I'll do a write up on the trans project, but as a quick overview, the trans mod is relatively easy. The basics are moving the trans mount back 2 inches (front hole goes in the back spot) Trans mod requires installing the TH400 output shaft in the 4L85e, they are the same, so it fits in. Making a spacer ~3/4 thick to go between the trans and the transfercase. The bolt holes line up fine, but the sleeve sticks out of the transfercase too far. And lastly, lengthening the drive shaft. In my coach there was also a floor brace that needed a hammer taken to it to bend a section out of the way of the transfercase. Your coach will probably be different, you just need to look at what is behind your transfercase, as it will move back 2 inches.
Performance wise, the obvious is to swap the transfercase gears. This puts the cruise RPM at 2500 @ 70 mph in OD. Trans controller is a EZ-TCU ~$600 from Summit. Controller is easy to set up. Since you can program thresholds for TC lockup, you can match it to your engine torque characteristics. I have no trouble towing my 4600 lbs Grand Cherokee, and staying in lockup. I set the TC disengage for 50% throttle, which works out well. It will stay locked at 70 mph on any Midwestern freeway hill. Cruise requires 23% to 28% to hold 70, depending on the weather. One thing you notice is the trans internals feel very heavy. You can feel an inertia difference between the TH400 and the 4L85e. It feels inefficient unless it is in lockup. Of course in lockup, that brought the mileage up by about 1 mpg. My front differential had 3.53 gears in it. When I blew it, I went back to the stock 3.73. I really wish I had not done that, as I really felt like I lost mileage. I thought I was coming out of lockup too easily for towing on 2 lane roads, but the reality is that it made little difference in power and still needed to just be programed differently. Its funny, these 502s have an amazing amount of torque in the low end. When I first installed the trans, I was having issues reading the rear speed sensor (reluctor ring missing). While out on test drives, it was shifting into 4th gear at 15 mph. Even doing that, this thing would run smooth, and still accelerate up to speed. I assume your case would be even more so, with a blower.
_________________ Dave
The Flying Fortress '83 Revcon Prince 31' FWD 502 w/Howell/GM 16197427 ECM/Edelbrock MPFI,Thorley's & Magnaflows, 4L85E 4 speed, KoniFSD, Yes it is SOLD
FMCA F298817
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