THM400 with GV OD will fit
A THM400 with a GV OD will fit. Did in my brother-in-law's GN. The fit is tight but like a glove with a 3" driveshaft. The Exhaust at the 'Y' may need to be tweaked just a tad. I can get some pics if you'd like. Won't have a good angle however unless we find a very clear day and a hoist.
The gear splitting is handy for the street but stuff gets too busy at the strip. Probably not necessary unless for some reason your gear spacing was waay off. Car is primarily street driven.
The setup is bullet proof which was the end goal. There is a delay (1/2 second) between engaging the unit and the shift into OD. Dis-engagement seems immediate. I believe they now have a more sophisticated controller which can be programmed for 'launch mode' and engage auto-shift at a certain MPH or engage/disengage with trans. You'll need to call for the specifics on their new controller, they don't describe it on their web site but believe Super Chevy did an article on the new setup for drag racing this past spring or summer.
You need to get it a signal in some manner.
Downsides of the GV/THM400 would primarly be the following:
a. more complicated installation. requires shortening of the driveshaft (believe this is the case with the 4L80).
b. complicated to electronically control with a manual valve body. Would require an 'on-off' negotation beween the shifter using an RPM activated or manually activated switch. The new controller may make this more easily done.
c. no converter lockup for highway cruising.
d. drive shaft loop runs up towards the end of the tunnel, right where the seat belts bolt thru.
d. cost?? (not sure how much more a 400/GV is than a 4L80 and associated electronics or 4L80 w/manual valve body). Built THM400 w/ manual valve body/trans brake is around $1,200. GV used to run $1800. Might now run $2200.
e. with no lockup free way mileage will suffer.
Benefits
a. 6 speed for the street.
b. unbreakable.
c. makes a 3speed non-lockup liveable on the freeway.
d. theoritcally could reduce RPM drop at the shift but to really test this out you need to electronically controll all of the shifts. Too busy/hard to do manually. Not necessary with a high HP car and loose converter.
Cards are out on whether this was a good investment or not. When we get further implementing the electronics for RPM and manually activated shifting will know more. When comparing with a THM400 definitely use. When compared with a 4L80, manual valve body, and lockup converter not sure.
Anyone with input on the elecronics would be appreciated. Have both air and electronically controlled shift mechanisms installed on a B&M pro-ratchet. Want to automatically dis-engage the GV as the trans shifts gears and enagage the GV IF the trans is 'off' and RPM hits nnnn. I think of it simply as a ping-pong between the shifter and the GV. If trans is on GV does not see a signal from the RPM switch. When shiftnoid sees a signal from the RPM switch it shifts the trans and in turn opens the RPM circuit to the GV for the next shift point. Some flavor of relay would seem to do the trick.
