Opinions on Diff Gears
Thread Starter
Melting Slicks
Joined: Feb 2007
Posts: 2,136
Likes: 62
From: West Kingston RI
Opinions on Diff Gears
I am pulling the rear apart on my 75 for new spring, shocks, offset training arm etc. was debating about changing rear gears, I believe I have 308 and am thinking about 356, never got into this end of things much. I have a mild 350 325 hp with a 200 4r both less than 1000 miles. Advantages and or disadvantages of the change? Thanks
CF JASOC Member
Joined: Feb 2006
Posts: 8,040
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From: Downtown Annapolis, MD. The Future is where we all have to live. Let's not screw it up.
St. Jude Donor '08-'09-'10-'11
What do you use the car for? Do much hiway driving/cruising?
I can tell you that my stock '71 L48 with 3.36 gears is turning 2600rpms @ 60 mph, and 3000rpms @ 70mph.
I can tell you that my stock '71 L48 with 3.36 gears is turning 2600rpms @ 60 mph, and 3000rpms @ 70mph.
Burning Brakes
Joined: Mar 2006
Posts: 793
Likes: 1
From: Houston Texas
My 4.56 is getting right about 3600 RPM at 60.
I would think you would enjoy a 3.55 in the car you have, a little quicker through the gears and a smige less MPG, but what good is the car if you can't have a little fun??
I would think you would enjoy a 3.55 in the car you have, a little quicker through the gears and a smige less MPG, but what good is the car if you can't have a little fun??
Thread Starter
Melting Slicks
Joined: Feb 2007
Posts: 2,136
Likes: 62
From: West Kingston RI
I will be using the car for cruising. Probably 50 50 city to highway. I know I was running about 3200rpms at 70 with the 400 auto not sure what it will be with the overdrive 200 tranny.
Le Mans Master
Joined: Dec 2007
Posts: 6,422
Likes: 591
From: McHenry Illinois
I have pretty much the same set up as you. At 60 with the 3.08 gear, engine is at 1485 rpm, and 1735 rpm at 70. I have a spare diff ready to put in mine that has 3.55 gears, that should put my rpm a little over 1700 at 60. Should be 2000 rpm at 70, the 200-4r has a .67 od.
Le Mans Master
Joined: Dec 2007
Posts: 6,422
Likes: 591
From: McHenry Illinois
http://www.summitracing.com/expertad...atioCalculator
Summit has an rpm gear calculator, for the 200-4r, just multiply the rpm by .67. I am running a 28" tire, most here have 26 or 27".
3200 at 70 indicates a 3.70 gear, Iyhink that would be ideal with the 200-4r, your 3.70 at 70 with the 200 would be around 2150 rpm.
Summit has an rpm gear calculator, for the 200-4r, just multiply the rpm by .67. I am running a 28" tire, most here have 26 or 27".
3200 at 70 indicates a 3.70 gear, Iyhink that would be ideal with the 200-4r, your 3.70 at 70 with the 200 would be around 2150 rpm.
Last edited by '75; May 31, 2012 at 04:11 PM.
