drivelikeIstoleit

I was doing some research on someone elses 500rwhp build and in the thread boost at 1 bar was mentioned. when i did the conversion 1 bar comes to 14.5psi. now in the thread build they were talking about dropping compression from 12:1 to 10:1, 10:1 wouldnt be streetable for 14psi from a supercharger or turbo would it? would 9.5 or 9.0:1 be more effective and efficient?

drivelikeIstoleit

all these turbo threads someone has to know, or atleast peak boost for 10.1:1 compression.

1CAMWNDR

iTrader: (21)

Generally a Supercharger will work with a little more compression. So, for a 14.5 psi build on a Supercharged motor I'd say 9.2:1-9.8:1; for a turbo motor which generally likes less compression, a 8.8:1-9.4:1. But really, any of those will work if your tuner knows what he is doing.

drivelikeIstoleit

thanx 1cam

TurboAv

iTrader: (6)

What octane is your Premium fuel? Here in AZ we have 91. Other places have 93. That makes a difference as well. I'm at 9.25:1 on my motor and the guys at Procharger said I should be able to get 15-18psi on 91 octane pump. We shall see.

elias_799

iTrader: (8)

10.25:1 and lots of meth !!!!

or you can be like me and go with 8.6:1 and not use meth and run 20 on pump gas

omore01

iTrader: (1)

+1, 8.6:1 for high boost on pump gas and no meth, no regrets going 8.6:1 here.

XtremeDime

iTrader: (16)

Sigh, our pump gas is 91 er maybe 90 here im running 9.75:1 w/turbo setup. Not optimal but it will work

OneBadTA

Compression, Heads, Fuel, all make a difference with boost. With 9.5:1 and stock unpolished heads with 93 octane you should be able to do around 16psi. My old SR20 engine with 9.0 pistons and polished head did 24psi on 93 octane. On the unpolished head and stock 8.5 pistons i could only get 20-21psi on 93 octane. The detonation threshold comes down to more than just fuel and compression.

drivelikeIstoleit

we got typical 91 octane as the highest but also have E85 on tap in town. Im going to assume Pat was talking about a s/c then since 10 to 1 was the lowest compression mentioned. does driving at 8.5-9.0:1 while saving up for the s/c or turbo effect the engine at all? would be a DD, just trying to decide the boost or no boost factor.

TurboAv

iTrader: (6)

Lower compression definitely affects how much power you make with no power adder. I'm not sure how much each compression point makes a difference though. A stock LS2 is 10.9:1 I think and if you drop it 2 points to 8.9:1 I image you would loose 50-75hp. Just a guess though.

Josh@KY-Turbo

iTrader: (120)

Run it at 10:1 compression. Run good forged Internals. Make the power witha combination of higher compression and lower boost. It will make for a much more responsive combination. It is after all looking to be a street car build.

No point in running 8.0-8.5:1 compression unless your building a race car and planning to push 30lbs of boost. Even then I would still shoot for a 9.0-9.5:1 compression ratio.

Big_Bird_WS6

iTrader: (7)

now throw e85 in this mix and it changes alot. i built my motor at 10 to 1 and plan to run 18psi. with e-85 i will be fine.

drivelikeIstoleit

all the replies help alot guys. what would you consider the safety zone for psi on a 10:1 forged motor Josh, 5-8psi? i think the closest track to me is in brainerd and thats still quite a journey, so yeah mostly street terror/minimal strip, unless i move.

TurboAv

iTrader: (6)

If you run E85 you can run a lot more boost. So pick which fuel you want.

Josh@KY-Turbo

iTrader: (120)

We have 110 octane at the pump. For 93 octane I would look at 8-10lbs. Figure 100% stock long blocks are roughly 10:1. Guys routinely run 10lbs or more. Forged components are more forgiving than the stock components. Saftey is in the tune.

caindo

iTrader: (4)

my ls2 combo was at ~11.9:1 with a d1sc pumping out ~740rwhp on pump 100. i prefer a peppy off the boost ride, and if i need the big big numbers there's e85 and c12/c16 readily available

MY99TAWS6

iTrader: (3)

My car is 9.5 to 1. My builder said if going to run alc/meth injection 9.5 is good . If not then 9.0 and 8.5 if going to try to track and daily drive the car at high boost on pump gas.
You can run higher boost on higher compression but you do have to take out timing. Too much timing pulled will make the car doggy and lose pretty good power. There are arguments about if lower compression is noticeable in daily driving. I know I do most of my driving off boost around town so didn't want to take the chance of making it doggy but this can also be a function of gear choices,cam,heads,displacement,intake manifold,etc.Lots of variables.
I might have went 10 to 1 or even higher if had ready supply of e85. We have think 3 stations in our entire country none near me.
So I would just pick 9.0 to 9.5 and work with that.Of course forged parts can tolerate more mistake in tuning which is usually going to be be too much timing or too lean a mixture.Stock pistons are fragile things dont take much to break the ringlands.

SilverSS

iTrader: (30)

Are you saying pump gas, 10:1 at 14.5psi as to the OP's original question? I'd love to bump it up from 9:1 to 10:1 on pump at 15psi if it will live.

Josh@KY-Turbo

iTrader: (120)

I have built several turbo setup for Cars with stock long block 10:1 compression engines. Some of them have run as high as 12-14lbs of boost and been fine. Yes the tune has to be conservative to keep the engines alive and happy. They made for very responsive and powerful cars. All were 93 octane cars. I wont say this was smart. These guys didnt care if their engine blew chunks.

Now if you are building a engine with Forged internals, why not shoot for 9.5-10:1? Forged pistons willl stand up to the cyclinder pressures better than stock pistons.