Recently finished up the swap from the TH350 to the 700R4 (had a shop do it... smart move). Got it from BTO. So far all's well and love that OD! There were problems with their crossmember not working on my '81. The PB pulley bracket was welded in the wrong spot so the angle was not right (minor) and the exhaust wouldn't bolt back up (major). They ended up modifying the old crossmember (not easy but doable). The exhaust is very close to the pan on the right rear side, but there's a heat shield at that point so it should be ok. Bought all the 'extras' but didn't need the inspection plate. The old one was trimmed for a larger opening to allow space for the back of the starter (ZZ4), so reused it. Shortened the driveshaft 3.125" and it fit perfectly. TV system was easy with their linkage kit, but it feels kinda tight as it's nearing the homed position (do have fully opened primaries at wot so it's not being restricted by the carb linkage). Any hints here would help (guess I could get on the phone to BTO.. duh). Maybe it's just a little newness tight? Got the ShiftWorks kit as well. The console plate didn't work out the way I wanted it to (it hides the pointer), so I modified it. For those that have used it on later C3's, here's a pic of how it turned out http://home.nc.rr.com/c3/Shift Plate for 81.jpg Now you can see the pointer even at night with your lights on (easy job).

BTO has you run several road tests (part of the warranty deal) that call for wot and it barked the tires in 2nd and 3rd gears! :D

Conclusion... The shift points are a tad on the low side (4700 in 1st and 4400 in 2nd), but for general cruising it's fine. It's also a tad agressive, but it's the way I like it and certainly not like my wife's Buick. I guess some tweaking of the TV system could resolve that but haven't got that far yet. Took it to the strip (1/8 mile) and made a run without manually shifting. 9.10 et. Next run I started in 2nd and manually shifted to 3rd at 5200 rpm's. 8.75 et and 1.995 60'. The track was too crowded to get another run in, but I want to see what happens manually shifting from 1st. That 8.75 was with a poor reaction time (.423 - that track doesn't use the .5 break) and the 9.10 et was excellent (.016). Running 3.54 gears. Tells me things are just going to get better.

I initially was going with the 200R4, but the 3.06 'fun 1st gear' of the 700 was too tempting. I was concerned of the larger gear spacing between 1st & 2nd, but it turns out to be no big deal. Coming out of 1st into 2nd is instant and even shifting at 4700 rpm barks 'em, so life is good. :cool:


[Modified by Chris81, 12:56 AM 10/17/2001]

 

Can you go into more detail about the problems you had with the crossmember?

I want to do this swap in a 1980, same crossmember, and would like to know all of the "gotchas" before hand.

 

The crossmember is actually a fine piece of work and solid. I think on mine they just welded the PB pulley braket in the wrong spot and it was hitting the floorpan. A little bending fixed that. Otherwise, the fit was perfect and it bolted right up. The major problem was clearance for the exhaust system. It wasn't even close to allowing enough room and it would have meant a major rework of the front Y section. A call to BTO had a response that they thought anyone that does this conversion also had plans to redo the exhaust system. Well, not at the moment in my case... Even though the shop modified the old crossmember and got it to work, I think I'm going to look for an '82 crossmember and an '82 700r4 tailshaft. I guess BTO ought to make this clear when you order their crossmember so you don't waste so much time (and extra money for the shop time). I hated to see it pulled off the car 'cause it really looked good under there.

 

on any of these conversions into a C3,the exhaust has to be re-routed to go around the "squared" corner of the 700r4,as compared to the angled corner of the th350. i had a local competent shop replace my system from the Y-pipe on back(it needed it).i checked with them b/4 the conversion and he said it was no problem to get it to go thru the hole in the x-member,and he didn't have much problem bending a pipe to fit.

 

Will hooker super comp headers fit with the 700R4?? i have these headers on my car and you said there was a problem with clearance.

 

I did this conversion on my '81 about two years ago. I used Hooker Super Comp headers, ordered the dual exhaust system from Mid Ameica (cut the pipes to fit the headers). I had to have the left hand pipe reshaped slightly around the pan on the 700R4, but not a real problem. When I did this conversion, I did it as a bolt-in, in order to be able to return my car back to stock, so I bought an '81 crossmember to modify from a salvage yard. Cut the original trans mount off and made one from 1/4" steel plates, welded to the crossmember. Chris Petris (of the Corvette Clinic) told me that he makes these mounts up. You might contact him as see if he has any already made up. I did my conversion before talking to him, "on a learn as you go" experience.

 

Chris, I love mine in a 1980. I had a cross member fabricated from 1 x 4 inch tublar steel, and it's recessed up so I could run 3 inch pipes under it and straight back from the hooker headers on both sides. A&S transmissions of Deerfield Beach, FL made it for me. It's a beautiful thing. Cut the emergency brake pulley off the stock one and welded to the new one. It's a beautiful thing. Jamie