Rear End Gearing Recommendation

[69SlowResto 19]

Hi guys, looking for some opinions on which gearing to run. 69 Coupe 302 with C4 automatic transmission. I will be rebuilding the engine with a 347 Stroker kit and Edelbrock top end with 4 barrel carb. I currently have a 8" rear end on there and will be keeping it for the time being. It currently has 2.79's. I was thinking of going with the 3.55's but wanted some opinions from some of the more knowledgable people on this site. Would the 3.25's be a better all around gear?

 

This car will strictly be a weekend cruiser for me. It will not see any race action. I would like to be able to take it on the freeway (not often) and not be driven nuts by the high revs. Fuel economy is not an issue for me.

 

Thanks in advance

 

Lee

[69shelbycoupe 11]

3.55's with a 26 in. tire at 60 mph you will be running at 2750 rpm

3.55's with a 27 in. tire at 60 mph you will be running at 2650 rpm

 

3.25 gears under same condition will lower your rpm by only 200 rpm

 

4.11's with a 26 in. tire at 60 mph you will be running at 3200 rpm

 

hope this helps based on decision of what rpm you want to be running at highway speeds

 

now for my opinion.

I think best all around street gear would be a set of 3.80's. These would be best performance without rpm running to high at highway speeds. The 3.55's will be economically better but you will lose excelleration performance

[maxum96 32]

Having run a variety of different gear ratios on the street with both non-overdrive and overdrive transmission, I'd recommend 3.00 to around 3.25 gears. Since your C4 doesn't have overdrive and you're not looking for off the line performance, you'll want something in that range for cruising.

[69SlowResto 19]

Thanks for the responses guys. I have some decisions to make and you have given me some food for thought. If anybody has anything else to add to the conversation please do.

[LoneWolf2U 136]

To keep the new build eng from seemly being a dog, I would not go more than the 3.25 gear for what your after noting your op.

I have a 3.50 behind a 351C 4sp and it does scream at 70+ on the open road.

 

The 2.79 behind a mild 289/C4 in the 68 cougar is slow off the line, but run it up to 25 mph and kick it and it will howl like a scalded dog.

But very quiet while cruising the highway and get 18+ mpg. :biggrin:

[69again 10]

I have a built 302, C4, 8", 295 40 17's and 355's. Rpm's way to high for highway cruising. Great for track, but don't need it for street driving. Before I spent the money on new gears, I would try what you have and then depending on how you want to accelerate, go from there. With the 8" you probably don't have a positive track/locker, correct? Mine without a locker and 355's you can barley give it any gas on take off without breaking the right tire loose. I am adding some sort of posi so I don't look like a teenager when I want to get up and go. dan

[6T9Mach1 12]

I ran my car with 3.50's on the highway often enough to know that you can do it but you arent going to be flying. If you dont plan on driving over 65-70 mph for extended periods of time you will be fine with 3.55's if you have a 26"+ tire.

[sportsroof69 13]

I also ran 3.50s, and still do for the time being. With a 26" tire, I can run 65 mph with now worries. I run 70 down the interstate, and it sits just under 3000 RPMs.

[LSG 15]

Slow, how about keeping the 8 with what you have, or find a 9 with 2.75 or 3 to 1 gears, then get an AOD. You can get a wide ratio 1st and 2nd to makeup for the highway axle, and still accelerate very nicely. The 3.00 + the overdrive will make the highway cruising much more enjoyable and better mileage and stress free. You want to enjoy driving around, right ? Why anyone who wants an Auto trans that has a small block would even bother with a C4 or C6 mystifies me. I like old stuff, I really do. But a 3 speed auto is NUTS in our current fuel/price situation. LSG