legacycentral bbs

what is the hp tp si ratio fror our cars, meaning that if i increase the boost by 1 psi howmuch more hpo and torque will i get, and what about 2 psi, and so on

This isnt 100% correct, but I go by the calculation that each psi give 7% of the stock hp. This works for low boost calculations it seems.

This means that the turbo engine, with no boost, is about 100 chp. Then if you take 7hp per psi, then 8 psi give you 156 chp. Pretty close.

These calculations worked out pretty good for me and my boosted NA. Since I started at 130 chp, 7% is 9.1 hp per psi. 7 psi is 64 ish additional hp which is 194 chp. I dynoed at 152, but this was with a bad coil wire and clogged fuel tank sock. But the 20% loss commonly associatted with AWD cars was pretty close.

The higher the compression ratio probably gives a larger percentage of power per psi, which is why I would like to try to get my NA up to 12 psi. If I ever have the money

That means my car at 15psi is 240.5chp. I believe it, based on how different a stock WRX feels. I estimated 230chp but more torque than the WRX, but I just pulled that number from nowhere.

well ur talking about a na setup with a turbo, i was hoping for more of the figues for a stock turbo, and even if it is around 7 hp per psi, isnt that too low, considering that a 89 supra turbo gets around 17 hp per psi.

It's not easy to calculate something like that because a) every turbo and engine combination will be different, b)the amount of power added will start to drop as the turbo is past its peak efficiency and c)the power will start to drop as the IC becomes heatsoaked, or not big enough for higher boost levels.

i understand that, and its y i said on a stock setup, without a ic. and on a range mabye from 8 to 14 psi, i would like to know which would be most effieient, and how much power i can get out of it at most.

I was talking about the stock turbo.

douglas vincent wrote:This means that the turbo engine, with no boost, is about 100 chp. Then if you take 7hp per psi, then 8 psi give you 156 chp. Pretty close.

The stock setup is worth about 7 hp for every psi of boost.

But admittedly, the higher you go, the more power you can get, ie the percentage increases, but I do not know the math formula for that.

BAC2.5 was getting 220 whp at 16psi, but he was/is HEAVILY modified to get this. Thats almost 300 chp.

I believe your guess. To oversimplify a TON, power should be proportional to the amount of air you get in the engine... and the amount of air should be proportional to absolute pressure (not boost) assuming the air isn't changing temperature too much.

If you go up 1psi (from 9psi to 10psi) you're raising the absolute pressure by 4%. So, if you raise your 160hp by 4%, that would be about 7hp increase. Perfect!

HMMMMMMM


I am very intrigued by this. I have alot done to my motor and am getting even more still since the warped head. Just got the delta Cams so valve job, and port/polish here we come. I wonder if the little things like the kniving/polishing or my throttle body and honing my intake manifold will help.

oh and I just won a TD05 housing on ebay, so I am gonna get a 16G or 18G for a wrx.