Transmission change
Thread Starter
Safety Car
Joined: Dec 2012
Posts: 3,818
Likes: 1,728
From: Summerville SC
Transmission change
I have a 78 with a tired 350 engine & 350 auto trans. I am starting to build up a new engine, maybe get close to 350-400 hp tops, plan on a regualr driver, even doing some long distance trips. Wife wants to keep the auto trans, so the question is what would be a good replacement, maybe with an overdrive to boost mpg, without having to add all kinds of electronics and /or driveshaft mods. I'm even open to keeping the TH350, just looking for some options to look into. Thx.
Melting Slicks
Joined: Jun 2011
Posts: 3,116
Likes: 598
I have a 78 with a tired 350 engine & 350 auto trans. I am starting to build up a new engine, maybe get close to 350-400 hp tops, plan on a regualr driver, even doing some long distance trips. Wife wants to keep the auto trans, so the question is what would be a good replacement, maybe with an overdrive to boost mpg, without having to add all kinds of electronics and /or driveshaft mods. I'm even open to keeping the TH350, just looking for some options to look into. Thx.
Drifting
Joined: Oct 2012
Posts: 1,524
Likes: 61
From: Medina Ohio
The only OD options you have are the 700r4 and 200-4r. The 2004r is an easier swap as it is nearly identical in dimensions as the TH350. You can use your original driveshaft. The 700r4 is longer and the shaft needs shortened as well as mount modified.
The 200 has a first gear of 2.74 compared to the 2.52 of the 350. So an increase in acceleration. The 700 has a steep 3.06 which can be too much depending on what rear end you have. The 200 has a .67 overdrive, slightly lower then the .70 of the 700.
There are quite a few write ups on the conversion here on the forum if you look. Typically the 200 is the way to go. They do get pricey when required to handle higher then stock HP & TQ.
The 200 has a first gear of 2.74 compared to the 2.52 of the 350. So an increase in acceleration. The 700 has a steep 3.06 which can be too much depending on what rear end you have. The 200 has a .67 overdrive, slightly lower then the .70 of the 700.
There are quite a few write ups on the conversion here on the forum if you look. Typically the 200 is the way to go. They do get pricey when required to handle higher then stock HP & TQ.
Pro
Joined: May 2008
Posts: 582
Likes: 9
My 79 Vette had a TH350 but I had changed it out to a Richmond super T-10 about 6 years ago. I love the manual, but I plan on going to a 5 speed with a over drive, most likely a tremec tko 600.
I did a th 350 to 700r4 in a 71 C-10 truck back in 1997 and it was the best mod ever to that truck. 250,000 miles and still works and the truck runs low 13 sec quarter miles and gets 17 mpg. it would be a very easy swap. What gears do you have? If you have 3.55 gears that will work well with the 700, but if you have high gears like 3.07 than it may be too low a rpm for the engine depending on your set up.
I did a th 350 to 700r4 in a 71 C-10 truck back in 1997 and it was the best mod ever to that truck. 250,000 miles and still works and the truck runs low 13 sec quarter miles and gets 17 mpg. it would be a very easy swap. What gears do you have? If you have 3.55 gears that will work well with the 700, but if you have high gears like 3.07 than it may be too low a rpm for the engine depending on your set up.
Thread Starter
Safety Car
Joined: Dec 2012
Posts: 3,818
Likes: 1,728
From: Summerville SC
Thanks for the input. I'll be crawling under the car and confirm the rear gear ratio and will start looking around at the 200. Will also do some more searches. For my needs, a lot of driving, I would give up some HP for an overdrive if that's what the 200 calls for. Thanks for help in going the right direction.
Le Mans Master
Joined: Aug 2010
Posts: 9,272
Likes: 17
I bought a Craigslist 2004R ,rebuilt it , added a bunch of reliability/hy-po parts, best upgrade next to the borg. Easiest auto to rebuild, plenty of info on line, no special tools needed except for feeler gauges. But, for the money spent and the time involved, could have bought one already done and been driving sooner. The two costs going either way were pretty much the same, the only difference was the time involved . If you've never rebuilt an auto and would like to learn, its the one to do it with. hope this helps
Thread Starter
Safety Car
Joined: Dec 2012
Posts: 3,818
Likes: 1,728
From: Summerville SC
Thanks OldAlaska. Pretty sure I am going in the 200r direction, already looking on cl. i've never done an auto before, and I'm going to study up on what is involved. When I get to that chapter in my build I probably will be in touch.
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Verdad Gallardo
Team Owner
Joined: Jul 1999
Posts: 65,492
Likes: 230
From: Orange Park Florida
On the core you use, the one I had came from a 80's 305-350 Elky....
and so you need to know that you get a CORE without any extensive trash in the pan.....MY trans was fairly clean, and no metal in the pan....so it rebuilt easy as pie.....but I did spend almost a week on it, on/off, just a project....
tried to help a friend here, do one, he got a core that was full of trash, steel/aluminum, crap in the pan....
and it gave us nothing but trouble...3rd time around he took it to a shop....and so last I heard he was ok with it.....got transferred to Norfolk and so far outta town.....so outta contact....
and so you need to know that you get a CORE without any extensive trash in the pan.....MY trans was fairly clean, and no metal in the pan....so it rebuilt easy as pie.....but I did spend almost a week on it, on/off, just a project....
tried to help a friend here, do one, he got a core that was full of trash, steel/aluminum, crap in the pan....
and it gave us nothing but trouble...3rd time around he took it to a shop....and so last I heard he was ok with it.....got transferred to Norfolk and so far outta town.....so outta contact....
Burning Brakes
Joined: Oct 2010
Posts: 1,192
Likes: 7
From: Wentzville MO
Thanks for the input. I'll be crawling under the car and confirm the rear gear ratio and will start looking around at the 200. Will also do some more searches. For my needs, a lot of driving, I would give up some HP for an overdrive if that's what the 200 calls for. Thanks for help in going the right direction.
Heel & Toe
Joined: Nov 2018
Posts: 17
Likes: 1
From: Sherwood, AR
Ibanez is absolutely right on the mark. I had mentioned a 400r but had my numbers wrong. The 2004r is what I meant. Here is a link that explains it nicely:
https://www.hemmings.com/magazine/hm...s/3694151.html
https://www.hemmings.com/magazine/hm...s/3694151.html
Le Mans Master
Joined: Aug 2010
Posts: 5,339
Likes: 546
From: Central Texas
I purchased a built 200 4R from Art Carr at California Performance Transmission. I have a 3:54 rear gear in the '81. I love the way this transmission upshifts under power. I can get out on the 80 mph tollway now and cruise.
The BEST part? The installation was a breeze! I purchased a new aftermarket transmission crossmember and everything fell into place. The friend that I had helping me is a Pontiac man. He couldn't believe how easy the swap was.
Craig
Whoops! Old thread.
The BEST part? The installation was a breeze! I purchased a new aftermarket transmission crossmember and everything fell into place. The friend that I had helping me is a Pontiac man. He couldn't believe how easy the swap was.
Craig
Whoops! Old thread.
Last edited by Street Rat; Feb 24, 2019 at 09:24 AM.
Thread Starter
Safety Car
Joined: Dec 2012
Posts: 3,818
Likes: 1,728
From: Summerville SC
As said above, the 200R4 was a piece of cake install. Didn't have to change anything except put an extra detent in the shifter for the extra gear. FYI, if you are putting a cooler in for the trans, it gets a little tight on that side near the floor. Get it all figured out ahead, OR some guys just cut a hole in the floor near where the fittings will go. Easy upgrade for my '78. Good luck.
NCM Grand Opening Veteran
Joined: Sep 2005
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From: South of giving a damn
St. Jude Donor '11, '17
It's not polite to resurrect old threads. Best way is to ask your question or state your problem and just provide a link to the old thread.
Heel & Toe
Joined: Nov 2018
Posts: 17
Likes: 1
From: Sherwood, AR
Ratflinger,
I may be a noob at this forum stuff, but it would be because of my age, not my intelligence. You young kids may be good at this stuff but I’m not. I spent all my time being shot, knived and beaten while wearing a badge and serving and protecting. So you might want to show a little respect for I didn’t mean to resurrect an old thread. There are no written rules that would tell me these things.
So I apologize if I’ve offended anyone.
I may be a noob at this forum stuff, but it would be because of my age, not my intelligence. You young kids may be good at this stuff but I’m not. I spent all my time being shot, knived and beaten while wearing a badge and serving and protecting. So you might want to show a little respect for I didn’t mean to resurrect an old thread. There are no written rules that would tell me these things.
So I apologize if I’ve offended anyone.
Thread Starter
Safety Car
Joined: Dec 2012
Posts: 3,818
Likes: 1,728
From: Summerville SC
No offense here. I am an old guy, and I haven't read all these old threads and the questions they raise so I look forward to any NEW information I can come across. I have even reached out to people who posted in those OLD threads to ask follow up questions and most of them are more than happy to reply. Eventually anything old becomes new again. I have some disco shoes and paisley ties in my closet just waiting....and waiting..
Le Mans Master
Joined: Aug 2010
Posts: 5,339
Likes: 546
From: Central Texas
Race Director
Joined: Jan 2003
Posts: 18,341
Likes: 101
If you're older Corvette is a Daily driver I could see going to the overdrive Transmission.......but you really should seriously consider how you'll use the car.
I put a 450HP 383 in my car two years ago. The Turbo 350 lasted all of 200 miles or so under the far more serious torque before blowing away 3rd gear.
I gave an over-drive trans serious consideration but ultimately came to the conclusion that I'd be better served by a TCI Super Street Fighter Turbo 350. My car is driven too few miles each year to justify the expense and problems that come with a conversion to a 4 speed auto that is as strong. I might have chosen differently though if I did a lot of miles on the highway each year....but at this point my old C3 is a car that only sees 1,000 miles or less per year.....and virtually none of it is highway cruising.
I put a 450HP 383 in my car two years ago. The Turbo 350 lasted all of 200 miles or so under the far more serious torque before blowing away 3rd gear.
I gave an over-drive trans serious consideration but ultimately came to the conclusion that I'd be better served by a TCI Super Street Fighter Turbo 350. My car is driven too few miles each year to justify the expense and problems that come with a conversion to a 4 speed auto that is as strong. I might have chosen differently though if I did a lot of miles on the highway each year....but at this point my old C3 is a car that only sees 1,000 miles or less per year.....and virtually none of it is highway cruising.
Last edited by Krystal; Mar 2, 2019 at 09:37 AM.