CnmyTeg

im about to have abacus build a motor for me, theyre sleeving my block right now, and its time to order pistons.....im getting so many different opinions on what compression to go.....please help!! what compression do you recommend and why. by the way its a ls motor, stock compression is 9.2 :1.
HELP!!

Cosmo

Depends on how much boost you want to run. The higher you run, the lower static compression you should have (i.e. compression ratio). A lot of factory turbo cars have 8.0 or 8.5:1 compression. I wouldn't go any higher than 8.5:1 for any turbo car. In this case, less is more. The lower compression you run, the higher you can turn up the boost. Of course, there are other variables (fuel, timing, turbo efficiency, intercooling, etc.) to consider.....

Greaser

do you care about low end/off boost torque? if so, stick with 9:1 or 9.5:1 my white car runs a 9:1 piston setup and i can boost up to 14psi without any detonation.

if you want to be safe then stick with 8:1 or 8.5:1. you will need to raise the boost to make the same power a higher compression lower boost setup would have made.


its all a tradeoff.



on the race car, I recently found out my pistons advertised at 9:1 were actually more like 11:1. I used to run 12psi on that setup all the time. 20 with race gas.

CnmyTeg

damn...i dont want my car to be dumpy out of boost, and i dont want to have to run massive amounts of boost to make power, but i dont want to detonate or have a unreliable motor either...i made 238 on 13pnds on my stock ls motor, so if i drop compression to 8.8: 1 ill have to run like 17pnds to make the same power? but if i raise compression to like 9.5:1 then ill only have to run 10pnds to make the same power right? but with higher compression its a little less reliable right?

Cosmo

Well, final compression ratio is what makes power. Sort of. It's far too in depth to cover here. But, my car has a 8:1 compression ratio, and has decent bottom end. It won't hang with a V8 on bottom, but by 3000 I'm at about 12 pounds of boost, and at 20 psi by 3900 rpm, so you hardly notice the lack of power. If you run a huge turbo, you will obviously have more lag, and less low end power. But, if you run a T3/T4 like most Honda/Acura guys, you won't notice the lack of low end power.

uptownspeedstar

My 2 cents...Id go with a higher compression like 11.5:1 low compression is just a band-aid for bad tuning.Plus with Higher compression youll get alot less turbo lag.

Cosmo

Umm... yeah. That's exactly why people run low compression.....

reXer

Please go read about compression vs boost and effective compression ratios. Not reaching your power goals because you chose a compression that's too high is a bad thing. The greatest tuners in the world can't break a detonation threshold.

hahaha

MORE IMPATIENT

my 2 cents , if you run that low of compression in a honda that is 1.8 liters, that is already lacking low end torque your car is gonna be so dumpy out of boost and its gonna take even longer to spool up, the reason your wrx hits boost so fast is cause that tiny turbo and your larger motor, 1.8 liter motors like our hondas are running 9:2:1 compression stock and we still have turbo lag on t3/to4e turbos, my turbo didnt hit full boost until around 4600-4800 rpm, you lower that compression and its gonna take even longer to hit boost, yea you might be able to run more boost, but why, to make the same power you could have on less boost with higher compression, i dont see the point in lowering compression especially when his block is gonna be fully built and sleeved, the car will be a dog out of boost and good luck making any more power on pump gas than you would have keeping compression higher or at least stock ratio.......

MORE IMPATIENT

i believe i told him the same thing on the phone earlier, thank you for backing me up on that theory.........but the person building the motor and getting everything together knows what hes doing and is respected by all, 10 second honda, cant argue with that, results are results.............