Posted by C. Garbee from 209.170.133.144 (dialup-2-133-144.rdu.portbridge.com) on Tuesday, April 02, 2002 at 10:25PM :
In Reply to: 4Bt diesel again posted by Tim from 24.136.38.214 (cpe-gan-24-136-38-214-cmcpe.ncf.coxexpress.com) on Tuesday, April 02, 2002 at 7:31PM :
Trim the oil pan (two inches or so).
Add a two-inch block between your springs and front axle.
Add a full-length leaf to your front springs.
If you have the engine high enough that you have to lower the air intake tube, you likely will have the transmission hitting the floor pan and will also have a nasty drive line angle on the short shaft.
For 4.88 gears, 0.75:1 OD, 40" tires, I get 2616 rpm at 85mph (faster than the Cummins 4BT is governed…).
Better way to look at is to figure that you want the engine to turn around 2250rpm (90%) to 2375 (95%). With your stated gears, OD, and tires, that would give you a cruise at 2250rpm of 75mph (which, oddly, is how fast I typically run down the interstate in my M37 with the 4BT…).
BTW: I use the calculators at: http://www.race-cars.net/calculators/mph_calculator.html