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Author Topic:   Rear Gears and RPM
smayo964
Dirt Newbie

Total posts: 2
posted September 19, 2001 10:52 AM
I'm in the process of moving into the modified ranks from street stock and in the process of building a new chassis. One area of confusion is the rear gear for these cars. What is a normal gear ratio range for an approx. 3/8 mile, high bank, fast track? What engine RPM ranges should I expect? Thanx for the help.

CNC DOC
Dirt Roller

Total posts: 23
posted September 19, 2001 06:37 PM
Most guys around here are running a 5.14 or 5.29 gear. Around 6800 to 7200rpm.

smayo964
Dirt Newbie

Total posts: 2
posted September 20, 2001 07:05 AM
Thanx CNC DOC for the info. Is the gear ratio shown the final ratio (trans x rear gear), or just the rear gear. I was running approx. total ratio of 6.90 in the street car and turned 6,700. If those are total ratios given (5.14/5.29), are they that low to keep wheel spin under control? Just trying to get a better understanding of the setup.

FS93
Dirt Roller

Total posts: 6
posted September 20, 2001 05:49 PM UIN: 3107810
He is listing the final gear ratio. We either run a 5.29 or a 5.43 and turn 7-7200. Most modified drivers dont do a lot of running in second gear or anything like the street stockers do. In my old factory stock on a 1/**i track we ran in second gear(saginaw 3 spd) for a final drive of 6.52(1.75x3.73). The mod we run a 5.83 rear gear and run it in third which is a 1:1 ratio. The reason for the big difference in gears is the most street stocks run larger tires, adn need more gear to pull them to the same RPM. Hope this helps.

CNC DOC
Dirt Roller

Total posts: 23
posted September 20, 2001 07:20 PM
Street stocks are also alot heavier than a modified. Modifieds here in Ohio are running in the 600 to 650hp range. I know of some that are over 700hp. These are a couple of more reasons for the difference in gears between the street stocks and modifieds.

Racer4
Dirt Forum Racer

Total posts: 98
posted September 20, 2001 09:21 PM
In Other words you can think of the Modified as really very much faster and lighter than you street stocker, they just still have to turn left. If it was just a drag race the Modified would completely kill the heavier Stocker, they have to make the turn, that's why it may not be that evident in lap times.

Racer14K
Dirt Roller

Total posts: 15
posted September 22, 2001 12:25 PM
At I-55 Raceway in Pevely,Mo. which is a high banked 3/8 track, most of the mods running roller cam, high compression engines are running 5:14s. 5:29s on the flat tappet engines. If the the track stay's tacky I would go with the 5:29.

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