turbo 400 vs 350

[tubecatgs]

Simple questions for most but I just have no idea but can you use a buick turbo 400 tranny with a buick 350 engine. Both in the 70-72 time frame. if anyone could explain this to me i would appreciate it. Thanks

[Turbo Loyd]

Will bolt right onto the engine, as long as you have a BOP TH 400 transmission. Will have to move the crossmember back and get a drive shaft that is shorter and has the TH 400 yoke.

Takes more HP to operate a TH 400.

[tubecatgs]

thanks.

the car currently has a 455 that' not running. I was going to put a rebuilt 350 in it for a year or 2 until I can redo the 455. So the car has the TH400 and driveshaft in it already.Will the 350 just drop it and replace the 455 or will I still have to make any modications to the position of the tranny or lenght or the driveshaft?? Some one mentioned that I may need a "kickdown" switch, I'm not sure what that is?? If the car doesn't already have it I mat need to know what it is and where can I buy one etc. Thanks again

Brad <img src="http://forums.aaca.org/images/graemlins/cool.gif" alt="" />

[Bill Stoneberg]

A kickdown switch mounts on the manifold and when you nail the gas, it basically kicks the tranny into a lower gear.

Some people run a small switch under the dash for racing or whatever. They want to get off the line quicker, you flip the swithch and its like putting it in low.

[The Old Guy]

The kickdown switch is used to shift from drive into passing gear. if you are fortunate enough to have an early TH400 with the "switch pitch option" then you will benefit from being able to control the stators in the convertor for a racing application.

[NTX5467]

IF there are no switches near the carb linkage (rear of the carburetor, on the intake manifold), the kickdown switch will be mounted on the accel pedal mounting under the instrument panel. A simple slide switch, with a dowel that contacts a lever on the top of the accel pedal mechanism.

The THM400 (and variations) uses an electric signal to trigger a "forced downshift" (due to sudden throttle openning) from direct (3rd) to either second or low, depending upon road speed at the time of the additional throttle input. On the THM 350 and others, this electric signal is replaced with a cable mechanism that attaches to the carb linkage AT the carburetor (before cables, there were solid rods).

In other situations, a "part-throttle downshift" can happen (usually just to the next lowest gear, typically from direct to second) when the throttle is openned enough to lower the manifold vacuum enough to trigger a downshift, but without going to "WOT" (wide open throttle). On the THM 400 and THM350s, these are orchestrated by the vacuum modulator valve rather than the respective WOT downshift mechanisms.

As I perceive you'r talking about changing the 455 V-8 for a 350 V-8, I suspect the mounts and lenghts should be pretty much the same, but I could be wrong. If they ARE the same, it should be an engine swap only. Be sure that you mark all of the wiring harnesses BEFORE you take anything out so that you can interface them with what's on the 350 V-8 (from the 455 V-8). Many things could well be in the same locations, but you never know.

All things considered, unless the car is your ONLY car, you might be better off to wait and rebuild the 455 rather than go to the time and expense of swapping in a Buick 350 V-8. You might be doing all of the labor yourself, but your time is worth something . . . Doing a stock, OEM-production level rebuild on the 455 should be fine as is--lots of torque and such to make things happen--rather than try to improve on what's already there (in a vehicle that can weigh 4500 lbs, empty). OR, you could rebuild the 350 for additional mid-range torque, swap in it, and leave it . . . all things considered (including fuel economy and prices!).

Just some thoughts,

NTX5467

[tubecatgs]

I have been on vacation and TRULY APPRECIATE all the feedback I have received while I was away. I will take a better look at the set up and read these posts a couple more times and let you allmknow how I am making out. Thanks again.