oram

my 74 vette with 4 speed standard shift ..... at 60 mph my tack registers 2800 rpm's ... it seems to me that the engine is turning to fast at highway speeds .... would like some opinions on this ....thanks

midyearvette

sounds like youre running a 3.70......

Peterbuilt

You can jack up the rear and spin the tire once and count haw many times the driveshaft turns or use this www.richmondgear.com/101032.html PG.

yel76low

What tires do you have?

225/70/15's and a 3.70 rear gear would give you 2723 rpm at 60 mph... so if you've got slightly smaller tires 2800 sounds right on.

Attfay Elleybay

Mine was about 4000 at 60 before the 200r4.

Ganey

There were optional rear axle ratios so higher than "normal" is common when lower rear gears were ordered mainly for drag racing incl. street. ...

Eddie 70

Oram, I am sure you know this but you have to remember, there were no overdrive transmissions in corvettes when they were new in 74. Final drive ratio was 1:1. Most cars today are much lower and the final drive is .80 with some as low as .50. This really cut the rpms down and helps out with the gas mileage plus it makes the car seem to ride that much easier and smoother.

oram

thanks everyone for replying ... my tire size is 255/60/15... just took her out on the highway at 60 mph looks like about 2725 rpm's... if i had a higher ratio rear end i assume this well bring down the rpm's at the same speed... what other affect would this have on performance ?

DRIVESHAFT

A higher (lower numerically) gear ratio will bring your cruise rpm down, but will result in slower acceleration.

flynhi

I have a very nice 3.08 for sale that will drop your cruise RPM considerably and raise your gas mileage.
$350 plus shipping from Austin, Tx.
Will

OzzyTom

AND make his vette accellerate like a Toyota Prius to boot

Oram... you need to decide what you want.
How do you use your vette?

If you do a lot of highway miles, then you have a case to concern yourself about fuel economy.

If you're like a lot of us, the vette is a weekend toy.
It's a performance car.
And the good ones are noisy, shake the fillings out of your teeth and drink gasolene quicker than a turpentined cat.

If you really want to have your cake, and eat it too...
then an overdrive gearbox is what you want.

bashcraft

What gears do you have? 5.13's?

oram

how do i tell what gears i have?

CCrane65

See post #3 above.

cc

Mike Ward

Tire size has no effect on speedometer readings.

joewill

agreed, are you sure that when your speedo says 60 that you are going 60?
check it on a gps or a measured mile to be sure..
but still the bottom line is if you want to lower your cruise rpm, get a numerically lower gear... ie. 3.08...

I have 2.73's and run 60 at 2000 rpm.. it is hard to lay rubber even in 1st gear with my 454... but it is a nice quiet low rpm cruise..

Attfay Elleybay

I'm guessing 4.56

fantic

Oram. I have the same set up in my 77. When I bought the car the speedo was off quite a bit. Checked with gps and found out I had the wrong plastic gears on the speedo drive. I've learned to live with the high rpm's and just drive a little slower on the highway.Just enjoy the ride.

ED69ray

IMO, 3:08 is too tall to run with a 4 speed.

If I was running a BB with mucho torque I'd look at 3:36 and 3:55

For a SB 3:70 or 3:55 would be my guess depending on M-20 or M-21

good Luck, Ed

fe1ixdakatt

So you're familiar with my car, I see.

I have a 3.70 and only do city driving. I can't imagine anything less because I love the way it throws me back in my seat when I take off. When I'm doing 60 mph I sound like I'm doing 120 though, but it's a small price to pay for the jackrabbit starts. I don't ever take her on the freeway as a result, though. I'm not even sure she'd hit 100 mph.