Rear gear 1/8 vs 1/4

Discussion in 'Manton Push Rods Top Alcohol Tech Questions' started by Soldierboy0098, Jun 28, 2017.

  1. Soldierboy0098

    Soldierboy0098 Active Member

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    Hi guys,

    Just for giggles what king of rear gear difference would you need to go from running 1/8 mile to a 1/4 mile.

    App is for roots blown pro mod using a converter, 36" slicks, 4.56 gear for the eight mile and about 9600 rpm max.

    I have seen dragster guys go from a 4.10 to a 3.90 and that worked so I am wondering if its about .20 difference.

    What do the NHRA guys use? as my car is basically and NHRA pro mod with a little more overdrive and about 100 lbs less weight.

    Thanks guys,
    Trev
     
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  2. sean70ss

    sean70ss Member

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    I know a few of the pro boost teams are running 10500, 11200 rpm. with a 4 speed to keep the shift points tight. 4.56 to 4.71 gear range. but you can gear the trans as well to work with your starting line ratio.
     
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  3. jay70cuda

    jay70cuda Member

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    Same combo as yours. 4.56 gear for 1/4 mile is what I've always ran. You'll need a 5.0 for 1/8 mile but it has its limits. I shift at 9500 go they the lights at 9700.
     
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  4. Soldierboy0098

    Soldierboy0098 Active Member

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    With our over drive if we run over 9800 the blower efficiency falls off so that's about our max, some of the guys run the lower od blowers or clutches and have to rev it harder. Thanks Sean
     
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  5. Soldierboy0098

    Soldierboy0098 Active Member

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    That's about right where we would need to be, Thanks Jay
     
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  6. Jason Green

    Jason Green Member

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    Didn't the NHRA mandate a 4.86 year once upon a time for blown PM?
     
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  7. Soldierboy0098

    Soldierboy0098 Active Member

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    Just looked and they have a max (numerically) of 4.57:1. I am now realizing with my 11" MW rear end I may not have enough gear for the 1/8 mile but would be good in 1/4 which sucks because I have no interest in running NHRA at the moment and we only have 1 1/4 mile event. The other problem is they don't make any higher (Numerically) gears for the 11" from what I can see. Bugger me...lol. I guess I am stuck playing with trans ratios to fix that.
     
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  8. sean70ss

    sean70ss Member

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    Hope your great Trevor think of you often and all you have been doing. Hope you get down the track as well brother. Sean
     
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  9. Mike Canter

    Mike Canter Top Dragster

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    Trevor what transmission with how many gears are you using?
     
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  10. Soldierboy0098

    Soldierboy0098 Active Member

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    B&J or Liberty and a quick drive (Possibly lockup). Roots would be a 3 spd, screw would be a 2 speed but I am not sure if I can get my car light enough (Or if I even want to run PX financially) for pro extreme and that is the only reason I would run the screw. It weighed 2450 with a 2 spd lenco drive and screw blown hemi but it has steel breaks, a wing like my dragster has that can be removed, steel wheely bars, and a very heavy steel drive shaft tunnel. Also car was built in 2000 and ran ADRL pro extreme from like 2006-2009 or 2010 and updated in 2013 so she is isn't a spring chicken though I am not sure if that matters e.t. wise.
     
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  11. Soldierboy0098

    Soldierboy0098 Active Member

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    Hi Sean,

    Thanks for keeping me in your thoughts.

    I was doing really well for the last year or so and have a few really big irons in the fire and was even looking at finally getting the car out late this year but the VA decided to cut my pay by claiming they never received a one page form that all I had to do was sign and date. I watched my attorney's office fax it to them and it went though but they used that as an excuse so if it's not fixed by October I will be selling everything I own house, car, and all and become another statistic. I have the attorney fighting it and the congressman involved but neither of them really do much so I am currently trying to go on as if this won't happen but only time will tell.

    How have you been?

    Trev
     
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  12. bob szabo

    bob szabo FC / altered

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    Here are two articles we wrote for IHRA about quarter mile to eighth mile relations with conversion math useful for gearing:

    https://racecarbook.com/articles/comparison.html
    https://racecarbook.com/articles/mph.html

    Bob Szabo
    bob@racecarbook.com
    https://racecarbook.com
    https://airdensityonline.com
    https://airdensityonline.com/tracks/ << free air density and air density 3 day forecast for various tracks in USA, Canada, and AU
    https://airdensityonline.com/free-calcs/ << free air density calculator to determine AD from corrected or uncorrected barometer, vapor pressure, due point, and water grains for tuning.
     
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