4.2 to 4.0...logical???

[Beefy85CJ7]

1050414

I found an 87 cherokee with a strong running 4.0l engine in it...128k rebuilt...and i also own an 85 cj with a 4.2l in it in need of hp and gas mileage...now would i get any real gain outta doing the swap (while also putting my intake and holley carb on the 4.0, therefore eliminating the fuel injection)...you may be wondering why i wanna keep my carb...well simple really...i like the throttle response of the holley, the cherokee is an automatic (therefore needing the right computer to adapt to the new setup with the T-5 transmission), and i'll have a problem with the bellhousing since i have no cut out or flywheel for the "speed sensor"...so i figured i would stay carbed for now til i can solutionize these problems...



So anyway...my real question is how much of a benefit or loss this would give me???...will there be a good increase of hp's? too much decrease in torque???...i go trailing alot and appreciate the low end torque of the 4.2l so this is a concern...but need the hp's and gas mileage of a 4.0l for daily on road use...Anyone done this before or can shed light on the subject???

[addsig]

 

[RayOvac]

1050504

If its an 87 cherokee then its not the 4.0HO...the engines changed slightly in HP in 91.



The 4.0 engine from 87-90 is the "Power Tech" 177HP @ 4750 rpm, 220ft lb @ 4000 rpm(I think its TBI)



In 91 they went to the MPI "Power Tech HO" 190 hp @ 4750 rpm, 220 ft lb @ 4,000 rpm



96 and newer got an update....225ft lb torque @ 3000 rpm



Your 4.2 gets around 112HP @ 3200rpm and 210ft lb torque @ 2000 rpm



With the engine you are getting you will get around 65 more HP...but you will lose much of the great low end torque....the torque is there but at 4Krpm as opposed to 2K. Honestly if it were me I would keep the fuel injection....that is where your real gain in HP and mileage will be...I have never heard of someone running a 4.0 with a carb. I'm not even sure if the 4.2 intake will bolt to the 4.0 (I don't think it will). I would try to get a computer and flywheel off of a 4.0 with a manual transmission behind it so you could have everything balanced right....I don't think the 4.2 flywheel will work. Also for the crank position sensor you could just cut out a hole in your bell and drill and tap a couple holes to mount it.





[addsig]

 

[Bounty__Hunter]

1050525

I don't think it would be worth the trouble, unless you were switching to a HO 4.0L AND keeping the fuel injection. Keep that torquey 4.2L

[addsig]

 

[jprtroy]

1050528

When I installed my Mopar multi-port fuel injection on my 258 (4.2l) I had no idea how responsive it would become! There is no carburator in the world (in my mind) that can match the responsiveness of my kit! I have ABSOULTLY no pause/hesitation in my throttle now. It's like a friggin "pocket rocket" motorcycle engin now.

Needles to say, I was very pleased. One of the drawbacks of carburation, is they don't play well on angles! (going up rocky hills!) Fuel injection, does play well on hills!

Can't really say I've ever heard of anyone swappin in a fuel injected motor to carb it.

[addsig]

 

[Beefy85CJ7]

1050569

ok guess i'll stay with the 4.2l for now...just wish that for that torque it wouldn't guzzle so much gas...i'm getting around 10 mpg, if that, with the upgrades i already did...any tips to increase gas mileage with this old beast? and/or hp's?[addsig]

 

[Bounty__Hunter]

1050638

<TABLE BORDER=0 ALIGN=CENTER WIDTH=85%><TR><TD><font class="pn-sub">Quote:</font><HR></TD></TR><TR><TD><FONT class="pn-sub"><BLOCKQUOTE>getting around 10 mpg, if that, with the upgrades i already did...any tips to increase gas mileage with this old beast? and/or hp's?</BLOCKQUOTE></FONT></TD></TR><TR><TD><HR></TD></TR></TABLE>



Switch to synthetic fluids in the engine/transmission/transfer/diffs. This will reduce parasitic drag on the engine. Change your driving habits, take more time starting from a dead stop and shift sooner (I know, not as fun). Slow down to the speed limit, it will drastically improve mileage. Make sure the engine is tuned up, including no vacuum leaks and the PVC system operating correctly.



Only a small list

[addsig]