I have a 85 Camaro with 88 305 TBI with 700r4 trans. When I'm running about 72-73 MPH the tach in showing around 3000 RPM, does anyone have guess what the final drive ratio is. The price of gas these days I might go to something that gets better gas mileage and still has pretty good pep. Anyone have any suggestions.
Thanks.

 

what size tires?

Go back to the TGO main page and under the tech articles you should find a 'tech equasion' page that will allow you to calculate your gears.

 

Thanks, I'll check out the Tech Pages, I have 25.5 t0 26" inch tires and wheels together on 16" IROC wheels.

I checked the tech page and looks like I have a 3.42 ratio final drive.
Thanks.

The speedometer is about 7 miles fast at Interstate speed.
Maybe a 3.07 would be ok.

 

you cant use your stock tach to determine final drive ratio as even a couple hundred RPMs will through it off

if you have the 700R4 you probably have 3.08 in there now..

 

Actually, if the gears have never been changed, a 305 TBI car with the 700r4 trans ALWAYS come stock with 2.73's. TBI cars with the T5 manual trans got 3.08's stock. If your tach is even somewhat accurate, you're not running 2.73's anymore. This has been said in about a million different posts now. If you want to figure out what gears you have, just remove the rearend cover and take a look. A couple of quarts of gear lube and a little rtv don't cost much.

 

Yeah but it's an 85 car with a later TBI motor swapped in (I'm assuming with an 85 rear in it) so it could be different ratio than a TBI originally came with.

When I had my 92 Camaro with 700R4 I swapped in a set of 4.10s in the back with stock tire size and it would turn about that many RPMs in overdrive at that speed. Obviously, no factory Camaro of that vintage ever came with anything close to 4.10s. I'm guessing you either have a tach that's off or somebody changed the rear gears.

Here's a quick rear end ratio check I've found useful over the years.....

Jack ONE rear wheel off the ground.
Put tranny in neutral, parking brake off
Put a mark on the wheel and another one on the driveshaft (chalk, grease pencil- whatever is easily visible to you).
Spin the wheel exactly 10 revolutions while you count driveshaft revolutions (and fractions of a revolution).
Take that number and multiply it by 2. Then divide it by 10
The result is your rear end ratio.

It's as accurate as your observations and the fact that there's always a little "slop" in the drivetrain that will throw things off slightly.

 

Thanks Damom... I'll run that test this weekend. All I know is that it makes old Chuck (me) smile, when the old Camaro gives my big mouth friend's (supposely hot running, by all accounts) 88 Mustang GT all he wants for lunch up to 90 MPH. And it's a lot better looking than his mustang.
I'm sure it's a stock 305 TBI motor with a Performance Chip. But, with gas prices going up & up I may have to park it except on a nice Sunday or Weekend. Thanks again.