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Old 12-30-2016, 01:50 PM   #1 (permalink)
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koh/baja1000 gearing

i posted this in desert racing forum, but thought id post it here too to try and get more answers. I've been building over the last few years a tacoma truggy that is mainly used for rock crawling, but Ive tried to make it as universally off road-able, bullet proof as possible, while still being able to go fast. I would like to one day run the baja 1000 and KOH in it, not to be competitive, but more for bragging rights.
I am currently running one ton axles d60 up front and 10.25 sterling in the rear, and I want to know what you recommend for gearing running 42's. The truck currently has a 4.7L v8 and transmission out of a 2001 tundra, but I do plan on eventually swapping with a supercharged drivetrain from a newer tundra.
Right now the two gear ratios I'm considering is 5.38 and 6.17, the rig is a off road only trailer queen, and I want the best ratio possible. from what I know about gearing it seems the 5.38 will be to low to go fast enough, and with the 6.17 it will create to much torque and because the teeth are so small it could break easily. I know yukon has a lifetime warranty you can buy for their gears so right now I'm leaning more towards 6.17, but I want to know what people with experience doing those races have to say about it.
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Old 12-30-2016, 02:23 PM   #2 (permalink)
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We are building our KOH/Baja buggy now and the plans are to run 5.83 or 6.20's, but then again we are running Gearworks 10" HP centers, GW R&P, and GW spool and locker.

Its really a toss up for us, and we may end up with one dropout for Baja, and one for KOH or other local races. You really need to determine do you want top end speed or acceleration as well as the area you are at.
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Old 12-30-2016, 02:46 PM   #3 (permalink)
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We are building our KOH/Baja buggy now and the plans are to run 5.83 or 6.20's, but then again we are running Gearworks 10" HP centers, GW R&P, and GW spool and locker.



Its really a toss up for us, and we may end up with one dropout for Baja, and one for KOH or other local races. You really need to determine do you want top end speed or acceleration as well as the area you are at.


I think I would want top end speed over acceleration because like I said it's not so much about being competitive, just finishing one piece
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Old 12-30-2016, 02:53 PM   #4 (permalink)
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Also understand that the average speed for the baja 100 is around 50mph. Im not sure what it is for KOH but I'll guess its not to far off.
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Old 12-30-2016, 02:55 PM   #5 (permalink)
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Also understand that the average speed for the baja 100 is around 50mph. Im not sure what it is for KOH but I'll guess its not to far off.


That I did not know, I assumed it was a lot higher
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Old 12-30-2016, 04:18 PM   #6 (permalink)
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I would run as low of a gear as your can get in the housings and not be a strength and reliability issue. The last two years I co-drove in a rig with gearworks 6.20's, CBM LS with a TH400. It would go 107 still, but didn't even really need low range. Changed to 5.83 to pick up a few MPH and you could really feel the difference in power, it definitely took an acceleration hit. Also, 5.38's are the lowest ratio available for a HP 60, 6.17's only go into low pinion. I assumed since you mention a sterling rear that you have the matching HP 60 front? I have a jeep a stroker motor with 5.38's on 39's with HP 60's front and rear. I'd put 6.20's in it if I could and I drive it on the pavement still.

If your building a street able truck to run KOH your average speed will probably more like 20 ~ 25 mph. Cody Addington's average speed in 2012 in his Toyota was 17 MPH. The big dogs with unlimited IFS cars I bet average 40~45
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Old 12-30-2016, 04:24 PM   #7 (permalink)
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I do have the matching 60 front. Both came axles came out of a 89 f350. When you went from 6.20 to 5.83 you're saying it could go fast but not accelerate as fast? I though Yukon had 6.17 for hp d60
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Old 12-30-2016, 05:23 PM   #8 (permalink)
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I think I would want top end speed over acceleration because like I said it's not so much about being competitive, just finishing one piece
I think you've got that backwards.

If you want to finish, don't go fast. I co-drove two DNFs, and going too fast for the equipment was the common problem.

I'd go for the stronger gears, and smaller tires. SxSs and Class 11s finish with small tires.

Don't get sucked into being competitive.
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Old 12-30-2016, 07:20 PM   #9 (permalink)
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It depends on the engine/cam honestly. You want the best 0-100mph or so which is dependent on weight, displacement, gears, etc.

If you have an engine where the power band is 4000-7500 rpm, more numerical gear.
If your engine is a torque monster from 2000-4000 rpm, less numerical gear.

The cheap way to figure this out is with a clock on how quick it rips through first gear vs "top gear" or RPM vs MPH gain per second. Maybe build both third members and have them on hand?

Last edited by scouter77; 12-30-2016 at 07:30 PM.
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Old 12-30-2016, 10:51 PM   #10 (permalink)
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That I did not know, I assumed it was a lot higher
Take into account the amount of time spent at 15-20mph.

I'd gear it to go about 100-115 comfortabley on the top end. Not off the rev limiter but fairly high in the powerband.

If you don't have the suspension for it I doubt you'll see speeds that high, but you can always get your low speed through the transfer case gearing. It's way less frustrating to run lower rpm on the top end instead of running out of gear and bouncing off the rev limiter for miles.

Honestly 42s and 5.13-5.38 sounds about right. You can always go to an atlas with several low ranges too.
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Old 12-30-2016, 11:14 PM   #11 (permalink)
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You can only go to a 5.38 is th hp60 or 10.25.

Maybe consider the atlas with 2.7/1.5 gears. You may want to step down a bit in the 4.10 range to get the final drive to the ~6:1 range.
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