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Old June 4th, 2016, 01:46 AM
Chuck78 Chuck78 is offline
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Location: Columbus OH
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Default Re: 5 speed/o.d. swap comparisons - WC/S10 T5 hybrid, NV4500, A833 MY6, Tremec 3550 Mustang

TJ, no SM420's here... I had an SM318 3 on the tree, but the 1st/reverse gear exploded on me... it had an sm318 originally, then a Camaro T5 2 owners ago, then an SM318 again from last owner, then I blew that up hauling a heavy load with a lead foot, my dad have me a free Chevy Vega Saginaw wide ratio 4 speed (1st gear around 3.31 or 3.34?), ran pretty great but a synchro and some bearings are worn.


With 275/60-15 Firestone Firehawk Indy 500's (my favorite performance tire, no longer available in 15 inch!!!), 3.07 one legged Dana 44, Saginaw 4 speed 1:1 4th, 305D with HEI & 500cfm Holley, I was able to push it above 21mpg driving it very conservatively. I think I got even 23mpg highway with 6 passengers and camping gear in the hills& mountains of West Virginia! I have never heard of anyone from the 60-66 Yahoo group days having ever gotten that kind of fuel mileage in a GMC big block v6.
With the 351, I wonder if adapting a very small Rochester Quadrajet 4 bbl to the manifold would help it with better mileage? With the low limited rpm of these engines, the cfm requirements are not terribly high, where most 283/289/327/350/etc v8 performance applications rev much higher, requiring far more cfm. We make all the power down low, lots of grunt on the bottom!

I am hoping with an overdrive 5th, a deeper 1st gear when needed, & a tighter gear spread 2nd- through 5th with an AX15 2wd Jeep/Dakota trans, that I can get similar fuel mileage with this new former museum exhibit 351C that I just arranged a deal on.

Last edited by Chuck78; June 4th, 2016 at 02:02 AM.
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