I've posted several times before about this while researching this project; I finally got this thing done and decided it deserved its own thread.
As indicated in the thread title, I did the 258 to 4.0 cylinder head upgrade and am very satisfied with the results.
When I bought my '83 CJ-7 a few years ago, the PO had removed all the emissions equipment so it wouldn't pass inspection. For a little more money than it would have cost to fix all that, I was able to install a MPFI system from CustomEFIS. I wanted to swap the 258 cylinder head for the 4.0 version but just wasn't able to do it at the time but when the head gasket blew a few weeks ago I decided to take advantage of the opportunity to do the upgrade.
I finally had the time - and the weather - over the end of last week and through the weekend to get the job done.
I had already installed MPFI so I didn't have to deal with fuel injection this time around, only the cylinder head and associated parts.
I purchased a head from AutoZone for approx. $375 ($100 core charge, refunded) and was able to specify the 7120 casting code, which they actually got right on the first try. I also ordered a set of pushrods just in case, which turned out to be a good move because the 4.0 pushrod is a slightly different length than the CJ part. While I was at it, I bought new pivots and bridges because they were very inexpensive. Also got the gaskets (4.0 versions), etc. Only parts I reused were the cylinder head and rocker arm bolts.
Then I went to Pull-A-Part where I got a valve cover and associated plumbing, stainless header with expansion joints, exhaust pipe and valve cover for $48.
I got a good metal valve cover and exhaust pipe from a '94 Grand Cherokee, but that vehicle had the standard exhaust manifold so I kept looking until I found a '96 that had the one with expansion joints. Out of about eight Cherokees of appropriate vintage in the yard that still had an exhaust system, only two had the desirable header and one of those was an engine fire victim so I felt fortunate to get one in good condition.
Note - I had heard that the standard header had a tendency to crack. I looked at a good number of Cherokees with the standard header, and although they appeared to be made of stainless, every one of them had a visible crack where the two groups of three pipes from the front and rear cylinders come together.
Removal of the old parts was straightforward. I'd been running synthetic oil (Mobil 1) in part because I'd always heard about its cleaning properties, and the pushrods, rockers, etc. in the old head were clean and shiny with no deposits at all, so I felt good about re-using the rockers. Most of the ones I looked at in the junk yard varied from crusty to gunked-up, so I'll continue using the Mobil 1.
Sorry I don't have a great tale of struggle and strife to entertain y'all with, but for once the new parts just bolted right up with minimal fuss. As suggested in other threads on this topic, I acquired some of the biodegradable packing peanuts and stuffed them into the coolant passages that are supposed to be blocked, then used pop-sickle sticks to lay in some J-B Weld. (Mineral spirits works well to dissolve and wipe off the excess.) There was some settling as the JB Weld seeped in amongst the peanuts, so I decided to make a second pass with the gray goo. If you do this be sure you pack the passages well. A poster in another thread mentioned that the JB Weld step might not really be necessary as the 4.0 head is solid in that area, but I decided not to tempt fate (or the head gasket) and do it anyway.
One thing that I hadn't seen mentioned anywhere - if so I missed it - is that the head bolts on the CJ are 1/2" diameter while the YJ ones are 9/16" so if you aren't planning on re-using your head bolts you should order the CJ parts.
The only real challenge was how to muscle that heavy new head into place. I weighed it, and it was 75 pounds before adding the rocker arms and pivots so the 77 pounds reported elsewhere is pretty accurate.
After experimenting with various approaches, I remembered I had a block and tackle that my father-in-law used to hang various four-legged, antler-wearing critters he'd shot, so I propped the hood up with a couple of two-by-fours and used the b-and-t to lower the head into place. Total piece of cake, made even easier when my wife showed up to hold the rope while I steered the head into place. I used the 22-45-110 method to torque it all down (100 ft-lbs w/Lok-Tite for #11).
All in all, I was completely amazed at how simple the work turned out to be. It took me all weekend, but only because this was my first such project and I was extra cautious not to screw anything up.
Now, to what you're all wondering about: the "after." (Again, bear in mind that unlike all other posters I've seen, I already had MPFI installed, using a '91 intake manifold. The improvements I note are thus identifiable as resulting from the head swap itself, not the total upgrade.) Even though I already had fuel injection and it started easily, the engine now leaps to life as soon as I turn the key and idles quietly, though perhaps a tad faster than before.
In terms of performance, I don't know about 40 extra ponies, but I can certainly feel a significant seat-of-the-pants difference. Peak power seems to have moved up to a slightly higher rpm, although that's a little misleading because there's an overall power increase. There's still plenty of torque at the low end but the peak is at higher rpms than before. I notice a substantial increase in acceleration from a standing start; my wife was following me to the muffler shop and commented on how fast it took off. If I punch it, for example coming out of a parking lot and turning into the road, the wheels will try to spin, which they never did before.
Roll-on acceleration is brisk, and the engine accelerates easily with none of the urgency the old 258 always seemed to have. Once at highway speed it just lopes along smoothly at 70-75 with lots of throttle left. I also noticed that it rarely downshifts when accelerating (automatic tranny) as it used to do. In traffic at medium speeds, it gets up to speed effortlessly and then seems to just coast along, compared to what it used to be like. While it will never be a sports car, it has definitely transformed my CJ and given it a new attitude.
That's the quick version; I'll be happy to answer any questions anybody might have. Below are a few pictures; the first is my block-and-tackle solution for installing the new 77-pound head. Images two through five are the old exhaust manifold, the new header I used, the type that you don't want because it's prone to crack and a picture of the typical crack on that type of header.
As indicated in the thread title, I did the 258 to 4.0 cylinder head upgrade and am very satisfied with the results.
When I bought my '83 CJ-7 a few years ago, the PO had removed all the emissions equipment so it wouldn't pass inspection. For a little more money than it would have cost to fix all that, I was able to install a MPFI system from CustomEFIS. I wanted to swap the 258 cylinder head for the 4.0 version but just wasn't able to do it at the time but when the head gasket blew a few weeks ago I decided to take advantage of the opportunity to do the upgrade.
I finally had the time - and the weather - over the end of last week and through the weekend to get the job done.
I had already installed MPFI so I didn't have to deal with fuel injection this time around, only the cylinder head and associated parts.
I purchased a head from AutoZone for approx. $375 ($100 core charge, refunded) and was able to specify the 7120 casting code, which they actually got right on the first try. I also ordered a set of pushrods just in case, which turned out to be a good move because the 4.0 pushrod is a slightly different length than the CJ part. While I was at it, I bought new pivots and bridges because they were very inexpensive. Also got the gaskets (4.0 versions), etc. Only parts I reused were the cylinder head and rocker arm bolts.
Then I went to Pull-A-Part where I got a valve cover and associated plumbing, stainless header with expansion joints, exhaust pipe and valve cover for $48.
I got a good metal valve cover and exhaust pipe from a '94 Grand Cherokee, but that vehicle had the standard exhaust manifold so I kept looking until I found a '96 that had the one with expansion joints. Out of about eight Cherokees of appropriate vintage in the yard that still had an exhaust system, only two had the desirable header and one of those was an engine fire victim so I felt fortunate to get one in good condition.
Note - I had heard that the standard header had a tendency to crack. I looked at a good number of Cherokees with the standard header, and although they appeared to be made of stainless, every one of them had a visible crack where the two groups of three pipes from the front and rear cylinders come together.
Removal of the old parts was straightforward. I'd been running synthetic oil (Mobil 1) in part because I'd always heard about its cleaning properties, and the pushrods, rockers, etc. in the old head were clean and shiny with no deposits at all, so I felt good about re-using the rockers. Most of the ones I looked at in the junk yard varied from crusty to gunked-up, so I'll continue using the Mobil 1.
Sorry I don't have a great tale of struggle and strife to entertain y'all with, but for once the new parts just bolted right up with minimal fuss. As suggested in other threads on this topic, I acquired some of the biodegradable packing peanuts and stuffed them into the coolant passages that are supposed to be blocked, then used pop-sickle sticks to lay in some J-B Weld. (Mineral spirits works well to dissolve and wipe off the excess.) There was some settling as the JB Weld seeped in amongst the peanuts, so I decided to make a second pass with the gray goo. If you do this be sure you pack the passages well. A poster in another thread mentioned that the JB Weld step might not really be necessary as the 4.0 head is solid in that area, but I decided not to tempt fate (or the head gasket) and do it anyway.
One thing that I hadn't seen mentioned anywhere - if so I missed it - is that the head bolts on the CJ are 1/2" diameter while the YJ ones are 9/16" so if you aren't planning on re-using your head bolts you should order the CJ parts.
The only real challenge was how to muscle that heavy new head into place. I weighed it, and it was 75 pounds before adding the rocker arms and pivots so the 77 pounds reported elsewhere is pretty accurate.
After experimenting with various approaches, I remembered I had a block and tackle that my father-in-law used to hang various four-legged, antler-wearing critters he'd shot, so I propped the hood up with a couple of two-by-fours and used the b-and-t to lower the head into place. Total piece of cake, made even easier when my wife showed up to hold the rope while I steered the head into place. I used the 22-45-110 method to torque it all down (100 ft-lbs w/Lok-Tite for #11).
All in all, I was completely amazed at how simple the work turned out to be. It took me all weekend, but only because this was my first such project and I was extra cautious not to screw anything up.
Now, to what you're all wondering about: the "after." (Again, bear in mind that unlike all other posters I've seen, I already had MPFI installed, using a '91 intake manifold. The improvements I note are thus identifiable as resulting from the head swap itself, not the total upgrade.) Even though I already had fuel injection and it started easily, the engine now leaps to life as soon as I turn the key and idles quietly, though perhaps a tad faster than before.
In terms of performance, I don't know about 40 extra ponies, but I can certainly feel a significant seat-of-the-pants difference. Peak power seems to have moved up to a slightly higher rpm, although that's a little misleading because there's an overall power increase. There's still plenty of torque at the low end but the peak is at higher rpms than before. I notice a substantial increase in acceleration from a standing start; my wife was following me to the muffler shop and commented on how fast it took off. If I punch it, for example coming out of a parking lot and turning into the road, the wheels will try to spin, which they never did before.
Roll-on acceleration is brisk, and the engine accelerates easily with none of the urgency the old 258 always seemed to have. Once at highway speed it just lopes along smoothly at 70-75 with lots of throttle left. I also noticed that it rarely downshifts when accelerating (automatic tranny) as it used to do. In traffic at medium speeds, it gets up to speed effortlessly and then seems to just coast along, compared to what it used to be like. While it will never be a sports car, it has definitely transformed my CJ and given it a new attitude.
That's the quick version; I'll be happy to answer any questions anybody might have. Below are a few pictures; the first is my block-and-tackle solution for installing the new 77-pound head. Images two through five are the old exhaust manifold, the new header I used, the type that you don't want because it's prone to crack and a picture of the typical crack on that type of header.
