I have a 86 258 and wondering if a earlier head would up my compression to get a little more power out of it. If so what year.What were the CC's of the heads. Would a 232 head work? What is the CFM of the 1bbl and 2bbl carbs? THANKS :confused:

sWAP ON A 4.0 L head. You can find info on that swap on this BB. It's supposed to add up to 40hp.

yabut, will my carbed intake and exh. manifold fit it?

Your intake will fit but not your exhaust.

I have heard allot of perple talking about this, is it really worth doing? I am taking the head off of my 86 258 tonight. I am considering putting on a 4.0 head instead of reworking the one I have. It will cost me $125 for a junk yard head, $125 for an exhaust manifold, $??? for reworking the junk yard head. Can you really feel a big difference? I know everyone says 40hp but what about torque? 40hp sounds too good to be true to me.

wheres all the HP come from?? is it bigger valves,smaller chambers,bigger ports,??:confused:

I have no personal experiance, but they flow better. Do the search. All the info is here.

i dont see any thing about a 4.0 head swap??:mad:

I did a 4.0L head swap onto my 1990 Jeep wrangler 4.2L block. Tons more power!!! And I did a Mopar MPI at the same time with a borla header and stage 2 Jet performance chip, etc, etc. My Jeep runs like a champ now and its got 100,000 miles on the stock motor. It was like night and day after doing these conversions. :D I have an article on our website. Check it out. here is the link or go to my RoCk SkuLLz website and go to the Tech Articles. If you have any questions let me know.

4.0L Head conversion article:

http://www.off-road.com/jeep/new/40conv.html

Mopar MPI install article on 4.0L head:

http://www.off-road.com/jeep/new/mopar1.html


Bye Bye shitty as Carb!

http://www.off-road.com/jeep/tech/engine/40headconv/11.jpg

http://www.off-road.com/jeep/tech/engine/40headconv/129.jpg

http://www.off-road.com/jeep/tech/engine/40headconv/153.jpg

http://www.off-road.com/jeep/tech/mpi/72.jpg

http://www.off-road.com/jeep/tech/mpi/73.jpg

What did u use to fill i the extra cooling holes, is it really OK to use a two part epoxy like JB weld??? Ive heard that and have questions about its durability. I also heard the Mopar MPFI kit is a PITA, and doesnt work quite right on a 258, maybe its cause you swapped to the 4.0 head??!!

Try www.monsterslayer.com/jeep

Originally posted by jslamerman
What did u use to fill i the extra cooling holes, is it really OK to use a two part epoxy like JB weld??? Ive heard that and have questions about its durability. I also heard the Mopar MPFI kit is a PITA, and doesnt work quite right on a 258, maybe its cause you swapped to the 4.0 head??!!

I used some "quick-steel" super high strength epoxy putty stuff to fill in my holes. then just sanded the excess off untill it was smooth with the head. As for the MPI kits. A couple of my firends run them and there are perfect. They dont have quite as much power as i do but they still run like 4.0L's

do you lose your low end power and gain mid range. Has anyone done the swap and keep it carberatored.I'm looking for low to midrange power increase. THANKS:roxy:

If you swap on a 4.0 head you will keep your torque. The torque is mostly generated by the stroke of the piston. The 258 uses longer rod and crankshaft than the 4.0. What this means is that the 258 likes lower RPM's where the 4.0 likes higher RPM's. When you strap on the 4.0 head you are basically making a 4.5 liter stroker. The cool thing about that type of motor is that you get the horsepower of the 4.0 and the torque of the 4.2. All of that is wrapped up in a nice 6 cylinder package. I swapped in the whole 4.0 and I miss the torque now. I am going to swap in the 4.2 crank and rods though making my motor a 4.5 instead. Also, If you are going through all the trouble of swapping on the head. Go FUEL INJECTION. Don't waste your time on a crappy carb. You will be dissapointed if stay with the carb.
Have fun!
Joe

40hp is a lot for just a head swap. Wheres it come from?? BIGGER valves,smaller CC's,BIGGER ports,WHERE :question:

Originally posted by Ranger Dave
40hp is a lot for just a head swap. Wheres it come from?? BIGGER valves,smaller CC's,BIGGER ports,WHERE :question:

Mainly due to the design of the intake port. The older 258 heads used a port design on the intake side that was basically a 90* turn from intake manifold to valve. The 91 and later 4.0 heads used more of a 45* turn so it flows much better. The combustion chamber on the 4.0 head appears to be smaller as well, resulting in a compression ratio of about 9.5:1, depending on which head gasket is used.

Thank YOU PUTZBOY
do you know what the CC's are in the two heads :question:

Originally posted by Ranger Dave
Thank YOU PUTZBOY
do you know what the CC's are in the two heads :question:

No, I sure don't. Here's a great link I found while searching around for stuff. Lots of good info and side by side comparisons of the 2 heads.

http://monsterslayer.com/jeep/40Head/40Head.htm

I have yet to do mine, the head is sitting on the front porch right now. I may work on it this weekend.

Originally posted by Putzboy


No, I sure don't. Here's a great link I found while searching around for stuff. Lots of good info and side by side comparisons of the 2 heads.

http://monsterslayer.com/jeep/40Head/40Head.htm



Well, it sound like time to break in a new batch of 4.0 head conversion converts ... :flipoff2:

A few years ago, Mike Brink, Tim Weaver and I started comparing notes on the then new head conversion idea.
Tim started compiling the Q & A format plus the port and touque drawings for the article that I formated and store on my monsterslayer site that I posted and have been upgrading and maintaining since 1999. (25,000+ hits!)

In fact, at this moment we are having a lively and constructive session on the off-road BBS discussing and comparing notes on water jacket plugging techniques .....
Go to ...
4.0 head thread on ORC (http://bbs.off-road.com/wwwthreads//showflat.pl?Cat=&Board=offroadjeepshort&Number=702202&page=1&view=collapsed&sb=5)

what year 4.0 head should i look for. Is there any year better than the other :roxy:

Originally posted by Ranger Dave
what year 4.0 head should i look for. Is there any year better than the other :roxy:

91 and later HO motors. They have the "high port" design on the intake ports.

Stuman,
I'm certainly no expert.. But i've read something like 40 pages about this swap "researching it" and I must say I don't think anyone's losing their plugs.. first of all realize that a solid gasket not a holed one is going to be over those sealed holes and I for one don't believe that there will be enough pressure from either side of that hole"water pressure one sideonly?" to create enough force to push one out. If you've ever dealt with high dollar epoxy you'll know that it's incredibly strong. and In general it acts like a metal."contraction,expansion" lastly.. there are a couple machine shops on ebay that will sell you a fixed head. that in and of itself might be worth your time. since they also guarantee them.

best of luck
I'm certainly going to go this route if i
keep the straight 6. Mostly I'm inclined to keep the torque i have unless a higher torque engine is out there.no i'm not putting that cummins diesel in :flipoff2: