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04-18-2017, 06:10 PM
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#1 |
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Registered User
Join Date: Oct 2012
Location: Austin, TX
Posts: 34
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Gear Ratio Help
I have a '72 SWB GMC that I am currently swapping out the old 350 for an LS1.
I have a 700R4 Tranny that I am keeping. I don't plan on tacking the truck to track but want it to come off the line but will also see some good highway miles. I plan to replace the current rally wheels for 20'' US Mags in the coming months. What gear ratio would everyone recommend given my set up and how I plan to drive. I'm currently thinking 3.73 but would love everyone's advice. |
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04-18-2017, 06:40 PM
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#2 |
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Registered User
Join Date: Aug 2016
Location: Lake Forest, CA
Posts: 2,177
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Re: Gear Ratio Help
3.42 would make it run about 1500 RPM at 65-70.
__________________
"Work hard, use your vacation days." 1970 C15 GMC Long Bed 1986 C20 Scottsdale 1983 K2500 Sierra Classic Suburban 6.2 Instagram: C10sofOC |
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04-18-2017, 06:51 PM
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#3 |
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Senior Member
 Join Date: Mar 2003
Location: Colfax-California
Posts: 8,593
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Re: Gear Ratio Help
With the 3.73 and the 700r your final drive in 4th will be comparable to a 2.68 rear gear ratio. The 3.42 = 2.66
I'd go for the 3.73. It's been used numerous times here on the board and there are plenty of testimonials backing that up. A quick search would have produced those results |
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04-18-2017, 07:25 PM
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#4 |
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Registered User
Join Date: Jul 2011
Location: Mt Brydges Ontario
Posts: 181
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Re: Gear Ratio Help
I have 3.42 with the 700r4 and I am going to change it to 3.73. 3.42 are little too tall for my set up.
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04-18-2017, 07:52 PM
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#5 |
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Registered User
Join Date: Jul 2015
Location: Alberta
Posts: 161
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Re: Gear Ratio Help
Tire height plays a part in the equation as well.
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04-18-2017, 09:04 PM
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#6 |
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Registered User
Join Date: Oct 2016
Location: Dallas Texas
Posts: 3,151
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Re: Gear Ratio Help
3.73 + 700r4 ( MPH is off by ~10 so actual is about 90 in pic )
__________________
67 C10 fleet fuel injected '70 402, 700r4, 3.73 posi 07 335 sport turbo 6sp 94 Trans Am GT LT1 6sp posi -- sold after 22yrs 99 540 sport V8 6sp -- sold 73 240z L24 4sp -- given to friend 68 C10 step 350/350 3.73 open -- sold |
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04-18-2017, 09:22 PM
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#7 | |
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Registered User
Join Date: Jul 2015
Location: Cleveland Texas
Posts: 109
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Re: Gear Ratio Help
Quote:
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04-18-2017, 10:46 PM
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#8 |
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Senior Member
Join Date: Oct 2009
Location: Godley, TX
Posts: 17,976
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Re: Gear Ratio Help
I vote 3.73, but pick your poison! 4 ratios and 4 tire diameters to compare.
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04-18-2017, 11:13 PM
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#9 |
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Registered User
Join Date: Aug 2012
Location: Midland, TX
Posts: 1,267
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Re: Gear Ratio Help
Running 3.73 behind my 700r4 with 29" tires and love it. Runs about 2200rpm at 70, and get's about 16/17mpg on the highway. And you'll love 1st gear.
__________________
1969 RS/SS Z10 Camaro Pace coupe 1972 GMC Short Step buildhttp://67-72chevytrucks.com/vboard/s...=1#post6356218 1979 Mazda RX7 1979 Pontiac Trans Am WS6 & 1979 Pontiac Trans Am 10th Anniversary 1999 Honda Valkyrie 2006 Corvette Z06 2010 BMW 650i |
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04-20-2017, 10:33 AM
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#10 | |
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Registered User
Join Date: Oct 2016
Location: Dallas Texas
Posts: 3,151
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Re: Gear Ratio Help
Quote:
-klb
__________________
67 C10 fleet fuel injected '70 402, 700r4, 3.73 posi 07 335 sport turbo 6sp 94 Trans Am GT LT1 6sp posi -- sold after 22yrs 99 540 sport V8 6sp -- sold 73 240z L24 4sp -- given to friend 68 C10 step 350/350 3.73 open -- sold |
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