Boost ?
Burning Brakes
Joined: Sep 2005
Posts: 980
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From: Raleigh NC
In a positive displacement system (like the maggie), it's once your in boost all the way up (though the heat from compressing the air causes the system to "run out of air" so to speak). So if your running 7psi, you run 7psi throughout mass of the positive boost range.
On a centrifugal charger (like the procharger or paxton), boost increases with the RPM's at a rate of x^2. So if your running 8psi at 6000rpm, your running around 4psi at 3000rpm. In this case, you get max boost at your max rpm.
Burning Brakes
Joined: Sep 2005
Posts: 980
Likes: 0
From: Raleigh NC
I don't think it's a stupid question at all... Knowing what your getting out of your system lets you know how to better use that system to attain your goals.
Do keep in mind that the basic boost math is only half of it. The centrifugals tend to get higher numbers in the max rpm range, where as positive displacement blowers give great low end and start to run out of air up high do to heat/density gains and a loss of entropy change.
Edit: err.. that's heat gains resulting in density losses.. My bad, drinking beer ;0p
Do keep in mind that the basic boost math is only half of it. The centrifugals tend to get higher numbers in the max rpm range, where as positive displacement blowers give great low end and start to run out of air up high do to heat/density gains and a loss of entropy change.
Edit: err.. that's heat gains resulting in density losses.. My bad, drinking beer ;0p
Last edited by o0 zeno 0o; Mar 7, 2008 at 10:34 PM.
Burning Brakes
Joined: Sep 2005
Posts: 980
Likes: 0
From: Raleigh NC
I was a ME major, so I know the concept part of it... But as one of my old professor's use to say, there's nothing more dangerous than an Engineer with a toolbox.
Edit: ME == Mechanical Engineering, btw... Technically "Compressed Flow" is Aerospace Engineering material, so weigh it as you see fit.
Last edited by o0 zeno 0o; Mar 7, 2008 at 10:48 PM.
Melting Slicks
Joined: Apr 2005
Posts: 3,418
Likes: 1
From: Chicagoland Area IL
The purpose of the bypass valve is to protect compressor (ATI, Paxton, Votech...) or keep it from surging. That meaning because compressor is mechanically coupled it will produce X mass flow and depending on restriction X boost (oversimplified). So if you rev engine to 6000 RPM downshifting for corner, you do not need extra mass flow supercharger is producing...
A bypass valve simply vents excess flow (resulting in boost do to restriction) until vacuum is lost (high throttle opening). Or most simply put until you put your right foot into it.
It is somewhat normal to gently rev engine and not see boost with centri. The bypass valve is simply doing its job.
Oh, "o0 zeno 0o" it's not a squared but it is exponential when describing boost of centrifugal.
Mike
Melting Slicks
Joined: Apr 2005
Posts: 3,418
Likes: 1
From: Chicagoland Area IL
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Burning Brakes
Joined: Sep 2005
Posts: 980
Likes: 0
From: Raleigh NC
Although this will go down hill quick... revving your engine with no or little load should not get you much boost with centri do to bypass valve!
The purpose of the bypass valve is to protect compressor (ATI, Paxton, Votech...) or keep it from surging. That meaning because compressor is mechanically coupled it will produce X mass flow and depending on restriction X boost (oversimplified). So if you rev engine to 6000 RPM downshifting for corner, you do not need extra mass flow supercharger is producing...
A bypass valve simply vents excess flow (resulting in boost do to restriction) until vacuum is lost (high throttle opening). Or most simply put until you put your right foot into it.
It is somewhat normal to gently rev engine and not see boost with centri. The bypass valve is simply doing its job.
Oh, "o0 zeno 0o" it's not a squared but it is exponential when describing boost of centrifugal.
Mike
The purpose of the bypass valve is to protect compressor (ATI, Paxton, Votech...) or keep it from surging. That meaning because compressor is mechanically coupled it will produce X mass flow and depending on restriction X boost (oversimplified). So if you rev engine to 6000 RPM downshifting for corner, you do not need extra mass flow supercharger is producing...
A bypass valve simply vents excess flow (resulting in boost do to restriction) until vacuum is lost (high throttle opening). Or most simply put until you put your right foot into it.
It is somewhat normal to gently rev engine and not see boost with centri. The bypass valve is simply doing its job.
Oh, "o0 zeno 0o" it's not a squared but it is exponential when describing boost of centrifugal.
Mike
Burning Brakes
Joined: Sep 2005
Posts: 980
Likes: 0
From: Raleigh NC
Burning Brakes
Joined: Dec 2004
Posts: 810
Likes: 1
From: Turbocharged in NC
Simple answer for me, at WOT, my boost climbs to 160kpa by 3500 rpm and my boost controller has it stay there until red line. I have the APS twin turbo kit, and a manual boost controller. No hard math. Since they're turbos though, I have actually hit max boost by 3000 rpm before when upshifting, and if it isn't a WOT run, it may never hit max boost.
Last edited by wewing; Mar 8, 2008 at 10:36 AM.