For those who have made the change from the 4.2 to the 4.0 head I am interested to hear your input.

I have an MPI 258 with a mildly ported and polished 4.2 head. Considering making the change for the improved power and quieter valvetrain.

My engine is definetly screamin on the freeway and I am only at 24-2500 RPM's.

So how impressed or happy are you?

Mine made all the diference in the world. woke the motor up out of a deep sleep.

THEN I went ahead and built a stroked 4.0, and all I can say is if you really want power get a 4.0 block and use your 4.2 inners and stroke it.


but for what it was the 4.0 head was my fav modification I had done

i did the 4.0 head change and it made a big diff in hi and lower rpm ranges.did a straight swap with no porting or polishing, didn"t want to give up low end grunt. lrm

No more pinging!
I gained a lot of RPM, meaning it didn't sound like the motor was coming apart at 3800rpm.
I went from 32's to 35 at the same time and the Jeep felt faster off the line on up to highway speeds.

My engine is definetly screamin on the freeway and I am only at 24-2500 RPM's.
The headswap wont change your RPM range, you'll still have a 4500 redline and the motor will sound the same. Only way to change that is with gearing or swapping in an entire 4.0.

Anyway, the headswap is well worth it. I started out with a mildly built 258 (833 pistons, 260 Comp cam, TFI, Weber carb). I had pretty good power with this settup, then i came across some interesting parts: a 4.0 HO head, clifford intake, and an Edelbrock 500cfm.

After 2 years of it sitting on the shelf i finally decided to swap it in. The power and torque increase was amazeing. Hands down more getup and go then a typical 4.0 and a lot of stock V8's. I used an XJ header and a glasspack with the settup.

Has anyone used the HESCO 4.0L head? The site claims 50 HP for the 4.2L and 30 for the 4.0L. Its sounds good but they want a ton of cash...so not worth it!!

Defintely worth it, done two of them, both from Clearwater in Florida. They've built and sold tons of these and the price is right, they arrive as promised, and they work well.

Linky (http://cgi.ebay.com/ebaymotors/AMC-JEEP-258-4-0-H-O-Conversion-Cylinder-Head_W0QQcmdZViewItemQQcategoryZ33617QQihZ008QQite mZ180077390403QQrdZ1QQsspagenameZWDVW)

I have seen the cleerwater heads before, seems awful cheap for a head ready to go. How many miles are you getting on these heads?

Anyone run 1.6 roller rockers with this head? How badly does it affect the lift?

I have seen the cleerwater heads before, seems awful jeep for a head ready to go. How many mile are you getting on these heads??

I have one with maybe 2 or 3000 and another with at least 40,000, bith working well. Couple of my friends are running them too. No problems with any of them.

The 4.2 pushrods are still used with a 4.0 head aren't they?

The 4.2 pushrods are still used with a 4.0 head aren't they?

Unless your head gets decked too much in order to clean up the welds, yes. This hasn't happened to me, but I know it can.

i have done 3 or 4 of them and every time the owner loves it. it makes them into hot rod 6's for shure. i would go for it!

Hey chrisjeep7 are you also using cleerwater heads?

Cant speak for the clearwater head, but just the standard 4.0 HO head makes a HUGE difference.

I used the 4.2 push rods with mine. they are a bit longer (1/16th) than the 4.0 ones. 9 5/8 vs 9 11/16th 's

Dan

Is there a provision for the temp sending unit in the 4.0 head? Mine on my 4.2 is located behind #6. Just curious where it is at on the new one.

Yep, same spot.

guess I'll be the lone nay sayer, granted I did mine using the old carb intake manifold and holley projection, so my fuel system wasn't the best possible to take advantage of the increased flow. Flowmaster, 2.5 exhaust, header, and a HESCO RVOB6, all done in quick succession to the 4.0 head swap got me a mild increase in mileage and the YJ slowed down going up hills just a bit less. There was a mild increase in low end torque and a mild increase in overall power.

I wish I had stroked it right off the bat... And take it for what it's worth but my advice is stop trying to POLISH THAT TURD, the 4.0 stroker is cheaper in the long run. and there's no comparing the power of the two.

My XJ has a 4.6 budget build stroker and it is easilly twice as powerful as the old 4.2 in my YJ was. I say "was" because it's been pulled for it's rods and crank for the stroker that's being built to replace it.

anyone taken a 4.0 head, had it rebuilt, and used the high temp epoxy to plug the holes.... I cant find a machine shop that will weld the holes for me..... Im getting inpatient, and wana get this swap done! Any problems with leaking?

Ive also heard NOT to use a MOPAR head gasket. They have rivets in them that do not allow that head to seat right on the block and cause leakage...

I have heard of the epoxy being used, but never done or seen it done.

I had mine welded up at a local place. Guy was leary at first but said he would try it and it worked out great. Was even better when I found out he needed a 258 head and intake, so we just did a swap.

I had mine machined for small freeze plugs. Maybe your shop could do that.

I tried that also actually, lol. I saw that on one of the writeups that I found... 3/4" flat freeze plugs.... The machine shop said that it would interfear with the valves or somthing like that.... they wouldnt do it.

Are the Exhaust/Manifold bolts the same size for both?

Are the Exhaust/Manifold bolts the same size for both?

For a 90 to a 91 they are

So I have the head on order, valve cover, head washers, bolts, exhaust, and exhaust bolts. Is there anything else I am forgetting?

Are the thermostat housings different?

I am looking forward to getting this set up.

So I have the head on order, valve cover, head washers, bolts, exhaust, and exhaust bolts. Is there anything else I am forgetting?

Are the thermostat housings different?

I am looking forward to getting this set up.

They are.

ARe you running it with the carb or the FI.

The carb you can use the 258 t stat housing, but the 4.0 one you need to use a 4.0 one because it has a temp sensor built into it. which you need for the computer

I have several customers who have done this swap with either just the head or the whole late model h.o.4.0 motors. Easily eliminate the wiring.

anyone taken a 4.0 head, had it rebuilt, and used the high temp epoxy to plug the holes.... I cant find a machine shop that will weld the holes for me..... Im getting inpatient, and wana get this swap done! Any problems with leaking?

Ive also heard NOT to use a MOPAR head gasket. They have rivets in them that do not allow that head to seat right on the block and cause leakage...

I had the same problem getting somebody to do it, every place I called said I was crazy for trying that, then my dad knew somebody that owned a engine shop that only does huge industrial diesel engines. He talked to that guy and they did it on the side for me and then told me not to tell anybody where I got it done, haha. I guess I got lucky so just be persistant, IMO weldin is 10x better than doin the epoxy route, at least you won't be worried about the epoxy not holdin and peace of mind is always nice. I have also heard the same thing about the Mopar head gasket, I just got the Fel-Pro from Autozone and it works great!

Are the Exhaust/Manifold bolts the same size for both?

I'm pretty sure they the same size cause I was one bolt short when I did mine so I went and swiped one off my 258 head. At least that's what I think I did.

I have several customers who have done this swap with either just the head or the whole late model h.o.4.0 motors. Easily eliminate the wiring.

When your customers switch to a 4.0 head or the entire 4.0, what intake do they run with your kit? I've been looking at the Clifford 4.0 intake.

I have never thought of this swap but it would be a great swap looking at it now.

my brother has a bone stock 4.2 in his 72 commando, will the 4.0 head bolt up to a block this early?

my brother has a bone stock 4.2 in his 72 commando, will the 4.0 head bolt up to a block this early?

yup, but there won't be a lot of value to the swap unless he does the fuel injection swap at the same time, IMO.

my brother has a bone stock 4.2 in his 72 commando, will the 4.0 head bolt up to a block this early?


The nice thing about his block is it will have 1/2" head bolts so he won't have to use the bushings to adapt the 7/16" bolts of the later 258's since the 4.0L heads require 1/2" head bolts. And I would agree on doing the fuel injection at the same time!

good advice guys, as far as the fi goes, aside form the head, intake and ecm, wouldnt the fuel pump need to be upgraded to an electronic one, i doubt the carb 5-9 lbs would be up to it.....

I belive your right.

When your customers switch to a 4.0 head or the entire 4.0, what intake do they run with your kit? I've been looking at the Clifford 4.0 intake.

It uses the stock late model intake. Our equipment mounts on the throttle body. That way you just swap in the older distributor and call it a day:grinpimp: