Houston999

iTrader: (3)

from 11:1 to 12:1 comp. how much gain should i see? with a stock displacment T rex and 90/90

GOaT Cheese

No other changes? Comp. ratio increase only? Gain will be negligable. If increase of comp. is to take advantage of more aggressive compenents that need higher comp., then who knows.

2001 Pewter WS6

iTrader: (43)

Around 2%

slow trap

iTrader: (22)

hmm,i thought it would be around 4 %.
is your dcr way low at 11:0 cr ?

ArcticZ28

iTrader: (14)

That would be the only logical reason to raise SCR.

DONAIMIAN

iTrader: (18)

What cam? If you have one of the bigger cams, then you would see a deffinate gain. But with something on the small side, I dont think it would be worth it.

PREDATOR-Z

~ 4%,
let us say you were making 400rwhp, so aproximately 16 rwhp +/-

Spinmonster

and 20 rwtq.....who said negligable

Compression is the single biggest reason why guys never get the power they read others getting.

sickss228

iTrader: (27)

True The rule of thumb is for every one full point increase in compression you will see a horsepower increase of 4%

bigdsz

iTrader: (1)

Yeah, but it also increases the chance of detonation. My friend recently wiped out #7. He was running 59cc AFR's, so the CR was maybe 11.7 to 1. The engine couldn't handle it on pump gas. At least now he's got an iron 408.

Spinmonster

That is a tuning issue not what his staic CR was. If you have12:1 static at 8.4-8.7 DCR, it is no more dangerous than a moderate cam at 11:1 which has the same DCR. Static doesnt determine the ability to run pump gas.

Not to mention the other variables of what his quench distance was, combustion chamber carbon deposits and quality of fuel which can cause detonation in a stock motor.

sickss228

iTrader: (27)

Yeah I've seen setups that have 12.5:1 SCR and run fine on pump gas, its all in the tune.

Gauge

iTrader: (3)

What "more agressive components" need higher compression, and how does it help them?

Biggs

Depends on the combo and the tune, I have seen an 800 hp bbc go from 12.5 to 14 and only gain 2 hp The last motor of mine that was also a bbc went from 11.7 to 12.6 and gain 0 mph (no dyno available) but those are bbc with dome pistons and I think the flame travel was hurt and prevented any real gains. If you have a decent size cam I would say 4% but a small cam detonation will get in the way of any useable power. Unless you are needing the compression to support a large cam or fighting high altitude, the returns are not as good as you might think.. It is all about getting your cranking compression (dcr) right for the elevation where you race and the fuel your using.

JakeFusion

iTrader: (7)

Although, I love high compression (never run less than 12.1:1 on pump gas myself and no less than 8.4:1 DCR), you have to realize that the bearings and all the other components in your engine are subjected to extreme pressure with a very high DCR. Also, you need a cooling system that is far better than stock. Extremely tight quench also helps fight detonation (I run .030" or so). TR6s gapped at .045" or so, good fuel, and a GREAT tune all help.

GuitsBoy

iTrader: (4)

Big motors typically have large enough cams to bleed off DCR. This is why you see strokers at 12:1+ that act like 346 at 11:0.

PREDATOR-Z

I run 11.75 on 8.65 DCR, .040 quench and TR6 gapped at .040.
94 Octane and no issues.
Still at early tuning stage and 468 rwhp on A4
Static compression is not what we should look at, it is Dynamic and Good DCR will vary with DA as mentionned above.
So it is good to do all research and to understand what works for you in your environment while putting a combo together.

racer7088

If you are building a good engine with good heads and cam you will not be able to keep adding compression. Most 12+ to 1 engine I see in Houston don't make good power or detonate a lot and are hard to tune. They don't run good mph either unless they are way light etc. Now with race gas I would certainly add more compression but with 100 degree Houston weather and rush hour traffic etc. I just don't see any good in these high compression deals on the street.

If everythings right and you are running a REALLY big cam you might be able to do it but the heads, cam and intake are there to increase VE not REDUCE it so you can't always add way more compression with a cam simply because it's bigger or the "dcr" numbers would be better. Basically you guys are semi right but there's a definite limit to how far you can go and still be safe on pump gas. I don't go over 11.50 usually even with pretty big cams and have had several 550+ RWHP cars with no detonation problems at all.

When you take apart the 12+ to 1 engines from most shops you start seeing problems related to the compression and the resulting detonation. Remember NHRA and IHRA Pro Stock engine builders couldn't even run much over 12 to 1 at the engine masters competition and these guys were running cams bigger than we are talking about. Several engines were destroyed trying to run that high a compression on pump gas. The overall consensus there was 11.5 to 1 was probably the limit on the engines that weren't turds and made big power. If you CAN run 12.5 to one on pump gas basically your engine has to be a pretty bad combo if it hurts cylinder pressure that much that you can run 12.5 to 1.

GuitsBoy

iTrader: (4)

I would assume that these motors have much higher volumetric efficiency than what we're talking about. When we crunch numbers, we compare the DCR to other LS1 motors that have similar volumetric efficiency. If you calculate the same DCR on a race motor with 20% more volumetric efficiency, theres gonna be 20% more air in that cylinder leading to detonation. Calculating compression ratios, static or dynamic, do not take volumetric efficiency into consideration. They just assume 100% VE. Thats fine as a rule of thumb for comparing LS1 to LS1, but when you compare LS1 vs. a prostock or nascar motor, its apples and oranges.

racer7088

These weren't pro stock engines. They are regular engines with production based parts and the LS1 is as good or better than any of them. The LS1 experiences similar VE as does any well tuned engine with great heads and an awsome manifold like the FAST 90mm.

The LS1 is actually banned fom Engine Masters.