As you are aware, I'm installing at 500+ inch Cadillac engine in my '89 Suburban. I have a great Th400 in there now, but would eventually like an overdrive. This leads to a few questions.
1. Is the bellhousing pattern the same between the TH400/4L80E/6L80E? If so that will be awesome as I can get an adapter between the Caddy BOP pattern and the Chevy TH400 pattern for about $60.
2. Transfer case. If and when I go to a 4L or 6L, I will be needing a transfer case with a passenger side drop. I think there is an NP205 on the TH400 now, and I would like to keep it as it's a very strong case from what I've heard. Who makes an adapter between this case and the 4L/6L transmission?
3. Controller. Is it possible or even recommended to run the 4L or 6L without electronic control or is it an electric solenoid transmission? Looking at controller prices made me gulp a bit.
Thanks for any previous experiences you've had on these very strong transmissions.
Woofwagon
1) - yes
2 - it won't fit.... it's a larger 6 bolt pattern... that said, you have another choice that's actually an upgrade - swap in a Dana 60 from a Ford then use the t-case that comes with your 6L80e
3) - no, it won't move without a controller. I know someone who just adapted a 6L60e into an H3, it works well, now... but it took some doing to get it there including a new output shaft
You don't need a 6 speed, really. 6 speeds are excellent for making my 5.3 move the 6000 lbs I haul with me in my H3 - but they are pointless when you have the power and torque to overcome the gear changes. A friend did a 6BT Cummins swap into a late 80s Blazer - he had 3.73 gears, he went down to 3.23 gear because he had plenty of torque but was running balls-flat-out at 60 mph.
Finally, the 205 is great except it has a terrible low range (1.92:1)... to me, that's where I'd spend my money. You can either get a gear Vendors for $2500 to go behind the t-case, or a black box then swap axle ratios to take advantage of the 6:1 ratio you'll have with the black box (or similar).
If you must have extra gears - manual transmission, those don't overheat under high-loads.