Cylinder Head Compatibility?

[Makahveli]

I visit the junk yard every now and then and rarely or sometimes don't see an explorer. I find that explorers just don't last long at these yards with there record on repairs or what-not. I'm gonna do some port and polishing soon and was wondering what heads are interchangable with the 4.0L engine? I heard some rangers and aerostars are but what years and will any modifications need to be made? I seen plenty of bronco2's and aerostars and there was only 1 explorer there that was already stripped. Anybody know whats what?

 

[boostranger]

91-94 4.0's use small dish pistons with large chamber heads

95-99?(maybe 2000) used large dish pistons with small chamber heads

99/00 and later used the same piston and chamber as the 95-99 but had smaller exhaust ports

all of these heads will bolt onto and of the other blocks.

early pistons with late heads gets you high compression (somewhere around 10.2-1)

late pistons with early heads lowers compression (8.0-1 or so)

I am currently running the early pistons with the late heads, with no other mods to the engine. Even running 93 octane i still have drivability problems.

I would not reccomend doind this unless you have a way of adjusting the ignition timing(EDIT) or have other engine modifications to allow better cylinder filling, such as ported heads, cam, big TB and mass air, etc

I will be going back to the correct head as soon as i get the $$

 

[Makahveli]

ignition? can that be done or fix in a programed chip?

 

[Makahveli]

higher compression means more or a chance to blow head gaskets right??

 

[MustangShane]

Only if your timing is off. Predetonation is what kills HG's.

 

[Maniak]

Finding good heads from a yard isn't going to be easy.. I went through 3 sets before I have up and just got a rebuilt set.. cost was $550 for a set of heads.. adn I got $150 back from my heads (as cores.. one was ok.. other was toast).

When you are looking at the heads.. the ones that say 93TM are better (thicker castings).. the 90TM is the same but thinner castings..

~Mark

 

[Makahveli]

Does port and polishing lower compression?

 

[Maniak]

port and polishing usually referes to the work done on the intake runners.. Not the combustion chamber. Since the work is above the valves, it doesn't affect the compression.

~Mark

 

[Makahveli]

I ment in the area that the valves seat open and close at

 

[Maniak]

If you do anything in the combustion chamber side to take away material, you will lower compression. I think you would have to take off quite a bit to make any difference though.

Last time I had the heads on of our 92 x (had a spark plug blow up in a cylinder) I took a sanding disc (2") and took out all the carbon etc from the walls of the combustion chamber (and top of the pistons).. Since I did that, I have had no pinging (I used to get some ping on hills in OD/Lockup when it was 105F+ out).

~Mark

 

[CDW6212R]

As the compression is raised, more cam is needed to purposely balance(lower) the bottom end cylinder pressure. A small cam with high compression forces the timing to be backed off to reduce the cylinder pressure. Matching the cam to a higher compression will allow good ignition timing to be maintained, achieving better overall power.

If you make a significant change in the compression, you need to make a change in the camshaft also. Regards,
Don

 

[Makahveli]

so are you saying only the 422 cam was worthy of that compression or 410 maybe?

 

[CDW6212R]

My point was that there is a different ideal cam for every different combination of major factors, compression being a huge factor. If the compression isn't changed very much, then the original cam will probably be fine.

As an example, Most 302 Mustangs since the early 70's have had compression ratios below 9.0:1, usually around 8.5-8.8. If one of those engines were built into an 10.5:1 engine, the stock or mild cams would be very poor choices for it. A ton of power can be had with the right cam, and raising the compression. It takes a very well matched cam to run the higher compression ratios, without preignition or loss of power.

If a big change is made to the compression, a better camshaft should be used. It should be chosen by a cam manufacturer cam tech. Try to consult with one before finalizing all engine parts. They are familier with a lot of combinations, but not all. Good luck,
Don