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Thread: 1/8 mile gear only

  1. #1
    Senior Member MASTER BUILDER
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    1/8 mile gear only

    I've got a guestion about rear gears. I have a 85 camaro 2500# 434- 665 HP powerglide 1.76 - 9'' 514 gear -32x14'' tires runs 9.70 @140 mph in the 1/4 and 6.20 112mph in the 1/8 with 1.43 60' if I wanted to just run 1/8 mile could I change the gear ratio to a 5.40 or lower and get better 1/8 mile times.
    I had a 69 chevell 2900# 675hp 421 and I used a 5.36 a 4.88 and a 4.56 with 29x11.5 tires and it always ran 6.50 1/8 with all 3 gears I never figured that out. I just got me a new car.
    I'm still trying to learn so any help would be Thankful.
    Andy

  2. #2
    Senior Member DYNO OPERATOR
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    I went from a 3.73 to a 4.10 in my Firebird and slowed down in the 1/8th. Probably b/c is was spinning and I didn't know it. Still have the 4.10's but upgraded the convertor and suspension.

  3. #3
    Senior Member MASTER BUILDER
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    The lower the gear (higher number) the harder its going to launch. but it will also rev out quicker. If you can maintain traction at launch that'd be good.
    The object is to keep the car within its power range. You need to know what your rpm power range is. You may be reaching the limit too slowly or too quickly and changing gear too late. You want to be launching with enough revs to have the car within its power range immediately.

    Try these online calculators. The ones down the bottom help with tire size, gear ratio etc. Should help.

    http://www.golenengineservice.com/html/calculators.html
    It Ain't Over Til Its NOVA - 634ci of S*#t Your Pants!

  4. #4
    Senior Member MASTER BUILDER
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    Thank you Chevy fireball. them calculaters are pretty neat. but some of them don't add up, But some are exact to my car specs. so that tells me there is a lot more than meets the eye. but I guess thats what keeps this so much of a challenge and so much fun. just to see what you can do to make yours just a little bit faster. Thanks for your Time and Reply.
    Andy Byrd

  5. #5
    Senior Member MASTER BUILDER
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    Andy I noticed with their calculators that the hp results are Horse power at the rear wheels not at the flywheel like they say.
    It Ain't Over Til Its NOVA - 634ci of S*#t Your Pants!

  6. #6
    Senior Member RACING JUNKIE
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    Andy if you have the option I'd probably run the 4:88 and a 1.80 straight cut plantery. Your 60ft should stay about the same but it will be alot easier on the life of your engine. With your Chevelle, it weighed more so it needed more gear. As you lighten your car, a lower in number gear should show an improvement now.

  7. #7
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    Cheyfireball. your right and that makes a lot of difference between flywheel and rear wheel H/P. Thanks-Andy

    dParker Thank you. and you are saying the same thing that a Man at the track told me. go with a 4.88 But I didnt want to sound stupid so I didnt ask [why go with a higher gear for 1/8 mile only] now this is where I get lost. and Now I'm gonna ask . would the 1/8 be like the 1/4 I've read where you want your trap RPM to be around 5% more than your engines highest H/P rpm I don't have my dyno sheet in front of me but lets say it is 665 h/p @ 6500 rpm . should I go through at 6800 to 7000. I'm shifting @ 7000 now. and when it shifts wow that thing just rockets down the track. I'm only going to be running 1/8 mile. this was a thought that I had. can you set up this car to run a better 1/4 mile time by putting in a 4.88 and @ the same time it will be quicker in the 1/8. Rather than just gearing it for the 1/8 only. set me straight here because I need to Learn these kinds of things. I'm 54 years old and youd think Id done learnt this but here I am. Thanks to all yall I might learn something- Andy Byrd

  8. #8
    Senior Member RACING JUNKIE
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    Quote Originally Posted by andybyrd
    Cheyfireball. your right and that makes a lot of difference between flywheel and rear wheel H/P. Thanks-Andy

    dParker Thank you. and you are saying the same thing that a Man at the track told me. go with a 4.88 But I didnt want to sound stupid so I didnt ask [why go with a higher gear for 1/8 mile onlyAndy Byrd
    I sound stupid 90% of the time...who cares? Ask anyway that's how we learn. There is a bunch of knowledge floating around on these boards.

  9. #9
    Senior Member MASTER BUILDER
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    Thanks Tod. I just went back 5 months here reading every post on rear gear Ratios questions and they are about the same as mine. they all go like this : [tell me what gear I need to get the best ET at the stripe] well thats what I wanted anyway. it would save me alot of time and Money but I it ain't that easy. even all the calculaters are different. I hit one and it says I should be @ 5.90 1/8 and another says 6.36 so I'll go with all the help you guys give and see what happens. and I will let you all know the out come. keep up the HELPING US I can't speak for everyone but I'll sure be asking more.
    Thanks Guys Andy Byrd

  10. #10
    Senior Member RACING JUNKIE
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    Quote Originally Posted by andybyrd
    Cheyfireball. your right and that makes a lot of difference between flywheel and rear wheel H/P. Thanks-Andy

    dParker Thank you. and you are saying the same thing that a Man at the track told me. go with a 4.88 But I didnt want to sound stupid so I didnt ask [why go with a higher gear for 1/8 mile only] now this is where I get lost. and Now I'm gonna ask . would the 1/8 be like the 1/4 I've read where you want your trap RPM to be around 5% more than your engines highest H/P rpm I don't have my dyno sheet in front of me but lets say it is 665 h/p @ 6500 rpm . should I go through at 6800 to 7000. I'm shifting @ 7000 now. and when it shifts wow that thing just rockets down the track. I'm only going to be running 1/8 mile. this was a thought that I had. can you set up this car to run a better 1/4 mile time by putting in a 4.88 and @ the same time it will be quicker in the 1/8. Rather than just gearing it for the 1/8 only. set me straight here because I need to Learn these kinds of things. I'm 54 years old and youd think Id done learnt this but here I am. Thanks to all yall I might learn something- Andy Byrd
    Andy I may look at bracketracing different than others. If your wanting to run the absolute best in the eighth run 6:50 gears and turn your motor 9000rpm. But we're bracket racing, so if I can run within a tenth of my fastest possible time and be easy on my engine thats what I'm looking for. Just a small compromise to keep my sh#t together. Your car probably won't run any faster with the 4:88 but it should be close and be easier on parts. Sometimes if you don't have a big cam and a low gear in your rearend you can run out of cam before you get to the finish line. If you have an engine that flattens out on rpm less than 7000rpm. Its a good idea to put a smaller gear in the rear end, kinda keeps you engine pulling hard all the way thru the quarter.


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