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Old 04-26-2004, 03:01 PM   #1
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Default Pulley size?

Looking at swapping SC pulley on unmodded L67, what'* the best diameter for this?
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Old 04-26-2004, 03:08 PM   #2
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http://www.bonnevilleclub.com/techinfo/?article=50

There is all the info you need to know on pully'*.

PS: I have a 2.5 on mine and it is mildly modded (very mildly). A 32.5 is a good choice for any upgrade, just don't go smaller thatn that without major upgrades.
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Old 04-26-2004, 03:39 PM   #3
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I agree. 2.5 is for you. www.pulleyboys.com

But make sure you upgrade your intake first.
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Old 04-26-2004, 05:00 PM   #4
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How much of an advantage if any is there to go down to 2.4 on a 94-95? We still arnt spinning faster than the 92-93'* and have more airflow going through.
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Old 04-27-2004, 12:39 PM   #5
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Good question Bassplayincrowe I was wondering the same thing..... hows come we cant go down to the 2.2 pulley like the 92/93? Our superchargers would be spinning the same speed, so why would we have more of a heat problem?
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Old 04-27-2004, 04:01 PM   #6
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2.4 will actually kill performance. You're spinning into the inefficient heat-loss zone of the SC. Read the PB FAQ in Techinfo. I've discussed this at length with Brian.

In order to go smaller than a 2.5 on a 94/95 or 2.2 on a 92/93, you must intercool or water-inject, or it will cost you performance, not gain.
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Old 04-30-2004, 03:34 PM   #7
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I've read the PB Tech article a few times through and it really doens't answer any questions Will.

If the 92/93'* can run a 2.2 or so without modification, why can't the 94/95'* go to 2.4? If anything the 94/95'* could do this better as they have better airflow through the super.They are basically the same thing just the 94/95'* were ported.
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Old 04-30-2004, 03:39 PM   #8
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Quote:
If the 92/93'* can run a 2.2 or so without modification, why can't the 94/95'* go to 2.4? If anything the 94/95'* could do this better as they have better airflow through the super.They are basically the same thing just the 94/95'* were ported.
EXACTLY!!! I had the exact same question...
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Old 04-30-2004, 07:56 PM   #9
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With your larger pulley you are making the same amount of boost as they are with the smaller one. Compressing air generates heat, and since you are compressing the same amount of air it will make about the same amount of heat, even with the 94/95 blower being ported. Like willwren said, when you start going to pullies that small you are going to hurt yourself more than not, because the blower is going to be trying to make more boost than it is efficient in doing, so it will just make a lot of heat and a little more boost. But that hotter air, along with the extra drag on the engine due to having to spin the blower faster overrides the extra power you are going to get from the additional boost.

For instance, on my dads GTP he can run a 2.6" pulley with 0kr. He can also run a 2.55 & 2.45" pulley with 0kr. However, with the 2.6" pulley the car is faster than it is with the smaller pullies because the blower doesn't make much more boost with the smaller pullies and it makes a lot more heat and requires more power from the engine to turn it that fast because it is out of its efficiency range. And the M90 is a lot more efficient than the M62. You would think that the M90 would make the same heat with the 2.3" pulley as the M62, however it is moving so much more air that it is creating a lot more heat. This is the same reason that the M112 hybrid (M112 rotors in an M90 case) has to have a much larger pulley than the M90 to make the same amount of boost. If you put the same size pulley on it, it will be trying to move so much air that it will just heat it up way too much.

I don't know if that made any sense at all, but thast the best I can do right now to explain it.

Shawn
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Old 05-01-2004, 08:41 PM   #10
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You nailed it, Shawn.

In a nutshell, if you have a 92/93, 2.2 or 2.25 is the smallest you can safely run. For 94/95, it'* 2.5 or 2.55, both cases are true because of the lack of a Series 1 intercooler. You MIGHT be able to go smaller with water injection, but you'd have a very expensive setup to gain that power back.
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