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Author Topic:   perfect gear ratio
gearhart
Dirt Newbie

Total posts: 4
posted August 30, 2004 06:26 PM  
what gear ratio do most of you guys use on 3/8 mile tracks with a good horsepower engine

leapinlizard
Dirt Freak

Total posts: 402
posted August 30, 2004 07:04 PM  
5:67 on a 26" tire

black95gst
Dirt Roller

Total posts: 15
posted August 30, 2004 08:06 PM  
Wow we run 6.20's on a 3/8 mile track here.

mod70
unregistered Total posts: 15
posted August 30, 2004 08:07 PM           send a private message to black95gst   Edit/Delete Message   Reply w/QuoteBBBBBB
5.67 should turn between 7000 to 7500. 5.83 will go to 8300 give or take.

zeroracing
Dirt Forum Champ
Total posts: 1875
posted August 30, 2004 08:14 PM  
i run 5.83 on a short 3/8 and i turn about 7000 max most nights.

black95gst
Dirt Roller

Total posts: 15
posted August 30, 2004 08:49 PM  
6.20's will give you anywhere from 7200-7500 here what kinda tracks are you guys racing at???

mod70
unregistered Total posts: 15
posted August 30, 2004 10:03 PM           send a private message to black95gst   Edit/Delete Message   Reply w/QuoteBBBBBB
Med banked tacky 3/8ths. I don't see how you're keepin your RPM's that low with a 6.20. You running A-mods?

z - I was getting 7200 at CMS before they made it bigger. That was with 5.67. I usually get 6800 to 7000 at LA, but that's flat dry/slick.

[This message has been edited by mod70 (edited August 30, 2004).]

racer17j
Dirt Forum Champ
Total posts: 5390
posted August 30, 2004 10:15 PM  
with a 5.29 i turn 7000 at sedalia
with a 5.83 i turn 6800-7000 7100 max at cms. thats right now, last year i only would turn about 6400-6700 max.

black95gst
Dirt Roller

Total posts: 15
posted August 30, 2004 11:03 PM  
360 mod.

imcaracer84
Dirt Full Roller

Total posts: 33
posted September 02, 2004 08:39 AM  
Ok guys this one has confused me... With all the things you have been posting I am lost. I run 5:43's on a tacky 3/8 and rapped out my big 406 at over 8000. I am moving down to 5:14's. I just do not understand the large amout of differance everyone is having. can someone clue me in a little?

dirtbuster
Dirt Forum Champ
Total posts: 2007
posted September 02, 2004 08:47 AM  
Some of it will depend on of course the motor you have and the track length, banking, grip, high or low line, etc. But some of the difference is also in how heavy some cars are compared to others, how light the rotating assembly or driveline is etc. I know we pulled 50# of lead off the car last week to see what would happen and we gained 150 rpms with the same gear on the same track.

klw45black
Dirt Full Roller

Total posts: 42
posted September 02, 2004 09:35 AM  
Couldn't some of the spread be caused by diff. transmissions used?? I think car weight, rotating mass & grip have the most to do with it. But I also found weak or wrong valve springs can act as a rpm limiter, motor didn't miss a beat but just wouldn't rev, changed nothing but springs and the motor pulled hard & clean to 8000

leapinlizard
Dirt Freak

Total posts: 402
posted September 02, 2004 10:32 AM  
I think wheel spin has a lot to do with the total RPM. Assuming everything is in good working order driveline wise, also assuming everyone ran a 26" tall tire. The only other variable left is either the track length changes or the wheel spins most of the time. IMO wheel spin is wasted power and if that power is wasted than why spend the extra money making it?

Our car turns 6000 going in with zero wheel spin with 900 ft of straight. Our car makes positive traction at the 100' marker. That leaves 850 ft we aren't spinning tires, wasting fuel and breaking parts. And the car is very controllable. Our engine, I built, makes around 400hp and makes near that in torque from 1500 all the way through 6500. We a have a set of ported 882's by me and a total of 1500 from carb to pan. Since the torque is flat, it's very responsive to throttle input so we have to make the tires do more work. It's cheaper than any 8000rpm motor and runs just as well. This is why we run a higher gear than most and let the torque do the work rather than horsepower and compensating with more mechanical leverage.

zeroracing
Dirt Forum Champ
Total posts: 1875
posted September 02, 2004 10:47 AM  
i use a falcon tranny, with very very little wheelspin. the vavle springs are good. also i run on gas, but the main reason for the low rpms is because little to no wheelspin.

jay116
Dirt Freak

Total posts: 428
posted September 02, 2004 01:46 PM  
I agree with Jay116, there is no right answer here. As with a good race engines its the combination that makes things happen not one particular thing.

There are to many variables, track size, shape, engine combo and or drivers style. Run what you can get to work and be fast with, its not the right way its just another way.

klw45black
Dirt Full Roller

Total posts: 42
posted September 02, 2004 02:11 PM  
I agree with you leapin' torque is king. I took gear out of my car last part of season & the car is more driveable & works the rear more smoothly as opposed to wild wheel spin. Made me want to try even less gear. But there is a trade off. Too little mech leverage will find a weak spot if the grip is there, cast cranks, cheap or stock rod bolts & any thing else from there on back. The valve springs and the 8000 rpm I was refering to was not in this car but from my drag racing days. I don't agree that more HP requires steeper gears. It has more to do with the given engines ability to produce enough torque & HP between it's rpm boundries to maintaine the internal & external inertia requirements. And to keep it in motion and how this ability matches or doesn't match with the car and the track that it's racing on plus the drivers style. A top fuel dragster makes in excess of 6000hp, has huge sticky tires, a timed clutch package but only needs a 3.9 rear gear.

Racer14K
Dirt Freak

Total posts: 387
posted September 02, 2004 04:22 PM  
High banked fast 3/8's
5.37 @ 7700 - 7800

This is with lightweight crank, brinn trans, lightweight gears and spool on 27.5 hoosier e-mods. 5.29 and 5.43 are the most popular at the track I race at, but the guys with the big dollar motors are running 5.67's. With a 3 link car the norm used to be 5.14 and 5.29 but the bar cars seem to be in the 5.43 range.

[This message has been edited by Racer14K (edited September 02, 2004).]

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