Turbo 350 vs. 700-R4 (3 vs. 4 gears)
September 1, 2002
By Scott Lewis
Now that the Powerglide, a 2 speed automatic transmission, in my 67 Camaro is unusable I have to decide what will replace it. I am 99% sure the transmission is beyond a simple repair, and I don't plan to spend any money trying to fix it. That leaves me to decide between replacing the Powerglide with a different transmission. That basically leaves me with two choices: a Turbo 350 (short for Turbo-Hydromatic 350, or TH350) three speed automatic or a 700-R4 4 speed automatic with overdrive.
A short tail house TH350 fits in the same space as a Powerglide. This truly is a bolt in swap. The TH350 uses the same yoke (most of the time) as a Powerglide, so the driveshaft can be used as is. The linkage on the transmission is the same, so I could use the stock shifter in my car. I will need to replace the gate inside the shifter and the gear indicator lens so I can shift to all three gears and know what gear I am in. I will also need to get a dipstick (approx. $25). This should be easy from a restoration company. Other than that it is a no-brainer.
I did this exact swap in a 1970 Chevelle. I built a mild 350 for that car. Two months later the Powerglide would not shift into 2nd gear. I got a junk yard Turbo 350 and it just bolted it in. I did not use the stock shifter on that car, and that would be the only difference this time around.
My brother-in-law's brother is a transmission mechanic. He lives in Houston but comes to San Antonio frequently. He told be he can provide me with a Turbo 350 completely rebuilt with a torque convert, flexplate and shift kit for $550. I should be on the road for about $600.
The 700-R4 is longer than the Powerglide and TH350, by about 3 inches. That means two major issues to installing one in my 67 Camaro. 1) The crossmember that holds the back of the transmission up will not work, requiring me to buy a crossmember made for this swap. Such a cross member costs around $150. 2) The driveshaft will be too long. I will need to have it shortened.
My transmission connection in Houston gave me a price of $750 for a rebuilt 700-R4 transmission. I will assume for a moment that he would start with a 88-93 core. These are not electronically controlled, however, even these years have electronic lockup torque converters. Since my brother-in-law spoke with his brother, I am not 100% sure the $750 price includes a torque converter and flexplate, but I would think so.
There are a number of items that I will probably need to make this swap work. A Yoke for the new transmission ($65), wiring harness for the lockup torque converter ($70), Dipstick ($25), inspection cover ($25), shifter conversion kit ($55) and the TV (throttle-valve) cable ($95 for kit). This last item I understand is very important to provide proper throttle position to the transmission for shifting. (Note: I got all these prices from www.700R4.com. They had everything listed on one site, and were the most reasonably priced place on the internet for the transmission itself at $866.)
That adds things up... quickly. Let's see... if I do my math right that's $1,235. Plus tax and shipping... your mileage may vary.
Why would I want to spend twice as much for the 700-R4. For three reasons. 1) Overdrive! With the 0.70:1 overdrive 4th gear I should see a significant boost in gas mileage on my car. I would also see less wear and tear on the engine since it will be running at a lower RPM on the highway. 2) Better acceleration. The 700-R4 has a first gear of 3.06:1 while the TH350 has a 2.52:1 first gear. First gear multiplies the torque of the engine for acceleration. Having the numerically higher first gear means the 700-R4 should provide a noticeable improvement in off-the-line acceleration. 3) Because it would be cool... I want it... it can be done. There is something about hot rodding that can't be put into a simple yes or no answer. You just want it. Why do people increase the power of a Viper, Corvette or whatever... surely they don't NEED the extra power. But there are companies lining up to make more power for the Viper, Corvette, Porches, BMWs, Mercedes, etc.
This came up as I was looking for information on performing a 700-R4 swap. It seems the earlier 200-4R transmission is a viable transmission. The 200-4R has a reputation for being unreliable. It is smaller, and many believe a weaker, transmission than the later 700-R4. The TH200 transmission (the "father" of the 200-4R) was designed as a light weight transmission that provides less parasitic loss through the drive train. The idea being (in the mid seventies, after the first oil crisis) that if more of the engine's power could make it to the wheels than better mileage could be attained. Those early transmissions were prone to failure. And yes, the early 200-4R, a four speed overdrive version of the TH200, was also prone to premature failures.
But the 200-4R received many improvements over its life. At its peak it was used in the Buick Grand National. This was a turbocharged Regal that generated 255 net horsepower. At the time it was 10 more horsepower than the Corvette was available with (245hp). And the GNX version of the Big Bad Buick was for a short period of time... the fastest car made in America... with a 200-4R transmission.
There are a some pluses and minuses to choosing a 200-4R over the 700-R4. On the plus side, it is lighter and more efficient, so it should allow more power to get to the tires, and (as it was designed) provide a little better mileage in a low to moderate horsepower car. The 200-4R is within 1/8" of the length of the TH-350 and the Powerglide AND uses the same yoke as the TH-350. This means I would not have to shorten the driveshaft, or get another yoke.
However, there are a couple of drawbacks. First, the mounting point on the 200-4R is at the very tail of the transmission. About 5-6" farther back that a TH-350 or Powerglide. I have not yet seen a crossmember available for this transmission in an early Camaro. I might have to fabricate one. Something I currently don't have the skill to do. Also, the 200-4R is less known and less common. I may have a harder time getting one in a comparable condition to the 700-R4 above. I have not mentioned this option to my transmission mechanic connection in Houston.
Without accurate pricing I cannot say what the 200-4R will cost. Assuming I could get a 200-4R for about the same as the 700-R4, then I could possibly save a couple of hundred dollars with this swap. I would not need an electronic control unit for the lockup torque converter. But I would have to get help with the crossmember.
This will warrant more research.
I am still on the fence. A friend mentioned that I should save up for the 700-R4. After all I have a working car (my 93 Camaro is running fine, especially with the new, cold A/C) so I can wait. I also mention elsewhere on my site, "I am a patient man." "Why settle," my friend said.
But then there is the fact that I only got about 5 or 6 weeks behind the wheel of my new convertible, and now it just sits in my garage. Fall is coming, and in Southern Texas that will be perfect weather for driving a convertible. When I made my "I am patient" statement I was thinking along the lines of modifications to a car that was in running condition, not one that needed an expensive repair.
Do you have any ideas? I would like to hear your opinion on the matter... especially if you have knowledge about the various swaps.
Time will tell. I'll keep you informed.