how can i make power with a 4.2

[TerryMason]

have you upgraded the ignition yet?

http://www.jeepz.com/forum/showthread.php?t=16904 (TFI ignition upgrade)

It made a huge improvement in my 85 cj7, and was really cheap.

[chaos.258]

To Mike B, This is what I did to my 4.2. Remove stock carb. intake and exhaust manifolds. Replace with 390cfm Holley carb. Model 4160 P/N 0-8007. Replace intake manifold with Offenhauser alum. intake P/N 6257-DP. Replace exhaust manifold with Pasesetter 6-2-1 header P/N 70-1128. This will solve some of your vacuum problems, give you more horsepower and better m.p.g. Parts for this project were about $900.00. The next phase of this project is going to be an ignition and coil upgrade probably M.S.D. These are a few things you might want to consider before you spend the big bucks on a new aluminum head. What the hell, swap the head too. Long live the 4.2.

[RBLUE]

GEAR'S/tera-low 4.3-1

[WV77CJ5]

So is the Weber 32/36 no good for a '77 CJ5 4.2L?? I am trying to upgrade mine and can't decide which carb to purchase and get a good value.

[franked]

OK this is a good time to ask, I have a 78 Cj7, will that efi conversion work for me?, bay area CA, same smog checks you got in So-Cal. And is there a header avail for these jeeps, 258 I6?

[ursman]

REALISTICALLY ... I would keep your 4.2L if it's not blowing smoke to bad from rings/valves, for budget reasons. A Weber is good so long as you aren't in a smog state (I don't know what Canada's smog laws are). If you don't have to worry about smog, then remove the AIR tubes/pump as applicable along with extraneous vac lines. For max carb power, i'd go with the Weber 38 as it has the largest venturis/secondaries. I went with the Weber for a few years but got tired of having to yank it all off when it came time for emissions testing. I saved up and got the Howell TBI which is probably the biggest single improvement you can do to any 4.2L. The driveability and power are unbeatable. I also went with Terry's advice on the TFI upgrade. If you're on a budget (like most of us!) This is a good step in the right direction. Also, any good muffler shop would be able to fab up some custom exhaust for a good canuck price!

[franked]

CHAOS.258 wrote:

Replace intake manifold with Offenhauser alum. intake P/N 6257-DP. Replace exhaust manifold with Pacesetter 6-2-1 header P/N 70-1128. This will solve some of your vacuum problems, give you more horsepower and better m.p.g. Parts for this project were about $900.00.
are these parts CARB certified for california emissions?

[chaos.258]

Make power with 4.2 - Remove stock carb, intake & exhaust manifolds. Install Pasesetter header, 390 cfm Holley carb, Offenhauser alum intake. Will add 40+ horsepower and improve mpg's on stock 258. The engine will stop pinging, while using regular gasoline. If this is still not enough power, up-grade ignition & coil.

[franked]

I out the Howell EFI on my jeep and love it, I still could use more power, will that offenhouser manifold work in the the place of stock, (I still want my Throttle body bolted to this) and where do I find those? header and manifold.

[fullhouse]

GREAt! I bet this should work.

Make power with 4.2 - Remove stock carb, intake & exhaust manifolds. Install Pasesetter header, 390 cfm Holley carb, Offenhauser alum intake. Will add 40+ horsepower and improve mpg's on stock 258. The engine will stop pinging, while using regular gasoline. If this is still not enough power, up-grade ignition & coil.

[franked]

I did the ignition, a little better, mine must have been working ok though.

[fullhouse]

I think you just need to upgrade your engine. . . better use new one.

[carnuck]

I'd do the 4.0L head swap, put in a 4.0L or build a 4.6L stroker. As soon as I'm feeling better, I'll be putting the head (and exhaust manifold along with EFI) on my '82 Spirit's 4.2L

[franked]

only problem with the 4.0 head swap, I need to retain EGR for smog testing, and have a C.A.R.B.(california air resources board) number on any non stock parts(as in Header) that I put on there. I was told that the 88-89 4.2 exhaust/intake still retains the EGR, before Chrysler took over in 90, and that it has better flow, any parts recommendations would be apreiciated. Thanks

[carnuck]

You can run the Renix EFI intake which has the EGR port still (87 to '90 XJ) I did that for my stroker so I can run regular gas should I happen to run out of LPG on a long trip.

[fullhouse]

cool suggestion! All suggestions are good, can we hear from you? what advice did you take and work?

[franked]

Never heard of a renix EFI manifold, is that a stock part I can look for at the junkyards? What about bolting that on the 4.0 head, I have smoke when I start the engine for a few seconds, If I am going to do anything to the head on this thing, It's going away in favor of the 4.0. And anyone know which stock exhaust I need for this with EGR stuff?

[carnuck]

You can run a stock '87 to '90 XJ head with intake and exhaust (you might need a couple other goodies like the PS brackets and alt bracket if yours isn't serpentine belt. The 4.2L harmonic balancer is 3/8" offset forwards from the 4.0L one as well)

[carnuck]

renix is '87 to '90 BTW

[buckaroo kid]

Go with a Clifford intake with a 390 4bbrl holley carb if you don't have to worry about emmissions.