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Author Topic:   What Gears to use?
jimshar
Dirt Full Roller

Total posts: 67
posted January 31, 2005 03:58 AM  
I have an 81 mustang 2.3 with a 4 speed trans, we will be racing on a 1/4 mile dirt track, what gear ratio should I use in the rear? How do I figure out the ratio? I have heard you have to measure the tire diamater,count the splines on the trans and do some sort of a calculation but not to sure. Any help would be great.

b4racing
Dirt Forum Champ
Total posts: 626
posted January 31, 2005 07:51 AM  
what is the track like big .25 sweeping corners, paper clip, what is the roll out on your tires. What is your target rpm with your engine? I can get you close with this info.

jimshar
Dirt Full Roller

Total posts: 67
posted January 31, 2005 08:40 AM  
quote:
Originally posted by b4racing:
what is the track like big .25 sweeping corners, paper clip, what is the roll out on your tires. What is your target rpm with your engine? I can get you close with this info.

The track is a 1/4 mile dirt oval with slight banking, looking to get 7200 to 7400 RPMs, 14" tires (are you looking for the diameter of the tire when you say "roll out)

jimshar
Dirt Full Roller

Total posts: 67
posted January 31, 2005 08:44 AM  
quote:
Originally posted by b4racing:
what is the track like big .25 sweeping corners, paper clip, what is the roll out on your tires. What is your target rpm with your engine? I can get you close with this info.

Tire diameter is 80"-81"

b4racing
Dirt Forum Champ
Total posts: 626
posted January 31, 2005 02:56 PM  
try a 345 rear gear with 2.14 trannie if that over shoots you then go with either the 327 rear or 197 trannie if not enough trya 373 rear. but the first is where I would start with a 373 and 214 82" roll out I ran about 7800 with one engine and 7600 with the other. Later and good luck Bobby

jimshar
Dirt Full Roller

Total posts: 67
posted January 31, 2005 03:44 PM  
Thanks, its a start.


quote:
Originally posted by b4racing:
try a 345 rear gear with 2.14 trannie if that over shoots you then go with either the 327 rear or 197 trannie if not enough trya 373 rear. but the first is where I would start with a 373 and 214 82" roll out I ran about 7800 with one engine and 7600 with the other. Later and good luck Bobby


str8racing
Dirt Full Roller

Total posts: 65
posted February 15, 2005 04:59 PM  
how do you tell what gears in tranny?

way2fast
Dirt Maniac

Total posts: 104
posted February 15, 2005 06:51 PM  
My cousin was running at a 1/4 mile, creek county speedway in kellyville, and was running a 1.98 and a 4.11 and was only turnin around 6,000 with about a
215/60 or 65/15 tire

racerman707
Dirt Freak

Total posts: 374
posted February 18, 2005 10:52 AM  
Pull the trans. Put it in the gear you want to check, mark the tailshaft housing and the splines on output shaft lined up with each other. Do the front shaft the same way making sure not to turn the transmission. Now turn the front shaft and count the turns while somebody else counts the rear shaft. When they both line up, stop, divide one number into the other. There you have it.

Shawn P Martin
Dirt Full Roller

Total posts: 33
posted February 25, 2005 09:48 PM  
4 speed manual trans. from 1974 to about 1983 are 214 in the 2nd. gear you want a 355 rearend. if you have a 197 2nd gear in a 5speed trans. you want a 373 rearend and locked. Run 225/60/14 to get about 7600 to 7800 rpm. Run 225/60/15 to get about 7400 to 7600 rpm. You are looking for some 780 final drive on the 1/4 mile tracks. Feed Your Need For SPEED

popeye14709
Dirt Forum Racer

Total posts: 86
posted February 26, 2005 06:29 AM  
Just a little on what Shawn P. stated the 355 would be fine but thats only if Jim isnt runnin the 7.5 rear end... i would run the 373's but our mustang for a small 1/4 mile we have to run 410's just to be able to drive out of the corners if not the car bogs down below 4000 rpm and OUR motor just will not run at them r's... its either change to the 410's or run small 13" tires on the car...but this is my opinion thats all.....

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Dirt is for Racing Asphalt is for Getting there!

jimshar
Dirt Full Roller

Total posts: 67
posted February 26, 2005 08:24 AM  
I believe the original rear (which is stock) is the 7.5. Thanks for all the imput guys.Will have to see what works best.
quote:
Originally posted by popeye14709:
Just a little on what Shawn P. stated the 355 would be fine but thats only if Jim isnt runnin the 7.5 rear end... i would run the 373's but our mustang for a small 1/4 mile we have to run 410's just to be able to drive out of the corners if not the car bogs down below 4000 rpm and OUR motor just will not run at them r's... its either change to the 410's or run small 13" tires on the car...but this is my opinion thats all.....



Dunnracing98
Dirt Full Roller

Total posts: 63
posted February 28, 2005 01:16 PM  
quote:
Originally posted by jimshar:
I believe the original rear (which is stock) is the 7.5. Thanks for all the imput guys.Will have to see what works best.

I run 14 tires with a 4.11 rear end and pull around 7 grand on my tach on 3/8 mile track got all the power i need

racerman707
Dirt Freak

Total posts: 374
posted March 02, 2005 10:21 AM  
From '74-'83 there were at least 4 different gear ratios available. Pinto's had 1.97, 1.99, 2.14. Some Mustang 2s had 1.81 course spline. Mustangs had 2.14 from '79 up. Yours should be 2.14 but need to count the splines to make sure. Don't rule out running third gear. A smaller pinion transfers power to the ring gear better.

jimshar
Dirt Full Roller

Total posts: 67
posted March 02, 2005 12:17 PM  
Thanks for the info.
quote:
Originally posted by racerman707:
From '74-'83 there were at least 4 different gear ratios available. Pinto's had 1.97, 1.99, 2.14. Some Mustang 2s had 1.81 course spline. Mustangs had 2.14 from '79 up. Yours should be 2.14 but need to count the splines to make sure. Don't rule out running third gear. A smaller pinion transfers power to the ring gear better.


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