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05-16-2010, 06:38 PM
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#1 |
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Registered User
Join Date: Sep 2009
Location: Live Oak Florida
Posts: 8
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rearend gear swap
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ok guys i really need some advice on a lower gear for my 91 k1500. had transmission rebuilt with heavyduty servos (700 r4) just had engine rebuilt board 30 over with flat tappet cam 290duration with a 298 lift and i caint feel any diffrence while im pullin my airboat granted an airboat has its share of wind resistance but were only talkin maybe a 1500 pound with trailer and all now i am runnin 15x10 wheels with 35x12.50 mud tires would a 4.10 gear ratio 4.11 be where i get my best peformance any ideas or advice? |
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05-16-2010, 11:09 PM
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#2 | |
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Future TOTM Winner
Join Date: Aug 2006
Location: Bulverde, TX
Posts: 2,692
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Re: rearend gear swap
Quote:
I look here whenever I am trying to determine gearing. For everyday driving you probably want your RPMs at highway speeds to be around 2000 in overdrive. Although you shouldn't be pulling in OD with that tranny. Another thing to keep in mind when using a gearing calculator is that your actual tire height is likely different than what is stamped on the tire. For a 35x12.5 I usually put in a tire size of 34 inches. Hope this helps a little.
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72 Chevy CST K5 HIGHLANDER BLAZER Getting a 6.0,NV4500,NP205,14BFF (Currently laying all over the place in little pieces) 72 Chevy swb step-side "LS" 6.0 Here's a build thread of sorts 2002 HD2500 Crew Cab, 8.1L Allison 4x4 Daily Driver Check it out www.lsdyno.com Last edited by Critter; 05-16-2010 at 11:10 PM. |
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05-17-2010, 10:15 AM
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#3 |
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Registered User
Join Date: Feb 2000
Location: Modesto, CA
Posts: 1,842
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Re: rearend gear swap
I agree, with that auto & 35s 4.56 is were you will 'feel' a difference. If you get 4.10s you'll allways be wondering what 4.56s would have been like.
 
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1972 K5 MPFI454/Sm465/Np205/D60/14FFd/Re-Centerd H1s w/Swamper Iroks 
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05-17-2010, 09:15 PM
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#4 |
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Registered User
Join Date: Jul 2009
Location: La Crosse, WI
Posts: 218
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Re: rearend gear swap
First what is your current gear ratio?
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Currently truckless, previous trucks: 67 K20, 87 K10 aka V10 & 72 C10 |
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05-18-2010, 07:53 PM
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#5 |
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Registered User
Join Date: Dec 1999
Location: Austin, TX, USA
Posts: 7,728
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Re: rearend gear swap
Are you going to pull in OD, or in third? Please post more cam specs. The lift # at the cam? The duration advertised at .001 or somewhere else? What is the .050 duration (best # to compare cams IMO)?
If you have 3.42's now and the cam is 230+ degrees at .050 you aren't going to have any power. You need a cam with 210-215 degrees at .050 max IMO. 3.42 and 35" tires are OK with no OD, but in OD and pulling a trailer you have missed the curve completely. If you currently have 3.73, pulling in 3rd shouldn't be so bad.
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44 Willys MB 52 M38A1 64 Corvette Coupe 68 Camaro 'vert LT1 & TH700 69 Z/28 355 12.6's @110 69 Chevy Short Step 4 1/2"/7" drop 72 Jimmy 4WD 4spd 4" & 35's 02 GMC 2500HD 4x4 Duramax |
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05-18-2010, 08:49 PM
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#6 |
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Registered User
Join Date: Mar 2007
Location: Connecticut
Posts: 581
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Re: rearend gear swap
x2 on the cam...
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"I'll Procrastinate Tomorrow" quote by LEEVON 71 K10 long fleet (sons truck) new 370hp 355, sm465 np205, 3.73's 33's 70 K20 long fleet 98 G3500 work van |
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