I'm in!! I don't see why anyone needs to be PM'ed about this but I'm willing to learn more!

 

+1 APPROXIMATELY... TAHTS FOR THE MOST PART TRUE

 

i have seen 0hp going from 14-17psi when the turbo was just out of steam and over 50rwhp going from 16-17psi when the turbo was right in its sweet spot.

 

Can you elaborate on a turbo's sweet spot? I know that positive displacement chargers can be over spun rendering them inefficient, is it the same with centrifugal ones?

 

heres what I have always thought there is no real answer across the board. At 14.7 psi you double the atmosphere or doubled cubic inches of the engine. So say you have a 350 to start then dump 15psi you will have some losses. So now your engine is moving the air of a a 700 inch engine. That does not mean you doubled the HP you just doubled the air/flow going into that engine. You have also increase the load on all rotating parts and that costs you hp.

just my .02

 

things get a little technical on this one but i will give it a shot. i will post up 2 turbo maps. one of a t76, another from a pt88. the maps are a little hard to read at first but very cool once you get them figured out. you can clearly see why i made no more power going from 14-17psi on the t76 and why the pt88 did so well.





this is on my 408. with the t76 at 14psi i ran out of power at 640rwhp. i could get more boost but the intake temps went up very fast and i gained no power. we will call 640rwhp = 800fwhp = 80lbs of air. 14psi on that chart is a little under 2.0pr. you can see how at that level i was on the edge of the chart and as i added boost it was just spining the turbo faster but not really able to push any more air. air just got hotter.

now look at the pt88. 14psi(2.0pr) and 80lb's. i am right near the middle of the island. on a drag race set up it is ideal to be near the middle of that island. as i turned up the boost the turbo was able to push more air without geting out of its eff range. that turbo just kept making close to 50rwhp/psi right up to 1000rwhp then all the sudden it was just done.

turbo maps are fun to look at but just looking at the map will only tell part of the story. while the pt88 was great at making power it was very laggy. too laggy for most people in their daily driver.

 

Any pump or compressor has different efficiencies given the rpm thier spun at and how much "stuff" they're moving. Whether you're compressing air or refrigerant or anything, you'll have "sweet spot" on the compressor map where it operates as efficient as it can. The sweet spot is dictated by the rpm of the compressor/pump, the mass flow rate or volumetric flow rate, and the pressure ratio when it's most efficient. When you start to push one of these variables, the compressor/pump will start to operate outside of the sweet spot.

In parish's case he was probably asking the turbo to push more air, consequently it spun more rpm and it went out of the sweet spot and probably off the compressor map all together. When efficiency goes down, the temperature goes up which part of the reason why he saw no power gain with increased boost.

Just because you're not in the center island sweet spot doesn't mean it won't make power or it won't work. Its just not optimal.

edit:HA! You beat me to it Parish.

 

here is a quick calculator to give you the estimate...

http://www.eaton.com/EatonCom/Produc...iteId=EatonCom

click on the 'simulator' link

 

That is a really high hp/psi number even for a turbo. How much boost are you running? Did you get it dynoed before you had the turbo on it?