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#1 |
Registered User
Join Date: Dec 2010
Location: Red Level, Al
Posts: 175
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To swap or not to swap
my 81 stepside is pushing about 3k rpm at 65mph i feel like its turning a little too hard. i currently have a set of limited slip 3.73 in the truck but my parts truck has a set of 3.08's. would the gas mileage increase be worth swapping them or should i keep the 3.73. i do some in town driving with about 40% highway at 65 mph. im running a 350 bored .40, flattops, set of fairly decent heads. tranny is a turbo 350. tire size is 275 60 15
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81 Stepside http://67-72chevytrucks.com/vboard/s...d.php?t=435795 |
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#2 |
Senior Member
Join Date: Nov 2003
Location: Brookings, SD
Posts: 10,497
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Re: To swap or not to swap
A 700r4 would give you the best of both worlds, is that an option?
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Some people are like slinkies, they aren't good for anything, but you can't help but smile when you see one tumble down the stairs. |
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#3 |
Registered User
Join Date: Dec 2010
Location: Red Level, Al
Posts: 175
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Re: To swap or not to swap
it could be an option later but i just built this tranny it has maby 300 miles on it
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81 Stepside http://67-72chevytrucks.com/vboard/s...d.php?t=435795 |
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#4 |
Registered User
Join Date: Jan 2010
Location: Loveland, CO
Posts: 1,921
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Re: To swap or not to swap
3.08's will definitly lower rpm's and help fuel mileage. It will hurt your acceleration a little bit, but with your tire size it wont be that bad.
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Zach 1970 Chevrolet Custom Camper K20 1971 GMC Super K2500, 12V/NV4500 swap in progress 1971 Chevrolet Custom C10 1972 Chevrolet Custom Deluxe C20, 5.3/4L60E 1972 Oldsmobile Cutlass Supreme, 455/TH400, 3.73 posi 2004 GMC Sierra 2500HD, LB7/Allison, CCSB 2005 GMC Sierra 1500, 5.3/4L60E, CCSB |
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#5 |
BAD BOW-Silverado XST
Join Date: May 2000
Location: Senior Member from Austin, TX
Posts: 6,431
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Re: To swap or not to swap
With that much highway, yea swap in the 3.08. I run that gear with a 700R4. If you were closer, I would take the 3.73 axel off your hands.
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#6 |
Registered User
Join Date: Dec 2010
Location: Red Level, Al
Posts: 175
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Re: To swap or not to swap
You would be surprised how many people want a 3.73 limited slip
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81 Stepside http://67-72chevytrucks.com/vboard/s...d.php?t=435795 |
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#7 |
Senior Member
Join Date: Nov 2003
Location: Brookings, SD
Posts: 10,497
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Re: To swap or not to swap
You have an engine with what seems a few performance goodies in it, but then you want to raise your rearend gearing to get better mileage. Will you be happy with the swap?
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Some people are like slinkies, they aren't good for anything, but you can't help but smile when you see one tumble down the stairs. |
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#8 |
Registered User
Join Date: Sep 2009
Location: Western Oklahoma
Posts: 48
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Re: To swap or not to swap
According to the variables you have given (Turbo 350 {final drive ratio 1.0}, RPM, and tire size) this calculator indicates 63 mph at 3000 RPM is only achieved with 4.11 rear end gears. Perhaps your tach or speedometer is in error.
You can calculate the rpm you will need to turn with the same combination of variables with a 3.08 rear gear by trial and error in the RPM box, or using the slider tab. Just keep testing rpm numbers until you get the speed you are looking for.http://www.markwilliams.com/calculators.aspx edit to add: you can change variables like transmission type, wheel size ect. to look at different options. This is a fantastic planning tool to use!!! A 700r4 AND 3.08's will cut your rpm in half!!! Last edited by JaggedEdge; 08-06-2011 at 09:45 PM. |
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#9 | |
Registered User
Join Date: Nov 2009
Location: Parachute, CO
Posts: 183
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Re: To swap or not to swap
Quote:
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1984 1ton 4x4 crew cab dually 6.2 diesel,465,205,D60,D70,1987 3/4ton 4x4 suburban 5.7 FI350,TH400,208,1985 CJ-7 FI406,465,205,D60,FF14, 1970 Jeepster 350,465,205,D44,FF14, |
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