Jeep 4.0 or GM 4.3 in YJ

marvilusone

marvilusone

Well-Known Member
Joined
Oct 21, 2007
Location
Charleston, SC
I have an '87 YJ and have been thinking about building it since it won't sell. In everyones opinion, what motor should I run in it? It was originally a carbed 4.2 so there is no fuel injection wiring at all, so no matter what motor goes in I will need a harness. Building/buying the harness is not a problem. I like the power of both motors but I am alot more familiar with the GM 4.3. I know the 4.0 is a bolt in as far as motor and trans mounts go but with the 4.3 I can use a TH350 and a 205 which, as far as I know is alot stronger than the Jeep auto and 231. Like I said, I'm looking for opinions and some ups and downs to each option to help me figure out which way to go. TIA
 
I have a 2000 TJ with the 4.0 and a 1995 YJ with a 1993 4.3 Vortec. The 4.3 is alot more engine than the 4.0. If you go with the 4.3, the CMPI has a lot more power than the TBI. From what I researched, the 1993 model year was one of the best years for the 4.3 Vortec. When mounting the 4.3 to the YJ, you will buy the same engine mounts as is used for a 350 swap. I had to get a new radiator too as the inlet and outlet were on opposite sides of the factory 4 cylinder the YJ had.
 
4.3 just get-r-done
 
take the crank and rods out of the 4.2 and put them in a 4.0 and make it a stroker motor-you won't be disappointed! a lot less work and money than a complete drivetrain swap.
 
+10000000 on the crank and rods.

then bore it .060 over and make it a 4.7, like I did. Sucker is a beast, and a torque monster down low. The 4.0 is an increadibly easy motor to build and work on too.
 
4.3 is a good motor, but it doesent make the torque I want in my rig. My girl has a blazer with the 4.3 and I like it for running around town, and it runs well on the interstate, but I cant see picking it over my stroker. The 4.3 has good power in mid rpm range, but the 4.0 or 4.7 has power right off idle.

Consider a cummins turbo diesel swap. I know a guy that got one and a NV4500(I think) out of a merita breadtruck and put it in his YJ. Or do the standard 350 swap.
 
^^^ agreed, complete bs

4.0 is a good motor, i think it does better at low end. plus when you stoke it they are plenty able from what i have seen.
 
My "stock stroker" 4.6/4.0 pushes my 5k lb jeep on 35's to a 10.6 1/8th mile. 4.0 stroker is strong EVERYWHERE in the usable rpm range.

I also vote for the stroker.

Since you already have the 87-91 crank, you don't have to machine the snout either. All you need is a complete 4.0. Building the stroker is like rebuilding a regular 4.0, you just swap the crank and rods when you assemble.
 
old buggy had a warmed up 4.0. New one has a 4.3.

4.0 has balls, is indestructable(i know this for a fact!)
lots of torque. But, its long, its heavy,

4.3. plenty of power (for me), lighter, easier to package due to length.
Travis's motor is bad ass.
My next buggy will be 4.3 powered again.
 
just curious, what's all involved in doing a 4.0 stroker. Is it simply just swapping over the 4.2 crank, and 4.2 rods? What else is there needed to do?
 
for a 4.5L you just swap the crank and rods. A 4.6 is bored an additional .040 over, and a 4.7L is bored .060 over. I opted for a 4.7. Other than that it is a standard rebuild.
 
any idea on the power increase just doing the 4.2 crank and rods?
 
is there anything wrong with the 4.2L?...If not why dont you just put fuel injection on it?...that to me would be the EASIEST thing to do. As far as the 4.0l stroker or the 4.3l.....My opinion is this...I would go with the stroker , period. If you are going to the trouble of the 4.3 swap you would be better off going with a 350.The 4.3 is NO comparison in my opinion , to a 4.0L on the trail. If you have ever owned a straight 6 engine you know what I am talking about.

As far as the power increase of just the 4.2 crank and rod , i dont think it would be tremendous. You would be able to tell but you gots to tear the motor down anyways you better just do it right the first time.
 
I own two 4.0s (TJ, Grand Cherokee) and one 4.3 (YJ). The 4.3 is my trail vehicle. The 4.0s have torque, but my 4.3 (bored .030) has more HP. The 4.3 also allows for a longer rear driveshaft. At the end of the day, if I was starting all over, I would honestly pick based on $$$.
 
It seems as if both motors have their up and downs. I have a Jeep 4.0, Jeep 4.2 and a GM 4.3 so the cost of the motor is not an issue. I guess I will be basing my decision on tranny/tcase combos. The TH350/NP205 is a very strong combo and will bolt right up to the 4.3. The AW4/NP231 is durable but not as strong as the GM steup. Also with using the 205 I will have a pass side drop on the front and it will allow me to use GM/Dodge axles which are fairly easy to come by. The other reason I think I will be going with the 4.3 is the fact that I know those motors inside and out and it will be very easy to swap in a small block down the road if I decide I need more power. This is going to be a trail/rock rig so I'm not going to need a whole sh!t ton of power anyways. I appreciate all the help I've gotten here. Thanks again.
 
marvilusone said:
The AW4/NP231 is durable but not as strong as the GM steup.
Click to expand...



MAYBE on the 205/231 bit but...

The AW4 is the same box as the toyota A304 that the tuner guys push over 500 hp in the supras. Neither the 4.7 or 4.3 would be anywhere near too much power for it.

As for the t-case, mine held up to my dumbass shifting into R at 35 mph in patchy snow, spun the wheels backwards at speed before it stalled out. Still runs like a champ.

I'd say stay with the mopar/aisin-warner parts, the 4.0 makes the vast majority of its torque at pretty low rpms, but also the reason I say that is it's what I know, so I understand just building what you're more familiar with.

Either way it sounds like a cool build, how bout some pics!
 
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