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Old 01-24-2007, 01:01 AM   #1
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Default Smaller pulley = Lower boost????

Replaced my 2.365" pulley with a 2.2", new belt. Tested and had 1.5-2lbs lower boost on my s1 L67. WHY????

Two short runs on dirt registered approx 8lbs vs. 10 lbs with the LARGER pulley...
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Old 01-24-2007, 01:21 AM   #2
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Does your custom setup utilize the knock sensors? Can you scan for KR? If it'* like the stock PCM it will take time to learn the new level of boost, and for the initial break-in it may run lower boost until it learns to compensate for the added boost.
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Old 01-24-2007, 02:47 AM   #3
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The computer could be pulling boost due to KR. It also could be the belt slipping as well, yes it is new but its possible that maybe you needed to actually go with a smaller belt for that pulley size so it wouldn't slip.
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Old 01-24-2007, 11:24 AM   #4
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I believe he does not have a BCS. So my guess is belt slip. IMO, a larger SC belt tensioner pulley will work better by increasing belt wrap and keeping good tension. You can get it from ZZP.
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Old 01-24-2007, 11:42 AM   #5
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I installed a new smaller belt. I'm sure there is no belt slip. I am not using a stock computer - LYNX engine management, is using engine speed, CPS and O2. I do not have a KR sensor.
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Old 01-24-2007, 11:54 AM   #6
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What does that leave? Nothing else changed?

I still think a larger tensioner pulley works better.
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Old 01-24-2007, 12:38 PM   #7
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If he'* sure there'* no slip, no need for a larger tensioner. As well...most regular parts stores sell pullies. No need to buy one and pay shipping.
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Old 01-24-2007, 12:45 PM   #8
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My point was if the PCM can't dump boost and you don't have any belt slip, what else could cause lower boost with a smaller pulley.

Did you blow a gasket out? Did you ever unplug the lower port of your boost control actuator? Although I see a plugged lower chamber not allowing as much vacuum at idle and coasting.

Maybe you developed a BCA leak?
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Old 01-24-2007, 01:05 PM   #9
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If it'* not a boost dump issue, it could be an issue with creating FAR too much heat. Hot air is less dense. That pulley is very likely hurting your performance greatly, and running the risk of popping a piston or a valve.

There'* only one car here that has succesfully run smaller than a 2.4" pulley on a Gen3 94/95 top end. And I had to do ALOT of work to get it to run the 2.2 and the 2.0".
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Old 01-24-2007, 01:07 PM   #10
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The air wouldn't be hotter till it was already in the LIM, though, right? Ideal gas law tells me that would INCREASE pressure.
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