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| | | Joined: Dec 2013 Posts: 41 'Bolter | | 'Bolter Joined: Dec 2013 Posts: 41 | Hey guys,
My 1964 GMC/C10 hybrid needs major diff work and I was wondering what ratio to use. It has a Chevy 283 2 bbl mated to a SM420 4 speed and currently a 3.54 rear end. I've run the numbers on using the 3.54 or switching to 3.07 and I'm leaning towards the 3.07 for top end speed at lower RPMs, but, I'm not sure what the 283 likes to run at. Any suggestions?
Brian | | | | | Joined: Feb 2014 Posts: 215 Shop Shark | | Shop Shark Joined: Feb 2014 Posts: 215 | The 3.07 was an option with the 283 and manual trans in the C10. The engine is rated at 4400 RPM. With the granny gear in that 4 speed, you'll do fine! I have that trans behind a 350 V8 with a 3.73 axle and it's too easy to spin tires starting in low gear. Switching to a TH700R4 in a couple of weeks for better drivability and mileage.
Last edited by Woodswarrior; 03/31/2014 12:37 AM.
| | | | | Joined: Jul 2008 Posts: 1,262 Shop Shark | | Shop Shark Joined: Jul 2008 Posts: 1,262 | Highway speed on a small block V8 should, ideally, be about 2200-2400 rpm. | | | | | Joined: Dec 2013 Posts: 41 'Bolter | | 'Bolter Joined: Dec 2013 Posts: 41 | Thanks guys. At 2400 rpm, which is at it's torque peak, with the 3.54 I should be able to cruise at about 60mph, with the 3.07 it'd be about 67mph. Hmmm, my pinion seal and bearing are shot and it's going into the shop tomorrow, so if the ring and pinion are bad I'll switch to the 3.07. If it's just a seal and bearings then I'll keep the 3.54. It's a GMC chassis anyway, so the standard 3.07 or option 3.54 is correct.
I'm debating on whether to swap the cab and motor to make it 100% GMC or swap the frame to make it 100% Chevy. | | |
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