02-18-2010, 10:57 AM
|
#11 (permalink)
|
|
Base Member
Join Date: Jun 2009
Location: Germany
Age: 51
Posts: 38
Drives: 370Z
Rep Power: 16
|
Quote:
Originally Posted by RCZ
^ a change in temperature might make a 20whp difference. No one is saying the supercharger is blowing hot air either. I am assuming charge temperatures are hotter with the sc, but not enough to justify that much variation in hp. Remember that there is an intercooler between the turbos and the engine as well as between the sc and the engine. That cooler should be able to bring the air temps down to similar levels.
5psi is not harder to imagine than 20psi. Its the same thing.
Are we to assume that this supercharger is blowing hot air by your logic? I certainly hope not. We know charge air temp makes a difference, but their tt kit made like 400 at 5psi. How is the sc making 400 at 10psi.
|
I didn't mean to make any assumptions on the supercharger, I just wanted to point out that your "5 psi is 5 psi" statement and your conclusion regarding how everything that puts out 5 psi should be making the same power is simply wrong.
Because I am lazy (and the fact that I am not a native english speaker) I will "lend" a good explaination of efficiency I found in another forum:
Quote:
Using the equation above from Garret (and supported by Corky Bell).
Actual Flow = Map (ambient+boost) x Volumetric efficiency x RPM/2 x displacement
all divided by gas flow and intake temps.
Our scenario: 10lbs boost on large and small turbo assuming intake temps are the same for both. Yes this is possible if the larger turbo was not intercooled. Just bare with me..lol Also assume that both setups have the same amount of exhaust backpressure (ignore reality for a second will ya ;o)...)
.....................small turbo.......... large turbo
Boost.................10PSI................10PSI
flow....................less...................more
RPM...................fixed.................fixed
Displ..................fixed..................fixe d
intake temp........fixed..................fixed
exhst bck press...fixed..................fixed
gas constant.......fixed..................fixed
VE......................less...................more
Conclusion: If intake temps, backpressure, boost and RPM are held constant for both setups the larger turbo will make more power because volumetric efficiency has increased due to the greater flow of the larger compressor wheel at 10PSI.
DECREASED INTAKE TEMPS and BACKPRESSURE ARE NOT THE ONLY REASONS FOR PERFORMANCE GAIN.
But the above conclusion is ofcourse incomplete in the real world as larger turbos do decrease backpressure (further stimulating volumetric efficiency)
and
A larger turbo running within it 73% efficiency island or there abouts will produce a more dense intake charge assuming that the same intercooler is used for both setups.
The end result of a larger turbo operating in it's efficiency range is more power, but it comes from increased flow, as well as reduced exhaust backpressure and lower intake temps.
|
|
|
|
Similar Threads
24Likes
Threaded Mode
