FE Power Forums
FE Power Forums => FE Technical Forum => Topic started by: gregaba on July 22, 2022, 01:03:57 PM
-
Looks like my compression is going to be higher then I expected. I was thinking of 11.4-1 with my set up.
I did my final set up on the short block yesterday and I was finally able to measure the piston height. They stick out above the block .006.
Cometic .040 gasket's.
Using a online caculator I come up with 12.26-1 compression ratio using the Edlebrock cc of 76 cc.
This will increase after the heads are re surfaced as they are not flat enough for me.
I have a couple cases of 105 race gas booster which will be OK for what I will be using the car for.
I was going to use Rocket fuel but the price just got to be to much.
This should hold me untill next year when my CNG conversion will be ready. I guess I will find out if everything works next year.
Greg
-
I don't know your engine specs so, I can't tell you how much a .051 thick head gasket will lower the CR but, here are three available gaskets .051 and one .050:
Clevite 3389 .050 x 4.33 12.065cc
Cometic Gaskets C5840-051 .051 x 4.44 12.71cc
Fel-Pro 8045 PT .051 x 4.200 not round 11.86cc
Fel-Pro 8554 PT .051 x 4.330 not round 4.33 x 4.57 est 12.70cc
If this is your Cometic gasket, you can figure the reduction, using the above:
Cometic Gaskets C5835-040 .040 x 4.25 9.30cc
-
Thanks Frank
Engine spec's are
bore 4.164
stroke 3.98
Blocked decked to 10.155
Scat forged h beam rod's
Race tec flat forged pistons.
block square decked and blueprinted.
internal balanced to 1 gram.
TCI Rattler balancer.
Edelbrock heads with 2.19-1.73 ss valves.
Harland sharp rockers
POP stand's.
POP hv oil pump.
Jays intake adapter'
Jays timing cover and adjustable timing set.
CVR electric water pump and Jays adapter's.
Trick Flow track heat 351 intake.
1050 dominator carb.
Will be pushing 6r80 tran's with speed gem's adapter.
Circle D torque converter 3400 stall.
Rear is
Strange with 4.11 ratio.
Greg
-
You'll have to wait until your heads are clipped before you can do a final compression ratio calculation. Then you can determine what kind of fuel or fuel mix you'll need.
However, you'll for sure need a set of .050" head gaskets. A .034" piston/head clearance is too tight IMO. I have tried .036" and saw imprints in the carbon on the pistons.
-
Greg,
This is what I came up with using the minimum valve relief of 5cc and a top land with of .250.
I use the Diamond Piston calculator, the most accurate that I've found.
Looks like you have plenty of room to cut your heads.
PS
The Fel-Pro 8045 PT .051 x 4.200 not round 11.86cc is probably to small for your bore.
-
Out of curiosity, are there any octane boosters that actually work? Something you could carry with you to throw in the tank if you were running on the edge with 94 octane and you were out of town and couldn't get "good gas?"
-
Brent
Thanks for the reply. I knew I would have to wait for my heads to be finished to get the final ratio.
When they are done I can cc the head's and clay the pistons and see what I have.
I was just a little concerned about getting a 12.26-1 before I did the head's. I think I can live with the 12-1 but not suer about 13 to one.
Frank
Thanks for the chart's. They are very usefull. I saved them for reference.
Chrisss31
Not sure if any of these booster's work.
Nothing I have tried in the past seemed to work.
I just read some good review's on the engine lab's site and decided to give the Race Gas booster a try.
The bad thing about living here is I can only get 91 octane locally and have to drive 70 miles round trip to get anything any higher.
No E85 available without making a 160 mile round trip.
I do have a local source for 100% methanol if I wanted ro spend the small fortune to convert to it that but I would have to buy 55 gallon's at a time and srore it in my shop which I am not comfortable doing.
That is the reason I decided to run CNG in the car.
Greg
-
Out of curiosity, are there any octane boosters that actually work? Something you could carry with you to throw in the tank if you were running on the edge with 94 octane and you were out of town and couldn't get "good gas?"
I have had very good performance with VP's Octanium octane booster
I see many good reviews about the Race Gas product.
Lots of folks swear by the Torco octane booster and have for years.
Might want to look into a water/meth system if you're running 12:1 on the street. I had a Snow system on my blown car and liked it very much.
-
One of the future upgrades is a Snow system. It will be installed when the engine is installed.
I just have not seen much about people running them here, but with anything over 10 1/2 to 1 I think on pump gas they are a must.
Greg
-
I wouldn't hesitate going with a .060 gasket if you need to pull a little compression. .054 quench is still good quench and can let you buy back some compression
-
I am considering that but will wait and see what I have.
I am just using the car for a toy and not a daily driver, it will just be something to hit the road on a friday or saturday night with a occasional trip to the car's and coffee show.
It will hit the strip about 2 or 3 time's a year but that will have to wait on the cal track's and other upgrade's.
Greg
-
Just to reiterate what Brent said though, .040s won't work...you need something different regardless of the compression if they are .006 proud
-
Race Gas Ultra quieted things down for me. ( 11.3 compression as shown by Whistler).
A box of 6 quarts goes for around $175.00
-
Ross
I am afarid you and Brent are right. I guess I will have a new set of .040 Cometic's for sale soon.
I still want to wait untill my head's are done and I can do a final check on them.
JB I ordered the Race Gas 105. It doesn't say Ultra anywhere on the can, Cost was the same.
Greg
-
We have been around the block once or twice :)
However, I cannot come up with the numbers you are coming up with
If I use a .040 gasket, .006 deck, and no valve relieve at all, with 74 cc (all guesses), I get 11.74 ....not that you can run it that way, but certainly tighter than what you reported
If I use a .060 gasket, 4.40 gasket bore, (realistic for a .006 proud piston), a 74 cc chamber, and 5 cc of valve relief (which seems low for a Racetech), .006 proud deck, I get 10.59. CORRECTED
If you could provide a picture of the label on the Racetecs to show exactly the compression height and valve relief, we can see if makes sense.
ON EDIT: The reason for my last comment is that it is very difficult to measure deck clearance without a dual dial deck bridge. Often even being careful with a single you can induce rock. I like to do it with the degree wheel on, with TDC found with a piston stop and a dual dial to take all possibility of rock out of it
-
Ross, your quite a bit off of my CR calculations. Can you give tell us the specs that you use so, I can see how you came up with yours?
The .050/.051 gasket is the one to use, it will give a bit more detonation resistance over a .060 gasket.
-
Frank, I might have typo'd something, our numbers look close, all my numbers were in my post, I will go back and check. Regardless, his 12+ numbers aren't correct
However, I would NOT say .044 quench will be more resistant than .054 quench, it isn't linear by any means. We all like to hit the .046 range, but in practice, .054 is good quench, and in his case, might buy him a little less compression.
I will say I generally build them .006-,008 proud, and like to use the blue Felpro in street applications, so not arguing with a target of .046 when the engine is built for it, but the definitive statement that one gasket IS the one to use just isn't a true statement with quench, it's a range. Additionally, this engine happens to have some quirks that it takes a little flexibility to help him get there since compression and deck height were discovered after the part purchase...a little backwards, but we've all been there
Frank - On edit....I was just looking at the D cam he is running and trying to figure out where Greg really is. I feel like we are running on assumption after assumption, chamber, gasket bore, valve relief clearance, ICL, effective duration, deck clearance procedures.... If he is on 107, assuming his deck clearance is correct and we get a resolution of chamber size. I'd actually agree that .050 is better, both for compression numbers and a more common quench distance.
However, I am going to quiet down until we get some real numbers and/or procedure verification
-
I guess it will ba a while before I can get final number's on what is really needed for my engine.
I am going to take the head's to Texas when Charles can get to them. He is a one man shop and is all way's behind so it take's a while before he can finish a job but his work is excellent.
I sure do hate the 6 to 8 hour drive there and back.
i degreed my cam last week and the number's were right on intake centerline was 102.
Lobe seperation is 107.
Lobe lift was measured at .3550.
Measured gasket bore on the cometic's is 4.143 [I ordered gasket's with 4.165 from Summit but that's not what I got] which I just measured today and am thinking this is wrong for my 4.164 bore so I will be buying new gasket's, after all it's only money.
I should have the head's back in a couple month's and will be able to get accurate measurement's when I get them back.
Thanks for all the help.
Greg
-
I think you could ship them to your cylinder head guy cheaper than you could drive them there at $4.50 a gallon.
-
I have lost to many item's shipping them.
last time was a $2000.00 stereo processor that it looked like someone drove a forklift though.
My gas is $2.09 a gallon as I run on CNG in my F-250.
Still would rather ship but can't depend on the shipper's not to losr my stuff and with the wait time for new head's I just don't want to chance it.
Greg
-
Greg, that is another product in their line. The Ultra will ramp up the octane even more. You may be fine with the 105.
I don’t run the Ultra at the full dosage. I can tell when I need to add some to the 93 that is available here.
Good luck
-
Out of curiosity, are there any octane boosters that actually work? Something you could carry with you to throw in the tank if you were running on the edge with 94 octane and you were out of town and couldn't get "good gas?"
I have had very good performance with VP's Octanium octane booster
I see many good reviews about the Race Gas product.
Lots of folks swear by the Torco octane booster and have for years.
Might want to look into a water/meth system if you're running 12:1 on the street. I had a Snow system on my blown car and liked it very much.
Same as Tommy , VP Racing Madditive Octanium works and it works good , highly recommend , you can get leaded and unleaded
-
Can you degree the cam so the intake valve closes a bit later which would reduce cylinder pressure and octane requirement?
-
On that CR, I personally wouldn't run anything less than straight VP110. I'm mixing 40/60 already pump 91/110 to keep the plugs clean on current US pump fuel. I buy VP by the drum.
-
I just ran the DCR numbers for the "D" cam, set at 102° ICL (3° advanced over factory setting) the intake closes at 87° ABDC, giving a DCR of 6.78, with a 76cc head and 6.9 with a 74cc head.
87 octane gas can run on 7.5 DCR but, when this engine get in it's tq range, it will need more. It could possibly get by with 93 octane but, you'll need to be careful approaching full throttle.
-
Thanks for the reply's.
I will try to answer in order. Will try not to miss anyone.
6667fan
I will give the ultra a look, didn't know about it.
ephilpott
Thanks, will check it out.
427LX
I have jay's adjustable timing set and can adjust timing fairly easy.
Falcone67
How much did the last drum cost and how many gallons is in a drum 55?. What compression ratio are you running?
frnkeore
Thanks for figureing that out. I wish I was better at math but it has been a problem my whole life.
I don't think I would trust 87 anyway and not sure I would trust 93 if I could get it.
Thank's everyone every answer is a help.
Greg
-
To help explain DCR, you are working off of what I will call "net" CID, while your B&S are "gross" CID. Mechanically, you rarely produce your power from the "gross" CID, it's always "net" that produces the power.
The net CID occurs after the intake valve closes and compression starts building (just like you can't have compression while the spark plug is out of the head). DCR works with the position that the crank is in, when that valve closes. In this case, 87°. So, there is no compression until after 87° ABDC. With a 3.984 stroke, that only leaves a actual stroke of 2.408 or, 262.4 CID (4.164x2.408). That's why the DCR is so low, with the "D" cam. The engine doesn't get any bigger but, at higher rpm, the VE can increase, "ramming" more A/F into the cyl but, it can't regain it's 434 CID, unless it can exceed 1.654 VE. What ever it's VE is, it will occur near it's max engine torque and only a dyno will be able to give those numbers.
You could recompute the VE CR at that point but, you have to have that from the dyno. VE CR, is my term.
-
Thanks for the explianation. I really don't understand how to get a dcr as when I was learning mechanic's in the 60's it was never taught.
The guy on street outlaw's who drive's the red 55 chevy has his shop a 1/4 mile from me and I have talked to him about using his dyno to break in and tune my engine when it is ready.
We didn't discuse cost and I am a little concerned about that. I would like to keep it under a $1000.00 if possible but I havn't had a engine on the dyno other then a wheel dyno since I quit racing in the 90's.
Greg
-
Greg, it takes a special calculator to figure it out. The Cliff's notes version of it is that you can't make compression until all the valves are shut. The cam dictates when the valves shut and we specifically look at when the intake valve shuts.
DCR is a fun tool, but it's not the end-all-be-all. You also have to have dyno experience to know what number correlates to "safe" and "not safe" with a specific octane rating. I do say "dyno" because a dyno is harder on an engine than a vehicle can ever be. You also have to take into account how efficient the engine is. Some engines are over-achievers, in that they have over 100% volumetric efficiency. That's when DCR kinda goes out the window. You just can't keep increasing the compression ratio and putting a bigger cam in (or retarding cam timing) to make it work.
Of course, you're playing it the correct way and waiting until you get all actual numbers. We can all sit here and bench race compression ratios until the cows come home, but it doesn't mean squat if you don't have actual numbers.
-
And in the end, no matter how much info you have, you better be able to read plugs. Still lots of variables that just can't be accounted for, like elevation, air density, temp etc. All which can change from day to day, whether it's from travel or just weather changes. Better to be safe than sorry.
-
And with the ignition systems we have today it’s harder to read plugs.
-
And with the ignition systems we have today it’s harder to read plugs.
Not when it comes to pre-ignition. The tell tale signs of peppering on the porcelain are actually easier to spot with less sooting. The engine will tell you when it's not happy, you just have to read the clues.
I know a dyno session isn't cheap, but it's well worth the money. A lot of things can be determined in one dyno session, much easier than trying to hash things out in the car.
-
DCR is a fun tool, but it's not the end-all-be-all. You also have to have dyno experience to know what number correlates to "safe" and "not safe" with a specific octane rating. I do say "dyno" because a dyno is harder on an engine than a vehicle can ever be. You also have to take into account how efficient the engine is. Some engines are over-achievers, in that they have over 100% volumetric efficiency. That's when DCR kinda goes out the window. You just can't keep increasing the compression ratio and putting a bigger cam in (or retarding cam timing) to make it work.
I have been preaching that for years now...
-
DCR is a fun tool, but it's not the end-all-be-all. You also have to have dyno experience to know what number correlates to "safe" and "not safe" with a specific octane rating. I do say "dyno" because a dyno is harder on an engine than a vehicle can ever be. You also have to take into account how efficient the engine is. Some engines are over-achievers, in that they have over 100% volumetric efficiency. That's when DCR kinda goes out the window. You just can't keep increasing the compression ratio and putting a bigger cam in (or retarding cam timing) to make it work.
I have been preaching that for years now...
The DCR calc on my 351C says I'm good for 91~93. Plugs say "no, you're not" - hence the heavy dose of 110 to the fuel cell. Plus - the VP "settles" the car and makes more consistent runs than plain pump fuel. The 302 has 9.5:1 and when that engine is pressed into bracket race service, it gets the same 60/40 mix of VP/pump with the same result. The seasonal blends plus 10% ethanol is hell on dial ins LOL.