I have a 388. Not a huge bit of compression for smog legal purposes. I have a 700R4 Trans and it is still running on the 273 gear ration peg leg. At 4th gear i have basically no power. I do drive it everyday and i do not want a complete gas guzzler, But i do want power. I will settle for one or the other though. What is a good gear ration to run with it, all the way around. I have heard 305 , 375 . i dont know though. Thanks , by the way should i run a posi, or peg leg ?????
Diesel

Look through some of the earlier posts in this forum, or do a search. There is a pretty good discussion in this thread (http://elcaminocentral.com/ftopict-20681.html). I know there are more in here too, good luck.

3.31 or 3.42 I have 3.42 in my Z71...good off the line, not great gas mileage but it doesn't suck either (gas that is). Definately posi!

Anything in the low-mid 3s should work well. Higher numerical ratios will have the engine spinning too fast at highway speeds, while lower nuumerical ratios may have the engine spinning too slowly at highway cruise speeds to run the accessories.

Highway acceleration can be significantly improved by the use of a torque converter with a stall speed of 2000-2500, and a kit to unlock the TCC at low vacuum.

I would go with theelcaminofactory's suggestion on gear ratios and posi. Since you've already got an engine that is capable of putting the power to the ground, why not look for a Buick turbo 8.5 inch rear out of a Grand National or T-type. Look for one that already has a posi and the gear ratio you desire, then you could just swap out the whole rear. Look to spend $500-$1000 for one.

Another thing you will want to take into consideration is what tire size you're running. If you're running a taller than stock tire you will want to go with an even lower gear ration (numerically higher) in order to compensate for the difference. Of course you don't want to go too low or else you'll throw your gas mileage out the window. Take a look at this site click here (http://www.4lo.com/calc/gearratio.htm), it has a calculator wherein you can input all the information on your vehicle, and see what rpm your engine will be running at a given speed with a given rear end ratio and tire. Since this calculator is set up for 4x4 use, if you use it just put a 1 in the area for transfer case ratio since our 4x2 Elcos don't utilize a transfer case.

This helped me while deciding what to do with my transmission.
p.s. note, your tire size can play an important part in your rear ratios.

http://www.et-studios.com/motorsports/gears/gears.html

I'm running 3.55's with a TH700 (final drive ratio 2.75:1 give or take) and am real happy with it. It revs about 2400 RPM at 70MPH with 275-50-15 rear tires and the converter locked up.

3.73:1 wouldn't be too much.

Both gear ratios offer a killer low gear ratio in the 11:1 range.

mnunn wrote: I'm running 3.55's with a TH700 (final drive ratio 2.75:1 give or take) and am real happy with it. It revs about 2400 RPM at 70MPH with 275-50-15 rear tires and the converter locked up.

I totally agree. I run a 2400 stall convertor, 700r4 and 3.50 in a nine inch with 24.5 inch tall tires. It is a great all around setup. Quick off the line and great highway cruising.