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post #1 of (permalink) Old 09-10-2001, 07:22 PM Thread Starter
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cruising rpm and gearing

I'm in the middle of a frame-up rebuild on my '76 CJ-7. It has the 258, and a TH400 slushbox with the quadratrac system. I was surprised to find that according the letter code (L) on the rear axle, the axles are geared at 4.10. This seems a bit high for the TH400 with stock P235 tires. Supposedly this Jeep was used on a farm, so it probably never saw the highway.

I'm considering going to college 5+ hours away in the mountains, so highway speed will be important to me. On my '83 CJ-7 that I drive everyday, my cruising rpm is about 2100 at 65mph. With these 4.10 gears, the '76 CJ-7 would have to be running around 3100 RPM to hold 65 with 30" stockish tires. I would like to go to 33"s, which would bring the RPMs down to about 2700.

What RPM is everyone running their inline 6 at on the highway? what is the ideal RPM for highway cruising?
any input would be appreciated! thanks


Mark
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post #2 of (permalink) Old 09-10-2001, 08:00 PM
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Re: cruising rpm and gearing

4.10's with 33's is not that bad.. im running the same gears with 35's.. when i had 33's i was running 3.73's.. hell i used to run that ole I6 at 2700 all day long..

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post #3 of (permalink) Old 09-10-2001, 09:07 PM
 
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Re: cruising rpm and gearing

Hmm, I just go till it sounds good, normally cruse at 1500, gear up at 2000, and down at 1250. Any higher and it gets kinda loud.
Friend of mine said soon he's gona make his VW louder then my Jeep, I just laughed hysterically and told him he's never heared it reving at over 2000 RPM.

I've bliped it up to 3000-4000 before, but its real real loud, the whole thing shakes, and the frame visibly tourques.


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post #4 of (permalink) Old 09-10-2001, 09:40 PM
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Re: cruising rpm and gearing

Check this link out for a gear calculator http://www.4lo.com You'll need to fill five of the six areas. For highway speeds, use 1:1 for both transmission / transfer case areas.
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post #5 of (permalink) Old 09-10-2001, 09:54 PM Thread Starter
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Re: cruising rpm and gearing

Yeah, I've been using the calculators from 4lo.com.. but what I'm trying to figure out is the ideal highway cruising rpm for the 258, and how flexible it is. I've read some posts that say 2700rpm+ is pushing too hard on the engine, and it wouldn't be very efficient for long trips. Does anyone run 4.10s and 33"s?
thanks



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post #6 of (permalink) Old 09-11-2001, 07:04 PM
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Re: cruising rpm and gearing

I completely agree with Infernozx. I run my 258 in that general area, But that is mostly for efficiense. Running at around 3000 should not do any harm but your milage will suck.

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