borg warner to th350

[drat]

so i was all set to do the 700r swap on my 1969 avanti rqa0319 but was recomended to do a 350 turbo tranny as i am pushing 400-450 ponies now with a cam, exhaust, ignition, manifold, headers, carb, etc.

has anyone done this? it seems the 700r is more popular of a swap, but if the 350 is more robust and slightly smaller and cheaper why isnt it more popular?

[Gunslinger]

It's possibly cheaper to do a TH350 as they're less popular outside of racing, though will do the job. The overdrive transmission is popular because it cuts engine rpm's and saves fuel. Basically...if you're gonna spend the money anyway, install a tranny that will save you fuel costs.

I have the 700R4 conversion on my '70 and like it but I've since learned the 200R4 may be a better conversion as it has a better spread of gears and can be built as strong as a 700. The 700 has an extremely low first gear and a very abrupt 1-2 upshift...it was designed for much heavier cars. Some have said they had to make some tranny tunnel modifications when converting to a 700R4. My car didn't have such problems but a different b/u light and neutral safety switch setup had to be fabbed. That might be as much due to a bigger diameter exhaust system as anything...2 1/2" pipes vs. the original 2" pipes.

[drat]

with my foot i am told i will tear up a 700r, so the th350 isnt an overdrive but a 4 speed... that will still save some rpms and a little fuel in the freeway right?

im looking for a little more drivability on the free way and be able to still go hammer down. i blew the borg warner having fun goin sideways...

[drat]

with my foot i am told i will tear up a 700r, so the th350 isnt an overdrive but a 4 speed... that will still save some rpms and a little fuel in the freeway right?

im looking for a little more drivability on the free way and be able to still go hammer down. i blew the borg warner having fun goin sideways...

[Gunslinger]

The TH350 is a 3-speed automatic, not a 4-speed. I doubt if you could tear up a 700R4...they're very tough transmissions. You would shred your rear tires long before you hurt the tranny.

With the TH350 you'll run the rpm's up very quick and accelerate engine wear compared to the 700R4 or 200R4.

[drat]

gotcha...

[Avanti83]

If you check the HP and more importantly torque ratings of either tranny, you will find you are above the stock rating of either one so you will need one that's built for your needs.

Before you go either way, talk to someone that know what they are talking about and get the trans with the best rearend ratio for your needs. Probably wouldn't hurt to upgrade your posi to a better setup too. If you don't have posi, don't worry about upgrading the rest. Not enough traction to cause issues.

It won't be cheap but if you are serious about what you have in power then put the best equipment and tires behind it and drive happily.

[fred88]

so i was all set to do the 700r swap on my 1969 avanti rqa0319 but was recomended to do a 350 turbo tranny as i am pushing 400-450 ponies now with a cam, exhaust, ignition, manifold, headers, carb, etc.

has anyone done this? it seems the 700r is more popular of a swap, but if the 350 is more robust and slightly smaller and cheaper why isnt it more popular?

Because the 350 isn't any stronger than the 700, the 400 is, but not by much. If you plan on actually driving your car, not just racing it, an overdrive makes more sense. You can use a higher ratio rear for your burn outs, and drive down the freeway without running your expensive to replace engine at 4000 RPM all the time. Since you have an Avanti, I think you would be better off with a 200 built to your needs, no clearance issues, no fiberglass tunnel modifications. Remember to check your rear end max torque ratings also. Nothing worse than spinning the splines off an axle--if you're still running the old Dana 44 tapered axle rear, that only has 19 spline axles and will probably shear off a hub pretty easy at that HP range. Fiberglass doesn't do well with a rear wheel going missing or coming off at 90.

Edited September 5, 2016 by fred88

[wildfelr]

RQB 3263 Wildfelr 81/305 My swap from a th350 to a 700 was completed a year or so ago and detailed here in the forum. It was one of the best mods i did to 3263....currently cruising at 1750 at 70mph and 21 mpg ...I would never recommend trying to make a race car/cruiser out of an Avanti. It probably wont do either very well..build a cruiser (700r4) and buy a Camero or something...youll be happier and richer in the end.....read my trans swap posts ...and goooood luck....BILL RQB3263