how much compression is too much?

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hemichuck

hemichuck

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im building this 408 for a car that will probably end up getting raced more than anything, mostly just trying to use up all the parts laying around my garage. The short block is all forged, Scat crank, Eagle rods and Probe flat top Pistons with valve notches. They have a zero deck. I have a Mopar Performance 557 lift solid cam. I have a couple of sets of heads I can use but that's where the compression question comes into play. I have a set of Edelbrocks with 63cc chambers, on this short block with a .040 head gasket you have around 11.75 compression, you can bump up to a Cometic gasket that's .070 and get it down to 10.8 compression. Is 11.75 too much? I remember running the old 12.5 TRW Pistons back in the day but that was with open chambered heads. I'd like to hear some opinions from people who race, I've been out of the racing game for a while but my son is kind of shoving me back in.
 
20 different people will give you 20 different answers. Guys will swear on a bible they ran 13.5 compression on pump gas. Good luck on your question. You have opened up a can of worms.
 
compress until you ping, then dial it back. Sorry, had to say it once in my life. I hear reverse cooling helps, ie head into block. Modern quench has raised it considerably.
 
Way back when in the 1970's I had a 1963 Dart that was literally stripped out, it had a 340 that was .060 over with TRW 12.5 to one domed Pistons, a Crane Zip 518 solid cam with 518 lift and I can't remember the advertised duration but I do remember it was [email protected] so plenty of duration. Here's where it gets fun, it had 273 closed chambered heads that had been massively ported, so much in fact that they were full of Devcon everywhere they had gotten into the water jacket. It was topped off with a 340 Torker intake and a Holley 750 double pumper and 1 5/8 fender well headers. Odd combo to say the least but it had some serious compression. I never got around to calculating what the compression was but when you uncapped it there was a really crisp exhaust note, it almost had a crackle like a fueler. We used to drive that thing around on pump gas, but it would eat some head gaskets.
 
My other option is a set of W2 heads with 72cc chambers which would put compression around 10.2 but I figured with the aluminum heads you could get away with a little more compression. I know the old Direct Connection Racing packages about 11.to 1 compression in the 11 second bracket.i assume racing gas will also make a big difference with ratios up in the 11.7 range
 
Too much compression for what?
 
If you're running race gas, what's the problem? I run about a 11.5 to 1, aluminum head, on my 360 , Sunoco 110 octane.
 
That's what my thoughts were, I've been building street cars for so long under the constraints of crappy fuel that my mind set has just moved away from high compression. I think for now I'm going with the 11.7 combo and if I want more later I have a set of 58cc W2's that would bump me up a little more.
 
I get Sunoco 110 out of the pump here for my KTM 300. But it can not go directly into a car.... So I am hesitant to build too much compression for fear I will run low in an inconvenient place.
When I ran a 12.5:1 W2 motor I kept a barrel of 110 in my garage. Its got a very long shelf life if stored properly.
 
hemichuck said:
I wish we could get Sunoco 110 at the pump around here, I have to drive 15 miles to the drag strip to get it.
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im lucky, i drive right by the local dirt track on the way to work, there's two gas stations that sell Sunoco 110 at the pump and one actually still sells the lead filled Turbo Blue 110 still!
 
hemichuck said:
I wish we could get Sunoco 110 at the pump around here, I have to drive 15 miles to the drag strip to get it.
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RACE GAS | Racing Fuel Concentrate

Run this instead.

I have for over 5 years and thousands of miles on a big block, solid roller motor with 12:1 comp. I'm not easy on my car and I built it to drive so it gets it's fair share of abuse. When mixed, it's less expensive than Sunoco. Sunoco makes 106 octane (Sometimes) and Race-gas makes up to 107 octane (Consistently)

Race-Gas is more affordable? Looks like it!
Sunoco = $13.00/gallon ($65.00 for 5 gallon can)
Race-fuel = $8.00/gallon (6 ounces of RF ($5.63) mixed with 1 gallon of 93 octane pump fuel( $2.37/gal)) (A 32 oz can of Race-Fuel is $29.99)

It's awesome stuff and it works as advertised. I used to worry about how far I could drive my car, but now I can go cross country as I like.
If you don't believe me, feel free to call the guys at race-gas. They will talk your ear off and give you an education for free.

No I am not a paid spokesman, and no I do not get a discount for this review. :D

I've used it all from Sunoco to Av-gas and everything in between. This is the best stuff period. It always makes a consistent blend, and that's important.

Back to your regular program.......................
 
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momoparman said:
RACE GAS | Racing Fuel Concentrate

Run this instead.

I have for over 5 years and thousands of miles on a big block, solid roller motor with 12:1 comp. I'm not easy on my car and I built it to drive so it gets it's fair share of abuse. When mixed, it's about the same price as Sunoco. Sunoco makes 106 octane (Sometimes) and Race-gas makes up to 105 octane (Consistently)

It's awesome stuff and it works as advertised. I used to worry about how far I could drive my car, but now I can go cross country as I like.
If you don't believe me, feel free to call the guys at race-gas. They will talk your ear off and give you an education for free.

No I am not a paid spokesman, and no I do not get a discount for this review. :D

I've used it all from Sunoco to Av-gas and everything in between. This is the best stuff period. It always makes a consistent blend, and that's important.

Back to your regular program.......................
Click to expand...
whats that stuff run?
 
If you are running race gas, then run what ever compression you like. General rules for pump gas, no more than 10.7:1 with aluminum heads, 9.8:1 with iron heads....opinions will vary, and there are a ton of variables (e.g. if you have a huge cam bleeding off a lot of cylinder pressure you could run more static compression).

My old 410 motor was 10.8:1 on pump gas, worked great. Switched it over to e85, still worked great. With that said, my 410 re-build that I'm starting now will be 13:1 on e85....should run low 10's.
 
flyfish said:
If you are running race gas, then run what ever compression you like. General rules for pump gas, no more than 10.7:1 with aluminum heads, 9.8:1 with iron heads....opinions will vary, and there are a ton of variables (e.g. if you have a huge cam bleeding off a lot of cylinder pressure you could run more static compression).

My old 410 motor was 10.8:1 on pump gas, worked great. Switched it over to e85, still worked great. With that said, my 410 re-build that I'm starting now will be 13:1 on e85....should run low 10's.
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not to steal the thread, but did you have any issues running on e85 at all?
 
momoparman said:
$30.00 for a bottle.

To make 105 octane costs about $8.00 per gallon. That's using 1 gallon of 93 octane pump gas @ $2.37/gal and 6 ounces of race gas @ $0.93/oz.
Sunoco is almost $13.00 per gallon.
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nice. Ill have to check this afternoon, see what prices are around here. how many gallons does that bottle make?
 
It depends on your blend. Can holds 32 ounces.

105 octane would be 5.33 gallons per can. That equates to $41.85 for 5.33 gallons of 105 octane fuel. $7.85/gallon
101 octane would be 8 gallons per can. That equates to $48.96 for 8 gallons of 101 octane fuel. $6.12/gallon.

ETC....

If you buy it by the case on the website they give you free shipping.
 
dukeboy_318 said:
not to steal the thread, but did you have any issues running on e85 at all?
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No real issues, just ran cooler and about 2 tenths quicker. If I let it sit for too long without running it (over a month) occasionally the little bullet shaped check balls under the squirters (I don't remember the technical term for those) would stick. Easy to dislodge with a little WD-40, or a light tapping on the carb body.
 
hemichuck said:
im building this 408 for a car that will probably end up getting raced more than anything, mostly just trying to use up all the parts laying around my garage. The short block is all forged, Scat crank, Eagle rods and Probe flat top Pistons with valve notches. They have a zero deck. I have a Mopar Performance 557 lift solid cam. I have a couple of sets of heads I can use but that's where the compression question comes into play. I have a set of Edelbrocks with 63cc chambers, on this short block with a .040 head gasket you have around 11.75 compression, you can bump up to a Cometic gasket that's .070 and get it down to 10.8 compression. Is 11.75 too much? I remember running the old 12.5 TRW Pistons back in the day but that was with open chambered heads. I'd like to hear some opinions from people who race, I've been out of the racing game for a while but my son is kind of shoving me back in.
Click to expand...

My small block is 10.9 comp. and was built to run on 91 octane. I race it and drive it on 93 octane. It has aluminum heads and not a very big duration cam. My cranking cylinder pressure is between 195 and 201 lbs. I decided after my last motor that I would not have another motor that I have to run race gas in. Some people run as high as 12/1 compression on pump gas but they have big duration cams and low cylinder pressure.
 
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