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Username Post: Rear differential Ratio        (Topic#357612)
kirk55 
Member
Posts: 36
kirk55
Loc: Dennison MN
Reg: 01-03-03
08-11-19 05:18 PM - Post#2772986    

I am currently running 4:11 gears behind a 350/Muncie M-21 and am spinning about 3500 at sixty five mph I would like to get the steep gears out and go with a shallower set 3:73 or 3:56. any recommendations?

55 210 post 350 4 speed
02 Silverado 2500 hd duramax
99 S ten


 


acardon 
Ultra Senior Member
Posts: 11298
acardon
Loc: DFW TEXAS
Reg: 03-25-05
08-11-19 05:47 PM - Post#2772988    
    In response to kirk55

You apparently have 25.5" tires, so a 3.55 will give you a little over 3,000 RPM. Link to RPM calculator

Don
66 Corvair (driving)
57 2dr HT (driving)
56 2dr HT (waiting to be restored)


 
Mel Foye 
*VIP* Founding Member
Posts: 4905
Mel Foye
Reg: 09-29-00
08-11-19 05:51 PM - Post#2772989    
    In response to kirk55

Even though I lived in 4 different areas of Minnesota I had to do a search to find your town.
So my guess is you don't put on that many miles in town driving around.
Unless your have small height rear tires the ratio, rpms and mph seem off. It would be good to have all factors exact.
If you don't put on a lot of miles every time you go out I would leave the 4:11s as a sbc can live forever at 3,500. YMMV




 
kirk55 
Member
Posts: 36
kirk55
Loc: Dennison MN
Reg: 01-03-03
08-11-19 06:40 PM - Post#2772993    
    In response to Mel Foye

Thanks for the reply. I am going to play with the rpm calculator a bit. Its not that I put on a lot of miles and gas mileage does not figure in the equation. Just want to get the rpms down so that I can hear the tunes. I know mufflers are cheaper than gears Thanks again.

55 210 post 350 4 speed
02 Silverado 2500 hd duramax
99 S ten


 
kirk55 
Member
Posts: 36
kirk55
Loc: Dennison MN
Reg: 01-03-03
08-11-19 06:52 PM - Post#2772994    
    In response to acardon

Yes, tires are 25 1/2 " that reads 3520 at 65 mph.
food for thought. Thanks

55 210 post 350 4 speed
02 Silverado 2500 hd duramax
99 S ten


 
YOUNG57 
Frequent Contributor
Posts: 1154

Loc: Tennessee
Reg: 12-06-10
08-11-19 06:57 PM - Post#2772995    
    In response to kirk55

The Muncie M21 & M22 are close ratio transmissions with high ratio 1st thru 3rd gears meant for city stop light to stop light and 60 mph highway driving so need low ratio rear ends to be effective. M21 & M22 were best with 411 and lower rear ends

You can certainly use a higher ratio rear end; it will just be a bit slower (stumble) from a dead stop and you need to feather / ride the clutch a bit more. That’s about the only down side for a street / highway driven car.

I have a M20 wide ratio which is best with a 355 rear end, but I have a 308 so I can run 70+ mph on interstate highways. It stumbles from a dead stop, so I have to feather / ride the clutch a bit.



Edited by YOUNG57 on 08-11-19 06:57 PM. Reason for edit: No reason given.

 
Mel Foye 
*VIP* Founding Member
Posts: 4905
Mel Foye
Reg: 09-29-00
08-12-19 08:54 PM - Post#2773102    
    In response to YOUNG57

Young57 you are not alone with being negative on using 3:08s but my personal experience with a 62 Vette with a 327-250hp, 3:08s and a 220 low let me take off w/o stumble or other than normal slip coming as the clutch pedal came up. Ran at the drags with them even many times. Close to 170,000 miles of daily Los Angeles city driving and I replaced just one clutch set up. A finger broke.
Around 170,000 went to a 400sbc still with those 3:08s and no problems. YMMV



 


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