4.0 Jeep head swap in a 4.2 L motor, test & tune 1/8 mile racing

After the 4.0 head swap in a 4.2 L motor, we got good results in the 1/8 mile test and tune. The CJ7 went .6 better in the eight mile ! This is a 1985 CJ7, 5 spd., motorcraft 2100 carburator, 4.56 gears, 35' tires, 6" lift, weight is 3740 lbs with driver and the best speed in the 8th was 60.54 mph. at Homestead Miami Speedway.

[@wiso2759]

Great... very Nice driving skills

[@xMSTWNTEDx]

Whooped that dodge! Very impressive

[@MrTheHillfolk]

Back in 87 a buddy's parents got a new Cherokee with the 4 liter. When he got his license finally he drove it occasionally. We were kinda shocked it whooped up pretty bad on a late 70s smogger Vette at a couple runs at a stoplight dragrace, it had some nut.

[@benjamintresham9649]

Some of the fastest cars are still carb mate.

[@jodell2023]

Awesome. I've been in debate of what to do.i got a great 4.2 and I was wanting to do the head swap. Anyway you would write up a build list of what you used and had to do?

[@81eagle]

You smoked him! Did the same swap to my Eagle, the 4.0L head really woke it up. I also installed a Comp Cam and some homebrew TBI. A little Moab action. kzbin.info/www/bejne/pqW2h6iBmsRljZI

[@Table1000]

nice run. Clifford performance claims that throwing chevy valves in a 4.2l head will even out flow the 4.0. How is mpg on a normal drive? thanks

[@johanmelv0gue595]

stroker?

[@benjaminsmith2899]

I have have a cammed up 1999 Cherokee. Maybe we can race?

[@chaunpatrick9549]

I am looking at a 4.2 motor locally for $200 to take the crank out and swap in my 4.0 Grand cherokee. Do you think I will run into any problems at all with the crank fitting? I am thinking I shouldnt have any issues. But me thinking is No Bueno sometimes. I haven't found too much on swapping the 258 crank.

[@STRAPPARTS]

yes thats how you built a stroker motor

[@bradleycampbell5933]

there are two ways for a stroker. from what i have read is the 258 crank. and you can go with 4.0 rods is the better way. or the 258 rods.. the pistons needs to be replaced because the height of the piston vs the location of the wrist pin vs the block deck needs to be sorted out.

[@MrPryceTagg1]

Looking to do the same thing, right now I have a carbed 4.0, just rebuilt,but I do have a complete 4.2 on the stand.What cam did you put in

[@STRAPPARTS]

MrPryceTagg1 The block is the 4.2 with the original 4.2 cam, crank and pistons, remember this is a push rod engine and the cam is in the block and Not the head. Hope this helps!

[@jon_pitt]

Wait, I just picked up an 89 wrangler with a 4.2 that needs help. Wtf do I need to do? Bro I need details, good lookin out..

[@URDAD939]

kzbin.info/aero/PLpcfFxafn4EL-VfrKQmaRtPM67vUthHXV

[@CmIFyC87]

Robertayyy what parts you looking for. Can probably look at shipping you some PM me

[@matt-jv8gh]

wait, you swapped the 4.2 head on and kept the carburetor?

[@STRAPPARTS]

Matt, we wanted to keep the carb! because is a CJ7 and for simplicity sake. The 4.0 head breathes better than the 4.2 because it has larger valves and ports!!!!

[@matt-jv8gh]

what kind of modification to the manifold did you have to do? and is there any significant gain or loss of carb over fuel injection?

[@91ranger1]

what type of header did you go with after the 4.0 head swap?

[@STRAPPARTS]

nate b : I used the one sold by Auto zone for the Jeep Cherokee 1990 4.0.

[@STRAPPARTS]

Note that there are a few places were trimming/grinding is required to fit the carbed intake on the 4.0 Head.

[@91ranger1]

STRAPPARTS : I figured a little modification had to be done for exhaust. I'm in the middle of a swap now. what head did you end up going with? also any other add ons? I got the 7120 and thinking of a upgraded cam for it

[@STRAPPARTS]

from a 97 or 98 Cherokee at the junkyard.

[@91ranger1]

thanks for the reply's. I hope mine turns out as well as yours once I'm done.

[@baileyfeldman5158]

what trans are you running

[@STRAPPARTS]

bailey feldman T5