Over the years of getting/giving advice, listening to the great people on the Toyota-Mods List, exposure to the Club4ag forums, and reading some specialized books, I've gathered some useful equations and conversion factors. I'll be adding more and more as I come across them...
Drivetrain
If you have your gear ratios, final drive ratio, and tire/wheel size info, you can calculate the vehicle speed in increments of 1000 rpm. It's useful for picking out tire-wheel combos for race use. For example, it'll show you if the smaller combo will force you to upshift to 3rd when the redline in 2nd gear used to be the norm.
Scott's Speed Calculator Program
This link will open up a new browser
The redline for the 4A-GE is 7700 rpm. In 5th gear (C52 tranny), it'll go 19.30 mph/1000 rpm. Multiply 19.30 by 7.7 (for 7,700 rpm) and we get 148.61 mph which explains the highly optimistic 150 mph speedo.
Suspension
How do you compare springs f/ different manufacturers when they list rates in lb/in and kg/mm?
Here ya go...
1 kg/mm = 55.88 lb/in 1 N/mm = 5.588 lb/in
Using this conversion factor, a 300 lb/in spring comes out to 5.369 kg/mm.