i've read all the threads about high and low compression on pump gas and all that. i'm talkin about a motor that will only be ran on race gas. since the motor is only gonna be run on race gas what limits higher compression 10:1+? what are the advantages and disadvantages of low compression (8.5:1 and lower) and higher compression (10:1 and higher) in race engine applications?

 

ttt

 

you need to figure out how much power you want, then figure out what gas you can run, then you can decide on compression.

personally i would go with a flat topped piston with as few "features" as possible. this will keep the heat more uniform across the top of hte piston and give the flame/mixture a smoother path. thats what i plan on doing in my race car.

depending on the head and chamber work that should get you around 9.5-10:1 compression. with that compression you can still run 350-400 on pump gas and have some fun on the street

 

well this car will only see the track, so i'm not really worried about pump gas drivability..

 

will you be rebuilding often?

 

hopefully not, but probably if something breaks then i'll rebuild it..

 

high compression, race gas, forged rods and pistons

 

Wouldnt low low low compression be good for a FULL race motor? like 8.5:1 or even a 8.0:1? I thought people just didnt use those on street setups but it would be good for full-race because of the amount of boost it could take. Please correct me if I am wrong.

 

low compression is the safer setup for street driven cars...If I were building a race car, I'd go 11:1 with 10-12psi on race gas

 

you use compression to control the ammount of power you can make on a specific octane fuel.

i have done over 500 on 7.8:1 2liter b16 with pump gas, you cant go much over 375hp on pump gas with flat top'd 9.8ish:1 pistons in a b18.

compression dosnt really matter untill you start pushing the limits of your fuel. if you make 300hp on 10psi with 10:1 you will make 300hp on 10psi with 8:1. the difference comes in when you start adding boost. you can add alot more boost with 8:1 than you can 10:1 on said gas. the higher octane gas you use the higher that limit becomes.

 

with 10:1 and c16 what are the limits???

 

it comes down to how much power you want and your max boost you can run and are running a 3bar map or 5 bar map?

 

Figure out what effective compression you are aiming for. Typically around 20:1 on pump gas with sleeves and forged internals, and probably not more than 22:1 on race gas.

The formula is:

((boost psi / 14.7) + 1) x static compression = effective compression

I run 22 pounds of boost with 8.4:1 static compression for 20.9:1 effective compression on a B16. That nets me 350-400WHP, depending on my turbo setup and tune (tuned by jdogg incidentally).

Generally speaking, the lower you go with your static compression, the more peak power you can make for a given effective compression, and the more off-boost performance you give up. So it's a balance between daily drivability and max power. If you're only going to be drag racing at the track, I'd say get your compression around 8:1 and turn up the boost until you hit 22:1 effective compression, with good tuning of course, otherwise you will just blow your stuff up.

 

I go back an forth even in my own brain on this debate. I used to be all about high compression, but recently ive changed my opinion. I don't want to be boost limited.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by quik sol &raquo;</TD></TR><TR><TD CLASS="quote">Wouldnt low low low compression be good for a FULL race motor? like 8.5:1 or even a 8.0:1? I thought people just didnt use those on street setups but it would be good for full-race because of the amount of boost it could take. Please correct me if I am wrong.</TD></TR></TABLE>


The reason people run low compression in street cars is because they are running pump gas and are worried about detonating on low octane. If you're running C16, who gives a **** about detonation, it's practically a non-issue with a fuel of that high octane. The higher compression will make a bit more power N/A, and then should make a little bit more power when boosted. I'd guess that going from 9:1 to 10:1 or even 10.5:1 might be worth 20 WHP on a 550-600 WHP setup.

 

You can run meth on 12/1 and loads of boost.... 900hp range

 

[QUOTE=rmcdaniels]Figure out what effective compression you are aiming for. Typically around 20:1 on pump gas with sleeves and forged internals, and probably not more than 22:1 on race gas.

The formula is:

((boost psi / 14.7) + 1) x static compression = effective compression

QUOTE]

well if i plug my current setup in that formula i can only boost 18lbs on race gas safely??? i'm currently running 10:1. what about all those other pro racers running 10:1-11:1 on race gas boosting 25-35lbs? how can they get away with it?

 

probably a better race gas than you.

 

effective compression is an ok rule of thumb sometimes.... but its more to do w/power than boost. i have done a couple of single cams boosting over 20psi, but only making 300hp and still on pump gas...