My highway rpm is about 3300. Is this okay for a 258? Whats the max rpm. Engine is rebuilt, bored 60 over.

wow:eek: i dont think mine will even turnn that fast if i tried

I'v wound it out to 4200 in third.

Originally posted by Mike Elrod
I'v wound it out to 4200 in third.

What's it breathing through???

I can't believe the BBD would support that

Thats way too fast! I ideally cruise at 2000-2200RPM on the highway in my YJ with a 258 (4.2)On the trail it is usually lower. It will wind up to 4000 but I usually upshift at around 3000. A stock YJ won't even rev that high but ignition upgrades help alot (I have a "juicebox" ignition). Why do you need to rev that high? Got stock tires and low gears or something?

Originally posted by Mike Elrod
My highway rpm is about 3300. Is this okay for a 258? Whats the max rpm. Engine is rebuilt, bored 60 over.

That's a bit too high. I run about 2600 @ 70mph. I wouldn't
want to go much higher than that. What do you have for a trans
and diff gears?

I run at about 4000 at 70 mph with a SM420, NP231 and 5.38's with 35's, but my little 2.5L loves it and I can pull any hill without down shifting. Not too great for gas, and I don't drive it on the highway much anymore anyway, why can't Klune build a underdrive / overdrive?

Originally posted by 4Bangler
I run at about 4000 at 70 mph with a SM420, NP231 and 5.38's with 35's, but my little 2.5L loves it and I can pull any hill without down shifting. Not too great for gas, and I don't drive it on the highway much anymore anyway, why can't Klune build a underdrive / overdrive?

Those I4's are supposed to run higher rpm's. 3300 is just to
high an rpm to run constantly for an I6.

ok.. is a 4.0L different?

Mine is happy at 3,000rpms, has power through to 5,000rpms.

I normally run it at 2,000rpms cruising, but pulling a grade I'll run at 3,500rpms for several miles at a time going over passes.

Or, are you guys just being gentle on your I6's?

I don't usually have mine anywhere above 3K RPM.

THere isnt a heck of alot of useable power beyond that anyway.

Sounds like you are a victim of gearing.

Hope your I6 can take it.

MJ

Not really a victim of gearing, stock drivetrain, 36" tires, 4.56 gears. I'm geared a little lower than stock after you account for tire size. I can still cruise at 60mph in 5th gear.

The I6 hasn't complained running it like that. I've found the power doesn't start to drop off until about 4,200rpms, maybe just a hair more.

i agree with Maine Jeepah it just dosent have any power up there i have tried it a number of times but i will shift at or before 3000 for crusing its 2100 with overdrive at about 70

Mine's a well built and balanced 4.2 w/P&P 4.0 head and MPI.
My shift sweet spot is between 3500 and 3800.
It will rev past 5000 but really, it starts running out of breath at around 4500.
Stock 4.2s ought to stay under 3500.

Originally posted by Mo


What's it breathing through???

I can't believe the BBD would support that I'v got a weber on it that I had to use my tip cleaners to open up the jets. It's my 258 in my scout. I' got a t 19 wide box, 4.56 and 35's.

4k is where my powerband drops off.. but the switth to 4th gear drops the r's to 2200 and there is no power there..
Boy do I need gears.

weber, decked head, header, HEI.

My 258 (rebuilt with about 15k on it) turns jsut under 3k at 70mph in 5th. That is with gasp 33's and 4.56's

When i get on it it will rev up to 3500 but thats it realy.

Stock carb opened up a little.

OK, so forgive me for sounding stupid about this, but a better carb or EFI allows the engine to rev at a much higher rate without losing power? Is that the way that they improve performance?

Originally posted by Victor
OK, so forgive me for sounding stupid about this, but a better carb or EFI allows the engine to rev at a much higher rate without losing power? Is that the way that they improve performance?

That's one way, the other way FI helps is that there's no fuel bowl to keep filled

Basically, the greater amount of correctly mixed fuel and air that can be stuffed into the combustion chamber with the most ease and most effeciently burned will produce more horsepower.

Longer valve lift, overlap and duration; positive pressure and ramed intake, efficient port and manifolding, correct advance, plus ease and scavaging of exhaust are some horsepower building techniques.

The 258 that I run is rebuilt 5000 ago, bored 60 over, RV cam, MSD Blaster II Coil, 8mm plug wires, and a carb off of a 72 Chevy 292. It cruises down the highway with 34"s and 4.10's at 2200 and has no power it drops to 2nd gear on my TH400 if I hit a grade. It however loves 2500 to 3500 but it very seldom sees anything over 3000 but has been as high as 4200 no problems.

Back when my YJ was in stock trim(those couple of weeks it was stock) I actually pulled 5800RPM a couple of times. That was with about 60,000m on it. It survived until 180,000m, and all that went bad was the cam bearings, leading to a loss of oil pressure.

The 258 is definitly a low RPM engine. The 4.0L however does not have as long of a stroke as the 4.2L, and can rev up higher with out being as hard on the engine.

My old 258 would peak (horsepower-wise) right around 3 grand. anything higher and that fawker sounded like she was ready to blow... :D

I've got A stock (crate motor, no cam) 258 with Clifford intake manifold and header, Holley 3200 350cfm 2BB carb with jacobs ignition, Ford Duraspark Distributor cap and rotor, big wires.
I turn like 3500 on the freeway doing 75mph (T-18, 4.88:1 gears, 34" Swampers)
I will run it at 3000 steady on the highway and have been doing so now for 5 years (since I installed it)
After I geared down my axles, while driving on the freeway at 3000 rpm I felt the gas pedal go down and my exhaust got really loud and suddenly had gobs of power.
I think my new exhaust finally blew out allowing more exhaust to flow, now I can turn up to 4000 rpms no problem.
However when it gets there I can tell the valves are pretty much floating so I try to keep it around 3500 max.

P.S. I have been hammering this motor for a while now and the only problems I have are carburation related (Carbs SUCK) as well as a leaky valve cover that I have given up hope on. (Yeah, yeah Aluminum v-cover will fix that prob, BS I say, thats what I have, it always ends up leaking).
When this motor craps out I want to transplant a 1999 Ford 4.6 FI from a F-150 into it for more torque, HP and performance.

Mark

Originally posted by Robert
Back when my YJ was in stock trim(those couple of weeks it was stock) I actually pulled 5800RPM a couple of times. That was with about 60,000m on it. It survived until 180,000m, and all that went bad was the cam bearings, leading to a loss of oil pressure.

The 258 is definitly a low RPM engine. The 4.0L however does not have as long of a stroke as the 4.2L, and can rev up higher with out being as hard on the engine.

5,800? My rev limiter kicks in at 5,500. :p

"5,800? My rev limiter kicks in at 5,500."

Yeah, mine too....but if you get a good bounce going...

I wish I could bump that limiter up a few, my 2.5 is still pulling hard when the rev limiter kicks, but now that I've got the SM420 I doubt I'll be doing and Dune blasting so maybe I don't need to look into this.

as well as a leaky valve cover that I have given up hope on. (Yeah, yeah Aluminum v-cover will fix that prob, BS I say, thats what I have, it always ends up leaking).

car wash once a week or as needed that was my fix