445 Stroker Build Help

[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.