how can i make power with a 4.2

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.
 
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.
 
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?
 

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! :shades:
 
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?
 
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.
 

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.
 
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.
Click to expand...
 

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

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.
 
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?
 

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)
 
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