Thanks all. I'll assume 3.36 and the next time I get a chance to peek under the car and read what's on the axle tube I'll post it so we can all congratulate ourselves.
Final drive ratio?
Thread Starter
Advanced
Joined: Nov 2011
Posts: 53
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From: Lynnwood WA
Final drive ratio?
Hello all,
I have a 69 coupe with a 350CI/350HP and 4-speed. I have not got under the car to read the rear end codes due to health issues and would lilke to know what the final drive ratio is.
I run 2700RPM in fourth gear at 60MPH. Assuming the instruments are right is it possible to tell the final drive ratio from this data?
I have a 69 coupe with a 350CI/350HP and 4-speed. I have not got under the car to read the rear end codes due to health issues and would lilke to know what the final drive ratio is.
I run 2700RPM in fourth gear at 60MPH. Assuming the instruments are right is it possible to tell the final drive ratio from this data?
Safety Car
Joined: Oct 2005
Posts: 3,570
Likes: 1
From: Algonac Michigan
If you can talk someone into getting under the car far enough to put a chalk mark on the driveshaft you can count the revolutions of the shaft in relation to the tires....But then I guess they could read the rear end too couldn't they???
Melting Slicks
Joined: Sep 2004
Posts: 3,216
Likes: 665
From: Northeast
Tire height for a 245/60/15 is 26.57
If you plug the info you provided (assuming rpm and speedo correct) 60mph, 2700 rpm then the ratio is 3.43. Close to the posi 3.36.
This is just the paper answer.
If you plug the info you provided (assuming rpm and speedo correct) 60mph, 2700 rpm then the ratio is 3.43. Close to the posi 3.36.
This is just the paper answer.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,112
From: Crossville TN
With the larger than stock tire size, I think that you do have a 3.36 rear gear. I have a 3.36 in my car and with high gear would run about 2600 at 60 mph...but my tires were not as big on the O.D. If you had the next larger gear (3.55), you would be turning more revs at 60 mph than you are showing.
Race Director
Joined: Jul 2001
Posts: 15,892
Likes: 42
To use the online calculators, it must be assumed that the original, stock tires are in place.
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Team Owner
Joined: Jan 2006
Posts: 37,637
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From: Crossville TN
I'm sorry, Mike. The OP said "...at 60 mph", not "at a speedo reading of 60 mph". How did he measure speed? Maybe with his GPS-capable navigator...I don't really know. But, the devil's in the details, I guess.
We'll keep trying to help folks. You should keep trying to pull the "fly **** out of the pepper". We each have our skills...
We'll keep trying to help folks. You should keep trying to pull the "fly **** out of the pepper". We each have our skills...
Race Director
Joined: Jul 2001
Posts: 15,892
Likes: 42
I'm sorry, Mike. The OP said "...at 60 mph", not "at a speedo reading of 60 mph". How did he measure speed? Maybe with his GPS-capable navigator...I don't really know. But, the devil's in the details, I guess.
We'll keep trying to help folks. You should keep trying to pull the "fly **** out of the pepper". We each have our skills...
We'll keep trying to help folks. You should keep trying to pull the "fly **** out of the pepper". We each have our skills...
