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Thread: Check my maths?

  1. #16
    Part of the furniture ajvx01's Avatar
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    Hi all,
    can someone check my maths before i get pulleys paid for please?

    Blower has:
    28 tooth pulley
    3.61 blower ratio
    Max engine RPM 6500rpm
    Max blower rpm 52000rpm

    So to achieve 50,000 blower rpm at 6000 engine rpm I need to use the below formula:

    Desired blower speed divided by (engine RPM*blower ratio) = drive ratio.
    Drive ratio*blower teeth = Crank Teeth

    Which =

    50,000/(6000*3.6)=2.32
    2.32*28=65 teeth on crank pulley

    So am i right to say i want a crank pulley 2.32 times bigger than my blower pulley?
    which would make it a 65 tooth gilmer pulley?

    And if this is correct what ratio should i be looking for my water pump and alternator in relationship to the crank pulley?

    really appreciate any help I can get on this in advance!
    willing to do domestic/commercial electrical work for car parts/panel work.

  2. #17
    Part of the furniture Deuce.'s Avatar
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    Isn't the WP usually 1:1 and alt is 2:1?

  3. #18
    Part of the furniture ajvx01's Avatar
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    Yeah the water pulley looks to be 1.1 but I don't have an alternator pulley to go off except the old Gilmer set which under charges at idle...

    Can anyone confirm 2.1 ratio for the alternator?

    Sent from my MHA-L09 using Tapatalk
    willing to do domestic/commercial electrical work for car parts/panel work.

  4. #19
    Not the Kingswood! hq308's Avatar
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    My Gilmer set works out at 1.85 to 1 and charges fine (39 tooth crank and 21 tooth alt) Water pump is 1 to 1

    What pitch is the blower pulley? My Gilmer is 3/8" pitch and the 39 tooth crank and water pump pulleys are quite close to each other. With a 65 tooth crank pulley you'll more than likely need to go with an electric water pump.

  5. #20
    Sure why not? 76lxhatch's Avatar
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    It varies a little but in that ball park. Water pumps usually slightly more than 1:1 (e.g. VN, water pump pulley is slightly smaller) but pretty close. Alternator can vary more, you really want it spinning at least 2000rpm at idle and ~16000rpm max.

  6. #21
    Part of the furniture ajvx01's Avatar
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    Quote Originally Posted by hq308 View Post
    My Gilmer set works out at 1.85 to 1 and charges fine (39 tooth crank and 21 tooth alt) Water pump is 1 to 1

    What pitch is the blower pulley? My Gilmer is 3/8" pitch and the 39 tooth crank and water pump pulleys are quite close to each other. With a 65 tooth crank pulley you'll more than likely need to go with an electric water pump.
    Yeah I'm just confirming what sizing I need then I will measure and see if it fits.. I think you may be correct though.

    Sent from my MHA-L09 using Tapatalk
    willing to do domestic/commercial electrical work for car parts/panel work.

  7. #22
    Part of the furniture ajvx01's Avatar
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    Quote Originally Posted by 76lxhatch View Post
    It varies a little but in that ball park. Water pumps usually slightly more than 1:1 (e.g. VN, water pump pulley is slightly smaller) but pretty close. Alternator can vary more, you really want it spinning at least 2000rpm at idle and ~16000rpm max.
    Great info, 2.1 will work great then.

    Sent from my MHA-L09 using Tapatalk
    willing to do domestic/commercial electrical work for car parts/panel work.

  8. #23
    Part of the furniture ajvx01's Avatar
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    Quote Originally Posted by hq308 View Post
    My Gilmer set works out at 1.85 to 1 and charges fine (39 tooth crank and 21 tooth alt) Water pump is 1 to 1

    What pitch is the blower pulley? My Gilmer is 3/8" pitch and the 39 tooth crank and water pump pulleys are quite close to each other. With a 65 tooth crank pulley you'll more than likely need to go with an electric water pump.
    Also this may be dumb but what do you mean by pitch?

    Sent from my MHA-L09 using Tapatalk
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  9. #24
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    like a thread, point to point TPI if that makes sense

  10. #25
    Not the Kingswood! hq308's Avatar
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    Pitch is the measurement centre to centre of the teeth. Basically how far they are spaced apart.

    Timing Belt Profiles & Pitches | Pfeifer Industries

  11. #26
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    correct, and can be measured at any identical points. usually the tip for ease of measuring

  12. #27
    Part of the furniture ajvx01's Avatar
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    Thanks guys! Haven't heard that before.

    Sent from my MHA-L09 using Tapatalk
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