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I'm not planning on putting fuel injection on my Jeep. That said, is the flow really that much more than the AMC 258 i6 / 4.2l head with an Offy, Holley 390, and eventually either a header or maybe just a new stock manifold? I'm sure there will be a minute gain, but not as big as a swap w/ fuel injection.
I understand if I go MPFI or TBI injection since those heads were designed for them, but the AMC 258 i6 / 4.2l is made for carbs!
Is it a waste of money to put on the head, if there isn't anything wrong with mine when it comes time to rebuild?
I have a AMC 258 i6 / 4.2l with a 4.0 head and an MC2100 carb. The head swap is documented as a 30 to 40 HP increase and the carb is smooth and dependable, easy to build and tune. I may do a TBI one day but for the present I am quite happy with the performance and the simplicity of what I have.
I would have to see some proof that the injection will make serious power increase. I have come to believe the injection would make the start and idle better and eliminate the AMC 258 i6 / 4.2l ' title as "coldest natured engine ever".
The proof I mention would have to be along the lines of before and after dyno comparisons.
Was it something you had to do at the time, or a decision? Was the performance increase as substatial as they say (40-50 HP is about a 40-50% gain in original HP)? Finally was it the only addition done to the Jeep at the time?
Was it something you had to do at the time, or a decision? Was the performance increase as substatial as they say (40-50 HP is about a 40-50% gain in original HP)? Finally was it the only addition done to the Jeep at the time?
the head change is kind of a package situation with the exhaust and intake being replaced with it and when I did my CJ the carb was changed as well and the head had a fresh deck and 3 angle valve job.
It was not me that had the dyno done but one of the other members of this forum, I do wish I could remember who. The increase is real.
The head requires some prep work and of course you have to find one, the heads from the outfit in Orlando are fine, had one on my J-10 for a lot of years. You need headers or the stock 4.0 exhaust, if you can find one that is not cracked, 4.0 push rods and the ability to check and adjust the pre load on them. It is a bit more than an afternoon project but worth the effort. One of the best upgrades to this upgrade I have seen in to install a weld in bung to allow the use of the EGR valve. One day if I ever have the need to remove the head I will do this and kick myself for not thinking of it to begin with.
cuban, my AMC 258 i6 / 4.2l already had the MPI, and ran real well cept for the pinging on the highway. I swapped in a Clearwater prepped 4.0 head and have been very pleased. The end result power gain is clearly noticeable, and the pinging is gone too. Not sure if theres a difference between early and later AMC 258 i6 / 4.2l 's, but I re-used my stock pushrods with no issues. With the help of a buddy, we had the whole swap done in about 5-6 hours (give or take a few beers) and she was ready to be towed to the exhaust shop.
I did the 4.0 head with the older pushrods as well. Everything swapped over from the AMC 258 i6 / 4.2l setup,... Holley, Offenhauser manifold, headers. The only thing I did to make it work was Dremel 2 half-moon slots under the intake runner flange(front and back) to allow the manifold to rest ON the 4.0 intake mounting pins...this adjusts for the raised Hi-port and makes sealing WAYYY easier.
I did the 4.0 head with the older pushrods as well. Everything swapped over from the AMC 258 i6 / 4.2l setup,... Holley, Offenhauser manifold, headers. The only thing I did to make it work was Dremel 2 half-moon slots under the intake runner flange(front and back) to allow the manifold to rest ON the 4.0 intake mounting pins...this adjusts for the raised Hi-port and makes sealing WAYYY easier.
I did the 4.0 head with the older pushrods as well. Everything swapped over from the AMC 258 i6 / 4.2l setup,... Holley, Offenhauser manifold, headers. The only thing I did to make it work was Dremel 2 half-moon slots under the intake runner flange(front and back) to allow the manifold to rest ON the 4.0 intake mounting pins...this adjusts for the raised Hi-port and makes sealing WAYYY easier.
I have a preference of assembling the head and manifolds before setting them on the block. A lot easier to line things up and torque things.
I think you have 7/16 head bolts and the head has 1/2" holes so some shims may be in order and you will need some larger washers to bridge the manifold mounting bolts.
I kind of prefer studs to the original bolts.
The actual change does not take a long time but sourcing everything and getting all your prep done takes a bit of time and work.
I had already read about the 1/2 spacers for the head bolts. I really wish my lathe wasn't up at my fathers house in PA. It would be so much easier to create those hold down spacers.
A good trick is to cut the heads from two 7/16 x as long as you can find bolts, thread them into the block to aid in lining up the head. this keeps the gasket in place, you do need to be able to lower the head level. I use an engine hoist to set the head. Some of you young bucks may just muscle it on but that ship has sailed for me. the head with manifolds attached is pretty heavy.
I'm not planning on putting fuel injection on my Jeep. That said, is the flow really that much more than the AMC 258 i6 / 4.2l head with an Offy, Holley 390, and eventually either a header or maybe just a new stock manifold? I'm sure there will be a minute gain, but not as big as a swap w/ fuel injection.
I understand if I go MPFI or TBI injection since those heads were designed for them, but the AMC 258 i6 / 4.2l is made for carbs!
Is it a waste of money to put on the head, if there isn't anything wrong with mine when it comes time to rebuild?
First of I am biased because We all know that I am a huge supporter of the MPFI conversion here considering my side business
The AMC 258 i6 / 4.2l intake runners are doglegged meaning that for air and fuel to leave your intake manifold (dry or wet) it has to flow through a 90 degree corner which naturally slows the velocity of the air and fuel. The 4.0 runner is at about a 45 ish degree angle from the intake manifold to the intake valves. The fuel/air mixture has a much more direct route into your cylinders.
You will see a night and day difference if you retain the the Carb on the 4.0 head, this is very well documented from people past experience.
If you late plan to go FI dont flirt with it, do the MPFI. You may as well skip TBI and go to the MPFI.
It isn't that much more complicated than the TBI, trust me I make these harnesses all the time for people. And honestly your are probably going to spend more on a bolt on TBI kit than you would pulling a 4.0 MPFI stuff from a donor if you buy new. And if you go junkyard TBI or buy a used bolt on kit there will probably more complication in the long run with figuring out what the PO forgot to give you or broke as well as the fact that even bolt on kits generally require tuning.
TBI will just be like having a very very well tuned carb. The computer will adjust the fuel to maintain the proper air to fuel mixture so you will see a good deal of improvement from your carb. The TBI still requires a wet intake and relies on the vacuum and gravity to feed your runners, as with your carb you will still get a richer mixture in the center cylinders than the ends.
MPFI will give you Night and day difference in performance. First the injectors are squirting the fuel directly into the runners so every cylinder has the same mixture of fuel/air. This will Improve the smoothness of your idle as well as the responsiveness of your throttle.
The 4.0 MPFI is also sequentially fired so the injector fires as the intake valve is opening which improves the atomization of the fuel.
If you can go MPFI definitely do it, you will not be disappointed. If the wiring is intimidating to you just PM me when the time comes and I will gladly be your guide to MPFI for free if you don't want one of my harnesses and want to make you own.
I have a AMC 258 i6 / 4.2l with a 4.0 head and an MC2100 carb. The head swap is documented as a 30 to 40 HP increase and the carb is smooth and dependable, easy to build and tune. I may do a TBI one day but for the present I am quite happy with the performance and the simplicity of what I have.
I would have to see some proof that the injection will make serious power increase. I have come to believe the injection would make the start and idle better and eliminate the AMC 258 i6 / 4.2l ' title as "coldest natured engine ever".
The proof I mention would have to be along the lines of before and after dyno comparisons.
Check out Tinman's info, He did a dyno with the carb/AMC 258 i6 / 4.2l head, carb/4.0 head, and MPFI and 4.0 head. Should be all the hard evidence you need.
