Another transmission question
Thread Starter
Instructor
Joined: Nov 2012
Posts: 209
Likes: 7
Another transmission question
Hey guys, i see a ton of info on here about swapping out my L48 TH350 to either a 200r4 or 700r4. I'm pretty well sold on going with a 200. But most threads i read only deal with like 3.73 rear end gears. Must be pretty popular. I'm curious what a 200r4 would do with my old ball 3.9 rear end gears? The previous owner installed them, don't know why that particular set. Should i be down sizing to something else? Right now my gas mileage is about 10-11 mpg and i'd like to get something with an od gear to help out.
Sorry guys I realize this is a beaten to death subject, just kind of trying to put myself in the right direction.
Sorry guys I realize this is a beaten to death subject, just kind of trying to put myself in the right direction.
Melting Slicks
Joined: Apr 2001
Posts: 2,030
Likes: 363
From: Lubbock Texas
IF your tires are near stock size (around 27" tall), your current setup should be around 3400 RPMs at 70 MPH.
Swapping to the 200-4R and keeping your 3.90s will get you around 2300 RPM at 70 MPH.
A 700R4 will get you around 2400 RPM at 70 MPH.
BUT, they say an ideal overall 1st gear ratio (transmission 1st gear x rear axle ratio) should be right at but no more than 10:1 for best driveability.
The 200-4R with 3.90s gets you a 10.7:1 1st gear ratio.
The 700R4 gets you a whopping tire smoking 11.9:1 1st gear ratio.
Your current TH350 with 3.90s gives you an almost ideal 9.83:1.
With either overdrive transmission, your cruise rpms will be good but you might have trouble hooking up when starting off if you keep the 3.90s.
If you are happy with your current off the line performance, you might be better off swapping to 3.55s or 3.70s with the 200-4R. 3.55s with the 200-4R gets you about the same overall 1st gear ratio as you have now (9.73:1). 3.70's gets you 10.14:1.
You could always make the swap to the 200-4R and drive it for awhile before deciding on a different rear axle ratio.
DC
Swapping to the 200-4R and keeping your 3.90s will get you around 2300 RPM at 70 MPH.
A 700R4 will get you around 2400 RPM at 70 MPH.
BUT, they say an ideal overall 1st gear ratio (transmission 1st gear x rear axle ratio) should be right at but no more than 10:1 for best driveability.
The 200-4R with 3.90s gets you a 10.7:1 1st gear ratio.
The 700R4 gets you a whopping tire smoking 11.9:1 1st gear ratio.
Your current TH350 with 3.90s gives you an almost ideal 9.83:1.
With either overdrive transmission, your cruise rpms will be good but you might have trouble hooking up when starting off if you keep the 3.90s.
If you are happy with your current off the line performance, you might be better off swapping to 3.55s or 3.70s with the 200-4R. 3.55s with the 200-4R gets you about the same overall 1st gear ratio as you have now (9.73:1). 3.70's gets you 10.14:1.
You could always make the swap to the 200-4R and drive it for awhile before deciding on a different rear axle ratio.
DC
Thread Starter
Instructor
Joined: Nov 2012
Posts: 209
Likes: 7
wow dc3 thanks for the great info, didn't expect that much! Cruising the highway right now at 70 @ 3400 is really annoying. In fact i drive 55 most everywhere because i hate the engine reved that high for long travels.
I think the thing to do will be to get a 200 and try it out. I haven't read any complaints about either or so i don't think i can go wrong. I think i'll get one from Bow-tie overdrives, lots of good feedback and then i basically have a brand new tranny.
I think the thing to do will be to get a 200 and try it out. I haven't read any complaints about either or so i don't think i can go wrong. I think i'll get one from Bow-tie overdrives, lots of good feedback and then i basically have a brand new tranny.
Melting Slicks
Joined: Apr 2001
Posts: 2,030
Likes: 363
From: Lubbock Texas
DC
