Advice on Choice for Rear Gear Ratio

[Steven B.]

Re: Advice on Choice for Rear Gear Ratio

I'm looking for advice on helping me choose a rear gear ratio. I have a '67 with a 383cu. in., 425 hp motor, 3.36:1 rear gear and a "close ratio" Trans with a 2.20:1 1st gear. Problem is, the car "bogs" too much when trying to pull out from a stop sign normally. I will be updating the trans with a new input shaft and cluster gear which will change this box to a "wide ratio" with a 2.52:1 1st gear. I don't feel that this will be enough change. So my problem is to change the rear to either a 3.55:1 or a 3.70:1 ring and pinion. Looking for someone's experience with the 3.55 combination. I don't want to end up with a "stump-puller" if I go with the 3.70's. Any advice? Boy it would be great if there was someone out there in the Spring City, PA area that has a car with a set of 3.55's that I could drive around the block a few times to feel those gears............Herb

Herb, what are your 383's cam specs, etc.? I have driven every combination since the 60's (and some not offered) and never had a problem with the combinations Chevy offered. Your 383 should be pulling alot more HP and Torque than what SB's came with from the factory. As Clem, Stu, and Gene stated I would check the engine specs. If 283's and 327's would pull those gears your 383 sure will unless the engine/cam requires too many rpms to get rolling without bogging. Alot of folks built street engines with the "biggest" cams they could ultimately requiring high rpms. I have a 355 with 400 HP/401 Torque, less HP than you have and likely less Torque. I have also ran 3.08's thru 3.90's with no bogging problems with any of them. Your 383 should even be able to pull 2.73's.

Steve

[Michael H.]

Re: Advice on Choice for Rear Gear Ratio

The 365 HP 64 coupe that we bought brand new came with a 3.08 and a 2.20 close ratio 1st gear. I hated it. I never could understand why anyone would have ordered such a combination. (car was dealer stock. I would never have ordered it that way) If I remember correctly, the car went almost 80 MPH in 1st gear.
Might have been ok racing at Daytona or Bonneville. Other than that....

My next new car was a 68 Z28 Camaro. That car was assembled with a 4.88 rear ratio. Lotta fun !

Most of the 63-65 FI Corvettes I've owned over the decades had 4.11's or 3.70's. I've been all over the country with a few 63 FI cars that had 4.11 and it wasn't a problem.

I always liked a 3.70 diff with a 2.20 1st in a big block.

I think a 3.70 is probably my all around favorite for all driving conditions.

I never liked the gear spread in a 2.54 wide ratio. Just seems like a wasted gear in the middle. A three speed is more logical.

Good thing a lot of different combinations were available, just like different colors. Everyone has their own favorite combination.