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Old 10-17-2019, 04:15 PM   #1
broberson
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Gearing for 1970 C10

My next project is a rebuilt tranny and new gears for the rear end. Im planning on a going with a 700R4, and maybe 3.73. Any suggestions for the gear ratio from anyone? I put in a 383 stroker, and Iím planning on highway driving, so any opinions will be appreciated.
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Old 10-17-2019, 04:38 PM   #2
mongocanfly
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Re: Gearing for 1970 C10

what size tires are you gonna run?
with a 28" tire and those ratios (.7 od and 3.73s) youll be turning 2037rpm at 65mph and 2193rpm at 70 mph
heres a rpm calculator thatll help you se whats going on....http://www.csgnetwork.com/multirpmcalc.html
you might want to consider 3.42s...that would give you 2011rpm at 70mph with a 28" tire
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Old 10-17-2019, 04:54 PM   #3
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Right now Iíve got 275/60/15 all around, and I believe is an 8Ē rim.
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Old 10-17-2019, 05:29 PM   #4
mongocanfly
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Re: Gearing for 1970 C10

275/60/15 is 28" tall so above rpm figures will be correct...
tire size chart
https://tiresize.com/conversion-chart/
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Old 10-17-2019, 09:50 PM   #5
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Re: Gearing for 1970 C10

On my 72 Cheyenne super swb I run a 295/50/15 tire in the rear with 3.42 gears, 700r4, and 383 CI engine. works for me, Good Luck on your choices..
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Old 10-17-2019, 11:52 PM   #6
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Re: Gearing for 1970 C10

I have an OD auto trans, 4.10 gears and 31" tires. Just over 2000 at 70 with the converter locked. Seems good to me.
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Old 10-18-2019, 08:04 AM   #7
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Re: Gearing for 1970 C10

I have 3.73's in my 66 with a 28" tall tire and the 700 and at 65 I am at about 1800. I have my lock up set at about 48 mph and that combo works well all around. Have thought about the swap to 3.42's and have a set but happy where its at. I plan to go up an inch on the next set of tires and see how that works.
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Old 10-19-2019, 08:28 PM   #8
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Re: Gearing for 1970 C10

Depending on the build of my engine, and carb size+style. I like my engine to spin about 2200-2500 rpm at desired drive rpm.

The slightly higher rpm works very good if your running let's say a 750cfm Holley.

If you want to run right at 2000 rpm or lower. Only a small Holley or Q-jet is going to have enough air flow for proper atomization of the fuel. Even then it never really got better fuel economy then before I regeared. Or my higher geared trucks didn't do worse then comparable friends trucks.

There was a thread on this site where a guy put a 5 speed behind his truck, and his mileage stayed the same or dropped slightly. I forget the exact details.

Depending on how your cam is. You need to be on the start of the torque curve for idealistic mpg. Tonight I am going to get a tunnel ram hopefully, and that means 3000 rpm for best mpg.
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Old 10-19-2019, 08:46 PM   #9
broberson
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Re: Gearing for 1970 C10

All of these sound great. How is the power off the line with those of you running a 3.50 and greater? I'm not looking to run 100 mph, I just want a good jump off the line. It also sounds like everyone is on the lower end of the RPMs, because I'd like to stay around 2500. I don't want to run wide open, or anything greater than 3000. I've got a 600 CFM edlebrock with an electric choke. I'm still trying to get the tuning dialed in. I'm running on the lean side, but its running really good. I do still need to set my total timing, but i've got to wait until I have an extra set of hands..
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Old 10-19-2019, 09:29 PM   #10
Ziegelsteinfaust
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Re: Gearing for 1970 C10

3.73's and a th700r4 first gear will be a great all around gear. Even 4.11's are not so bad if you like a bit more rpm.

A th700r4 is typically quicker out of the hole then a th350 or 400, but the part I hate on them is the big 1-2 gap. The quickness out of the hole depends on total gear ratio, and engine power. So it can be flipped to give another trans the advantage.

Basically you will have 3.73 performance with 2.73 mpg is the best way to describe the th700r4.
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Old 10-20-2019, 01:25 AM   #11
broberson
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Re: Gearing for 1970 C10

I've started pricing some gears on Summit.. I've got results from Excel, Richmond, USA Standard, and Alloy USA. Is there a better place to buy? What brand does everyone like?
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Old 10-20-2019, 08:40 AM   #12
mongocanfly
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Re: Gearing for 1970 C10

go with Yukon gears...some of the best out there
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Old 10-20-2019, 08:42 AM   #13
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Re: Gearing for 1970 C10

Quote:
Originally Posted by broberson View Post
I've started pricing some gears on Summit.. I've got results from Excel, Richmond, USA Standard, and Alloy USA. Is there a better place to buy? What brand does everyone like?
Since you are only searching and not buying, check out this site:
http://ronsmachiningservice.net/
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