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Technical gear change

Discussion in 'The Hokey Ass Message Board' started by chainsaw, May 20, 2019.

  1. All things equal how much 8th mile et improvement can I expect going from 3.55 to 4.62 ratio ? Is it possible to get 1 second improvement ? Thanks.
     
  2. squirrel
    Joined: Sep 23, 2004
    Posts: 43,180

    squirrel
    Member

    need to know a lot more info than that to figure out an answer. If the car is slow, then it's possible. If it's quick, not so much.
     
  3. Yea its slow, went 9.1 at 73 mph, 1.9823 60 ft, 8185 reaction on my only pass in the 8th mile. About 3100 lbs, maybe 300 hp, auto trans.
     
    Last edited: May 20, 2019
  4. Oldioron
    Joined: Dec 12, 2018
    Posts: 845

    Oldioron
    Member

    I don't think that it would be a full second but it can make other problems show up. I'd say it's good for maybe a .5 second if you don't have tire spin.
     
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  5. Look around for a 1/8th mile gear and RPM calculator, I know I have seen them. Figure out what RPM you want to spin at the finish line first.

    Here ya go. I just ran mine and came up with needing a 4.77 rear to get a 7.49 ET at 88.85 mph.
    http://www.wallaceracing.com/dragcalceigth.php
     
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  6. oj
    Joined: Jul 27, 2008
    Posts: 6,109

    oj
    Member

    When you first start racing it is pretty easy to find a second, just walk thru the staging lanes until you find a car like yours running a second quicker and he'll tell you how he did it. It'll be carb, ignition, torque convertor, weight shift, gear change, staging techique - mostly its about getting all them things to work together.
     
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  7. A spare 4.62 posi came with the car so that would be my only choice since I dont want to by another gear set.
     
  8. squirrel
    Joined: Sep 23, 2004
    Posts: 43,180

    squirrel
    Member

    let us know more about the engine and the rear tire size, and maybe we can provide a little more help. For example..what rpm does it run at the finish line now? what do you think is the max RPM of the engine? how much cam does it have? how much stall speed? etc. there's a whole lot of unknowns at this time, we can only make wild ass guesses.
     
  9. Dont know anything about the engine other then 68 302 with 289 heads, was told 10 to 1 comp., tunnel ram 2 500 edelbrocks, lumpy cam, still pulls at 6000 but dont like to take it above that. 28 inch et street radials, .Only been down the track once, didnt look at tach at finish line. Car looks like it could be fast but its not, just trying to pick up 1 second and I would be happy. Thought about going single 4 with nitrous but dont want to change the tunnel ram if I dont have to. Was hoping the gear change would get me close but then you have that pesky driving on the highway with 4.62 thing.
     
  10. Ghost28
    Joined: Nov 23, 2008
    Posts: 3,139

    Ghost28
    Member

    I'd say put them in just for the fun factor.
     
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  11. oj
    Joined: Jul 27, 2008
    Posts: 6,109

    oj
    Member

    Clutch? Automatic?
     
  12. squirrel
    Joined: Sep 23, 2004
    Posts: 43,180

    squirrel
    Member

    but we still have no idea of the stall speed

    we can figure out the trap rpm from mph and tire size and gear ratio
     
  13. Dont know the stall either. Going to take it to a vintage drag race in 3 weeks just to get some more times and watch the tach this time. After that just have to swap them out and see what happens since there are so many unknowns. Thanks for the responses guys.
     
  14. Unless that 302 is thoroughly used up, it'll turn 7K no problem...
     
  15. flamedabone
    Joined: Aug 3, 2001
    Posts: 4,474

    flamedabone
    ALLIANCE MEMBER

    Your 1.9 60' is not all that horrible, there is definitely a better ET at the big end if you can shave it down a bit. Details is what is going to solve your mystery. Things like what are your ignition timing numbers, are your carb butterflies all the way open at full throttle, what RPM are you foot braking at the line?

    -Abone.
     
  16. Ericnova72
    Joined: May 1, 2007
    Posts: 128

    Ericnova72
    Member

    Wallace Racing Calculator says that with those 1/8 mile ET, MPH, and weight numbers you are only making 203 HP at the flywheel based of the ET. If based of the MPH, then just 187 HP flywheel.
    Tunnel Ram is probably killing you more than anything, but entire carb and ignition tune specs need to be looked over..
    With a1.9 sixty foot time, it appears it is really going flat farther down the track....typical 1.9 sixty in a 3100 lb car gets an 8.5 or better ET.
     
  17. this is all new to me. I did hear it slightly missing right before the lights, like not getting enough fuel. Put richer metering rods in the carb but have to wait to see if it helped. Think the preasure is set at 4 1/2 or 5 for the edelbrock carbs.
     
  18. With ALL suggestions mentioned above ^ Being a DRIVER is worth a crap load of ET!
    You also have to be a mechanic, a tuner, and a listener, and not a speaker= race lingo for those new....... Been there, done that. Those who know, will know what I speak.
     
    loudbang likes this.
  19. Ericnova72
    Joined: May 1, 2007
    Posts: 128

    Ericnova72
    Member

    Richer metering jets won't help if their isn't enough fuel in the bowl, so it is more important to know what the fuel pressure is at half track or farther downtrack to the finish line than it is at idle in the pits.

    What pump are you using??
    If electric, where is it mounted?? What is it's GPH and pressure rating??
    What line size from tank to pump, and from pump to carb??
     

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