glenb1991

i've been looking more and more into my build, and at this point not sure if i wanna go turbo or n/a. Lets say i build for a turbo compression wise, what do i have to do, having a 9.5:1 compression to be able to run the car? i never understood compression completely so any info on it can be helpful, in the mean time, google here i come.

96capricemgr

9.5:1 will run NA, if you go big on the cam it may be a little soft on the bottomend lacking some torque and response but wont be too bad. Have to consider that for a LONG time all the OEM engines were in the 8s so 9.5 is still higher than a lot of engines that have been used over the years.

Some guys even built boosted LT1s at 8.x:1 compression, they just give up some of the response it could have had off boost.

glenb1991

ok so i guess around 9.5:1 is a decent medium then. Cuz i wanan run this car as is first, sits its being compltetely rebuilt, and i wanna break it in and what not off boost, and take it to the track off boost. so i mean, do i have to run a higher octane gas or what? i just never understood why boosted engines need a lower compression as compared to n/a motors. and yea i noticed a lot of the stock 4 bangers are in the <9 area thats what brought this question up.

Injuneer

You need lower octane fuel when you lower the compression ratio. Be sure to evaluate the "dynamic compression ratio" (DCR), not just the static compression ratio.

"Boost" increases the pressure of the combustion chamber charge BEFORE it is compressed. Since compression ratio is the ratio of the pressure in the cylinder with the piston at TDC compared to the pressure in the cylinder at BDC, increasing the pressure at BDC will dramatically increase the pressure at TDC, leading to higher chances of detonation and the resulting damage it does. The compression process also increases the temperature of the air charge. Higher compression ratios increase the temperature when the piston reaches TDC. The hotter the air/fuel charge at this point, the more likely you will run into pre-ignition or detonation. That's why high boost applications require an after-cooler, or an alcohol or water injection system to reduce the air charge temperatures.

glenb1991

so having a 9.5:1 in n/a i shouldnt run 93 octane? but when i put the boost in it will be fine to run the 93? or do you mean more like going between race gas like 100 octane in a boosted app and 93 in a n/a app all at 9.5:1 SRC

96capricemgr

In all likelyhood 87 would be fine NA and 93 once you boost it.

The b-body motors were 10:1 with iron heads and are fine on 87 octane, aluminum heads get away with more compression before detonation is an issue.

87bandit

just remember boost costs a pretty penny and unless you have some decent hp goals or just really want a boosted setup you might want to reconsider

glenb1991

well at this point, im rebuilding the whole car. the motor is getting refreshened, and if i can build it to a low compression, and throw the boost on later but still drive it n/a for now then thats what imma do. since im doign the tuning and will have a laptop in the car i will save two tunes, one for boost and one for n/a. i have an intercooler, bov, manifolds, and a small t304 turbo. the turbo will likely get replaced with a 70-80 trim, and the t304 will either get sold or put on the subi when the camaro is done. my hp goals are around 400 on boost.

Injuneer

You can EASILLY achieve 400rwHP on an NA LT1, without boost. If that's all you are after, you are going around it in completely the wrong way.

glenb1991

yea i kno its possible n/a, but if i can get it n/a then throw boost into the equation later down the road with minimal adjustments and hit 5-600 territory then thats prolly what imma do.

87bandit

it's gonna be pretty hard to hit 400rwhp n/a on a boost friendly app imo