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Old 05-29-2002, 11:25 PM   #10
sherifx
Scooby Guru
 
Member#: 10780
Join Date: Oct 2001
Chapter/Region: SCIC
Location: RIP #92
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---- BRZ
Galaxy Blue Silica

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Quote:
Originally posted by bingo
Sherif, your graph looks real pretty, but is incomplete. I guess 4 years of university in Physics and economics wasn't enough. Is the pressure ratio in bar? What are you referencing this against? How about another graph with another turbo to compare to...stock vs aftermarket etc. Alone it means nothing. Perhaps you can enlighten me?
Maybe I should retract my statement from before. You obviously (to me) haven't done research on turbocharging specifically. Let me start by clarifying that I am not the all knowing god of turbos but I do know a bit. I know enough to know that I don't have to sling my credentials around to make people think I know something. I know that the graph in actuality is quite complete. If you knew how to read the things, you would see that the pressure ratio is a measurement of: (14.7 + BOOST)/14.7 = X. It is not a boost level measurement but a ratio measurement. Secondly the graph at the bottom is quite simply what the cfm the turbo is capable of flowing. Now within the actual data plotted you will see the #'s: 60,65, 68,70,72, 75 & 76. These are measurements for efficiency. Now when you figure out what boost you're running, lets say for arguements sake, 16.5psi or 2.12PR... you draw a line across the graph and see where it falls. Now you calculate the cfm flow of the engine and plot it across this line (to my understanding). As long as you stay within 60% efficiency for most of the power band, you should be sitting pretty, power and efficiency wise. If you take the measurement at 2.12PR you would see that yes at 6000rpms you can extract nearly 400cfm, yet its outside the 60% efficiency range, which is the accepted and suggested range for an intercooled turbo engine. Now take what I explained and apply it to 22psi... and its ridiculous. The turbo is operating soo inefficiently for the majority of the rpm band, it ends up creating more heat, which == less dense air, which == less efficient combustion, which == less power... Take some time, pick up a book like Maximum Boost... like I have

sherif

Quote:
I want to know why there would be more back pressure with the stock turbo that would create these problems than with a larger turbo. I guess I am an analytical type of gut. Want to know the science behind it.
The answer for this can be derived from the info above. The turbo is essentially being "asked" to flow soo much air it becomes inefficient and can't spin as quickly as is necessary to fulfill the "request." Because of this inability to spin as quick as needed the air gets bunched up in the turbine and creates backpressure. A larger turbo does not have this trouble due to design reasons which I'm not really qualified to answer *shrug*
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