4.0 vs 4.2 what would you do?

Got a 98 4.0 with 130K miles on it.
Buddy has a rebuilt 4.2 with some 4.0 heads
Would I really gain alot by swapping out the 4.0 for the 4.2? Or should I just hang on to the 4.0 forever?
Have headers and muffler already just debating which engine they should go on.
thanks

Garthbmn7 said:

Got a 98 4.0 with 130K miles on it.
Buddy has a rebuilt 4.2 with some 4.0 heads
Would I really gain alot by swapping out the 4.0 for the 4.2? Or should I just hang on to the 4.0 forever?
Have headers and muffler already just debating which engine they should go on.
thanks

Click to expand...

:viking: So ... how many 4.0L heads can he fit on one 4.2L engine?

JK!

Your 4.0L is barely broken in. A friend and I have been debating the merits of tossing in a 4.2L with 4.0L heads rather than building a stroker, but that's for when the 4.0L ever dies -- which takes a looooooong time. You might gain a small amount of low-end torque, you would probably lose some top-end zip and RPMs. Gas mileage might stay the same, might improve by 1 or 2 MPG.

I don't see the point. If your engine was blown or dead, I'd say go for it by all means, but I can't see yanking a perfectly good engine for the very slight increases I think this would generate.

Garthbmn7 said:

Got a 98 4.0 with 130K miles on it.
Buddy has a rebuilt 4.2 with some 4.0 heads
Would I really gain alot by swapping out the 4.0 for the 4.2? Or should I just hang on to the 4.0 forever?
Have headers and muffler already just debating which engine they should go on.
thanks

Click to expand...

Combine the two and build a stroker. Go to my performance and my stroker websites for more info.
If the stroker isn't your cup of tea, a 4.0 head swap onto the 4.2 short block would be the next best thing. This'll really wake up the 4.2 (especially if you get rid of that horrible Carter 1bbl carb and replace it with a Weber 2bbl version); potentially a 40hp/20lbft gain from the head swap alone and possibly another 10hp from the carb swap. Gas mileage should actually improve because the engine will be much more efficient, though you might see a drop if you're too keen to use the extra performance.
_______________________________________________________________
- 1992 4.0 XJ Laredo UpCountry with modifications - 172k miles - AX15, NP231, D35c, D30
Estimated 240hp@5250rpm/280lbft@3500-4000rpm, 1/[email protected], race weight 3465lb
- Future mods -
4.6L stroker (under construction)
- Websites -
Jeep 4.0 performance, 4.6L stroker build-up
- Tech Webpages -
CTS resistor trick, Dual electric fans, IAT sensor relocation, Intake manifold heatshield, MAP adjuster, Oil temp. gauge install
- Info Pages -
Automotive formulae, Jeep 4.0 cam specs, Jeep engine dyno graphs

A friend of mine has the 4.0 head on the 4.2 and it really did alot along with the weber carb. Now we just did a fuel injection conversion from a 4.0 and it gets 20 mpg thats better than I get.