4.2L-4.0L head swap

[Choppermech]

First off, hello, nice site. Seems to be a good group of folks.

I just purchased a '72 (according to the data plate) or '77 (according to the body measurements) CJ5. She's in great shape either way. First Jeep I've ever owned after wanting one for quite a while. I'm very happy with it, but as we all know, you can never have enough. So... I've rebuilt a 4.2L and have heard that swapping out the 4.2 head for a 4.0 head with the cooling system holes plugged can add about another 40hp or so and might help improve full economy.
Anyone have any input on this?

 

[Bounty__Hunter]

Good choice on the swap, the 4.0L HO head is a big improvement. There are entire websites and forums for 4.0L mods, have you tried to google it?

 

[LVRockCrawler]

also... search on here - there have been posts in the past regarding it - should find what youre looking for ....

 

[Choppermech]

Thanks for the info.
Got the 4.2L back together and installed and after a complete rebuild she runs like a champ. Haven't even put the 4.0L head on it yet. Pulls real hard with the 4.10's and 33's.