4.0 head on 4.2L engine

[lakev2]

Wanted to recommend this swap to anyone running a 4.2L, what a difference.

The power from the engine is so much smoother its like a night and day difference. I wouldnt say there is more low end power but just more across the rpm range. Before I did the swap I read it is a 40hp increase, my but dyno says thats about right, with the greatest increase above 1500rpms.

What I used was a head and exhaust manifold from a 97 grand cherokee 2wd. The head has the 7120 casting number, which still has the temp sensor in rear of the head.

Some notes for reference:

make sure to get the pushrods and rockers from donor engine, the pushrods are shorter on the 4.0 head than the 4.2.

the late 4.2 valve cover is a direct fit on the 4.2 head, so if you have one keep it, so you don't have to change the breather/pcv routings.

when using the 97 2wd grand cherokee exhaust manifold, also get the downpipe, the o2 sensor bung is in there and its much easier to mate the downpipe to the existing exhaust rather than making a whole new one.

modifications-

Cylinder head. blocking coolant ports, use packing peanuts(corn starch based, dissolve in water), and epoxy/cold weld of choice. block the coolant ports on the intake side of head.

Some 4.2L blocks have a larger head mating surface, to where the coolant passages do not need to be blocked, i wasn't that lucky. It is a good idea to check before you block them off.

the powersteering bracket required clearancing at top of bracket where it bolts to intake manifold.

the intake manifold, the bosses for the dowel pin-remove 1/8" or so metal from bottom of boss, do not have to grind all the way through to hole.

also on the intake manifold, had to remove lower rear and lower front corner piece, about an 1/8" triangle of material to clear exhaust flange.

auto tranny shift linkage bracket. had to cut a large v out of the bracket to clear exhaust flange. after removing the material, put a brace on the topside of bracket to make up for material loss.

on the exhaust, removed old downpipe and cut converter square flange off with 2" pipe remaining, to mate to downpipe from 97 chero.


It is a long swap, took roughly 15hrs or so this weekend to complete, started early saturday and finished by noon on sunday.

Tuning, depending on fuel delivery system your running you made need to retune the carb or adjust settings on computer. I run a gm based tbi system, and no tuning was necessary, once the engine warmed up and entered closed loop, the o2 sensor kicked in and all was good.

[inVERt'D]

Cool mod, i dig stuff like this.

[lakev2]

For a comparison test last week, I was over at a friends house with his 04 rubi lj.

what we did was a seat of pants comparison between the two engines.

mine 4.2-4.0 head, chevy tbi, ford ignition(85 300ci I-6), tf999 tranny, 4.10 gears, and 35"tires

his 4.0-stock, stock auto tranny, 4.88 gears, and 37"tires

we drove one then other a on the street and up to 65 on highway, hands down the old hodgepodge engine pulled way smoother with zero hesitation or delay. we don't quite fully understand yet why his newer stock 4.0 is not even close in comparison.

Right now when driving the rubi, it almost feels like it is constantly slipping in the trans or torque converter, when compared to the old hodge podge.

He said that jeep has driven like that since he bought it with 15k miles(now 44k).

I don't have much experience at all with 95+ engines with obd2 and electronic trannies, but we will be looking around for ways to put some pep into his engine next. I told him we should just make a 4.7 stroker out of his with a 4.2 crank/rods.

[jimmyrig]

Awesome write up... Do you have any details on the TBI swap?

[lakev2]

I have a few saved, basic jist of it was an AFI harness and chip, custom adpater to 4.2L intake, then took everything else from an 89 s-10.

I would have pics of the 4.0 head swap, but alas, the broken camera denied me...haha.

After I clean it up a bit, I will take some pics of the specific mods for the 4.0 head swap, the manifolds, trans bracket clearance, and powersteering bracket clearance.

Next mod on the old hodgepodge as i like to call it now, is to dump the ford i-6 ignition and convert it to a gm hei. Had a couple problems with the ford setup on the trail, that I always think about when I am on the trail.

[4rheel]

Lakev2, could i do this swap and use the later model intake and tbi
i have a 87 yj.

[lakev2]

Lakev2, could i do this swap and use the later model intake and tbi
i have a 87 yj.

There are 3 options for doing this swap.

87 stock intake/carb
87 stock intake/tbi system(chevy/howell/afi)

or use intake from same engine that head came from, also use complete fuel injection(multipoint) from donor, harness, computer, sensors, fuel system.

The Jeep tbi from the renix engines(87xj-till they went mpfi) isnt suggested to use because it is harder to adapt for minor gains.

The head swap was the best mod I made to the 4.2L as far as performance gains.

Fuel injection will add driveability and reliability on the trails especially.

Being in Cali, there are a few things to keep in mind, if you swap to a newer Jeep fuel injection system then to smog requires a BAR referee certification the first time.
The swap to chevy/howell/afi style system has a smog executive order registered with carb, so as long as it is done properly and has the smog sticker, then any smog shop can check it.

[lakev2]

Tbi Swap, a few key points and instructions.

The first step is to chop the stock harness to eliminate the computer and uncessary relays/wiring from the engine.

For the stock harness, the essentials of what will happen is the "Nutter Bypass". This will bypass feedback from the stock computer and carburator in relation to your ignition. For the Nutter bypass follow this link. Ignore the carburator stepper motor instructions and make the changes to the wiring listed.

http://www.jeepforum.com/forum/f8/ho...bypass-522262/

Once the electrics of the computer and carburator no longer affect your ignition. remove the stock computer, trace out every wire that came from the stock computer and remove it.
What you should be left with is a couple wires going to the ignition module, lights, distributor, and sensors under the hood.

The pulse air system(pipes from exhaust to air cleaner) can be completely removed. On the exhaust downpipe, cut/patch, or cap/patch, the 1" exhaust piping that operated for the pulse air system. Completely remove all of the vacuumn hoses and the air cleaner system.

Now is the best time to arrange the vacuumn that will be used. The temperature controlled vacuumn switch will continue to be used as well as the charcoal canister, and vacuumn storage ball thingy.
There will be 5 vacuumn lines on the temperture vacuumn switch, with one port remaining open. The vacuumn port on the intake manifold will still be used to supply the front axle disconnect and the defrost vents.
Here is the vacuumn diagram for the tbi system. other than these lines, all that remains is the vacuumn for defrost and front axle.



Now that the vacuumn and wiring is set to go. Install the tbi computer and harness, and related sensors. The kit I used for this was the AFI harness and their chip. AFI offers chips for the two most common computers found in S-10's(the tbi unit comes from a 4.3 S-10).

One sensor had to be added for my application, the temp sensor to tell the computer to enter closed loop mode. The stock 4.2L oxygen sensor works perfectly with the tbi system.

If you chose to scavenge a stock harness from a 4.3 chassis, then you should have enough experience to have labeled everything and have the necessary relays and fuel pump.

Fuel pump, AFI provided an external fuel pump, relay, and filter. This can also be aquired at local Autozone or other common parts store, the E2000 pump is the pump that is most commonly used. The fuel filter is a standard inline filter that goes BEFORE the pump. Not sure on part # of filter, but will look it up and edit, considering i probably need to change mine soon been 8k miles on it.
Mounting the pump, What I did to retain as much stock appearance was cut and flared the stock fuel inlet line, this was done 10" from the tank. The fuel pump is mounted on a bracket welded to the frame, that places it above the stock skid plate. The filter is just behind the skid plate for ease of access, and is still along the frame rail.

Now that the Wiring, Exhaust, Vacuumn and Fuel pump are taken care of it is time to mount the Throttle body. The adapter plates are available from three vendors that I found, AFI, Howell, and one Ebay vendor(can't remember name, search 4.2 tbi). When mounting the adapter plate after installing the screws and before mounting the tbi on top, use good quality silicone on top of bolt heads to prevent vacuumn leaks. If the front bolt is not sealed on top(bolts are recessed slightly) then it will leak.
Mount the tbi, and plug in the injectors.

For the air cleaner there are a couple options. With a smog legal TBI system it is perfectly ok to run an open style air cleaner.
From my experience open style air cleaners belong on hot rods not 4x4's.
The air cleaner and riser assembly from an S-10 can be made to work, to maintain a stock appearance, and utilize the heat riser tube/vacuumn lines.
To make the air cleaner and riser work, there are two "tangs" on a stock air cleaner riser, that must be ground off. Grind those off and then the riser can be mounted in any orientation on the tbi itself. The hose from the riser goes to the rear of the valve cover. The stock snorkel and air cleaner clear the brake booster almost as if by design. Hook up the vacuumn line from the air cleaner assembly as it was on the donor vehicle. The heat riser tube can be made to fit from the 4.2L manifold to the air cleaner as well.

What you end up with in the end is a 5lbs loss in bs and unbeatable driveability on the trails.

I will add some photos later this week. Will be mixed between 4.0 Head mods and TBI swap.

[lakev2]

Thinking about it, there is a chassis dyno at the shop I work at, I may put it on there sometime soon, just to see the result. I would have done it at the beginning but I have only recently moved close to work.

On the chassis dyno we usually see 80% of rated hp(flywheel) to the wheels with a manual tranny and around 70% of rated hp with an auto.

The stock 4.2L is rated at 120hp in 1987, that would equal 84hp with my auto stock. Will see if I can get 120hp to the wheels out of it that would be about 175 or so at the flywheel.

[inVERt'D]

soooo, where are all the pics?

[lakev2]

waiting on me to wash the engine bay, and finish a few other things...today found a front axle seal leaking, gotta get that changed out asap before the weekend.

Will get them soon. May run the dyno on friday after i fix the seal on front end.

[method916]

There are 3 options for doing this swap.

87 stock intake/carb
87 stock intake/tbi system(chevy/howell/afi)

or use intake from same engine that head came from, also use complete fuel injection(multipoint) from donor, harness, computer, sensors, fuel system.

The Jeep tbi from the renix engines(87xj-till they went mpfi) isnt suggested to use because it is harder to adapt for minor gains.

The head swap was the best mod I made to the 4.2L as far as performance gains.

Fuel injection will add driveability and reliability on the trails especially.

Being in Cali, there are a few things to keep in mind, if you swap to a newer Jeep fuel injection system then to smog requires a BAR referee certification the first time.
The swap to chevy/howell/afi style system has a smog executive order registered with carb, so as long as it is done properly and has the smog sticker, then any smog shop can check it.

Hey man, this is an old thread but the nearest to what I'm interested in and also speaks of my highest concern holding me back. MY concern is the process of smog as I too am in California.. If I understand right normally they did a visual based some old photo from some old book source. So of course I'll need to therefor visit a BAR referee station. I'm wondering exactly what they look at. I picture 90% of the vacuum lines being gone. I am to call them and ask questions but figured I'd write you too because you've gone through the process.

Also, I'm wondering if after 4 years, how you setup has treated you. I'm replacing the exhaust manifold anyways right now.

Shoot me a response when you can please.

Thanks,
David

[aw12345]

Matt hasn't been on here for a long time. He used a emission decal from a Howell setup. Ran this years EMC race with thisw setup, didn't finish because of a briken front axle shaft. Other than that he has had years of happy wheeling with his YJ

[ranover]

Looks like a great mod but a costly upgrade. Have you tried get a dyno run to know if there is any HP increase/improvement?