Variable pitch th400 trannies are quite popular with the caddy big block/hot rod guys. I've heard that they wire the pitch switch to the break light switch and drag race with them. Here's a blurb from
http://www.mts.simplenet.com/ about the converter.
Q: I'm building a street/strip or street rod type machine. How do I mate up a 700R4 overdrive transmission to my big Caddy?
A: It can be done. Use our Cadillac to Chevrolet transmission adapter. But why would you want to? The second hardest thing to do after giving up your Chevrolet engine is giving up your Chevrolet drive train. Wimpy low torque street engines need steep rear gears to get rolling. Then, in order to cruise the interstate, overdrive is required to keep from buzzing themselves to death.
With 500 foot pounds or more of torque on tap, there are much better ways to get the job done. They are also stronger and cheaper. How's that for a winning situation.
The 700R4 has proven to blow up under the high torque engines. Sure you can spend a zillion dollars on tons of after market parts to make it live. You can also spend that same zillion bucks on the big bad boy 4L80E computer controlled overdrive trans. Don't bother. Here are the best options from low buck to ultra trick.
For the low buck set it's as easy as using conservative rear gears. Most street cars use a tire that is 28" tall or less. A 3. 25 rear gear matched to a Turbo 400 trans will run real stout. The Caddy's big torque will have no problem providing impressive performance geared as such. These are also quite suitable gears for highway use without "buzzing" the engine too much.
Want a little more kick? Use the above combo with a performance type 11" torque converter. This will really turn up the stout factor. However it will put a good dent in the fuel economy factor.
Still want your cake and be able to eat it too? Comb the wrecking yards for a 1965-66 Turbo 400 trans with a switch pitch torque converter. To me this is as slick a trans as you can use in your project. These beauties came from the factory with an adjustable stall speed converter. You read right. Simply hit a button and the converter vanes changed pitch inside the converter. Your stall speed now went from 2000 to 3000 at the touch of a button. Once the car is 100 feet out of the hole let go of the button. Now the converter flips back to the tighter low speed setting. Now loss of power for the top end charge. No loss of gas mileage with a slippy converter on the highway. Almost to slick for words.
Still not trick enough for you? How about this? You can wire the converter to your brake light switch. Now you can run a bit "too much" camshaft than you should. What happens is when you step on the brake to stop at the light the converter trips to high stall and loosens up. Your bad boy rump rump cam is now not fighting too tight a converter. It will idle much better in gear. No need to pop it into neutral. When the light changes just nail it and let up on the brake pedal. You leave the light under high stall and it automatically tightens up as your rolling.
If all of this isn't enough these transmissions are as tough as any Turbo 400. They will not break from the Cadillac’s massive torque. The added benefit is that the Turbo 400 trans is the cheapest transmission to rebuild there is. A top notch high performance professional rebuild costs less than your girlfriend could spend in a half hour at the mall.
There are even more tricks! If you want trick transmission and your Master card or Visa card will let you here's the ticket. By far the hot dual purpose trans in my opinion would be a Turbo 400 with the above converter. The added trick is to replace the internal gear ratios with lower after market units. By lowering the first and second gear ratios in the transmission we can really kick some butt. This trick is NOT for torque wimps.
By making first gear much lower in the transmission we can have the best of both world. We can run a mild rear axle ratio. Still real good for the highway cruise. However now our very low first gear in the transmission let's us leave the line like jack the bear. Once we reach third gear it no longer matters. Our transmission ratio is now at a normal 1:1 as it should be. Our mild rear gears are letting cruise without buzzing the engine. And no need for a wimpy expensive overdrive trans.
Here's why I say this combo is not for torque weaklings. What happens is the jump between ratios gets much bigger. Wimpy small blocks just die from a change like this. When a transmission with big jumps between gears is used, the RPM drop of the engine is much greater after a gear change than in a normal transmission. Engines with puny torque curves fall out of their peak torque range. They then slow down. Wimpy small blocks can't take it. They just lay down and bog to death. They don't have the torque it takes to keep accelerating after a huge gear change. It seems to take forever for them to then pull the tach needle back to redline.
That is NOT the case with our favorite engine. This is by far where the big Cadillac is KING. Our torque curve begins when you turn the key on. I don't care how steep that gear change was. With 500 foot pounds your butt is going to be pushed right back in the seat. The tach needle is going to get yanked right back to redline and ready for that next big shift. And you my friend will be looking WAY back in your rear view mirror for the guy who was next to you.
That's why I don't recommend a "Chevrolet" drive train behind a big Cadillac. The above methods take advantage of every single foot pound of torque these engines make. That's what it's all about. That how to use your Cadillac engine in a way the other wimps can only dream of.
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