need HELP with 4.2L -
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post #1 of 6 Old 02-02-2002, 07:42 PM Thread Starter
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Join Date: Feb 2002
Location: New Jersey
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need HELP with 4.2L

i have a 89 jeep wranglter with a 4.2 in it and after i put the 4" suspention lift ans 33's on it it is the biggest dog especially when wheeling. i have already a locked dana 44 rear with 3.73 and a dana 30 front. iv looked about fuel injection and even a stroker kit. what is the best thing to get more power besides a small block.

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post #2 of 6 Old 02-03-2002, 10:02 AM
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Join Date: Sep 2001
Location: FL
Posts: 162
Depending on the amount of dough you're willing to spend there are a bunch of options.
1. Weber carb 32/36 is $380 or so.
not that much of a power gain, but much better reliability and simplicity under the hood.

2. Ignition upgrades. sells a great upgrade for the stock distributor cap. It replaces the old cap with one from a F-150. I don't have this upgrade, but I've heard great things about it.
I don't know anyone who has done a new ignition box, but I bet you could find one if you looked around.
-Also go to this sight for 10 free Hp. www.outdoorwire/4x4/jeep/tech/electrical/jn-ignition99/ I did this upgrade and its really easy and cool.

3. There are other basic things you can do, such as new cam, valves, springs. Headers and Intake manifolds too. All this stuff can be found at

4. Another upgrade that more and more people are doing is the 4.0L head swap. This head has much better flow than the 4.2 and its pretty much bolt on. There's a good write up at
They claim its a 40 Hp increase.

There are other upgrades I'm sure, but I can't think of them off the top of my head. Email me at if you want more info.


95 YJ 2.5L 5 Speed

Fightin a war against Florida Rust!
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post #3 of 6 Old 02-05-2002, 07:16 PM
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It all comes down to budget. With that said, here's my 2 cents worth (hp gains are est):
1. Mopar fuel injection (60hp gain)Cost=$1850, including the balancer
2. 4.0 head swap (40hp gain)Cost $300-$500, depends what you can get a head for
3. Header/cat-back (10-15hp gain, debatable)Cost $300-$500
Note: I would not do the FI or Head on a tired power plant.
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post #4 of 6 Old 02-05-2002, 08:30 PM
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i would just put 4.10 or 4.56 gears. that would help out alot

85 CJ-7. 79 vette 350 conversion. 4.56 gears. Lockers. 4" Explorer Pro Comp suspension, 3" body lift. 38" Super Swamper TSL's. Looking to go SOA and take off the body lift.
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post #5 of 6 Old 02-12-2002, 12:32 AM
89 YJ
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Ok. Just found this forum and think it is great. I have a 89 yj 258 which I love. It is what you would call a stroker. The engine has many downfalls, but if you work with it it will make you happy. The first thing is to put a 4.0 High Output head on it. You will need the Headers off the 4.0 also. The mad is harder than they say, and I wont lie to you and say it was easy. I ported the head for a little extra fun and went to work on it. The main thing is I used stock intake and carb because I couldnt afford the fuel injection. So beware you have to notch the stock intake to fit under the carb and around the bolts outter spacing. You can see where when you try to line up the intake and exaust with the head. Its not hard, just takes a little time.

The other thing I did was to swap my 3.07 geas with a 4 cylinders 4.10 gears. Made a ton of difference. I can bury the speedo at 100 and keep climbing now Not recommended bucause above 85 is scary with the 4 inch lift and 31s. I plan on 33s this summer. Its a little undergeared with the 31s. The speedo was off by 10mph at 65 with 31s before gear swap, and is off about 7mph now, so should be really close to right with 33s.

Oh, and im gunna put a webber on it as soon as possible. The stock carb is nothing but problems.

The nutter bypass gave me worse fuel ecomomy, but is a good thing to do with quick disconnect wire plugs so if your on a trail and the computer goes out its a quick 2 wire changeover and your on your way

89 YJ Islander, AC,PS, 10 inch lift, 32 BFG MT's, sway quick disconnect, rear track bar quick disconnect, 400 watt 12 speaker cd player for tunes,8000lb warn 8274 with 150 ft cable, and a high lift jack.. Lockers, 35's, webber carb and jacobs ignition comming soon.
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post #6 of 6 Old 02-12-2002, 11:41 AM
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If you do not want fuel injection, go with a holley 390. Runs great If you have the time a 304 will bolt to your bellhouseing you must have the ax15 trans. Some wire mod. and motor mount changeing is required

89 yj 4.2, holley 390, clifford manifold, borla ss header, 2.5" bds lift, 1" shackle lift, 31x10.5x15 on stock jeep 8" alum. rims,

86 cj amc 304 bore 30 over, procomp cam, roller lifters, edelbrock intake and edelbrock shorty headers, holley carb, hmi distrib, Be cool raid, 2.5 procomp lift, 33x12.5x15 deep 10" Alum mag, dana 30f, 44r, tf999 auto with lokar shifter, 300 transfer, 8000lb winch, procomp bumpers, body rusted and abused.
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