per intake cfm, but that's really more in the canted valve range or dyno only IMHO. 

I still think less focus should be on a specific degree or two of a lobe, same with compression, and get that thing breathing.   Just as an example a small runner, like the TFS, or Blair's small runner pro-port, would add a significant amount of cylinder fill, both normal atmospheric and during overlap.  A better set of heads will do more than a 1/4 point of compression or a 3-4 degree change in a lobe.  Get a 300 cfm small fast port and match parts and the 500 is far easier IMHO.

Needless to say, the quality of your offset carb spacers will also affect that.  Not too worried about adding plenum on a 445 inch motor with early cam timing and a properly sized port, but, if those spacers add some sort of goofy turbulence or force the mixture to make corners it doesn't want to, it won't be as happy

That being said, I agree with Brent and Barry 100%.  Stay at or under 10-ish SCR, don't push the limits of DCR (which just means cam appropriately), and the RPM range and power level is perfect for a custom hydraulic roller, especially if you can get a better flowing head on there. 

I'd also remind that Barry made some good power with an off the shelf cam he didn't expect to use, not that I recommend that here, but I'd push hard to convince you and everyone else that "the right heads make real power" and the other stuff supports the airflow.  WAY oversimplified of course, but the fast guys do head work, car show guys do big cams.

As far as the gear ratio discussion, going back, 2.75 X 3.50 = 9.625, I have no idea what you were doing with your "uptick" I assume it was to account for converter slippage, but don't do that.  At low torque cruise a converter will not be slipping.  The stall speed is for a given torque and resistance, and a higher stall converter won't be slipping at cruise because you have neither high torque required or high resistance.  I don't mind the 2.75 gear, puts it in the right place, but still make sure you have a quality converter company look at what you have for dyno results and make sure it matches.  Too tight or too loose are a bitch on the street

One last comment on the nitrous, "a 2 second shot at most" is more worrisome than saying you will stand on it IMHO.  Build the engine to the desired use.  If you want nitrous at that level, spark retard and dedicated fuel supply is a minimum in my opinion, and having it set up as a 2 stage would be preferred as it would come on easier than just jamming it all in there.  That being said, it's all about risk vs reward, if you want to take the risk, do it man, just do everything.  Build it the best you can to hold 700 hp, if the block splits, it splits.  I personally would want an aftermarket block for that, but it may last for a long time.  Just don't think that you'll manage the engine;s internal safety while holding the button, a lot will be going on when 700 hp starts eating up pavement

[jayb]

This is a neat discussion.  I'd say this first, 500 shouldn't be hard to hit IMHO.   I am not sure why Jay's old magazine builds fought that number, but as Scott said, that's 1.12 hp per cid.  Not unreasonable, even in a tight spaced wedge like an FE, but with the cylinder head as picked, as posted, it makes it harder.

The reason for the HP number on that engine was pretty simple, really:

1.  Flat tappet, budget cam.  That whole engine came in at $6K.

2.  Honest dyno numbers 

A hydraulic roller makes a big difference, as Brent mentioned.  But a basic street/strip porting job makes a big difference too, and will allow that HP peak without going to the expense of a roller cam setup.  Of course, there are other advantages to going with a roller cam...

[Barry_R]

2.  Honest dyno numbers 

That quote alone is a big statement in the internet world

[Drew Pojedinec]

Now I'm no engine builder.... just a dude that owns a few fe vehicles. 
From my perspective in a heavy car driven on the street, I feel trading a little horsepower for a little compression is a great investment in enjoyable cruising.

If you run 93 and the engine is 9.5:1 it's an easy tune to stay safe, the engine itself is much more tolerant of random street conditions.
If you run 93 and the engine is 11:1, sure you *can* do it.... but what about when you are stuck waiting for a train to cross the street while the engine has 215 degree water temps, and your electric fan just blew a fuse?

If you are looking at "Max Performance, nitrous saturated engine, blah blah blah"  well that is cool, but do that.
I've seen a lot of people chasing all of the above in a build and they end up with nothing really working out well.

Jay,
Your 390 stroker budget engine has inspired more people than you know.  It showed that the ole dinosaur could hit respectable numbers with nothing overly expensive or trick.  The real variable with that build is finding decent deals on certain factory parts like rockers.  Either way, still a great build, and still relevant.

[scott foxwell]

2.  Honest dyno numbers 

That quote alone is a big statement in the internet world

Everyone's dyno is honest. Just ask them.

[scott foxwell]

One thing I'm learning about the FE. The block is definitely the Achilles heel. I think with the right combination, even some iron head combinations can make over 600hp. Much more than that, all the discussions about cams, heads, compression, induction, N20, etc. are moot. Pointless to even go there and expect any reliability. We definitely need another source for a good after market block and one that doesn't feel the need to gouge the market on price.

[Thumperbird]

Thanks everyone, this is a great discussion, exactly what I was hoping for, at least for me in that it enables trade off decisions based on a nice variety of inputs.

I will back the nitrous off.  I believe the MSD 6AL has an input I can toggle to retard timing should I give it a shot.
If I blow it up then I will try again I suppose with that "affordable" aftermarket block Scott and all are looking for.
Street strip dress the heads, Jay has provided a local shop recommendation for that work.
Already committed to Hyd. roller, Harland Sharp bar/rockers, Morel lifters.
May not be quite so concerned about CR, 10.25 might be good, but thinking I want to stay above 8 DCR
I will post a CAD model of the spacer some time here just for fun, it is nothing fancy at all.
Yes, how it impacts flow concerns me but am hoping a combination of 1" 4 hole spacer, followed by nitrous plate, followed by offset spacer will give me a nice "mix" of physics to yield a uniform flow.

My favorite quote so far "but the fast guys do head work, car show guys do big cams"
I do want it to idle and behave a little racy but want to back it up with some real responsive go as well, thinking of this as a hybrid, in between the car show bling and the track in terms of performance.

Thanks again, keep it coming and if there are more out there willing to give 2 cents worth I would appreciate it!
Back to building my paint booth so I can spray some epoxy primer tomorrow, of course it has to be the coldest day of the year so far.
 

 

[Barry_R]

Think of DCR as a "go-no go" type of tool.  Useful directional information but not to be used as any sort of a target. 

An old school big open chamber with a huge blob of a dome, coupled with big valves and a big & short lazy intake port will generate the same DCR as a tight heart shaped chamber with a spherical dish piston and a fast & long port - - as long as bore/stroke/cam/compression remains the same.  It should be painfully obvious that they will have vastly different fuel tolerance.

Thats my biggest gripe about folks that get too fixated on it.
Use it as a disqualifier as in "whoa that might not be good" and it will serve you well.

[scott foxwell]

Dynamic compression ratio is almost a contradiction of terms.
Compression ratio is a static measurement based on fixed values.
Dynamic compression ratio would be better termed as dynamic cylinder pressure.

[My427stang]

Think of DCR as a "go-no go" type of tool.  Useful directional information but not to be used as any sort of a target. 

An old school big open chamber with a huge blob of a dome, coupled with big valves and a big & short lazy intake port will generate the same DCR as a tight heart shaped chamber with a spherical dish piston and a fast & long port - - as long as bore/stroke/cam/compression remains the same.  It should be painfully obvious that they will have vastly different fuel tolerance.

Thats my biggest gripe about folks that get too fixated on it.
Use it as a disqualifier as in "whoa that might not be good" and it will serve you well.

Barry, I agree with your message, DCR should not be an end all and it is just another analysis tool to look at interaction of parts. 

However, your example would equally say that static compression ratio is bad too.  Big chamber big dome loose quench  vs tight and clean combo does the same thing using static numbers as it does with DCR  In the end, using any number without knowledge is dangerous

Don't get me wrong, I 100% agree with you that it is not a single factor, but I don't know of any single factor is attempted to be used as much, except SCR, which is equally misleading for the same reasons.  "10.5:1 compression is too much on the street"  That's true, that's false, depends on lot's of things as you point out.   

I also like what you said about "whoa that might not be good" thats a very good way, and I will add that you need a consistent method to calculate and you have to actually measure the variables.  Too many people guess at cam location, SCR, chamber size, you name it, and the effects are the same for any blueprinting. 

My hunch? I think that because DCRwas misnamed when originally coined, people love to hate it.  I know I am preaching to the choir, so not directly pointing at you, but people either over-love it, or hate it, seems to be no in between.

Dynamic compression ratio is almost a contradiction of terms.
Compression ratio is a static measurement based on fixed values.
Dynamic compression ratio would be better termed as dynamic cylinder pressure.

Scott, your comment is what I refer to as the curse of DCR being misnamed.  I understand what you are getting at, but most naysayers fight about the lack of dynamic events in DCR.  THAT'S why it's misnamed.  Its not dynamic at all, it doesn't account for inertia, overlap, water hammer effect, none of that.  It should have been named "valve-event adjusted compression ratio"  Because all it does is calculate a compression ratio from when the intake valve closes to the top of the stroke.  It's not dynamic, and it doesn't really even account for any movement in the engine other than the intake valve closing point and some connecting rod movement.  It's literally just a different start and stop point for the standard compression ratio calculation.

Despite that, I am a DCR fan, as well as an SCR fan, a degree wheel fan, a torque wrench fan, as well as a bunch of other tools that can help

[scott foxwell]

Scott, your comment is what I refer to as the curse of DCR being misnamed.  I understand what you are getting at, but most naysayers fight about the lack of dynamic events in DCR.  THAT'S why it's misnamed.  Its not dynamic at all, it doesn't account for inertia, overlap, water hammer effect, none of that.  It should have been named "valve-event adjusted compression ratio"  Because all it does is calculate a compression ratio from when the intake valve closes to the top of the stroke.  It's not dynamic, and it doesn't really even account for any movement in the engine other than the intake valve closing point and some connecting rod movement.  It's literally just a different start and stop point for the standard compression ratio calculation.

Despite that, I am a DCR fan, as well as an SCR fan, a degree wheel fan, a torque wrench fan, as well as a bunch of other tools that can help

I know what it is but the whole issue is cylinder pressure, and it's used to try and give a more realistic representation of just that. So I'll ask...it's a ratio from when the valve closes...at what rpm? At what temperature? Is the cylinder pressure going to be the same at any rpm, at any temperature? What about the effect of VE on cylinder pressure? With what induction? IMO the number is all but irrelevant. It's extremely dynamic.

[My427stang]

We are saying the same thing, DCR (as calculated by the calculators) is not dynamic, but cylinder pressure is.

However, SCR is not dynamic either, it doesn't account for heat, quench, atmospheric pressure, overlap etc, but nobody complains, people do have strong feelings about DCR though.

So yes cylinder pressure is dynamic, but DCR and SCR are NOT dynamic, but by using dynamic in the name it makes many people want to throw it out, when like SCR, it's just another mathematical analysis

If for some reason I didn't make my point, what I am trying to say is, every time someone discounts DCR, swap SCR in the sentence.  The same bitch applies, but far less people dislike SCR discussion despite it having the same shortfalls when forecasting cylinder pressure

[blykins]

.....but thinking I want to stay above 8 DCR

My question to that would be..........why?

It's just a number.  As the others have been discussing, it's just a number to watch out of the corner of your eye to make sure you don't screw anything up. 

If you raise that DCR number, you have to do it by these ways:

1.  Raise SCR.  Again, not a good idea as you can actually hit over 100% VE.
2.  Advance the cam timing more.  Sometimes an option, sometimes not, but the cam as a whole has to reflect that change. 
3.  Shorten the advertised duration.  Not a good idea either as that means a more aggressive lobe if you keep the .050" duration the same.
4.  Shorten the .050" and advertised durations together.  Again, not a good idea, because when you cut the .050" duration down, you will lower the peak hp rpm and potentially cut horsepower out. 

Don't focus on a number. 

[Barry_R]

However, SCR is not dynamic either, it doesn't account for heat, quench, atmospheric pressure, overlap etc, but nobody complains, people do have strong feelings about DCR though....

...The same bitch applies, but far less people dislike SCR discussion despite it having the same shortfalls when forecasting cylinder pressure

The reason there can be no "bitch" about static compression ratio is that it is a fixed mechanical calculation based upon physical measurements.  It is not in any way variable.  It is a ratio with a numerator and a denominator, and is not impacted by any operational factors.

Now the other variables as to induction design, chamber design, and piston characteristics - and how they impact performance and fuel tolerance are a whole separate but related discussion.  You can run more or less fuel quality or timing with variations in design but the ratio remains the ratio.

I do agree on the naming issue with DCR.  It is not dynamic or it would include variables for something - heat, speed, or anything that changes during the operation being measured.  It is not really a ratio because it does not really have a real numerator or denominator.  It is simply a comparative number - one which indeed has significant useful value when used in a proper context. 

I simply get concerned when I see folks that are fixated on optimizing a combination around a measurement value.  As such it should be an input - not an output.  I see the same thing with folks being in love with gapless rings because the leak down numbers are low - again optimizing a test rather than a operating system.

Its like evaluating a person based on just the number on the bathroom scale.  One guy with a potbelly and no muscles can weigh exactly the same as another guy with zero body fat and a ripped physique.  But if you evaluate using only the scale they appear identical.  (Unfortunately I am closer to the first guy in this example...)

[My427stang]

I agree with you Barry, and I hope you, Scott, or Jay (with the magazine motor comment) did not think I was calling you guys out.  I considered deleting the post because I really hate passionate forum debates nowadays, but Scott pulled the reply trigger pretty quick so I wanted to clean up my end of the discussion

In the end, SCR and DCR are both based on physical measurements and movement of reciprocating parts....that's my only argument against those who completely dismiss it, and if one can be used combined with adequate knowledge and experience, so can the other. 

Moreover, I think we all agree that DCR is merely one piece to the puzzle, like any other "thing" we can evaluate or change in a build, so we are pretty close. 

A 12:1 motor with a 320 duration cam may have good DCR numbers, but it doesn't mean much at some points in the curve, and two 9:1 motors, one with a dome and ton of deck clearance versus a tight quench and flat top could have the same SCR and DCR and act very differently as you point out.  To keep it on point, a 360 Ford is a great example of low SCR and DCR but not "right" 

Then add different elevations, temperatures and different supporting components, and it will change behavior.  I would never argue against that, and to be honest, I do not know of a calculator that can predict anything as dynamic as cylinder pressure, maybe Detroit has that stuff.  Pipemax will give you cranking compression at different RPM, but I can't say that it does anything that could predict all the different things that affect actual cylinder pressure in the variety of uses a street car finds itself loading and unloading throughout use

I do believe though, and I am preaching to the choir here....actually blueprinting the engine, building it to suit the use, and using the same DCR calculator without estimating measurements, and then building experience from the results of  those numbers, really does help.  I mean how did we know 9:1 SCR is generally streetable, IF a lot of other things are right?  ...experience

DCR can allow you to "lean" one way or another based on what you are trying to do, just like you said.  Honestly, for me, less than octane tolerance, I'd say it helps me tweak part throttle and idle vacuum in very general terms without going "too far"

Here's something that I would say is a problem with DCR though and what I would say people should "bitch" about...what is the one calculation we will all use for DCR so we can compare results?

I use PKelley's calculator and have about 15 builds on it of varying configurations, all street, more if you count other engines I haven't directly pulled wrenches on.  Doing a bench build 390 4V, Streetmaster, 9.72:1 SCR, .050 quench, HMV-272 HFT on 109 (which is actually a 268 degree cam using a standard .006 rise), comes out to 7.85 DCR.  All my stuff is measured. I expect that this engine will do fine on pump gas, but could be a little rattly in something real heavy.  However, I didn't want to retard the cam and dull idle vacuum, and it's a bench build, so no plan to change any parts, so I am happy with it

Pipemax said the DCR was 9.07 with a cranking compression of 172 psi and Wallace Racing says 7.85 with a cranking compression of 150. Which is right?

Probably none of them compared to each other, but I know a flat top wedge with a decent quench, iron heads and matching parts will be good with PKelley's numbers up to about 8:1.  So I made my decision to keep ICL at 109, even though I likely would have wanted a little more idle vacuum.  However, if I always used Stan's program, not PKelley, I would likely trust 9.07 just as much.  So, IMHO, the biggest issue of DCR is that the computation of measured values is done so differently by different people

Now, SCR has only one formula, got it, but people still misuse that too.  Think of how many 10:1 390s are out there, except for the fact that they are deep below deck, run an 8554 gasket and the chambers are bigger than advertised   Also, let's take a 360, keep the pistons .090 in the hole and add some dome to get to 9:1 SCR...ugh

If we don't agree, it's OK, nobody loses their birthday and I have no reason to convert anyone to the dark side of engine build calculators, because in the end, as you said, engines can't read LOL

[Thumperbird]

OK, new winner for best quote so far.
"Its like evaluating a person based on just the number on the bathroom scale.  One guy with a potbelly and no muscles can weigh exactly the same as another guy with zero body fat and a ripped physique.  But if you evaluate using only the scale they appear identical.  (Unfortunately I am closer to the first guy in this example...)"

All of these #'s are reference points to consider and they have relational significance, static and dynamic. I will no longer get stuck or fixated on a specific value other than selecting some combination of specifics that I and whom ever I purchase from feel is the best fit for the heavy car.

I intend to study the relationships of duration, overlap, LSA, ICL, etc. a bit more here, being a visual learner I need to see some graphs or be able to play with a program at least for education sake, I understand bench top analysis is very limited.  Is there any freeware out there worth playing with?

Definitely going to open up the heads and I almost wish now I would have gone with a lighter valve train but too late for that and I guess if I push things too much anyways I will destroy the block.  Can that centerline section between the cam and mains be strengthened in any way so it does not split?
Thanks.

[Thumperbird]

Thanks My427Stang, our posts crossed each other.
I agree, the threads that get heated are no fun, it is so easy and natural to a degree to interpret or to take things how one wants from written words when in a face to face the tone would be so much different.

I've decided I need individual valve servo control so I can dial things in, wish that was out there for reasonable money.

Keep the info. coming guys, more thoughts on specific duration, LSA, ICL, and lift targets? (combinations)
Thanks all.

[scott foxwell]

...

[My427stang]

I can calculate SCR without even having the parts in hand. It doesn't change in a running engine.
DCR or dynamic compression ratio... IMO there is no such thing. The word dynamic, alone, says it all...changing. It's a changing number and it changes throughout the operation of the engine. It might be useful as a reference, but I've never used it. Couldn't care less about it. Get the valve events right for the combination and it is what it is.

Scott, nobody is saying DCR predicts a running engine except you, and DCR is calculated before you buy parts, just like SCR, and it doesn't change in a running engine. (other than potentially a little timing chain stretch)

It is ONLY SCR adjusted for intake valve closure and piston dwell, that's it.  Not trying to make you use it, but you continue to get hung up on the word dynamic, it's a stupid word that doesn't apply, we should shoot the guy who used it and change the name.

[My427stang]

OK, new winner for best quote so far.
"Its like evaluating a person based on just the number on the bathroom scale.  One guy with a potbelly and no muscles can weigh exactly the same as another guy with zero body fat and a ripped physique.  But if you evaluate using only the scale they appear identical.  (Unfortunately I am closer to the first guy in this example...)"

All of these #'s are reference points to consider and they have relational significance, static and dynamic. I will no longer get stuck or fixated on a specific value other than selecting some combination of specifics that I and whom ever I purchase from feel is the best fit for the heavy car.

I intend to study the relationships of duration, overlap, LSA, ICL, etc. a bit more here, being a visual learner I need to see some graphs or be able to play with a program at least for education sake, I understand bench top analysis is very limited.  Is there any freeware out there worth playing with?

Definitely going to open up the heads and I almost wish now I would have gone with a lighter valve train but too late for that and I guess if I push things too much anyways I will destroy the block.  Can that centerline section between the cam and mains be strengthened in any way so it does not split?
Thanks.

So learnin' is good LOL

However, remember that numbers can sometimes drive you to two goofy sayings "can't see the forest for the trees"  and "penny wise but pound foolish"

500 hp is absolutely doable, and reliably with a 445.  Good heads, a little rubbing on the intake roof and port match, cam to support the rpm range, and compression to match the build and fuel. 

If you are eager to learn, I would learn more about port volume, port length, cross section, quench distance, modern ring packs, bore finishes, and blueprinting everything to really know what you have.  That's where it's at.   Not discounting the benefit of a good cam, but man, there is an incredible range of cams that will have slight differences but still meet your goals. 

Additionally, when you learn about each of those, let them "lean you one way" no single variable is a MUST, each can be tweaked and offset, and in many cases, have to be for a street car that runs in a wide range of use and environment

Last thing is, don't sweat the lightweight valvetrain at the RPM you are running.  A good steel retainer and the right spring pressures, even with a 3/8 valve will run very strong and easily stay in control for your use

ON EDIT: Can the block be strengthened?  Not really..however, good machining, a real good balance job (as an example, on my 489 I rotated all the parts all the way out to the lower pulley and zero balanced the entire pressure plate and clutch assembly when we spun it), and selection of the lightest parts you can afford (pistons and rods) and to a lesser extent avoiding opening oil feeds all will make it more stable and less load for the block to "hold captive"

[Barry_R]

If we don't agree, it's OK, nobody loses their birthday

Are you sure we can't drop a couple birthdays?  I would not want to eliminate any of the future ones - and don't really need the change the first - but I have accumulated way to many "in between" and would gladly get rid of a few if it meant I could have my hair back in its original quantity and color... 

[blykins]

Ahhh, I remember the days of having hair.

[My427stang]

Ahhh, I remember the days of having hair.

No doubt!  and I will one day fit in the suit I bought in college (1990) so I am not throwing it away

[scott foxwell]

I can calculate SCR without even having the parts in hand. It doesn't change in a running engine.
DCR or dynamic compression ratio... IMO there is no such thing. The word dynamic, alone, says it all...changing. It's a changing number and it changes throughout the operation of the engine. It might be useful as a reference, but I've never used it. Couldn't care less about it. Get the valve events right for the combination and it is what it is.

Scott, nobody is saying DCR predicts a running engine except you, and DCR is calculated before you buy parts, just like SCR, and it doesn't change in a running engine. (other than potentially a little timing chain stretch) Hogwash. That's absurd. Change lash, it changes. Change rockers, it changes. Change valve spring pressure, it changes and if you think nothing more than a little chain stretch occurs in a running engine, well, I'll just reserve comment on that.

It is ONLY SCR adjusted for intake valve closure and piston dwell, that's it.  Not trying to make you use it, but you continue to get hung up on the word dynamic, it's a stupid word that doesn't apply, we should shoot the guy who used it and change the name.

I deleted my post because I really don't care one bit about DCR. Never used it, but since you went there, answer this:
How do you calculate it? (Rhetorical...don't have to answer) Even you talked above about all the variations in numbers:

Here's something that I would say is a problem with DCR though and what I would say people should "bitch" about...what is the one calculation we will all use for DCR so we can compare results?

You can not tell me that you can accurately calculate the exact crankshaft degree where the intake valve closes. Just way too many variables. A running engine, that all goes out the window. Even if you can get close or have a consensus, it's a useless number. It means nothing. It references nothing useful. That, of course, is just my opinion.

[KMcCullah]

I've always liked Werby's explanation of DCR. In a nutshell...how much air are you "trapping"?

http://www.network54.com/Forum/74182/thread/1481408780

[My427stang]

Scott I see that you deleted your post, sorry I quoted you and it stayed.  However, you posted, so take a breath and realize that there are many people out there that build engines, you included, and we all have ways we do things.   This is not a fight, I will be respectful and I hope we can learn from each other, or if I am actually a moron, I hope to learn from you.  Believe me nobody wants out of this discussion more than I do. 

1 - Good point on changing intake valve closing point with rocker or lash. I simplified and you jumped, good on you.  However, we aren't talking about accounting for lash, we are talking a hyd roller.  You bring up a good point though, if a solid lifter cam is rated at .020 tappet lift plus it has lash, if someone wants to compare it to a .006 rise hyd lobe, it takes a little measuring and adjustment.  In fact, it's important to know your advertised measurements regardless of design, because as I pointed out, my little bench build cam is rated at .004 which I had to measure to accurately compare to an equiv .006 lobe.  I will even add fuel to your side, because the calculators plan for a symmetrical lobe, so if you want to use an asymmetrical lobe, you need to think a little. It's all about the valve event, something you hold dear, and should. 

So how does someone account for rocker and lash changes?  Well, if I put even more stock in DCR than I recommend, I would degree the cam off the retainer to know real IVC, but that's getting a little anal for that reason, but I have seen some wildly crazy rocker ratios so it is worth doing for other reasons. Most rockers are pretty good on FE, but have one roll in with Comp or PRW and things can be very different

However, what do you do when you do a rocker or lash change anyway, ignoring DCR?  Are you going to regrind a cam for a rocker change or lash change?  It's simply a tuning tool, and it's easy to say, more lash DCR rises, less it drops, more rocker ratio same thing.  You are grasping at things that affect your cam recommendations just as much...change rockers, set up rocker sweep, pushrod length in a stud mounted rocker, all that DOES affect DCR, but it also affects how a cam Straub grinds for you will behave. So it's an argument that applies with or without DCR in the picture. No one calculation provides all the info

2 - I will also agree that you cannot calculate exactly the intake valve closing point on a running engine at all speeds  However, you claim "Get the valve events right"  Talking out both side of your mouth, because if we cannot accurately tell when a valve will close, how do you get valve events right?  IVC is a valve event and it's based off of crank location.....that's what DCR uses

3 - Finally how do I calculate?  I trust a calculator built by someone else with results that I use over and over again and built experience with.  However, it isn't rocket science, just some trigonometry, as a guy who understand engines and specifically valve events, open your mind a little.  It's simply the SCR calculation using the volume of the cylinder at IVC.  It's the SAME as SCR after you figure out IVC, although it is adjusted a bit for rod angularity, which I am not sure how they account for in the programs.

Here is Pat Kelley's math for reference, keep in mind, once you get the adjusted stroke, its just an SCR calc

Calculating DCR: Calculating the DCR requires some basic information and several calculations. First off, the remaining stroke after the intake closes must be determined. This takes three inputs: intake valve closing point, rod length, and the actual crank stroke, plus a little trig. Here are the formulas: (See the bottom of the page for a way around doing all this math.)

Variables used:

    RD = Rod horizontal Displacement in inches
    ICA = advertised Intake Closing timing (Angle) in degrees ABDC
    RR = Rod Distance in inches below crank CL
    RL = Rod Length
    PR1 = Piston Rise from RR in inches on crank CL.
    PR2 = Piston Rise from crank CL
    ST = STroke
    1/2ST = one half the STroke
    DST = Dynamic STroke length to use for DCR calcs

What's going on: First we need to find some of the above variables. We need to calculate RD and RR. Then, using these number, we find PR1 and PR2. Finally, we plug these number into a formula to find the Dynamic Stroke (DST).

Calcs:

    RD = 1/2ST * (sine ICA)
    RR = 1/2ST * (cosine ICA)
    PR1 = sq root of ((RL*RL) - (RD*RD))
    PR2 = PR1 - RR
    DST = ST - ((PR2 + 1/2ST) - RL)

This result is what I call the Dynamic Stroke (DST), the distance remaining to TDC after the intake valve closes. This is the critical dimension needed to determine the Dynamic Compression Ratio. After calculating the DST, this dimension is used in place of the crankshaft stroke length for calculating the DCR. Most any CR calculator will work. Just enter the DST as the stroke and the result is the Dynamic CR. Of course, the more accurate the entries are the more accurate the results will be.

[scott foxwell]

LOL...ME take a breath? That's rich.
I don't care how many 1000 word posts you write.
You seem to want to dominate the discussion so I'll just let it go. I said what I had to say. Sorry you don't agree but you're not going to shove your "opinion" down my throat.

[blykins]

Aren't forums fun?   

[fryedaddy]

Aren't forums fun?

its better than days of our lives as the world turns or another world

[andyf]

Not sure why a 445 build thread turned into a DCR discussion but I'll jump in and say that I find DCR to be generally a bad thing. That is, people who don't understand much grab onto the DCR as a comfort blanket that tells them they can run cheap gas in their high compression engine. I see this all day long on various forums where some guy with a 12:1 engine with a big cam says he can run cheap gas since his DCR is 8:1.

For some reason people don't understand that the DCR calculation only works at low speed. As soon as the engine comes up on the cam and VE gets close to 100% you've got a 12:1 engine on your hands and there she blows. I can't think of a single good reason to pay attention to DCR unless perhaps you are designing a tug boat engine that only runs at 1500 rpm. If you're working on a performance engine then you need to pay attention to what the wave theory fairy is going to bring in the intake valve. The wave theory fairy doesn't care about DCR, when the intake and exhaust hit their sweet spot the cylinder is filling up regardless of what the DCR is. That is why Pro Stock cars with low DCR's make 1500 hp.

[Thumperbird]

Can someone please describe what the "scavanging affect is and how a cam plays into it?
It is my simple understanding this is related to overlap among other things.
Is DCR, for what it is worth which is obviously very debateable, really a numeric indicator of some sort of scavanging effectiveness?

Thanks.

[blykins]

Scavenging is when the exhaust port helps the intake port.  Scavenging is important and is really important when you have a big, slow, lazy intake port.  However, it only works when both valves are open at the same time, which is directly related to overlap, but not related to DCR.  We keep an eye on overlap when we have lazy ports, or when vacuum is a key factor.  There are ways to manipulate it in each direction.

[My427stang]

Not sure why a 445 build thread turned into a DCR discussion but I'll jump in and say that I find DCR to be generally a bad thing. That is, people who don't understand much grab onto the DCR as a comfort blanket that tells them they can run cheap gas in their high compression engine. I see this all day long on various forums where some guy with a 12:1 engine with a big cam says he can run cheap gas since his DCR is 8:1.

For some reason people don't understand that the DCR calculation only works at low speed. As soon as the engine comes up on the cam and VE gets close to 100% you've got a 12:1 engine on your hands and there she blows. I can't think of a single good reason to pay attention to DCR unless perhaps you are designing a tug boat engine that only runs at 1500 rpm. If you're working on a performance engine then you need to pay attention to what the wave theory fairy is going to bring in the intake valve. The wave theory fairy doesn't care about DCR, when the intake and exhaust hit their sweet spot the cylinder is filling up regardless of what the DCR is. That is why Pro Stock cars with low DCR's make 1500 hp.

Andy I agree with you, especially the first paragraph, but we part a bit on the RPM discussion.  I can't respond without writing a book LOL but if it helps, I see why people don't like it. 

As you pointed out, it's not a tool to pick parts.  Nor is it a tool to make maximum horsepower, but I use it as a tool to verify, tweak, and back up build planning, and that planning has to be logical.  Like anything...garbage in=garbage out.  In fact, I would say I use DCR primarily on street engines to see if I have room to gain a little vacuum and part throttle torque from cam timing more than anything with a secondary "no-go" use as Barry said.

If someone uses it to pick parts, especially picking a cam to kill compression, it's the wrong use of a tool.  I don't believe in that use of DCR at all and honestly, the guy who will do that probably has big problems, with or without DCR.

FWIW, I also look at water hammer and wave theory, old school 5th cycle stuff, effects of overlap and primary pipe sizing, and you are 100% correct that there are forces inside that increase cylinder pressure that are way more important than DCR for creating the curve, never mind the N20 planned here.

If anyone wants to discuss how I use it, I am happy to share by PM or another post, but I am going to wave off to save you all  from my broken record

[turbohunter]

Ross some of us enjoy reading and mulling over your "1000 word posts".
What I have a hard time with is why others are so easily offended when someone has a different take on the subject.

[fe-starliner]

  "X 2"..... N/M

[Drew Pojedinec]

Ross some of us enjoy reading and mulling over your "1000 word posts".
What I have a hard time with is why others are so easily offended when someone has a different take on the subject.

Marc, I'm offended by you being offended regarding other people getting easily offended.
I thought I knew you better than this.....
 

[turbohunter]

LOL
Hard time, not offended

[plovett]

It's amazing how many people, even professional engine builders, don't understand what DCR is.  The crappy name is the biggest issue.  It sounds like what you would call cylinder pressure in a running engine.

If we could rename it that would help immensely.  Valves Closed Compression Ratio (VCCR)?  Or Cam Adjusted Compression Ratio (CACR)?

I think anybody who understands what it is, also understands it's limitations.   It's just one of many tools.  The tool is only as good as the one using it.   

JMO,

paulie

[scott foxwell]

It's amazing how many people, even professional engine builders, don't understand what DCR is.  The crappy name is the biggest issue.  It sounds like what you would call cylinder pressure in a running engine.

If we could rename it that would help immensely.  Valves Closed Compression Ratio (VCCR)?  Or Cam Adjusted Compression Ratio (CACR)?

I think anybody who understands what it is, also understands it's limitations.   It's just one of many tools.  The tool is only as good as the one using it.   

JMO,

paulie

I think calling it a ratio of any kind is the mistake. It's simply the result of the valve events. Not a design criteria or goal.

[plovett]

DCR is indeed a ratio.  It is the ratio of the volume in the cylinder and combustion chamber when the valve closes to the volume in the cylinder and combustion chamber when the piston is at TDC.

I agree it may be difficult to very accurately determine the volume when the valve closes.  No argument there.  But it's still a ratio.

JMO,

paulie

[scott foxwell]

DCR is indeed a ratio.  It is the ratio of the volume in the cylinder and combustion chamber when the valve closes to the volume in the cylinder and combustion chamber when the piston is at TDC.

I agree it may be difficult to very accurately determine the volume when the valve closes.  No argument there.  But it's still a ratio.

JMO,

paulie

Imaginary number that represents nothing useful other than to generate amusing internet discussions. Again, IMO.

[plovett]

Well not imaginary.  ANY number is only as good as your measuring tools.  No event anywhere in the world can be measured absolutely correctly.  There is always some error.  But just because there is error (lack of accuracy) doesn't mean the number is meaningless.  ALL measurements are inaccurate.  It's just a matter of how much.

JMO,

paulie

[Thumperbird]

This thread had turned into a DCR discussion but one other aspect I am looking to reserect a bit is the nitrous piece.
Since I finally got the dual carbs where I want them last summer it is time to finish the plumbing and prepare the nitrous system.  I think the engine is near the 500HP goal that was planned and the nitrous is a theoretical 200HP shot. 

Reminder there is a plate under each carb sitting on top of the offset spacers, it is a dual plane setup which I know may present some challenge/risk.  I have Edelbrock wet plates, can someone tell me if the orifice hole size # published is just the orifice id or is there some translation?

The sum of area of the bar holes (6 per bar) seems less than the area of the restrictor orifice upstream, this confuses me, seems like spray holes themselves are more restrictive.  Does anyone know what size the bar holes are supposed to be for an edelbrock square bore plate in their 250hp kit?

Was testing the system with compressed air on the car, not "hearing" the flow I think I should out of the spray bars, dumb me did not flush all that plumbing prior to assembly, off come the carbs again here some time to check and clean everything up.

May find some 50hp orifices for a total of 100hp to start with, nervous about 200 all in at once if it actually does what it is supposed to, car is plenty to manage as is being a boat and all.

[blykins]

700-750 hp on a factory block?

I’ve got spares when you split yours in half.