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Topic Review (Newest First)
09-08-2013 09:05 PM
1989yj4.2 Is there a specific thread for some one to swap 4.0 head and fuel injection to a 4.2?
08-29-2013 01:18 PM
Nundian101 I would love to make that switch to the 4.0 someday. how much would it cost all together guys?
08-29-2013 11:28 AM
BebeBlue Now that I'm here [newbie alert], and we're talking abt old YJs finding their way back on the road, what else should I be looking out for? The engine has been switched from carburetor to a 4.0 injection but again this is a 24 year-old piece of rubber & steel so what should be on my check list?
Again I appreciate all the help and red flags so don't be nice and give it all y'got!
08-29-2013 10:42 AM
BebeBlue
Quote:
Originally Posted by pelzworld View Post
Jeep buddy gave me a 4.2 engine and tranny with 50k on it, but it's been sitting. I have a 89 YJ with the identical set up. I want to rebuild the motor he gave me from top to bottom with some reasonable modifications. Intake, 4 barrel carb, Cam, header. Looking for input from those of you who've done this before including a suggested rebuild kit-might as well do the piston rings, valve seals, etc...while it apart. Thanks in advance.
Yes I'm with you on that one.. if you're already rebuilding the engine, take advantage of the situation and check EVERYTHING. My YJ was pre-owned and god only knows what the hekk the guy did (or didn't do) with it.. Anyhoo, watch out for the consequences of severe parts over-heating (mainly, dilatation of pistons or other hidden surprises..) because the damage is (or was) bad
08-28-2013 05:27 PM
roadyrob the machine shop I used was set up to grind cams, he took a new stock cam and ground it to his specs, he said it was close to a RV cam. the 4.2 head makes good torque at lower rpm's but the casting is very rough with casting ridges in the ports, they were removed and the head was port matched. IMHO the 4.0 head swap works great if you go with fuel injection, with a carb, not so great, the intake ports don't match the manifold to good unless you get the clifford 4.0 manifold, it also raises the peak torque rpm's. most of the power increase people are seeing is from the smaller combustion chamber raising the compression ratio and the 2.25 exhaust.
I didn't see a need for a header as the 4.2 doesn't really rev high enough to get much benefit from it, I just used a 2 1/2" cat and muffler.
I have a 5 speed trans.
08-28-2013 03:38 PM
pelzworld Much appreciated-no header or new cam eh? I knew about the 9.5 compression thing-stuck with the 4.2 head?? Standard or auto trans...
08-28-2013 08:43 AM
roadyrob ok, here goes, complete rebuild, balanced, head shaved to up compression to 9.5, head casting cleaned up and port matched, machine shop reground the cam simular to an rv grind, HEI ignition from CRT, offenhauser intake with holley 390cfm and 2 1/2" high flo cat and muffler from magnaflo.
I'm very happy with the way it turned out, starts of first turn, gets around 16mpg around town if I take it easy and plenty of power.
08-28-2013 08:03 AM
pelzworld Roady, tell me more about your build please-looking at doing cam, intake, header, carb or injection-some combination....
08-26-2013 07:46 AM
roadyrob if you plan on fuel injection go with the 4.0 head, should be able to get most of the parts from a junk yard. be sure to get a cam designed for FI.
I strongly disagree that the 390 holley is overkill. I have run one for about a year and feel that its the best carb i could run, great gas milage if I take it easy and plenty of power when I get on it. my motor isn't stock but it's not wildly modified either.
08-26-2013 07:15 AM
pelzworld Have spoken with a lot of peeps about this project with a variance of opinions. I already have a DUI distributor on it-One good friend, who is a mechanic, said to do a comp cam and go with fuel injection for overall reliability-agreed that the 390 4 barrel is overkill if I stuck with a carb and to go with weber 38. wont have to worry about new intake or header at this point. Will be looking for explorer 8.8 3.73 axle to put in the rear and will swap out gears in dana front for better response. However, I am still open to suggestions from those who have worked on these. This is not a daily driver for me-weekend trail vehicle.
08-20-2013 03:46 PM
BebeBlue I've got an old 1989 YJ. The engine (4.2 I6, carb) was in bad bad shape so had to replace it with a 1997 Cherokee I6 4.0 injection. I've been told that 4.0 is a more flexible option than the 4.2; thing is I've been told so many things I can't get enough and am posting here..

What d'y'all think?
These mechanical adventures are new to me so I need all feedback possible, what to look out for, etc..
08-20-2013 01:39 PM
roadyrob you can get plenty of power from the 4.2 if you build it right, not as much as a stroker but more than enough to beat a stock 4.0. do a rebuild, use high compression pistons or to save money shave the head to get the compression up to around 9.5. get a good cam, comp cams is a good choice, so is hesco. clean up the head casting and port match it to the intake, there are casting ridges in the ports that should be smoothed out, no need to polish as the 4.2 doesn't rev high enough to benefit from it. there are videos on utube that show how to port match.
offenhauser and clifford make 4bbl manifolds, sometimes you can find them used on ebay pretty cheap. the holley 390cfm carb is a great carb. for ignition run either a HEI or msd, I like the HEI from CRT performance. don't forget the exhaust, a header isn't really necessary but a 2 1/2" high flow cat and muffler really helps.
08-20-2013 12:54 PM
curt68 I've got a 1990 4.2 that was trashed in my jeep. Got a 1990 (late) 4.0 that in putting the 4.2 bottom end in it. In process so don't have any comments yet. Gonna be .030 over, shave the block to get 9.5 compression, comp cams 447 int/exh cam kit. Thinking about running a Clifford intake n 38DGES Weber, along with a header. Dunno what HP gonna have but think should be pretty good.
08-20-2013 12:42 PM
incizion Look around for a 91-95 4.0 long block, swap the head.

Use this web site Stroker to build a Stroker.

Clifford Performance :: Make 6 = 8Sells some pretty good stuff for the 4.2
08-20-2013 12:36 PM
pelzworld
4.2 rebuild

Jeep buddy gave me a 4.2 engine and tranny with 50k on it, but it's been sitting. I have a 89 YJ with the identical set up. I want to rebuild the motor he gave me from top to bottom with some reasonable modifications. Intake, 4 barrel carb, Cam, header. Looking for input from those of you who've done this before including a suggested rebuild kit-might as well do the piston rings, valve seals, etc...while it apart. Thanks in advance.

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