how can i make power with a 4.2

MikeB

MikeB

New member
i have an 87 yj with 4.2, im just wondering if there are any little things i can do to get a little more power out of it, right now im considering doing a head swap, i just have to find the parts to do it.
as you guys probably know, there are a lot of vaccum lines on those I6 engines. i have heard that some can be bypassed which can result in a little more horsepower....if anyone know about this or any other little tricks to get a little more out of that motor, please let me know
 
judge09 said:
Start with the easy stuff, better airflow. Intake and Headers. Then I would go the cam route.
Click to expand...

X2, but dont waste your money on a computer chip or a tb spacer. the chip can have adverse affects that far outweigh the performance (it can screw your compter up and cost you several hundred) and personally i think that the tb spacer is just a waste of money. dont forget, your still choking your engine if you open up one end and not the other. what i mean is if you do headers and intake (highly recommended, the headers on my 4cylinder are the reason i can go uphill on the interstate) get a muffler that will let it breathe a little more. there are all kinds available, i love the sound that comes out of my dads borla catback system on his rubicon. its mellow and mean... not load at all but you know that there is something there.
 

RE: what

Depends on how much power you want. The factory cylinder head is somewhat of a determining factor. You can build a nice little engine around the factory head, but it's the biggest hurdle if you plan to make a fire breathing monster out of it. Without a power adder(nitrous or forced induction), the key to wringing all the power out of the 258 is to reverse all of the compromises they made at the factory in an attempt to keep it emissions compliant. The exhaust sucks. The carb and intake manifold sucks. The ignition curve sucks. The camshaft sucks. The cylinder head sucks. The compression ratio is depressing. The......can I stop now?

What do you expect from this engine? How much power do you want?
 
a webber carb conversion elliminated my vaccum lines and computer and gave me serious horse power gain.you get carb spacers, all the gaskets, new carb, reusable filter, chrome filter covers and 15 to 20 horse power gain. easy to instal basicly plug n play. kit is by far the best 500.00 dollars spent watch out for emission laws though.- this is not an ad for webber carbs!
 
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I put a motorcraft 2100 carburetor from a mustang 5.0L on my jeep's 4.2L with a tb spacer that i drilled holes in to use as an adapter...Much cheaper than going with a webber, gets rid of all those nasty vaccum lines and still packs a punch...
 
Hey if you watch Trucks on SpikeTv, They'll show you. All they know how to do is Update exaust and intake for more power.
 

Holley 2300 2bbl with a headman header stock intake. Made my 4.2 come alive.
 
I have a 79 cj5 I6 4.2 with 31x10.50 and 3.55 gears not much has been changed on it yet (work in progress ) any way /\I took the old carter 2barrel and replaced it with a weber 32/36 and it took a little tweaking but it is runnking pretty good. The problem I am having it\s with the vacuum at idle the vacuum is pulling 20 psi and the advance module is fully open, I have been looking for different places to move the vac line but have not found any place to re-route it to. want to put headers and different intake on it . I considering centrifigal advance instead of vacuum until then it is up to the vacuum advance. it idles fine but have no power due to it being fully open at idle. any help would be appreciated thanks
 
I am using a dual fuel(gas and propane) system, and it kicks arse! It's cheap($300.00) and easy to put on. I bought an Impco system minus tanks and hoses for $120. About a bill for a good alluminum 8 gal. tank, and about $80 in wireing switches and hoses! Would do it again in a heart beat!
 

how does this dual fuel thing work? will it work on a 89 injected 4.0
 
8) I've not done one in a 4.0i. I dont think the advantages would be as noticeable. The main reason I did it on my 4.2 was flooding. The "side effects" were very favorable. As for putting one on your 4.0, Pane costs 2.19 a gallon.8)
 
This is for everyone that has a 4.2 with the stock carb or even aftermarket carb. About 3 years ago I purchased this kit

http://www.quadratec.com/products/17002_20D.htm

I am in So Cal and face probably the harshest smog restrictions in the country. With this kit I was able to dump 95% of my under hood smog equipment, I ended up with a slight horsepower increase and tremendous throttle response. I no longer stall or start rough, NO flooding, and our trips to our local mountains over 10,000' I have no more thin fuel mixture problems.

I know the kit looks expensive, but, trust me you will never look back. Any questions feel free to ask.
 

Dont waste your time buying cams, air intakes, computer chips, inake tornado's, nos, turbo, or whatever else someone could buy from a mag. If you are going to put the wrench time (and for the same price as a NOS system and alot less then a turbo) in you might as well swap in a 4.0L HO. Get the complete engine and wiring harness for the engine, change the fly wheel to match your '87 transmission, drop in the engine, find the 4 wires to connect to '87 harness to make your gauges work... but would be a good time to upgrade to manual guages.

OR

Buy said engine, remove everything from the head up(EFI etc..) and put it on your 4.2. you could run the thing upside down. Cause by the time the turbo spooled up to get up the rock your carb is going to be starving for fuel.

You will need to upgrade your fuel pump (and tank).
 
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