G2G

If you have a setup where all you do is add an aftermarket turbocharger, dyno before and after, you will see the gain that you get with the new turbocharger. But if you average the horsepower made over the boost level, you will get some number for 1 psi = some hp number. This is not accurate at all. Each individual turbocharger has a best efficiency range, where it produces the most horsepower for the amount of boost being created. So if you have an average for a turbocharger who's peak effiecency range is 25-35psi, and you calculated it at 20 psi, it won't be accurate, because you will produce more horsepower in the peak effiecency range. The horsepower produced by a turbo also begins to level off, meaning that for each psi of boost that you add, you don't get as great of a power increase as you did previously. This means that you have a parabolic curve up top. This means that if you calculate what hp you should have depending on the peak effiecency range it will be higher than the actual horsepower that you produce. You can not say that a turbocharger will produce x amount of hp per psi and expect it to be anywhere near the actual power that you produce. Otherwise you would see a completely linear hp curve from 0psi to xpsi. This would mean that on any turbo if you increase the boost you will see a completely linear curve in power that increases constantly. Take a stock S5 TII. It produces 200hp at 8psi. If we divide the hp by psi we get 25. Meaning that for each psi you generate 25 hp. So lets see how much a stock TII turbo should make at 45 psi. (45psi)x(25(hp/psi)) the psi cancels and you get 1125hp. So you're telling me that a stock TII turbo should produce 1125hp at 45psi. This is not at all the case.



- Hand

nopistons94

up to a certain effeciency, i dunno man im sorry but i still believe that theres a way to calculate it based on the flow chart of the turbo charger. Every one has its PSI where it stops making power and just starts pushing hot air. my starions stock turbo stops making power at 15psi but from 10psi - 15psi theres about a 5hp gain per PSI increase

G2G

If you know the volumetric efficiency, displacement, what boost you want to run, and the rpm, you can read a Compressor map and see how efficient the turbo is with the desired application and whether it will surge or not. Again that 5hp per psi is an average. Most likely if you graph psi vs hp, you will find that at one side or the other you will have a higher amount of hp being generated per psi, and a smaller amount of hp being generated per psi. Look at a compressor map and you will see that as you increase rpms you go through different efficeincy ranges, this means that at one point you'll be making more hp per psi than you will at another given rpm. If there was an absolute hp/psi you would have to stay in one efficeincy range the entire time.



- Hand

Dramon_Killer

PV = nRT

G2G

But do you know why PVR and T are capitalized?



- Hand

nopistons94

exactly. In the given compressers efficency range, thats how one of the dudes calculated the HP per PSI ratio. Now its only good from 0-15 PSI on the stock 12a turbo thats in my car, other than that like i said its just pushing hot air.

G2G

Look three compressor maps, with the boost levels drawn in vs rpm. NONE OF THEM STAY IN ONE EFFICIENCY RANGE!!!!!!!!!! I REPEAT NOOOOOOOOOOONE



- Hand