diff ratio

Discussion in 'PSI Superchargers Tech Questions' started by topalky511, Jul 4, 2004.

  1. topalky511

    topalky511 Member

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    i am wondering on a diff ratio for my alky dragster, i am running a 36 x 17 x 16 goodyear tire and dont want to turn the engine mucch harder than 9500 its a 511 ci stage three headed fatheaded engine with a 1671 and a promag 44 1.98 first and 1.56 2nd also im not sure if these are the best ratios for me in the lenco i was just sold the box and thats what it came with, dont want anyones major secrets just a basic start point to get it from a to b in one piece i hope, thansk guys any help much appreciated
     
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    topalky511, Jul 4, 2004
  2. Mike Canter

    Mike Canter Top Dragster
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    Well without you having some kind of previous run information it is pretty hard to compute that. I would say that it would be a 4.10 would keep you below the 9000 rpm range but if you were making tons of power you could get real close and have to consider a 3.89. A 4.30 is a better gear than a 4.10 because the teeth are a little thicker but your rpm is going to be higher.

    You are probably just going to have to chose a ratio see what it does then go to this website
    http://www.prestage.com/Car+Math/Gear+Ratios+and+Tire+Sizes+/default.aspx
    and put in all the data and re-compute. On your tire size you need to figure in the tire growth at the end which maybe as high as 10%.
     
    #2
    Mike Canter, Jul 4, 2004
  3. topalky511

    topalky511 Member

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    thanks mike
    that gives me a starting point, i know its very broad without having much data but thanks anyway, i wont be putting the 4.5 i had lying around then
     
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    topalky511, Jul 4, 2004
  4. Mike Canter

    Mike Canter Top Dragster
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    The IHRA/NHRA Promods have to use a 4.56 which results in the finish line rpms being in the 9000s so you are right you should stay away from that unless you want to run an 1/8 mile.
     
    #4
    Mike Canter, Jul 5, 2004
  5. Les Mellows

    Les Mellows New Member

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    I would reccomend a 4.56 gear and a 1.75/1.80 trans ratio. I would also reccomend a 34.50/17-16 tire for a very good track where it will accept higher wheel speeds initially .
     
    #5
    Les Mellows, Jul 6, 2004
  6. P/M Truck

    P/M Truck New Member

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    I find the Pro Racing "Drag Sim" software to be really useful in this regard (get it with the Pro Tools option though). You can evaluate tires, gears, ratios, and much more, for any given power curve. You can view either a conventional time slip, or you can view the various incrementals and data tables. You can also input your specific combo, and let the software iterate and spit out what it "thinks" is optimum. Maybe not super accurate, but very good as a comparative tool for evaluating different combos.
     
    #6
    P/M Truck, Jul 7, 2004
  7. Will Hanna

    Will Hanna We put the 'inside' in Top Alcohol
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    a hoosier 34.5 and 4.10 would be where i would start right off the top of my head, but not very experienced with roots. maybe marty thacker can help.
     
    #7
    Will Hanna, Jul 8, 2004
  8. 310TAD

    310TAD Top Alcohol

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    We always ran the Hoosier 34.5 tire and a 4.56 gear with the roots-blower. Running 470" engines & tranny ratios between 1.80 and 1.90, we were able to run low 5.70s at over 243 MPH without hitting 10,000 rpm at the finish line. Just quick thinking, I believe I would start with the 4.30 Hoosier and a 4.30 gear to do what your saying. My suggestion on the blower overdrive (for shifting at 9500 rpm) would be 48%.

    Good luck,
    Marty

    PS. Hi Will. Is it hot down there yet?
     
    #8
    310TAD, Jul 12, 2004
  9. 310TAD

    310TAD Top Alcohol

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    A 4.30 Hoosier ? (Ha-ha, beat you guys to it.)

    I meant a 34.5 Hoosier, with a 4.30 gear.

    Marty
     
    #9
    310TAD, Jul 12, 2004
  10. topalky511

    topalky511 Member

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    hey marty
    thanks heaps, its hard to get info on roots blown deals anymore everyone runs the screw blowers now, well if i stick with the 4.56 thats in the car and the 36" goodyears it should keep the revs down a bit we have a 1671 on it and its 44 over at the moment so ill start there, got to start somewere and work my way up, thanks heaps guys for the help really appreciated
    aaron hambridge
     
    #10
    topalky511, Jul 13, 2004

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