Hi guys, I am in the process of installing a 582ci shafiroff engine with T400 in a C20 1977 p/u.
I would like to know what diff gears to run as i have 4.11 s and are expecting to have to change.
Also a recommended supplier in the U.S for gears pls as i am in Australia.
This is one area where not doing the math can easily bite you in the ass, vs taking the time to do the calculations ,when you calculate the correct rear gear ratio, the factors I listed , and knowing the transmissions gear ratios ALL come into play when selecting the best match to the engine power curve.you simply stated you have a
TH400........with the stock gearing,..............2.48.....1.48....1.0
whats the truck weigh?
whats the tire diameter?
WHAT DIFFERENTIAL CHEVY 12 BOLT?,FORD 9", DANA 60?
whats the converter stall speed?
WHAT AXLES? (your going to need decent ones once the truck gets traction!
what rpm does the transmission shift at under max acceleration?
whats your intended use for the truck?
and I sure hope you have a decent transmission cooler
theres a whole lot of difference, in efficiency, between selecting the correct rear gear ratio,, example, for a fairly stock TH400 with a fairly stock stall speed converter, even with that impressive BBC engine ,that probably shifts at around 5500 rpm, under WOT, and what rear gear ratio you might want with,lets say a 3600 lb truck, and what you might select for a 4500 lb, vs a lightened truck used for maximizing performance that might weigh, nearer to 3200 lbs, especially a truck with a 3400 rpm stall converter with a shift kit that allows the engine to pull to 6200 rpm before it shifts, that extra weight and /or the extra and higher average rpm band will change the average power band rpm, and the weight will effect how much you can prioritize peak horse power vs peak torque in the gear choice.
its all a learning process, you want too simply want to mentally take a step back, take a deep breath or two,
and start testing to find out whats working correctly,in your current combo,
whats not working up to your expectations,and if its not meeting your goals, logically calculate what should change,
and then calculate what can be adjusted or if necessary parts that can be logically replaced, and re-tested,
if that required too improve the performance.
don,t make the all too common mistake of thinking adding horsepower is the only route to improved performance.
suspension mods, better shocks, better brakes, a stiffer frame, larger diameter and wider tires, and drive train gearing and removing weight,
and correctly setting up the cars chassis to more effectively apply weight transfer ratios,
swapping to lower weight parts,or stronger , or more durable parts, use of stronger drive train components, better matched gear ratios, all help
- runout should be less than 0,25 mm (0,010 inch).
- should be checked with the turbine in at least three positions. This insures that the converter will
not be internally out of balance. Overall balance should be held within 10 grams.
Internal Dimensional Standards:
Fit of pilot bushing
- 0,10 mm-0,20 mm (0,004 inch - 0,008 inch) typical.