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Old 06-14-2006, 01:07 AM   #11
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Quote:
Originally Posted by ZCRX87
what do you mean it dumps it?
The bypass would open untill it got less then 14-15 lbs. and then close once it saw that. Not eh safest thing in the world but you can bypass it and it will not dump boost. Safest thing is to get a custom PCM.

Don't think that you will be able to run nearly that much boost. Most Bonne'* have a hard time running 12 lbs. without KR.
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Old 06-14-2006, 09:30 AM   #12
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ZCRX, the M62 and M90 both reach a point (especially the Gen2 M62 you have) where the boost charge is so hot you lose efficiency. You may have a higher pressure, but it'* so hot that you lose power. Your cooling might help, but at the same time, the M62 also has an efficiency limit.

You cannot get that much boost out of it. It'* just not physically possible. I'm running a Gen3 top end on my 93 now, with an insanely small 2.2" pulley, but I've done alot of other prep work to the top end of the engine to get there. I may very well be beyond the point of good power returns. I have to characterize my water injection effects first, but may still end up moving back up in pulley size. As an point of comparison for you, I can produce the same boost as you if your car was running a 2.2", and my car was running a 2.5", but now I'm running a 2.2" as well. Make sense?

Your stock PCM will dump boost at a predetermined point based on lots of different conditions. It can be bypassed, but that is a very dangerous game to play. You have to allow the engine to protect itself, particularly when you understand the unique dangers to a forced induction engine under high boost.

If you want over 12psi of boost and you want it to work efficiently, you can't use a Roots blower. You need a centrifugal supercharger or a Turbo.
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Old 06-14-2006, 09:57 AM   #13
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so what options are there for making the ecm tolerate 20 psi?i was looking at the bypass vallve a couple months ago and i think it looked like it was just operated by a vaccume diaphram. how does the ecm control the bypass valve?
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Old 06-14-2006, 10:02 AM   #14
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www.gmtuners.com or www.sinisterperformance.com (they are one and the same), but you're not getting 20 psi out of an M62 even if you run the belt on the input shaft itself. You'll have a host of other problems you cannot overcome. And if you want to run that high of a boost pressure, remember that PRESSURE isn't the key. FLOW is the key. How are you going to efficiently get that flow through the manifold, into the heads, and out the ***?
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Old 06-14-2006, 12:18 PM   #15
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Not going to happen without a bigger blower. A bigger blower would require so much custom machine work you could buy a Corvette for the same price.

Since you are stuck with the M62 I will reiterate what has been said above. To get more boost you need to spin the blower faster. When you spin the blower faster you need to improve flow through the engine to avoid KR and other bad things. (BOOM)
When you improve flow boost goes down. (Boost is air stacked up in the intake.)

A good example is my M45'd VW. When I went with a ported head, ported and port matched intake, header and high flow cat I lost nearly 2psi of boost but gained 30+ hp.

You can stuff all the air in the world into the manifold but if it doesn't go into the cylinders and out the exhaust you will gain nothing.
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Old 06-14-2006, 12:25 PM   #16
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Boost pressure isn't doing anything for you. It'* reserve. If you don't use it, you gain nothing. When you make flow improvements to the top end of the engine, you WANT to see your boost pressure in the manifold drop. That means you're USING it, not just storing it.
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Old 06-14-2006, 02:03 PM   #17
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Quote:
Originally Posted by ZCRX87
so what options are there for making the ecm tolerate 20 psi?
None...the ECM has a 2 bar MAP sensor table, it cannot understand higher pressures.

Cheers,
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Old 06-14-2006, 02:39 PM   #18
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Well, in the Series I, the PCM has no clue how much pressure there is. The MAP is for the gauge only.
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Old 06-14-2006, 04:07 PM   #19
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Correct, the MAP is only for the boost indication (to the gauge). However, there are other conditions that can be met in the PCM that will dump boost via the BCS.
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Old 06-14-2006, 06:47 PM   #20
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so what does the sensor on the bypass valve do and how does it work? i tried to find it on a diagram but i'm not sure what it is called. could you mechanicly change the bypass pressure by adding resistance to the diaphram? i would just test it but i don't have my meter here.
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