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Discussion Starter · #1 ·
Has anyone put a 4.0 h.o. head on a 4.2 with a carburetor??? If so was it worth the gain if any??
I'm in calif.smog laws :(

 
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Discussion Starter · #3 ·
This question is one I was about to ask also. My neighbor threw a rod out the side of his 4.0 and the cam punched a hole in his timing cover so he's buying a remanufactured long block and is giving me his old head!!! I read Tim's writeup already and I too want to hear some first hand tales from people who didn't upgrade to MPI. I probably will do it whether the gains are noticable or not since my only costs will be machine work and gaskets, but I would still like to hear from others' experiences. If anyone can help with specific examples, please let us know!

 
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Discussion Starter · #4 ·
A local racecar mechanic, friend of my Dad's, is rebuilding my 258 and mating it to the 4.0 head. He said that he had heard about the swap and has always wanted to do one/wwwthreads_images/icons/smile.gif. However, when he took a look at the block and the head, he immediately saw that the head would have dome exposed water jackets that would have to be sealed. When I saw how much my 86 block (86 block in an 87, go figure?) let the head over lap and expose those triangular holes, I didn't think that I would trust a head gasket to seal them up. I asked the mechanic to leal up the exposed water jackets. I'll post how it was done when I get the engine back.

I also have the MPI waiting to be installed as soon as I get the engine back. The mechanic has had it for 3 weeks now. I'm getting kind of itchy to get it back. My jeep has been parked for ~4 months. I'm a senior in college and don't have time/money to get it done very fast. It was my daily driver. I'm lucky that my girlfriend lets me borrow her car for extended periods of time.

Robert87yj/wwwthreads_images/icons/tongue.gif
engine rebuild w/ MPI and 4.0 head underway
 
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Discussion Starter · #5 ·
Just did it, but also with significant modifications to the head. It is still running the Weber 32/26 and I think that clearly underpowers the system. Will be going with a 4bbl, probably a Holley. Actually the head work is the cost. The other costs are not that significant if you can find a good wrecked 4.0 vehicle. See my comments on this board about some of the trials in making the conversion that I have not read on other boards. The power and acceleration at low end is good, midrange is great, upper range is starvation. If you are in to just sound - it sounds more like a big block V8. My apologize to you V8 folks, but even more my apologize to the I6 persons.

Mindbender
CJ7 258
 
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Discussion Starter · #6 ·
Hey thanks for the info Robert. I was aware of the water passage problem and am planning to weld them shut before I take it in to be machined. What I am really interested in is performance gains. Will I feel it in the seat of my pants with the original carburetor and intake? Just in case someone wants to add that there is no substitute for cubic inches, that's what my '68 Camaro is for. I really want to keep the six because I like the low end torque. I'm just looking for a little more top end and may put MPI on eventually, so this will help with the pinging problem when (if)I do put it on. I hope this doesn't sound rude, but I am really looking for specific examples from those who have 4.0 heads with a carb already completed. Thanks again everybody. This board is absolutely tops for good, hard knowledge.

 
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Discussion Starter · #7 ·
Snowtow,
Welding up the water ports is a good idea, but it will depend on your block. I found from the research I did before choosing the 4.0head/MPI that different years of blocks mated up differently. My block had recesses that followed a curve a like a sine wave, out-in-out-in etc. The problem areas were where the block curved in between the pistons. The head I had was rectangular on the mounting surface to the block. The triangular water jackets on the outside were mostly exposed where the block curved in.

Good luck.

Robert87yj/wwwthreads_images/icons/tongue.gif
engine rebuild w/ MPI and 4.0 head underway
 

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It is scary to rely on just the gasket to seal off the water ports, but speaking from experience, it works fine. I have had mine for goning on 3 years now. You risk damaging the head while welding and machining it smooth. I can't comment on the carb, I have MPI.

Enjoying Montana's Big Sky (& rocks & rivers & mountians etc, You get the picture.)
 
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Discussion Starter · #9 ·
I checked with numerous welders and machinists and could find none that would weld the ports shut because of the closeness of the ports to the sides. Their concerns included warping of the head. So, I did the JB Weld think. And it has worked very well. I called the JB Weld company to confirm that it would hold, to check on the type of JB Weld and what and how I should prepare the ports for the JB Weld. The said yes it would handle the heat, that it had literally no shrinkage, that small write brush and a lacquer thinnner would be best. I did that, but ran into a problem with the JB Weld holding - it is fluid so it needed backing to hold it in place. I had read where someone said to fill the holes and then turn the head over on a very flat surface and the JB would flow downward. Well the JB is so fulid that I could trust that method....so...I and my machinist figured it needed some kind of backing that would not be permanent - and might even dissolve. So we ended up doing the following. Bought small flat bits of licorice candy - cherry flavored. Cut them in half so they would have a flat edge and slightly bigger than the port holes. Then, tied thread around the piece of licorice and pushed it through the hole and use a small screw driver to adjust it so it would back up the port. Then pulling snug on the thread tied it down to the studs for the head and used the value springs to tie to. From that point on it went very well. About 3-4 packages of JB Original. Allowed to dry for a couple of days, cut the thread, then ran hot water through the head to dissolve the licorice. The machinist shaved the extra JB that was standing slightly higher than the head. It fit. Since that time others have suggested that gummy bears might have added some class. I thought it better to be safe and fill them that to wait until I had a leak... even though I have heard some folks not have any trouble just using the head gasket. Good Luck.

Mindbender
CJ7 258
 
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Discussion Starter · #10 ·
Hey thanks for all of the tips about closing those water passages off. My block has the recesses also which would allow for a lot of head exposure. I'll give the JB Weld a try or possibly some other stuff that I have seen that isn't so fluid. Luckily I have a friend with a machine shop that all he does is race motors for a lot of local guys who run on the NHRA circuit. His quality is excellent and is a stickler for getting everything perfect. My only cost is a forged small block Chevy crank that's been collecting dust in my garage. I love having connections like that!

 
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