New 4.2 or new 4.0?

[captspillane]

I second that Gronk. I'm planning a roadtrip to make that happen once my first and foremost red SX4 is back together. It's always a pleasure to meet those who appreciate this site and our amazing Eagles.

I also agree fully that this site it the foremost place to find information. Its all there if you spend some time clicking and reading. I haven't encountered any other forum as friendly or useful.

As far as the best turn key solution, its a 4.0 long block with a Hesco MPI kit. That will cost you 2K for the long block and 2.5K for the complete ready-to-bolt together Hesco kit. If you're willing to do a little research, a competent mechanic would be willing to replace rings and bearings and install a new head, camshaft, and lifters for about 1K. There is potential to save alot of money besides capturing more performance for just a little bit of knowledge. The Hesco kit can be purchased from a mixture of new and used parts for about 1K if you're willing to spend some time doing research yourself. That brings you to about 2K total along with the cost of new clutch and other work done at the same time, versus about 5K for the off the shelf solution.

If I was to predict, I would say that you will end up buying a 4.0 long block, installing it, and then getting Gronk's 2150 kit along with an electric low pressure pump. You will then have everything running very well with the option of saving up for the Hesco kit at a later date if you really want that modernized pride. Alternatively you can bolt all your original 4.2 manifolds and accesories to the 4.0 block and drive it that way for a long time. That's the decision of most people once it comes time to pull the trigger.

You should not buy a 4.2 long block. A 4.2 short block is about 800 dollars cheaper, and a new head, camshaft, and head gasket can be bolted in place for less than that. Get a 4.0 if you're going to get a long block, even if you have to keep your old intake, Vbelt, exhaust, and such for awhile. The only thing you'll lose is a 40 dollar electric fuel pump, and you'll gain the head, camshaft, and lifters that you'll need for the MPI.

I personally expect my girlfriend and even my mother to drive my Eagles with comfort, and they are less forgiving than I am. They expect a smooth and flawless experience up to par with any modern car. The worst part is that they are also much more cynical and skeptical that my car's are even roadworthy because of their age, so it takes a clean modernized and expensive sounding drivetrain to gain their trust and affection. An Eagle has that potential for much less than the cost of a new car.

[captspillane]

We missed an important question to ask: are you going to keep the Vbelts or go with the 4.0 serpantine belt? I absolutley love the serpentine belt because it installs easier, lasts longer, and never slips or screeches. They are highly superior.

If you keep the V belts with an MPI fuel injection manifold there is one bolt hole that needs a slice with a grinder on the power steering pump. You also need a Hesco temp sensor adaptor that puts a brass fitting inline with the water pump inside the flexible hose because the V belt upper pulley blocks the hole for the temp sensor. Either exhaust manifold works, but you are best buying a new stainless steel 4.0 manifold off the evil bay. It costs just 90 dollars and its much less restriction without the cracking problems of the original used 4.2 or 4.0 manifolds. The biggest advantage to V belts is that you can continue to use the original AC pump.

If you go serpantine belt, you will need to go to a junkyard and get the brackets, AC pump, and power steering pump from a Cherokee. Even if you don't have AC its very hard to find a non-AC donor car and you're best just using it as an idle pulley or an onboard air compressor. Specifically you need a bracket from a 1995 and up Cherokee if you use a 4.2 short block because those have a slightly different alternator bracket. If you use a 4.0 long block you can use the 1992-era alternator bracket which also uses an older AC pump that will accept the original Eagle AC lines.

This is a decision you have to make before you buy your Hesco dampener, since there is one with Vbelt and a different one for Serpantine. You won't need that 350 dollar kit if you use a newer transmission like a NSG30, NV3550, or AX15. My 6 speed cost 600 dollars off Clist with literally 200 miles on it, and it saved me the cost of the Hesco kit.

[olymunch]

I also agree fully that this site it the foremost place to find information. Its all there if you spend some time clicking and reading. I haven't encountered any other forum as friendly or useful.

Agreed


I found an mpi kit for $1200 and if all the accessory components bolt right on then that does sound like the better option.

[mudkicker715]

Even better than a 4.0 is a 4.2 short block with a 4.0 head. This gives you longer stroke, slightly smaller pistons, and a slightly bigger overrall displacement. The difference is barely noticeable, but that does translate to as much power as a stock 4.0 but even more torque. By overboring the 4.2 short block during the rebuild you'll have a 4.5L engine.

A Jeep Stroker typically refers to a 4.0L short block with a 4.2L crank, which creates compression issues unless you shave the piston, but benefits from the larger piston size of the 4.0. Keeping the original 4.0 bore size also gives you 4.5L displacement, and overboring it gives you 4.7L or 4.9L displacement.

How does the head affect stroke. It doesn't.

Never had to shave my pistons on my stroker.

[captspillane]

Even better than a 4.0 is a 4.2 short block with a 4.0 head. This gives you longer stroke, slightly smaller pistons, and a slightly bigger overrall displacement.

How does the head affect stroke. It doesn't.

Never had to shave my pistons on my stroker.

You'll need to shave pistons if you want to use regular gas instead of premium without it pinging. The compression ratio is too high if you don't. Of course you might not care and might have worn rings to help lower the compression ratio.

The 4.2L short block has smaller pistons and a longer stroke than the 4.0L short block. The sentence makes perfect sense as it was written because its an obvious comparison between a 4.0 and 4.2, head and cam otherwise equal. Starting with a 4.2L short block (with 4.0 camshaft), bolting a 4.0 head on it and then comparing it to a 4.0 long block makes it slightly more powerful and with slightly more torque because of the difference in crankshaft. A 4.2 long block without the camshaft and head will work well with an MPI kit but just won't be as quite as good as if you had a 4.0 block, since the 4.0 already has both these. More torque and power comes from the head and camshaft than the slight difference in crankshaft.

A 4.2 with carter carb is junk. A 4.2 with 2150 carb is good. A 4.0 with 2150 carb is just as good. 4.2 long block with original camshaft and head but with MPI is great. 4.0 long block with mpi is better. 4.2 short block with 4.0 head and MPI is even better. 4.0 long block with 4.2 crank is better still. A 401 V8 is best.

[txjeeptx]

The easiest route to go for the best performance for the money you'll be spending is to get your stock engine rebuilt at a good machine shop, and have them install a mild performance cam. You can keep everything stock, and you'll have your "new" car with a minor performance enhancement from the cam. Maybe install an aftermarket aluminum valvecover, and upgrade to the MC 2100 carburetor, and do the TFI ignition upgrade. Then your car is mildly better than stock, but nowhere near as involved as the other swapping possibilities. You can even do the HESCO kit later, and swap in the 4.o HO head later(recommend CCH head, since its properly and professionally modified specifically for this swap). The key with staying with the stock 4.2 engine is to get a performance cam installed while the engine is out of the car - that's the main thing I'd recommend if you stick with the 4.2L. All other upgrades can be done with the engine in the car.

If you were to go with a 4.o HO long block, then your stock intake and exhaust manifolds will not line up with the ports on the 4.o head. It will necessitate either immediately going with the HESCO MPI kit or doing some modifications to the stock intake manifold, and there is no way the stock exhaust manifold will work, so you'll have to use the exhaust manifolds available for the 4.o(Renix non-HO or HO - 2 choices available). Neither of the 4.o exhausts will go in easily - both require modification of either the front axle bracket or the exhaust manifold itself(cutting/welding).

[mudkicker715]

Regular gas works fine in my stroker. motor was taken in to a shop to get machined. rings are new

A head does not give stroke as you said

[captspillane]

The key with staying with the stock 4.2 engine is to get a performance cam installed while the engine is out of the car - that's the main thing I'd recommend if you stick with the 4.2L. All other upgrades can be done with the engine in the car.

This is exactly why you should never buy a 4.2 long block. You need to remove the head to replace the camshaft, so you should only ever buy a 4.2 short block and a 4.0 head seperately. Both seperate cost less than a long block and you won't have to worry about converting the head later. A 4.0 long block already has a performance camshaft and the better head if you want to buy it ready to go.

The 4.0 head versus the 4.2 head is said to be a 30 to 40 HP difference. The camshaft accounts for 40 to 50 HP. Its exactly true that the cam is the single biggest difference and a new engine should not be installed without one.

I recommend Crane's RV cam if you like to drive below 3K RPM. Realize however, that the stock 4.0 camshaft is already a mild performance camshaft. If you set a 4.2 cam, 4.0 cam, and the crane cam down next to each other the difference in lobes is huge between the 4.2 and 4.0, but there is no noticeable difference between the Crane and 4.0 camshaft. The whole reason that AMC took a 115 HP motor and made it get 190 HP with less displacement is that they figured out how to make a mild performance camshaft on their own.

[txjeeptx]

Agreed, that you really don't want to buy a 4.2L long block, since you'd have to split it open to replace the cam, which is a must-do thing while the engine is not in the car, and its a do-it-now type thing, too. Rebuilding the 4.2 from your car is the best way to go, with a small increase in turn-around time, since it will have to be sent out to a machine shop. The mechanic can spend that time rebuilding the transmission, unless he planned on farming that job out, too.

So we've reached a concensus: If you have to buy a long block, the 4.o long block is the best way to go since it already has all the upgraded goodies like better cam(still not the best performace cam it could have, though) and head. The problems then will be in bolting up the manifolds and having to use an electric fuel pump, whether you go with injection or carb.

Good luck with whatever you decide to do. In the end, whatever you choose will probably prove to be very satisfying when its done.

[carnuck]

I'll assume you mean the 8 /14 and not the weak 7 1/4.
The 242 tcase will give you full time 4x4 for any condition like the NP119.

[captspillane]

did you get a description of the MPI kit that you found for 1200? If it includes a Hesco crank sensor kit you need to know if its a serpantine or Vbelt dampener. You'll need to know if it has the 4.0 thermostat housing or the Hesco water temp sensor conversion adaptor. If it isn't complete with fuel pump, sensor kit, and speedo adaptor than its not worth that much. If its just a box full of stuff pulled from a junkyard you'll have alot of work and cost left before your car is done.

In a sense you are buying a new head and camshaft that you don't want and don't need if you get the whole 4.2L long block. TxJeeptx just did a great job at summing up the consensus there. A short block is readily available for 1200 dollars, versus 2000 for a long block. Your old long block can be rebuilt for less than that but not by much. Clearwater Conversion Heads (water jackets welded shut before the head was decked) cost 500 dollars. A new Crane camshaft without lifters about 150 dollars.

You'll also get a much nicer timing chain set and timing cover with the 4.0 long block. If you have to pay for a new set during a rebuild, get the 4.0 version because the whole gear is metal. The timing cover has an anti-slap bumper in it that most 258's do not have, although its thicker in one corner than the 4.2L timing cover. I have a 4.0 timing cover on a V-belt 258 without AC, but that thicker hole might be a problem with some of the other possible accessory combinations. Some 258's had a metal spacer against the timing cover and the 4.0L incorporated that spacer into the casting.

"If you were to go with a 4.o HO long block, then your stock intake and exhaust manifolds will not line up with the ports on the 4.o head."

That's not true, you can use the original 4.2L intake and exhaust with a 4.0L block. I've seen it done but will have to go take pictures in my garage today for complete confidence in that as a fact. When comparing the 4.2L and 4.0L heads the intake is just pushed up higher instead of inline with the exhaust ports. The pattern itself is the same. Its a little weird because the intake and exhaust will no longer line up side to side like they used to which effects the washers on the bolts that clamp down on both manifolds. I consider it the same as reading that an MPI intake won't install with a 4.2L exhaust manifold, which my CJ8 has. Usually people combine a carb intake with a 4.0 exhaust manifold, but my Scrambler has a 4.0 MPI intake combined with a cast exhaust manifold. It was a single slice with a grinder to the very top of the power steering pump bracket to make a definite no become a definite yes.

I also do not consider the exhaust manifold a difficult installation because its a little shaving with a grinder to the edge of the axle hangar to make it work. The only reason its a weld on installation is because you need the new downpipe welded to your old exhaust, either of which a competent mechanic would not blink an eye at. Even if you end up with a carb initially, its still worthwhile to get the exhaust manifold switched over now. I love my new stainless evil bay version, brand new for 88 dollars.

You should never get an NP231. The NP242 has the same slip yoke and same part time 4wd, with the benefit of a working all wheel drive "part time 4WD." Its perfect for an Eagle. The low range makes a huge difference and its worth the change to your driveshaft. It also has a nifty internal oil pump. You can see my driveshaft solution in the latest posting on my project thread "Perkiomen Project Pics."

[68AMXGOPAC]

 Confused yet olymunch ?? lol, I am , but it's a good group of technical advice to print out and re-read and keep for reference.I can't keep it all straight just popping in here to read when  new post adds on.

[olymunch]

Hahahaha 
Ya It's definitely a lot but I'm grateful for it! Seems like every answer brings two questions, but that's ok;)

So do you all think that getting a 4.0 engine, installing a better cam, getting the mpi done, and getting the new exhaust manifold(eventually I'd like to do dual setup) is the fastest, probably cheapest option with the least amount labor?

Keeping in mind all the extras I'd have to do if I stayed with the 4.2, installing the mpi either way, and assuming that all the components bolt over to the 4.0 with the exception of the exhaust?

Right now I have a 1981 eagle with shift on the fly, it handled GREAT in the snow up here in Seattle so I think I'll keep that the way it is. I haven't even thought about new gears in the rear and really have no idea what I have. I can squeak the tires in first no problem and I can squeak em going from first to second easy. Although there does seem to be some wheel hop in the rear in the lower gears if I don't shift just right when it's in 2wd.
 
Initially I just want it to be a great road warrior and I'll take it off-road, trails, and hill climbing occasionally. When I upgrade to a solid front then I'll put in a new tc but still will prob want something that can operate in 4high on dry pavement with an air locker option.

[olymunch]

Oh and going thru my bookmarks I'm seeing a mpi kit from koller dodge for $1600 tho I'm sure I found one for $1200 but can't find it now. I haven't contacted them regarding the kit but will look into it to see what it comes with. I know that the harmonic ballancer is extra.

[captspillane]

Oh and going thru my bookmarks I'm seeing a mpi kit from koller dodge for $1600 tho I'm sure I found one for $1200 but can't find it now. I haven't contacted them regarding the kit but will look into it to see what it comes with. I know that the harmonic ballancer is extra.

That kit sounds rather incomplete. You will likely need much more to actually get your Eagle back on the road. You should go to the Hesco website and directly compare their prices to the Dodge kit. Hesco also has very good write ups that you can download to install their products. If you have only saved up that amount of money for the MPI conversion, you'll likely have to start looking at a Howel TBI kit or Gronk's 2150.

The Howel TBI kit is about 1200 dollars and it runs nearly as well as the MPI. Its a neglible difference. The biggest advantage is that you don't need a crank sensor. A crank sensor tells the computer where the flywheel is in order to know which cylinder to shoot gas into. The throttle body injection computer doesn't need this information because it is injecting a steady stream of gas and air for all the cylinders at once.

I'm not sure if I can post a direct link on this site, but if you google "Howell TBI" their website is the first return. Likewise "Hesco MPI" is the first return for their website.