Rear End Ratio question

[Mopar to ya]

My 318 / 904 / Dana 60 with 4.10 ran exactly that. At 70 mph I was running 4000 rpm. The final gearing is 1:1. When I installed the 408 I also installed a 200R4 overdrive transmission. Now I run 80 mph at 2800 rpm thanks to a .67 final gear.

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[C300]

Not sure if this is helping, but I prefer an 8 3/4" for street driving. Unless it's an over 550hp BB and a standard it's over kill. and heavy ! The other thing you can do is change the planetary gears in the transmission. that would give you a lower 1 gear, or do both planetary's for 1st and 2nd and then do a 3.23 rear gear with the same performance in the lower gears. still not cheap. need a Manual valve body too. Can then run the cam and converters that are for 3.73 or more.

 

[AJ/FormS]

Here is the math;

(RPM x TC)/ 1056 x R1 xR2 = MPH
where TC is tire circumference, and the Rs are gear ratios;R1 the diff, and R2 the tranny
So for you (3000 x 80.8)/1056 x 3.54 x 1 = 64.8 mph. The error factor in your reading would be due to TC slip, and/or calibration.

64.8/60 =8% slip/error , Very close to right on, Id say.

 

[sireland67]

Try a taller tire to kill the rpms way cheaper than gears or overdrive.

 

[Tjhoward84]

Try a taller tire to kill the rpms way cheaper than gears or overdrive.

What sized rest tire do you suggest? I need to keep the rims that are on the car. I believe they are 18 x 8.