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Thread: Availability of larger than stock pulley?

  1. #1
    Join Date
    Jan 2008
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    58

    Availability of larger than stock pulley?

    Hey guys,

    This will probably sound strange but I was wondering if anyone knew of a company offering "underdrive" pulleys for the SC, not the lightweight kind but ones that are actually larger than the stock 3-1/8" pulley.

    I am using an M90 for another car project and want to pull boost back a little bit because the motor's static CR is too high to use with 91 octane pump and the ~12PSI the M90 generates on an otherwise stock engine.

    Hopefully there is a vendor out there that sells such a thing.

    Something that just came to mind; anyone know if the pulley off a Pontiac GTP M90 will fit on the SC? I have read on here that it is a pressfit without provisions for a keyway but that could be machined in...the 6-rib would be fine as well.

    Thanks!
    Last edited by speedingminivan; 03-20-2009 at 01:36 PM.

  2. #2
    Join Date
    Apr 2004
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    sumter, south carolina
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    3,051
    well if the supercharger you have came from an 89-93 SC then you could find someone with a 94-95 supercharger pulley. its noticeably bigger when holding the 2 side by side.

  3. #3
    Join Date
    Jan 2008
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    58
    Of this I am aware, however the problem is I need something even bigger than that. On my car the early M90 stock pulley is good for around 12PSI, which is a little bit high for a 9.5:1 CR and only 91 octane CA pump swill, even intercooled.

    I'd like to bring it down to 8-10PSI for now until I find a better fueling solution, which will include alcohol injection...

    The GTP pulley is a good size because it is 3.4" instead of 3.125"...my crank pulley is a 5.3" so ideally I'd like to find something 3.5" or above but that gets into custom stuff..

  4. #4
    Join Date
    Mar 2009
    Posts
    4
    Get a custom pulley. It's the way to go.

  5. #5
    Join Date
    Apr 2004
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    sumter, south carolina
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    is there an octane plug on your new setup like there is on an SC ? that would stop it from advancing timing as much.

  6. #6
    Join Date
    Feb 2003
    Location
    NE PA
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    471
    Quote Originally Posted by speedingminivan View Post
    The GTP pulley is a good size because it is 3.4" instead of 3.125"...my crank pulley is a 5.3" so ideally I'd like to find something 3.5" or above but that gets into custom stuff..
    The stock GTP pulley is 3.8 (smaller sizes are available). Google Smooth Flow Pullies. He will machine you what you want or go to clubgp.com and pick up a used stock one to see if it fits. GTP are six rib as opposed to the SC eight rib.

  7. #7
    Join Date
    Jan 2008
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    58
    we have something called a fuel quality switch which is adjustable somewhat based on, well, available fuel quality. i plan on running it at the highest setting, which is something like 3 degrees timing retard and +6% fuel for safety.

    custom pulley huh....ill look into it then

  8. #8
    Join Date
    May 2007
    Location
    Wichita, KS
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    3,018
    the 3.8 sc engine is 9.5 to 1 in the 94/5 cars, back off your timing a bit... or get a bipes acu, it will allow you to run stock timing when in vac, and it retards it during boost, up to 14 degrees i believe.. then you could run a late pulley and keep things in check.

  9. #9
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    Outside KC MO
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    So...is this for a minivan? If so, figure out how to get an underdrive for the crank and use it. Not too tough but you can measure the distance from the balancer to the belt and have one matched to it off of a 5.0 or something and redrill it. My U/D pulley for the 5.8 is almost (if not) 2" smaller than stock.

    SWS

  10. #10
    Join Date
    Jan 2008
    Posts
    58
    this is for a 1985 Porsche 944. there isn't much room for a larger pulley down there.

    ill keep looking around and let you guys know if i find anything interesting.

  11. #11
    Join Date
    Apr 2002
    Location
    Madison, Ohio
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    I don't know if the GTP pulley will fit but I'm thinking it will. 6rib will be plenty for the low boost that you want to run. You should be able to pick up a stock GTP pulley for the cost of postage....
    Quote Originally Posted by Miller View Post
    Ya thats why i tape mine down. People think its bc i dont have a moonroof seal (which is true) but its really to keep my roof from ripping off .
    Email me here.

  12. #12
    Join Date
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    Outside KC MO
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    I think you misunderstood me. Smaller crank pulley slows the accessories down. Build one of those and try it.

    SWS

  13. #13
    Join Date
    Jan 2008
    Posts
    58
    candidate for oldest thread revival..

    i ended up getting a custom 4" diameter pulley made by these guys last year:
    http://www.southfloridapulleyhq.com/

    i sent them a stock SuperCoupe pulley to get dimensions off of and they whipped me up a 4" version in 2 weeks turnaround for $160 shipped.

    still wanting to stick the blower on that Porsche...maybe in another 9 years
    this is where it's been sitting waiting for me to have time to get to it, since about 2013.


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