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Discussion Starter · #1 ·
258 and hi rpm\'s

What do you guys think of running a 258 I-6 @2500 rpm's for 2 hours or so?
I'm thinking, if I should swap out third members for this trip to the cape. (cape cod)
I run 4:56, but have 3:50's i can throw in.
Should I swap it out? (should take about an hour)
Or should i just run it down there with the 4:56's

What do you think?
TIA

Rob
http://sites.netscape.net/tapboxerc/homepage
 
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Discussion Starter · #2 ·
Re: 258 and hi rpm\'s

Beat it like the proverbial red-headed stepchild. I drove my j10 from maine to wisconsin and back this winter-2600 miles round trip. 258 t176 3.31/31x10.5 I ran 2600-3100rpms all the way out and back with no problems. In fact, I got 15 mpg compared to my 13 mpg that I typically expect from my truck. I also found that at those high revs, it performed a lot better with 93 octane, at least it showed more power climbing the hills of western mass. the miles per dollar dropped from 10.8 to 10.1, though. 4 liter owners have reported a similar phenomena. Someone posted a few years back that they took a yj or xj wheeling, and it got stuck in 4 low. They had to drive home from the trail in low range, and the screaming 4.0 got better than average mileage on the return trip!

If you're concerned about spinning your gears that fast, I can't comment. The 258, however, will love it. That's my experience, anyway. Good luck, Brendan

Proud owner of the world's best running Carter BBD
 
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Discussion Starter · #3 ·
Re: 258 and hi rpm\'s

Hey Thanks, I wasn't sure if anyone would answer.
Not concerned about the gears. I was concerned with the 258, not sure if 2500 rpm's was too high for it, for such a long time, but you answered that!
Yeah, the 258 seems to do just fine @ 2500 and above. i was just wondering if anyone out there runs there 258 like this.

thanks again

Rob
http://sites.netscape.net/tapboxerc/homepage
 
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Discussion Starter · #4 ·
Re: 258 and hi rpm\'s

2500 is not considered high rpm, Be prepared for some oil slobber though.
One thing to remember, engines are machines, designed to do one thing, that is to run... keep the temp., oil pressure and rpm within spec. and they will run day in, day out, all day long, they don't get tired, they don't need a break after a few hours, and they don't care if they are running or not.
 

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Re: 258 and hi rpm\'s

How do you get the 258 to rev that High? My old 258 would rev to 3000RPM and just stop, I would not go any higher. Uphill or downhill, still 3000RPM!

Rodney C
1985 CJ7,302 V8,T18,D20,SOA,Shackles Reversed, 35" BFG AT's, Fiberglass Tub & Front End...
1990 Samurai,87 drive line,SOA+2.5" Add-A-Leaf,4.16's,5.12's,33" BFG's Mud's,Pony Carb...
 
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Discussion Starter · #6 ·
Re: 258 and hi rpm\'s

During that trip, I probably peaked out a few times at 3300 rpm. I have done the teamrush ignition upgrade, which truly lights up the 258. I don't know what to say about your 3000 rpm ceiling, for sure, but the ol' TR kit will enable the 258 to make power above 2500 rpm, whereas the stock duraspark system would rev up there, but wouldn't get the fuel to burn efficiently enough to build any additional power.

In a cj, I am surprised you couldn't break 3000. My only first hand 258 experience is in my longbed J10, which probably weighs nearly twice as much.

Honestly, If my engine was balanced with the flywheel, I would have run it higher than that! It came out of an auto, and I put a flywheel onto it, not knowing that the 258 has to be balanced with the flywheel on it. She shudders at around 2600 and 3200, which is why I ran it at around 27-3100 rip'ems. Brendan

Proud owner of the world's best running Carter BBD
 

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Re: 258 and hi rpm\'s

Just to make you worry I ran my 258 up to 3000 just like your's did and I spun a bearing. Why is it that ours only rev to 3000?? Rev limiter maybe?? Good luck

88 YJ Laredo 2" Body 31" Duelers MT MTX Sound Sys Just love fixing it every weekend...
 
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Discussion Starter · #8 ·
Re: 258 and hi rpm\'s

I run my 86 CJ7 as a daily driver. At 70mph it's at 2650rpm. I've run it this
way for 4 years with no problems. I've driven 600 mile trips without a hitch.

Gary
 
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Discussion Starter · #9 ·
Re: 258 and hi rpm\'s

most likly the reason for your 258 not going over 3000 is cross fireing in the distrbuter. this is caused by ozone build up in the stock small cap. Doing the Reamrush upgrade will fix this and improve power at all RPM's.

I have run my 258 as high as 4000 but don't like to take it over 2000. my crusing RPM with 33 inch tires 3.54 gears and .83 over drive is 1500 RPM, which is about 50 MPH. to pass I need to down shift but I feel better with the 258 turning nice and slow plus it gets better milage that way.

bandhmo
 
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