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Old 01-19-2007, 06:27 PM   #1
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Default I read Maximum Boost, now i have an easy question for you

Will the boost pressure be the same at a given rpm above boost threshold (e.g. 4750rpm) regardless of the position of the throttle (WOT or half or 2/3 throttle)? And regardless of load (gear or hill...)?

I thought yes...but some things i have read have indicated otherwise.

Thanks guys. I've never posted before but i have been reading here for a while, and i did not want to waste anyone's time before i did some research. I read Maximum Boost (and payed attention) but i am still oblivious to the obvious.
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Old 01-19-2007, 06:34 PM   #2
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Welcome to this forum.

I actually just gave ya my .02 on the other forum
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Old 01-19-2007, 06:47 PM   #3
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I don't understand it.

How?? I thought only one volume/pressure/speed of gas can be passing through the compresser wheel at a given rpm, right?

(i also posted this in the other place, but figured this might clarify my frustration)

Please if there is a simple answer, give it to me quick- i'm out of here in 13min, and wont be able to check again until monday.
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Old 01-19-2007, 06:53 PM   #4
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Once you get up to the set boost limit, if you reduce the throttle position to the point that the load is reduced, you will end up reducing boost pressure.
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Old 01-19-2007, 07:02 PM   #5
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Quote:
Originally Posted by olderguy View Post
Once you get up to the set boost limit, if you reduce the throttle position to the point that the load is reduced, you will end up reducing boost pressure.
thanks for the quick response. I am just having trouble conceptualizing the whole thing.

I'm out for the weekend. I will look this up on Monday when i get back (provided the boss does not take away the internet again) to see if you guys are able to help me grasp this seemingly impossible concept for me.
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Old 01-19-2007, 10:19 PM   #6
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Drive a turbo car and try it. It will instantly become understandable beyond someone just explaining it.
That is the only suggestion/explanation i can give though, olderguy told it the best way i know how to.
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Old 01-19-2007, 11:18 PM   #7
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i wondered this myself, and i think it has to do with gasses expanding and heat... when u are at say 4500.. only so much air can be pumped through your engine.. but the thing is when at say wide open throttle you are adding fuel to the air and combustion, whitch causes the air ro expand and creates heat... this expanding gass and heat actualy what drives the turbine, not just air flowing through it...

hope this helps
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Old 01-22-2007, 01:20 PM   #8
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You can have the same boost at the same rpm with different throttle angles. Remember the wastegate is regulating boost not just engine load.


Here is an example.

Car x is traveling at a sustained 130 mph in 5th gear with a throttle angle of 30% to maintain velocity. Boost is dead steady at 6psi, this is also the maximum amount that the system will see based on WG spring pressure. The driver decides to accelerate to 150 and opens the throttle to 100%. What happens to the boost? Ignoring any momentary spikes it should stay the same even though exhaust energy has increased as has the volume of air that the motor is using.

Does that make sense?
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