Differential question
Thread Starter
Racer
Joined: Jun 2009
Posts: 302
Likes: 2
From: Milton Delaware
Differential question
The codes on my differential for my 1973 coupe says it should be a 3:08 and at 50mph I am turning 2000rpms.. Does this sound right or did the previous owners have it changed? I can't burn rubber taking off and my 350 has no air pollution stuff on it (crate engine). Any idea what this might be? Seems awfully hard on gas. That' why I am sking for advice and help. Will the original 3:08 do better on gas and run better? I have the Eldelbrock 600 carb on it. Thanks for any come back
Race Director
Joined: Dec 1999
Posts: 19,610
Likes: 778
From: Forked River NJ
Yes that figures just about right. 3.08s are easier on gas than say 3.70s on the highway for sure. Might be a tune issue if it is sucking gas. Also might be a right foot issue, to heavy. 
Instructor
Joined: May 2007
Posts: 130
Likes: 0
From: Houston TX
The ratio is number of drive shaft revolutions per wheel revolutions. Easily checked by jacking the rear wheels and, with tranny in N, turn rear wheels one rev and count the drive shaft revs.
Can also check by calc backward using 2000 rpm divided by 3.08= tire revs/min then convert min to hr, in to miles using circumference of wheel, in. By my calcs it's about 48 mph.
Cheers,
Can also check by calc backward using 2000 rpm divided by 3.08= tire revs/min then convert min to hr, in to miles using circumference of wheel, in. By my calcs it's about 48 mph.
Cheers,
Thread Starter
Racer
Joined: Jun 2009
Posts: 302
Likes: 2
From: Milton Delaware
Not heavy on the foot issue, due to price of gas. So Evershark you are saying that I do have 3.08 rear?I thought a 3.08 will be decent on gas and that doing around 50mph.
If so, do I have a carb issue?
If so, do I have a carb issue?
Safety Car
Joined: Sep 2007
Posts: 4,443
Likes: 326
From: Indy Indiana
depends on your tire size too.. here is a decent calculator of tire size, rear end ratio, rpms turned at what speed.. there are others out there too..
I have a 2.73 that turns 2000 at 60 mph using 245x60R15 tires
I have a 2.73 that turns 2000 at 60 mph using 245x60R15 tires
Safety Car
Joined: Sep 2007
Posts: 4,443
Likes: 326
From: Indy Indiana
i get about 15 with a BB, but drive pretty easy.....
here's the link I forgot to post.. try this for your rpm calculation
http://700r4.com/speedoCalc/rpmcalc.shtml
here's the link I forgot to post.. try this for your rpm calculation
http://700r4.com/speedoCalc/rpmcalc.shtml
