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Discussion Starter #1
Hi. Ive got a 3.4 with the black supercharger. Over the past few months, Ive noticed a drop in boost pressure from a solid 5 psi to about 3 psi and I can indeed feel a loss in power. I have no vac/pressure leaks and the truck runs fine otherwise with no CEL.. I have almost 95k miles on the supercharger but I dont think its possible that it can loose boost with mileage/wear..

Any thoughts?
Thanks
Chris
:):)
 

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The stock toyota belt for the supercharger sucks. I'm running 12.5psi so I'm asking a lot more of it than you are, but I'd get black belt powder stuck to everything around the nose of the supercharger. I went through two belts in a year. I couldn't find the same length belt in a 4 rib aftermarket, but I did find a 6 rib ContiTech the right size. I used a razor blade and a block of wood to back it up and carefully cut the extra 2 ribs off one side. That belt has lasted 2 maybe 3 years and there's no more belt dust around the pulley.

Belt was a 6pk1570 and it's worked great.

One other thing to check is the bypass valve. If the vacuum can is coming loose from it's bracket it won't close the valve all the way. Mine was already broken when I bought it used, so I redid a couple of the rivets and used some wire to keep it clamped in place.

Also check for a leak between your boost gauge and the back of the supercharger. If the line has a crack or a leak at one of the fittings the gauge will read low.
 

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how are you running 12.5 psi, i have a 2.1 inch pulley and meth and can only get 10.3 psi
It's a VHR pulley that came with the used supercharger and it's a smidge under 2".
I measured it and the crank pulley and calculated at redline the supercharger is spinning at 17k rpms. According to eaton it's sucking up 40hp just to turn it at that point. That's a lot to ask of a 4 rib serpentine belt.

I wouldn't recommend it, it's hard on the bearings, the belt and the supercharger is out of its efficiency range. It is fun though. I have another pulley from a buick that I machined to fit that drops it down to 5.5psi. I use that for heavy cross country towing so I can let the cruise control hold it floored without worrying about blowing it up.

I'm up at 6k feet altitude in Wyoming right now and the boost is down to about 10.5psi from the thinner air.

Here's a chart on pulley size vs boost: http://www.pulleyboys.com/BoostLevels.htm#SKU64
 

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Discussion Starter #8
If the bearings are bad, it could be "loose".
Now, how is your tensioner? is it the dynamic tensioner? If so i would go about replacing it (read here http://www.customtacos.com/forum/showthread.php?t=150245&page=2 )
if that doesn't fix the problem, the bypass valve may not be closing all the way.
Hmm. The bypass valve... thats a good thought. I will indeed check that.
I do have the updated dynamic tensioner and an almost new belt on there, an OEM Toyota belt too. Ive dealt with belt slippage in the past and im confident that it is not slipping.
Thanks for the worth while idea on the bypass, I will look at it and check its operation with vacuum & boost pressure. :)
 

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Discussion Starter #9
The stock toyota belt for the supercharger sucks. I'm running 12.5psi so I'm asking a lot more of it than you are, but I'd get black belt powder stuck to everything around the nose of the supercharger. I went through two belts in a year. I couldn't find the same length belt in a 4 rib aftermarket, but I did find a 6 rib ContiTech the right size. I used a razor blade and a block of wood to back it up and carefully cut the extra 2 ribs off one side. That belt has lasted 2 maybe 3 years and there's no more belt dust around the pulley.

Belt was a 6pk1570 and it's worked great.

One other thing to check is the bypass valve. If the vacuum can is coming loose from it's bracket it won't close the valve all the way. Mine was already broken when I bought it used, so I redid a couple of the rivets and used some wire to keep it clamped in place.

Also check for a leak between your boost gauge and the back of the supercharger. If the line has a crack or a leak at one of the fittings the gauge will read low.
Thanks you also for the idea to check the bypass valve. Im going to check its operation with vac/boost pressure and make sure it did not pull loose those weak rivets, I do know the ones you are talking about...
As for the belt, Im still running the stock 2.37 pulley with a newer Toyota belt on an updated tensioner and all is well with it, Im confident of no slippage. I also did check the gauge port and vacuum line for cracks or leaks and it checks out with my hand pump tester, and it visually looks good & intact and both ends of the fittings are tight too.
thanks for the ideas:)
 

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Discussion Starter #10
are you progressively loosing boost or is it 3psi all the way threw your RPMs? if it is progressive your belt it probably sliping.
No, it hits about 3psi at WOT at about 2800-3k rpm, and stays linear throughout the rev range to red line never exceeding or surpassing 3psi. So just a solid 3psi..
 

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Discussion Starter #11
Welp, the bypass valve was indeed faulty, had a torn diaphragm. I ordered and got a new one from Magnussen Superchargers. I see 5 lbs of boost again. But now I got the P0171!!! I just got done fighting that code back in July and it was a battle. :mad:
 
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