258...4.0 Head swap vs stroker

[bentley]

1981 j10 258 4spd i want more power but still get 15+ mpg i was just wondering which way would be best, i am leaning toward the head swap and maybe the mopar fuel injection(are the two compatable or can you use the 4.0 fuel injection?) i would like to keep the lower end grunt of the 4.2 so i dont really want to swap in the entire 4.0 but maybe the 4.5L stroker setup, what would the cost of the stroker be could you do it for 3k? i dont want a v8 because on a good day in canada the cost of fuel is .90$ a litre during a long weekend disaster consperacy i have seen it 1.35 in my area so a v8 may be cheaper to do(i have a 360) it would be impossible to ever afford to drive.

Basiclly is th 4.5 cheap to do or should i go with the 4.0 head swap?

[tgreese]

The 4.0L HO fuel injection is the Mopar fuel injection. You can source it complete from an XJ or Wrangler - the same vehicle you get your 4.0L HO head from. The Mopar kit is meant for the 4.2L using the original head.

There's a forum just for 4.0L conversions at http://www.cjoffroad.com/ but it seems to be offline currently.

The shape of the torque curve is mostly determined by the bore:stroke ratio, so if you increase the bore with a 4.0L block, you'll lose some of the 'grunt' of the 4.2L. The new torque peak will be somewhere between the 4.2L and 4.0L peak.

[Kali]

i think you can buy complete strokers for under 3k (probably closer to 2k). as far as fuel economy goes, i think most of those strokers will be running 4 bbl carbs and wont net much over a similar powered v8. people have built strokers for under 1000, but you have to wait for good deals to pop up, and do most of the work yourself.

the 4.0 head swap is estimated to give somewhere around a 40hp gain. there are a few mods to be done to the head, as well as i think you have to use the 4.0 exhaust setup.

to maintain fuel economy and slightly boost power you should look into an HEI or TFI ignition upgrade, the 4.0 head swap, and a better carb (mc2100, weber 32/36 or weber 38, or a holley). fuel injection would be the best route to go with the 4.0 head swap, but i have read somewhere you have to modify your brake booster to make it all fit.

[jeeping1974]

just get a 4.7 stroker. go all out.

[jpcoutts]

I'd go for the 4.0 head and the fuel injection off of a late model 4.0 that way you get the best of both. Just the head swap will get you substantial gains due the better flow characteristics. Look for Terry Howe's article on the head swap. There are several but his is very complete. A junkyard fuel injection unit would be much cheaper but you'd really need to be comfortable with wiring to do it that way. The Mopar kit is complete and a true bolt-on. I believe it is dessigned to fit both the 4.2 and the better 4.0 heads so you can do it step by step if you want. I think I would do the head first but that's just my way of looking at it. Let us know what you decide.

[tgreese]

The Mopar kit is complete and a true bolt-on. I believe it is dessigned to fit both the 4.2 and the better 4.0 heads so you can do it step by step if you want.

The 81-on 258 aluminum intake manifold fits on the 4.0L head, so I think the compatibility of the Mopar kit with the 4.0L wasn't the main target, but just worked out that way.

The main thing the Mopar MPI kit gives you, besides being a bolt-on kit, is a crank position sensor (CPS) that bolts on the front of the engine and works from the crankshaft pulley. The factory MPI uses a CPS mounted in the bellhousing; there are ways to duplicate this, but you need to machine the bellhousing and use a flywheel from an MPI-equipped 4.0L.

In addition to needing a CPS, I recall it's the MPI intake manifold that interferes with the brake booster. You could use the aluminum 4.2L intake manifold with GM TBI (throttle body injection) and get most of the benefits of the MPI ... this is another pretty good option - simple and probably cheaper than the MPI. There are lots of sites on the net that discuss adapting the GM TBI - binderbulletin and bustedJeep come to mind.

[andy d]

Hey TG, I just noticed the addition of a CJ 6 to your sig, congrats!!! They are purty rare in these parts

[JeepsAndGuns]

Hey I would like to see some pics of that CJ-6. I was starting to think I was the only one with one. Mine is a '60 model.

But back on topic. If it was me, I would just build what you have. Since you have the 4.2, I would just swap on a 4.0 head and fuel injection. You can get retrofit kits to fix the CPS problem. They come with a new harmonic balancer and sensor that reads off of it.

[Knucklehead]

What TGrease said.

As far as the torque curve goes. Anytime you increase displacement, you increase torque...across the entire rpm range. The shorter stroke of the 4.0 would decrease torque. But, going to a larger bore while maintaining the 4.2 crank, will, only increase power. The cam is what really decides where the power comes on.

On mine I built a 4.6 stroker. When it still had the t-18 trans with 3.73 gears and 35 inch tires, it would run down the road better than the stock 360. And Mine is very mild and still carburated. I got 18 mpg before I put in the AX15 with O.D. Should be better now...if I ever get it done.

As far as MPI goes...I've done it on a baby jeep. It was not to bad and the CJ forum that Tgrease gave is where I got all my info for the swap. My truck will have it one of these days. BTW, all my MPI parts came from the same juckyard jeep. And, that is key. Life is easier if all your parts come from the same one vehicle, including all the sensors, cpu, and harness. Be sure to get the whole harness intacked; especially the power distribution center (which is near the battery). On a stroker, you will have to go to larger injectors. Some like the ones off a 5.0 mustang, as they dieliver enough fuel to prevent pinging. Also, be sure that you get a 91-94 OBD I system and not the more complicated OBD II system and from a maual trans vehicle. The computer will want the sensors from an auto if that is what it was for. This can be delt with, but it is easier if you don't have to. The OBD II s much more complicated. Also, there are only about 5 wires that need to be spliced into you existing harness to make this work. So, it's not to bad.

[tgreese]

Hey TG, I just noticed the addition of a CJ 6 to your sig, congrats!!! They are purty rare in these parts

Thanks - it's been here since Thursday night.



Lots more pictures here.

http://www.nmr.mgh.harvard.edu/~reese/ResizedJeepIPics/