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Old 04-05-2003, 08:51 PM   #1
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Default Less boost after SC pulley upgrade?

I just replaced the coupler and pulley in my M62 this weekend. I changed the pulley from a 2.8 to a 2.5. I also pulled the TB, alt, and valve covers. Once I had it all back together I started it up and everythig ran perfect. So I took it out on a test drive and I noticed the Boost gauge was only reading to about 5-6 psi in the top end of the rmp range. It would jump to around 8 psi when shifting into 2nd. There is more power there. 2nd gear goes like a bat out of hell but the boost only registers between 5-8 psi. Even when launching I can light 'em up better but it just doesn't register the boost at higher rpm'*.

I checked all the connections and they seem fine. I am wondering if the facrory airbox could be chokeing it down? A lack of incomming air at higher rpm'*? I am planning on getting a CAI REAL soon but wondering what you all think?
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Old 04-05-2003, 09:07 PM   #2
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How much boost did you have before? Is it possible you are running into this overboost protection I've heard about recently?
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Old 04-05-2003, 09:10 PM   #3
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Quote:
Originally Posted by jwikoff99
How much boost did you have before? Is it possible you are running into this overboost protection I've heard about recently?
I am getting about 1-3 psi less than I had before on the top end but I can feel more when taking off and shifting gears. It'* as if all the boost shifted more towards the lower rpm'*.

The other thing I thought it might be is a slipping belt. I am still using the stock belt and it does seem to be tight enough, but who knows.
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Old 04-06-2003, 01:24 AM   #4
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But you feel more power? You MUST have more boost then, and it'* just reading wrong. You wouldn't be the first to run into vacuum problems after pulling the SC, Gord. I did, a couple others, too.

How much more power do you feel? 5-10 hp is about the threshold for 'feeling' it. Did you use the sealant on both parts of the sc? I mean BOTH sides of the gear section? So it sealed the rotor casing too?
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Old 04-06-2003, 01:34 AM   #5
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Quote:
Originally Posted by willwren
But you feel more power? You MUST have more boost then, and it'* just reading wrong. You wouldn't be the first to run into vacuum problems after pulling the SC, Gord. I did, a couple others, too.

How much more power do you feel? 5-10 hp is about the threshold for 'feeling' it. Did you use the sealant on both parts of the sc? I mean BOTH sides of the gear section? So it sealed the rotor casing too?
I used sealant on all sides of the SC gear section. 2nd gear pulls like it has 40 more hp. From -10 psi to +5 psi goes by alot faster than it used to. Even mild acceleration has more "go" behind it. When It shifts to second you can see the gauge hit around 8 psi or so but then it slowly goes don to abourt 5-6 psi as it accelerats thru the gear. I agree too. I can feel the added boost. It almost seems as if the gauge is reading wrong.

Tomorrow I will do so more tests to see exactly how it reacts. I will also triple check my connections.

Thanks for all the posts on how to do this too by the way Willren. A year ago I could barely do my own brake job but now I can tear apart the upper part of the engine without freaking out. Thanks.
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Old 04-06-2003, 10:21 PM   #6
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I did a little reading on ClubGP and found a few interesting threads concerning this. No answers but a few more good questions.

http://www.clubgp.com/newforum/tm.as...ode=&smode=&*=

http://www.clubgp.com/newforum/tm.as...anguage=single

http://www.clubgp.com/newforum/tm.as...ode=&*=#599532

http://www.clubgp.com/newforum/tm.as...mode=&*=#31078


Could it be something to do with intake preassure vs */C preassure? Leaking vacum line (checked them already but...)? Poor boost gauge reading?

If I get time this week I will try to vacum test my lines and see if my scanner can give me anything useful for this.
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Old 04-09-2003, 04:51 AM   #7
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**** you have a good one. I'll poke around some more on this. Fuddyduddy, you have any thoughts on this?

I know your new exhaust will have a negative effect on the indicated boost to some extent, but it should've been minor, and you would have noticed it already. I'm wondering if you might have gotten some debris lodged in a vacuum line during the rebuild?

Maybe yank all the lines one by one and blow them out. I'd tell you to swap gauges with someone else, but that would be kinda a BITCH!
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Old 04-15-2003, 09:59 PM   #8
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Well, Not sure what is happening now but the gauge is starting to read up to about 9 PSI. It didn't just snap to it but it has been slowly climbing to it since I did the upgrade / repair. So it might just reach the 10+ PSI mark yet.
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Old 05-01-2003, 09:07 PM   #9
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Well, I am getting the needle up to almost 10 psi still, but I noticed one thing. Today I was taking off around a corner and just punched it. The needle slammed up to 9 psi or so and then fell back down to about 8 psi and maintained it (with slight fluctuation). When it dropped I could actually feel power go away. It was still fast as hell but I can tell there is so much more there that I haven't / can't tap yet. I think what is going on is this:

http://www.bonnevilleclub.com/forum/...pic.php?t=3605
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