Hello all I have been doing a lot of reading and I need some expert advice
I recently installed a 700r 84 model in my 67 rs which has original 308 rear
I am running 17 wheel tire combo measuring 12 3/8 ground to center
what would be my optimal gear for cruising
thanks all

 

as in 1st second or third? or gear ratio? By the way, you do know this is a THIRD GEN specific forum right? To answer your question it depends on how fast you "cruise" I've got 3:73 rear gears and i roll on the highway all the time, and i only got a three speed.

 

I'm sorry
I understand which forum I am a member of and posting on, I also thought it was clear I was talking about rear end gearing given the information I included. I did not realize since I was utilizing the drivetrain from a third gen in a first gen I was excluded from using this forum
"By the way, you do know this is a THIRD GEN specific forum right? "
appreciate your help

 

If we allowed every car and every engine to post here, this site would quickly become a non-thirdgen site. If you have a thirdgen engine swapped into your car, you're more than welcome to post here and ask questions about it.

Most people recommend 3.42's for a great compromise between street and strip. You can go up to 3.73's for a little more grunt at the cost of top end.

 

I would say 3.23 or 3.42...

 

I put a 700R4 and 3.42 gears in an '81 El Camino that I had several years ago and I loved it. It had 2.73s in it when I did the trans swap and I couldn't use overdrive at all. The 3.42 seemed perfect to me.

 

thanks kevin and xlr8tor and gear head that is the kind of response I was hoping for
I can do the math but there is no substitute for hearing from people who have had the experiences all ready on the road
by the way I have owned third gens too always a gm man and a mechanic for profession 90% under the hood not under the car
thanks

 

I had a '78 Camaro with the big rear spoiler, a stock, 130k miles 350 V8, a 3.08:1 gear, and 235/60R15s. Stock Quadrajet and intake, stock exhaust manifolds into a Hooker dual exhaust. 8 mpg. I installed a 700R-4, and the PainlessWiring lockup kit. 1800 rpm @ 65 mph = 25 mpg! If you have a mild cam upgrade, then maybe you'd do better with a 3.36:1. There is no 3.42:1 for your axle, and as long as you're running a 350, there's no need to upgrade the axle. Running a 3.73:1 gear in my '88 Camaro, with a carbureted 350, 700R-4, 235/60R15s, and the Painless kit, got me 2200 rpm @ 65 mph. This was a bit annoying, but first gear was as deep as I would ever want with an automatic. Great fun! To save you from searching, the formula for speedometer gears is 20168.068 divided by unloaded tire diameter, we'll call that Z. Z times number of drive gear teeth times axle ratio, call that Y. Y divided by 1000 gives number of driven gear teeth. for drive gears, there's 15, 17, 18 and 19, but no 16. Driven is 34-45 teeth, inclusive. Good luck!