I have a 85 MC SS running a 383 with a Turbo 350 transmission I had 411 gears in the car traded them with a friend of mine for a rear end with some 320 somethings I with the 411 gears my car would be at 3800 rpms before I reached 60 mph definitely geared for the track in my process of turning my car into a street car im wondering do I need to change my transmission as well or will these higher gears allow me to drive the car longer distance at a faster speed without my rpms being so high
G-body drivetrain
- Thread starter lowkeyfromUptown
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Go upin gear to a 3.55 or 3.73 and get a 4 speed automatic so you have overdrive. You'll have the best of both worlds.
Lower numerical gear will drop your rpms down. You CAN change out your trans but that is more money and I don't know your budget. For simplicity, a gear change will be a good start.
I have a 71 442 with a TH400 behind it with 3.08 gears. It has no problem at any speed and 80 mph is a breeze. 3.23 were standard, but 3.08 were optional gears. Someone ordered it that way. The dorks. 3.23 would have been an excellent compromise without an overdrive.
The TH350 is similar fashion. If you have 3 point 2 something rear gears now, you're in an EXCELLENT place for all around street driving. Sure, you'll miss the low end grunt it once had, but it'll make for friendlier driving on the highway. I can tell you, 3.91 is no joke at 60 mph, let alone 80. Getting rid of the 4.11s was a good move.
For the $$, just change out the speedo drive/driven gears to match your new 3.2x gears, and install that new rear end. That's a pretty simple swap IMO. But you need to find out exactly which gear ratio you have. Pop the rear end cover and count the teeth and do the math. Or check the ring gear for the tooth count stamps and do the math. You should change the fluid at least anyway.
As 79 GP 4 speed said, you can later add an OD transmission and then move up to 3.55 or 3.73 and have fun as well. It'll just cost you more $$.
The TH350 is similar fashion. If you have 3 point 2 something rear gears now, you're in an EXCELLENT place for all around street driving. Sure, you'll miss the low end grunt it once had, but it'll make for friendlier driving on the highway. I can tell you, 3.91 is no joke at 60 mph, let alone 80. Getting rid of the 4.11s was a good move.
For the $$, just change out the speedo drive/driven gears to match your new 3.2x gears, and install that new rear end. That's a pretty simple swap IMO. But you need to find out exactly which gear ratio you have. Pop the rear end cover and count the teeth and do the math. Or check the ring gear for the tooth count stamps and do the math. You should change the fluid at least anyway.
As 79 GP 4 speed said, you can later add an OD transmission and then move up to 3.55 or 3.73 and have fun as well. It'll just cost you more $$.
I am in a similar boat. My car has a th400 and 4:10 in the rear. 70 mph is 3600 rpm I will be changing to a 3:55 or 3:73 which ever I find the best deal on. If your car spends more time on the street then strip and you only have a three speed trans a 3:73 or 3:55 is a good middle ground and then keep the 4:11 in you ever thing you will get an OD trans.
Idk 430s with a th400 mine cruises about 3500 at about 60-65 but I'd rather have a faster car then a highway machine
I have Th350 and 411s and my plan is to put a 4L80E in before I change gears . I don’t want to drive on the interstate at 80 mph. I want to spend my time driving back roads and enjoying the drive. I’m not sure it’s worth going to 373 from 411 I dont know if it’s a big enough of a change to justify the cash
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