I am still planning and collecting parts for the Resto/Mod of my '73, 454, TH-400, 3.36 gears.
I drive mostly on highways with foothill, coastal and mountain roads thrown in for fun.
I'll be stroking my 454 to 496 and I'm still on the fence about swapping out my TH-400 and going with a 700-R4 or 200-4R for the overdrive.
For those who have made this swap, what did you have to cut or modify to swap the TH-400 to either the 700-R4 or the 200-4R?
If you had to modify the trans tunnel, were there any issues using the stock seats or center console pieces?
I know the 200-4R is the easier swap, but I'm having trouble finding one rated for the tq and hp ratings my motor may but putting out.
Thanks, Greg

 

You would be better off putting a 4l80 behind that BBC, a 700 can be built to handle the power but its only a matter of time till it quits.

 

That is another option I'm looking into.
Did you install a 4l80 into a C3?

 

I did the 700r4 swap behind my 406, and the first rendition lasted one week. Well,....four easy days checking for leaks, shift points, and normal performance,....and one hard second gear upshift on day five. Heard a crunch,..that one was done. Second one lasted a year, easy driving since I lost my nerve ...and it began to fail to downshift at stops. Had to get out yank the TV cable and eventually it would shift back to 1st. Yanked that and went th400. Been 10 years...hasn't skipped a beat.

BTW, the 700r4 I had was rated to 600 horse/lbs. I thought it would hold up.......I was very wrong. And the vender welched on the warranty.

For a BB with 3.36 gears....I'd keep the th400 hands down.

If you do the swap, you'll need a driveshaft, yoke, trans mount, but everything fits with no mods to the tunnel. Then the shifter is up to you. I went with a B&M Megashifter, because it had the option for OD or three speed, just remove a pin.

 

I had a 700R4 behind my 383 for many years. Its a straightforward swap. If you get the right tailshaft housing, it is a simple bolt in using parts from an '82 since they came from the factory with 700R4's. There is a kit to modify the factory shifter to select all four gears. I still have mine if you're interested. Relocate the park brake cable pulley on the crossmember. ( I have one of those available too.) You will have to shorten the driveshaft. I found one of the biggest hassles to be fabricating the exhaust to go around the transmission and through the holes in the crossmember. I moved the hole over a couple of inches to give me room. Setting up the TV cable is a challenge as well. Bowtie overdrives has good instructions on how to do it properly. Make sure you get that right - if its not correct its a shortcut to burning up your transmission. I share the concerns of others here that the 700R4 may not be strong enough to survive behind your big block. A 4L80 might be a better choice, but I have no idea how to make one of those fit. I can tell you that the swap to a four speed is the best mod you will ever make to the car. Makes it ten times more driveable. I went from spinning about 2900 rpm on the highway to about 2100. Not only that my mileage went from 16 mpg to 25.

 

no I have a bowtie overdrives 700r4 behind my 406. It is their stage 3, I have better heads waiting to go on the engine, we'll see how long it lasts. As for the exhaust and cross member get the bowtie overdrives is nice not having to Mess with those holes for exhaust.

 

The Big Block is my number one concern with the 700R4. I have found several rated for 630 hp but I've read that even though these are rated for 630 some people have had issues. I've found SST advertises a 4l80 complete kit rated up to 725 hp. The kit is supposed to have everything I need and they state no trans tunnel modifications.
More research...

 

I converted my small block 74 coupe from a th400 to a 700r4. Heres the shortlist for parts collecting and some options.

shortened drive shaft. Th350 slip yoke. Conversion ujoint to connect driveshaft to trans (th350 ujoint to th40p drive shaft...not needed if you use 4L80) Shifter adapter for where shifter cable attaches to trans (i made one from aluminum sflat stock, i also modded my stock shifter to get first gear...i might need new neutral safety.) . Modify crossmember OR get one from bow tie overdrives, torque converter lockup parts: there are optuons here, but a brake light switch made for cruise control, and vac switch.

on topic of crossmember; if using sidepipes, you can mod stock cross member. ( brake pulley and dremel to mounting holes by elongating them 3/4 inch towards rear. HOWEVER, if using 2 1/2 inch exhaust, its a bear to make bends around trans. I got a crossmember from BTO.

if you get a bto crossmember like i did, and later change to a 4L80 , you need to get another cross member and drive shaft. (For a future upgrade i'm considering the spendy TCI 6x 6 speed, which is a modded 4L80. Others have done 4l80s with no tunnel mods.

good luck, i love this mod.