4.0 and 4.2 . . . differences and similarities?? - Pirate4x4.Com : 4x4 and Off-Road Forum

GPNS-GR8 · 04-08-2007, 03:45 PM

Scored a good deal on an 88 XJ with a lower rod knock. I was hoping to just drop the pan throw in some new rod bearings and have a driver. But, after I put the new bearing in rod #1, it still had some slop in it.

I've got a 4.2 with a fresh rebuild on it sitting in the corner of the garage (out of an '88 YJ which is now running a small block).

My question is:

How similar are the two motors, i.e. could I swap the long blocks and run a fuel injected 4.2?? (quicker and cheaper) Would I be better off stroking the 4.0 with the 4.2 crank and rods?? (more time/cash, but cooler

)

What are my options/what would you do?

Xjcrawler736 · 04-08-2007, 04:19 PM

Do the stroker. Since you have all the stuff you need I would run with it. You will really like the torque you will get out of it.

When it comes to the blocks they have some differences. The 4.2 has a manual fuel pump on the side of the block which the 4.0 doesnt(pump in the tank) There is a couple other differences but i cant think of them right now. We did a stroker on my buddies CJ and were very happy with the results.

Strand · 04-08-2007, 07:35 PM

I'm doin research on just that same question.

I have
1. Soon to be retired 95XJ sport daily driver, engine in great condition, 4.0 HO, auto transmission.
2. My baby, 90 YJ 4.2, auto transmission.

Try this, http://jeep.off-road.com/jeep/articl....jsp?id=277013

Good luck.

GPNS-GR8 · 04-10-2007, 04:46 PM

Thanks for all the help guys!

I think if I were trying to upgrade a carbed 4.2 in a CJ or YJ, I would go with the head swap, but it looks like there are enough differences that it would be worth the extra cash/time to do the stroker. So . . .

I'll keep you posted as to the stroking progress

offroadjunkie · 04-10-2007, 11:38 PM

4.2s and 4.0 electronics dont really mix well.. its possible but from what ive heard its to much of a hassle. i would say fix the 4.0 or go to a junkyard and pick up a spare one with low miles for $600 bucks.

04-08-2007, 03:45 PM	#1 (permalink)
GPNS-GR8 Registered User Join Date: Apr 2005 Member # 46011 Location: Not quite there... Posts: 21	4.0 and 4.2 . . . differences and similarities?? Scored a good deal on an 88 XJ with a lower rod knock. I was hoping to just drop the pan throw in some new rod bearings and have a driver. But, after I put the new bearing in rod #1, it still had some slop in it. I've got a 4.2 with a fresh rebuild on it sitting in the corner of the garage (out of an '88 YJ which is now running a small block). My question is: How similar are the two motors, i.e. could I swap the long blocks and run a fuel injected 4.2?? (quicker and cheaper) Would I be better off stroking the 4.0 with the 4.2 crank and rods?? (more time/cash, but cooler ) What are my options/what would you do? __________________ --------------------------------------------------------- You have the right to remain silent. Anything you say will be misquoted and used against you.

04-08-2007, 04:19 PM	#2 (permalink)
Xjcrawler736 Zeus of the Sluice Join Date: Jan 2007 Member # 84970 Location: Lansdale, PA Posts: 3,858	Do the stroker. Since you have all the stuff you need I would run with it. You will really like the torque you will get out of it. When it comes to the blocks they have some differences. The 4.2 has a manual fuel pump on the side of the block which the 4.0 doesnt(pump in the tank) There is a couple other differences but i cant think of them right now. We did a stroker on my buddies CJ and were very happy with the results. __________________ Andy~ RCrocs/Line Mt. - Route 63 Motorsports #736 Ultra4 #4343 Co-driver - Molten Motorsports

04-10-2007, 04:46 PM	#4 (permalink)
GPNS-GR8 Registered User Join Date: Apr 2005 Member # 46011 Location: Not quite there... Posts: 21	Thanks for all the help guys! I think if I were trying to upgrade a carbed 4.2 in a CJ or YJ, I would go with the head swap, but it looks like there are enough differences that it would be worth the extra cash/time to do the stroker. So . . . I'll keep you posted as to the stroking progress __________________ --------------------------------------------------------- You have the right to remain silent. Anything you say will be misquoted and used against you.

04-10-2007, 11:38 PM	#5 (permalink)
offroadjunkie Registered User Join Date: Oct 2006 Member # 80641 Location: Lincoln, Ca/Denver, Co Posts: 1,302	4.2s and 4.0 electronics dont really mix well.. its possible but from what ive heard its to much of a hassle. i would say fix the 4.0 or go to a junkyard and pick up a spare one with low miles for $600 bucks. __________________ [QUOTE=beater82;10779355]You should try patriotism. That stuff can fuck some shit up.[/QUOTE] [QUOTE=DillWeed;9324924]Kid... you are looking for a dance club and you stumbled into an old school tavern full of mean drunks...Run for your life.[/QUOTE] 1990 yj, 44/60, d300, howell FI- sold

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04-08-2007, 07:35 PM	#3 (permalink)
Strand Registered User Join Date: Apr 2007 Member # 89241 Location: Toronto Posts: 7	I'm doin research on just that same question. I have 1. Soon to be retired 95XJ sport daily driver, engine in great condition, 4.0 HO, auto transmission. 2. My baby, 90 YJ 4.2, auto transmission. Try this, http://jeep.off-road.com/jeep/articl....jsp?id=277013 Good luck.