reelmagic Posted May 11, 2017 Report Share Posted May 11, 2017 My 720 I believe has the 3.7 rear in it, but I have a chance to buy a rear out of a 77 620, which I believe is the 4.375 gearing. Would anyone recommend this upgrade? I thought I might want to jump on this while I have the chance. I would just change out the 3rd member when I am ready to do it. Is the 4.375 too much gear? This is a toy not a daily, and my plan down the road is to do some performance upgrades (how far yet I am not sure, but I do tend to go overboard). Any thoughts? This is on a 5 speed truck. 1 Quote Link to comment
G-Duax Posted May 11, 2017 Report Share Posted May 11, 2017 Depends on your planned performance upgrades. Are you going to build for more power up top, or more around stock RPM ? I personally run a 4.62, and 4.56 on my 3-liter Cressida. Both engines are meant to make power in the upper range, and exceed factory red-lines. A turbo, large displacement set-up would probably like the 3.7s or 3.9s, as it will lesson wheel spin in lower gears. 1 Quote Link to comment
reelmagic Posted May 12, 2017 Author Report Share Posted May 12, 2017 It will probably stay stock for a while. Down the road who knows. I know I've read that the gear swap wakes up the truck a bit, but I was wondering if 4.375 is too much and should I look for 4.11? 1 Quote Link to comment
G-Duax Posted May 12, 2017 Report Share Posted May 12, 2017 Yes, it will give a little more acceleration, but.......... It will also throw your speedo off by the same percentage, and speedo gears are not that easy to come by. And it will also cut your fuel mileage. 4.3 gears spin the day light out of the engine at freeway speeds. On my old 521, with a stock L16, it was so bad that I put big tall tires on the rear to slow the engine down. I think they were 235x75-15. The little 8mm rod bolts still didn't like 80 mph, and let go, scattering bits of pistons, rods, and block material down the highway late one night. A fully built engine can take long halls 6500, stock ones don't like it. So keep that in mind. 2 Quote Link to comment
datzenmike Posted May 13, 2017 Report Share Posted May 13, 2017 Only later Z24 720 with 3.70 was the automatic. Assume P195/75R14 In 3rd gear torque converter locked with 3.70 diff..... 60 MPH... 2,930 RPM with 4.375 diff... 60 MPH... 3,459 RPM... the Z24 would have no problem revving at this all day. 1 Quote Link to comment
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.