ls1408cp

iTrader: (37)

How much power does adding compression make?
two of the exact same motors one running pump gas at 12:1 and one running 14:1 on race gas both have the same cams. How much more power will the race gas one make?

The Alchemist

iTrader: (19)

That's kind of a loaded question and I'm not certain, but whenever going with a larger cam, you essentially lower your dynamic compression because now the open valve bleeds off compression for a longer period duing the compression stroke.

I'd be interested in hearing what the difference is as well. Take a motor and put in a 0.060" head gasket, then swap it for a 0.040" gasket and see what the difference in power is.

Everything I've read and heard is that when you gain compression through decreasing quench distance, it is a win win situation since you add more power from compression, but don't pay the penalty with possible knock since decreasing the quench distance helps to reduce knock.

Maybe some of the engine builders on this site will chime in.

The Alchemist

iTrader: (19)

I'm looking to do exactly this, but unfortunately, I may need to flycut for safety since my heads are milled almost 0.040" already and add into the mix the larger intake valve.

I'd think it would be worth the hassle to flycut if someone were to show me that by going from a 0.060" to 0.040" gasket would yeild me another 15tq/15hp throughout the rpm range.

Thorny

iTrader: (14)

I think I've read somewhere that every full point increase in compression gives 2-3% increase in torque across the entire RPM range. I forget where I read that so I could be wrong.

Alchemist - Wouldn't you be negating the increase in compression by flycutting? If every .005 decrease in gasket thickness = 1 cc, then you would lose 4cc by swapping gaskets. How much volume does flycutting add? I was thinking around 2cc. Thats an awful lot of work for a 2cc drop which would net ~.3 increase in compression.

The Alchemist

iTrader: (19)

I guess it depends on how much you flycut. I'd think that to gain the 0.020" back from the thinner gakset, you'd lose less than 1cc in the flycut. So your net gain would still be positive, with the added benefit of tighter quench.

KCFormula

iTrader: (4)

The best formula I have found is based on thermal efficiency.
E= 1-(1/R^K-1)
E is the thermal efficency, R is the compression ratio and K is the coefficient for the adiabatic (SP?) expansion of air. Which means there is a lot of factors that play into it but when done right a good rule of thumb would be about 3-4%.

Dragkid1917

iTrader: (2)

Does anyone know how much you can mill the stock heads, or rather how much of a lift you can fit under the stock 241's because based on that I can figure out how much to mill them. I assume since a MS4 has an intake lift of .649 that its atleast that much. I understaind it also has to do with advance and retard, to find where the cam actually is, but installed at 0 degrees does anyone know? Also how thick are the stock head gaskets.

The Alchemist

iTrader: (19)

Cam lift, at least max lift, has nothing to do with piston to valve clearance since max lift occurs when the piston is 1.5-2 inches away from top dead center. The issue is duration. Think about it this way, as the piston is coming to top dead center on the exhaust stroke, at some point the intake valve will start to open, which is 'overlap' and that is a critical time for piston to valve clearance. The only way to measure this is to clay the piston and turn the motor over by hand and then the thickness left on the piston after the valve has been pressed into the clay. Even doing that isn't an exact measurement because metals will expand and stretch while running, which is why they give a safe minnimum clearance.

ls1408cp

iTrader: (37)

can someone answer this

gametech

iTrader: (1)

I thought KCformula explained it quite clearly. Approximately 3-4% power increase per point increase in compression can be expected, if all else is equal.

Thorny

iTrader: (14)

The power potential of both fuels are different, so its an apples to oranges comparison. A comparison of 10:1 to 12:1 using pump gas is going to be 6-8% more torque across the entire range, all things equal. However, keeping all things equal with a compression boost like that isn't always probable, timing and AFR may have to be adjusted to compensate for the added compression. If you're making 300lbs torque with 10:1, you're perhaps looking at 320lbs at the same RPM by raising compression 2 points alone.

Dragkid1917

iTrader: (2)

what is the thickness of the stock head gaskets?

Pro Stock John

iTrader: (34)

3-4% is what I've been told.

ls1408cp

iTrader: (37)

so 3-4% on a 800fwhp na motor would only be 32hp

Gregory

iTrader: (4)

You can go to the following web site for all kinds of calculators including one for adding compression. http://www.wallaceracing.com/Calculators.htm

racer7088

It depends on the VE that the engine is already making which is a product of the heads, cam timing, intake and exhaust systems. If you are already on the edge of detonation the extra compression will not help you and may hurt you by not letting you run the right amount of spark timing or A/F ratio etc.

Good running pump gas engines can rarely run much over 11-11.5 to one since pump gas fuel is of lower octane than race fuel. At the engine masters pump gas contest the good engines were even detonating at that sometimes but the winners were in that range. Keep in mind that these are pro-stock engine builders so the engines were pretty developed and had 2500-6500 rpm VE developing components and setup.

Now you look at NHRA Pro Stock and they run around 15 to 1 or so and run C-25 fuel or did the last time I checked. They can run 18 to 1 compression easily if they wanted to but they don't because they make less power due to detonation and tuning problems so again there's always a limit. If they only ran one dominator they would run more compression though of course but they have two of the big carbs.

What I will say is that if you can run super high compression (12+ to 1) on pump or (16+ to 1) race gas with adequate induction then usually the engine's not a good one unless it's the special olympics of racing as it often is on this website. We have run over 16 to 1 but again it's on an engine that has too small a TB or carb where they are starting to run out of air and have manifold vacuum so we have to.

racer7088

Their formula is semi sane and shows extremely diminishing returns but again I went from 750 hp at 15 to 1 and 980 hp by going to 150 to 1!

Of course the engine wont even run at 150 to 1 much less gain any 230 horsepower!

I think that formula's not way far off if you stay at normal race compression ratios but the gains from any compression increase are still just not there if you are also starting to have detonation problems as well.

BOWTIE

The numbers they are giving you are per point of compression. So, in theory, on an 800 hp set up, based on the previously mentioned ballpark averages, you would gain 48-64 hp going from 12:1 to 14:1.

ls1408cp

iTrader: (37)

I plan on running a c16 which is a 116 leaded. So whatever compression would be good with that and a correct cam with the right dcr. But I am not a engine builder so I will leave it to them.

racer7088

You can run a lot more compression with C16!