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Unread 04-11-2014, 10:11 AM   #1
Grims
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1983 CJ7 
 
Join Date: Jan 2008
Location: Houston, TX
Posts: 337
Best cruising RPM

What is the best RPM to drive at in a 258? I have a T5, 35s, 4:88 gears, and a mild comp cam. 1,500 RPM is what feels "right" for driving around town. It doesn't feel like it's lugging, and has plenty of acceleration. But, that seems really low.

Is there a sweet spot RPM that's best to keep it at?

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Unread 04-11-2014, 11:17 AM   #2
Mike Romain
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1986 CJ7 
 
Join Date: Nov 2007
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I get by far the best gas mileage running about 2300 rpm. With my 33's and 3.31 gears, that means 3rd around town and 4th on the highway. If I go to the taller gear, I lose about 5-10 mpg easy. Got way over 20 mpg with my stock except for no computer 258 and now get a nice 25 with my 4.0 HO, still with the stock 258 BBD and ignition on it. I do have an accel coil.
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86/00 CJ7 Laredo, 33x9.5 BFG AT's, 'glass nose to tail in '00, 'New' frame,wires and plumbing in '09. Carter BBD Carbed 4.0 HO in '10.
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Unread 04-11-2014, 12:12 PM   #3
Grims
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On a 600 mile trip at highway speeds doing about 70 at probably 3k RPM (didnt have a gauge then) I got about 14.5 miles to the gallon. Which I think is pretty good being my timing was far too retarded and my carb needed a rebuild. But, I wonder if 1,500 RPM is fine at in city speeds being my gears are so low.
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Unread 04-11-2014, 02:30 PM   #4
Mike Romain
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Double post
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86/00 CJ7 Laredo, 33x9.5 BFG AT's, 'glass nose to tail in '00, 'New' frame,wires and plumbing in '09. Carter BBD Carbed 4.0 HO in '10.
89 YJ Renegade. BBD Carbed 4.0 HO. Locked front and rear with 33x9.5 BFG AT's
Some Canadian Bush Jeep Runs and Build Photos: http://mikeromainjeeptrips.shutterfly.com (10 new albums added Sept 16/10)
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Unread 04-11-2014, 02:31 PM   #5
Mike Romain
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Quote:
Originally Posted by Grims View Post
On a 600 mile trip at highway speeds doing about 70 at probably 3k RPM (didnt have a gauge then) I got about 14.5 miles to the gallon. Which I think is pretty good being my timing was far too retarded and my carb needed a rebuild. But, I wonder if 1,500 RPM is fine at in city speeds being my gears are so low.
I find anything under 2000 drinks gas. I need too much pedal to adjust for small changes in wind or hills. Try it for a measured distance and do a milage check. That is what I do.
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86/00 CJ7 Laredo, 33x9.5 BFG AT's, 'glass nose to tail in '00, 'New' frame,wires and plumbing in '09. Carter BBD Carbed 4.0 HO in '10.
89 YJ Renegade. BBD Carbed 4.0 HO. Locked front and rear with 33x9.5 BFG AT's
Some Canadian Bush Jeep Runs and Build Photos: http://mikeromainjeeptrips.shutterfly.com (10 new albums added Sept 16/10)
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Unread 04-11-2014, 02:32 PM   #6
LumpyGrits
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2400-2600rpm seams to be the 4.2's 'sweet spot'.
LG
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Unread 04-11-2014, 02:40 PM   #7
Tigerjeep79
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65 mph gets me 2500 RPM. It seems about right, that's with 32" tires and 3:50 gears. I'm very happy with that setup.
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Unread 04-11-2014, 03:02 PM   #8
Grims
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I'll give it a shot. like I said at 1,500 RPM I have lots of power for anything I come in contact with (hills, trees, cars, small children) But, I'll give 2k a try. just feels like I'm in too high of a gear in that area. Letting off the gas gear brakes it.
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Unread 04-11-2014, 06:35 PM   #9
LumpyGrits
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At 1500, your lug'n it!
LG
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Unread 04-11-2014, 08:59 PM   #10
243
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Peak torque appears to be 1800-2000 depending on the year model, that is where I would want to be.

I am not even close (on highway) with 32" KM2's and 3.54s:

2050 @ 55

2800 @ 75

With an overdrive I would be better off:

1550 @ 55

2104 @ 75
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Unread 04-11-2014, 09:04 PM   #11
LumpyGrits
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Quote:
Originally Posted by 243 View Post
Peak torque appears to be 1800-2000 depending on the year model, that is where I would want to be.

I am not even close (on highway) with 32" KM2's and 3.54s:

2050 @ 55

2800 @ 75

With an overdrive I would be better off:

1550 @ 55

2104 @ 75
You don't want/need an OD with 3:54s!
Trust me-You want to keep the R's above 2200rpm.
I run 4:88 w/33s and a T5. it will run sweet all day at 2500-2600 rpm.
LG
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