Gearing with TurboHydramatic - The 1947 - Present Chevrolet & GMC Truck Message Board Network

asphaltburner · 10-30-2009, 12:29 AM

Frankentruck is running a TH400 and 4.11:1 front/rear gears right now with 33" tires. 1973 axles. I'd like to reduce the highway rpms by changing ring and pinion fore and aft but would like to ask for opinions from others running a similar setup.
3.73 gears sound OK, but 3.42 may provide the best low end acceleration and still lower top speed rpm sufficiently. My 350 V8 has enough HP and torque to turn low gears!
I'd like to hear from those of you with a similar mechanical setup. In your experience what axle gear ratio has worked best for you with your TH400/350? The truck needs to commute 40 miles roundtrip on the highway, but usually in bad weather. Then it's in 2WD high, 4x4 high, or FrontWD high (twin stick NP205),...low is reserved for terrible situations and mountain FUN!
May I ask your opinion on axle gear ratio? Expensive to do this properly,...I want the final product to be perfect!
I calculate 3000 rpm@70mph with 4.11 gears, 2730 rpm@70 with 3.73, and 2500rpm@70 with 3.42. Sound accurate?
Thanks, Todd.

10-30-2009, 12:29 AM	#1
asphaltburner Registered User Join Date: Jul 2008 Location: Ault, Colorado Posts: 862	Gearing with TurboHydramatic Frankentruck is running a TH400 and 4.11:1 front/rear gears right now with 33" tires. 1973 axles. I'd like to reduce the highway rpms by changing ring and pinion fore and aft but would like to ask for opinions from others running a similar setup. 3.73 gears sound OK, but 3.42 may provide the best low end acceleration and still lower top speed rpm sufficiently. My 350 V8 has enough HP and torque to turn low gears! I'd like to hear from those of you with a similar mechanical setup. In your experience what axle gear ratio has worked best for you with your TH400/350? The truck needs to commute 40 miles roundtrip on the highway, but usually in bad weather. Then it's in 2WD high, 4x4 high, or FrontWD high (twin stick NP205),...low is reserved for terrible situations and mountain FUN! May I ask your opinion on axle gear ratio? Expensive to do this properly,...I want the final product to be perfect! I calculate 3000 rpm@70mph with 4.11 gears, 2730 rpm@70 with 3.73, and 2500rpm@70 with 3.42. Sound accurate? Thanks, Todd. __________________ '78 3/4 ton 4x4 custom "Todd-built" FRANKENTRUCK! Last edited by asphaltburner; 10-30-2009 at 12:34 AM.



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