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Author Topic:   gears and rpm
Oldsmobile13
Dirt Full Roller

Total posts: 66
posted June 12, 2001 04:06 PM
I think i have been running too low geared.
I run on a 1/2 mile track with 2.75 gears, 15 inch tires, manual 3 speed and a 355 i hit about 5500 RPM too far into the turns. I still dont do to bad but do you think 5.14 or 3.00 gears will be better? These are all i have right now.
And Should i be running more like 7000 rpm.
thanx for your help

Oldsmobile13
Dirt Full Roller

Total posts: 66
posted June 13, 2001 12:50 AM
By the way I run an 83 cutlass with 225/70/15. How much exactly does this affect my gear ratio.

racer17j
Dirt Maniac

Total posts: 165
posted June 13, 2001 01:35 AM UIN: 54865418
what gear are you running in? do you have to run that big of a tire we have been running a 3.08 in second gear for years with a 205/70/14 comes out to be 82 in tire roll and i drop to a 78 in roll when i run on a 4/10 mile useuly run about 6500rpm going in to the corners hope this helps

49mtmod
Dirt Roller

Total posts: 13
posted June 13, 2001 08:32 AM
First, if you are running 5500 rpm and want to be running 7000 you are not geared too low, you are geared too high. The higher the gear number numerically, the lower the gear.

Also, I assume your are running in 2nd gear. If so, you need to find out what the second gear ratio is in the tranny. For example if you are running a saginaw with a 1.68 2nd gear, you would be running a 4.62 final (1.68 X 2.75). In that case, both the 3.00 (504 final) and the 5.14s would help. If it is a 1.89 second gear you would be running a 5.19 final. The 3.00 (5.67 final) would still help but the 5.14s would be going the wrong direction.

Oldsmobile13
Dirt Full Roller

Total posts: 66
posted June 13, 2001 11:01 AM
Yes you are correct, I meant to say that I was to high geared thanx for the correction and the advice.

4s racing
Dirt Forum Racer

Total posts: 77
posted June 14, 2001 10:52 AM
I have a simular question. i am running a ford with a 400 mod.with a FMX tranny 9" 2.75 gears i need to know what type of older vehicle came with 3.73 gears so i can change.

racer17j
Dirt Maniac

Total posts: 165
posted June 15, 2001 01:05 AM UIN: 54865418
i don't think they made a 373 in 9 in just 7.5 and 8.8 you would have to go with a 370 or 389... 373 is a gm gear i belives . i do know i've never seen one for a 9 in in any of my mags anyway

4s racing
Dirt Forum Racer

Total posts: 77
posted June 15, 2001 08:02 AM
thanks racer17j i got my sheet out and they are showing 3.7,3.75,3.82,and 3.89. i guess i been around the bow tie people to long LOL.is there any way to find what the ratio is without tearing the rearend apart.and counting gear teeth?i have acess to numerous rearends but don't want to tear them all down. what would be the ratio of 1.25to1.0 of the wheel. is there a formula that you kow of? any help would be great.

49mtmod
Dirt Roller

Total posts: 13
posted June 15, 2001 08:39 AM
A quick way to get an estimate of what gear ratio is in a rearend is to mark the pinion and then spin the tire/wheel 1 full rotation and count how many times the pinion turns. If the gears are 3.89s one rotation of the wheel should give you 3.89 rotations of the pinion.

4s racing
Dirt Forum Racer

Total posts: 77
posted June 15, 2001 10:23 PM
thank you 49mtmod you just made my day. I have been arguing with a freind of mine for 2 days that is what you can do.he kept telling me the only way was to tear it down and count ring teeth and pinion teeth. Then again he is a COON *** .LOL. but he is a good freind.

chevythunder93
Dirt Roller

Total posts: 7
posted June 16, 2001 12:10 PM
what is the gear ratio in a turbo 200?

racer17j
Dirt Maniac

Total posts: 165
posted June 16, 2001 09:10 PM UIN: 54865418
same as a t350 but it's a time bomb 2.72 1st 1.52 2nd 1 drive

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