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Author Topic:   Gear selection for 3/8 mile track?
fairlaniac
Dirt Maniac

Total posts: 110
posted June 15, 2005 07:36 AM  
What would be a decent gear to run on a 3/8 banked clay track? We currently run a 3.73 on a half mile track. We tach 6000-6200 at the end of the straight on the half miler. With the shorter straight on the 3/8 we want to be taching 6000 or so at the end of its straight as well. We run 2nd gear in a TH350 (1.52). Obviously tire diameter will affect the final ratio, Im just looking for a commercial gear to get me in the right neighborhood. We have a 4.11 and 4.88 gear set lying around. The 4.88 Im sure is out and the 4.11 may be borderline. I was wondering on a 3.90 but wed need to buy that. Car is a 3300 lb (w/driver) 82 Monte. The 3/8 mile track has a 3 hour open test day coming up and we want to take two assembled rears to work with as we want to start running their show.

Another thing, with this mathematical equation, we can figure out a lot of answers.

RPM x Tire Diam.
_________________ = Ratio

MPH x 336

With our current 3.73 and second gear in the TH350 being 1.52, our final drive is 5.67. Ive understood that a 6.00 is usually a good target. If we were to use 4.11s that would make it 6.25. Running 235/70/15 RR tire which way would I need to go on tire diameter to fool the ratio and get it closer to 6.00? Is there another equation that I could use?

Thanks,
Doug

------------------
Doug
"Lift for a second, that's where you'll finish!"

dm3
Dirt Full Roller

Total posts: 40
posted June 15, 2005 07:49 AM  
6.00 to 6.50 to 1 is the range we have running down here. I would give the 4.11's a shot with a 70 series tire in a 225 to 235 width - ie. P235-70R15. Go with a larger diameter tire to bring the effective ratio closer to 6.00. We've run the 6.00:1 ratio for several years. It works a lot better on dry slick and it's not as hard on the engine. We changed to a 6.20:1 because we went to a taller tire. We had run 6.33:1 with the P235-70R15's without any problems, but we were pulling 6500 RPM. The biggest reason we changed was the track kept going dry slick.

[This message has been edited by dm3 (edited June 15, 2005).]

Gomer T
Dirt Full Roller

Total posts: 36
posted June 15, 2005 06:31 PM  
We ran the th350 in 2nd with the 4.11's on a 3/8 mile track and turned 6200 rpms with 84" roll out on the tires.

racer17j
Dirt Forum Champ
Total posts: 5390
posted June 15, 2005 07:17 PM  
1st gear=252 241 rear end gear =607

stroker21x
Dirt Full Roller

Total posts: 37
posted June 21, 2005 04:43 PM  
A friend of mine ran a th350 in 1st gear running 273 rear gears and a 225/70/15 tire on a 3/8 mile track does this sound kinda of high?he did run a one wheel wonder if it had a spool would it make a difference?

bubba0six
Dirt Maniac

Total posts: 146
posted June 21, 2005 08:19 PM  
I think that you will find the 4.11 with the 2nd gear 1.52 = 6.24 will be perfect with 87-89 inch rollout. what track is it?

stroker21x
Dirt Full Roller

Total posts: 37
posted June 21, 2005 09:17 PM  
Its a track in MN we can not run more than a 3.56 gear

racer17j
Dirt Forum Champ
Total posts: 5390
posted June 21, 2005 10:11 PM  
Thanks for the input to all.

The track is Susquehanna Speedway (York, PA)

------------------
Doug
"Lift for a second, that's where you'll finish!"

Lings11
Dirt Newbie

Total posts: 1
posted June 22, 2005 11:38 AM  
I'd bring your 1/2 mile gears for practice at Susquehanna - it's definitely bigger than a 3/8 mile track, with pretty decent banking. It may not be a full half mile, but it's a fast track.

fairlaniac
Dirt Maniac

Total posts: 110
posted June 22, 2005 12:46 PM  
It's actually advertised length is 4/10 of a mile.

------------------
Doug
"Lift for a second, that's where you'll finish!"

racer17j
Dirt Forum Champ
Total posts: 5390
posted June 22, 2005 08:36 PM  
in that case lings is right just run what you have and maybe drop about 2-3 inches roll on the rear

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