How many PSI?

[jbwetzels]

Hi all i was just wondering if someone could enlighten me on how to figure how many psi i can run, i know it all depends on what parts you fit but lets just say i have a monster turbo is there some sort of formula?

[GrayZee]

Too many variables to answer, compression ratio, head design, fuel octane, intercooler, outside temp, air/fuel ratio and timing to name a few.

[jbwetzels]

ok then lets say i gave you all of these then how would you go buy figuring it out

[mtcookson]

from what i understand... usually with a larger turbo you'll run less pressure due to its higher air flow at any given pressure. with a smaller turbo that can provide the air of the larger turbo but at a higher pressure should get you the same amount of hp (maybe a bit less due to efficiency) however the pressure, being higher, should land you more torque (this is due to turbochargers theoretically increasing the displacement of an engine. for every 14.7 psi of boost, you are effectively increasing the displacement of the engine by two times. so, if you have a 3 liter v6 engine running 14.7 lbs. of boost it would be the equivalent of a n/a 6 liter v6.)

 

the only downside to running more pressure is it can be harder on the engine and the heat is probably a lot higher... but you should gain a good amount of torque.

[GrayZee]

Pressure VS airflow is more about your engine displacement (and intake plumbing) The more air you force into a small area the greater the pressure will be. So if you have a 2000cc engine then 10psi requires a certain amount of air, a 4000cc engine would require roughly twice as much air to acheive 10psi (depending on intake manifold, intercooler, plumbing, ect.) Having a bigger turbo on a smaller engine just means that the tubine will not have to spin as fast to push the same air as a smaller unit and can ultimatly reach even higher pressures if the engine is small enough. However if the turbo does not have to work as hard, less heat will be created. The downside of having a bigger turbo is that the lag factor will be increased. Picture a stock L28 turbocharger mounted on a big ole Kenworth highway tractor, I'm sure it would spool up INSTANTANIOUSLY but I doubt it could push enough air to pressurize an engine that size to even 2psi and it would probably burn out the turbo bearings in a matter of minutes.

[GrayZee]

ok then lets say i gave you all of these then how would you go buy figuring it out

 

I don't think there is any precise formula as that it would be too hard to calculate for the way every different engine responds to boost (and avoiding detonation) I think it would be easier for you to list off your setup and maybe somebody has enough knowledge and experience with that engine and can give a rough answer. For example, there is a load of knowlege here on the L28et, most people here seem to agree that 9 or 10 psi can be done without a intercooler and 20+psi can be done provided it is setup properly (good ecu tuning, timing, intercooler, strong bottom end, ect.. ) Of course people that are running 20psi realize that they are playing with fire and could possibly blow their engine at anytime.

[Clifton]

Big turbo or small, I slowly raise the boost till I here light knock and then back it off 2-3 psi.