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1979 Jeep CJ5 with 304 V8, T18 Transmission, Dana 20 Transfer case with TeraLow 3:1 gears, 4.88 axle gears, Detroit Locker up front and Ox Locker in back with 1 piece axle shafts, 36" SuperSwamper SX Tires, Shackle reversal, MileMarker Hydraulic winch, MSD 6A ignition.
Get another AMC 258 i6 / 4.2l or have yours rebuilt. Especially if you want to keep your distributor and intake and carb.
The AMC 258 i6 / 4.2l is a very good engine.
Ok well maybe not the intake, but def. the carb. 1 bbl are not cheap and the PO bought it brand new right before I got the jeep, and I just put a new distributor in it.
So with less restraints, what can be swapped in? I think a 4.0 will direct swap but I want to make daggum sure before I go get one. Exhaust is no biggy as I would get the manifold too.
The 4.0 can bolt up but the conversion to fuel injection on your Jeep will take some work. Putting a 1 barrel carb on a 4.0 motor to me is just not right. So it is new. big deal, sell it on ebay or something. Also that older style distributer may not work on the 4.0 because most of the timing is controlled by the ECU and your current motor is all mechanical. You realy need to just get yourself another AMC 258 i6 / 4.2l and call it a day.
1979 Jeep CJ5 with 304 V8, T18 Transmission, Dana 20 Transfer case with TeraLow 3:1 gears, 4.88 axle gears, Detroit Locker up front and Ox Locker in back with 1 piece axle shafts, 36" SuperSwamper SX Tires, Shackle reversal, MileMarker Hydraulic winch, MSD 6A ignition.
I still say get another AMC 258 i6 / 4.2l . They are good engines.
What do you want? More horsepower? Better gas mileage? Maybe I'm wrong but I get the feeling you want to avoid the AMC 258 i6 / 4.2l and I would need to know why before making a recommendation.
Even the simplest swaps always seem to have surprises.
More HP is a def reason, gas mileage does not matter at all. I know I can swap a 4.0 head on and gain some HP. The problem is why would I want to rebuild this bottom end when I can get a 50-60K complete running motor for less than what it will cost for a new pistons rings and block bore, with the possibility of needing a new crank and at least getting the crank turned and new bearings and all the other little things that go with a rebuild that are not much individually but cost a fortune over a month or so?
SO you see my question to me is VERY valid in wanting to ditch the 100HP AMC 258 i6 / 4.2l in favor of a newer motor with more HP for less than what a stock rebuild of this motor will cost me.
1982 Jeep CJ-7 350 Chevy V-8, SM-465 4-speed trans, Dana 300 Twin Stick, Narrowed and locked GM 14 bolt rear, Narrowed and locked Dana 44 front, 38.5" Super Swampers. Fiberglass tub. 6 point roll cage.
Doing the 4.0l swap can be quite involved. You will need a 4.0l flywheel and clutch since they have the notches for the crank sensor, you will need to make a notch in your bell housing to put the crank sensor in, you will need the harness and computer and wire that all in to your Jeep. You will need an electric fuel pump either in tank or one along the frame rail to support the fuel injection. It's quite a bit of work with quite a bit of downtime to do it properly without having a bunch of problems down the road.
So in short it will be quicker and easier to find a fresher AMC 258 i6 / 4.2l , throw a RV cam in it with a GM HEI distributor and a Motorcraft 2 barrel carb. You have plenty of power (the same if not more as a stock4.0), without all the downtime and guess work, plus it will still be a simple straight 6 without a computer and complex electronics to fail you later.
1979 Jeep CJ5 with 304 V8, T18 Transmission, Dana 20 Transfer case with TeraLow 3:1 gears, 4.88 axle gears, Detroit Locker up front and Ox Locker in back with 1 piece axle shafts, 36" SuperSwamper SX Tires, Shackle reversal, MileMarker Hydraulic winch, MSD 6A ignition.
Or you could go for an AMC V8.
since you don't care about gas mileage but want more power a AMC 304 , 360 or 401 V8 may be a good option. They are all the same externally (engine mounts, accessories and mounting). I love my AMC 304 . I don't use it as a daily driver, just off-roading. For that reason I don't mind 13 mpg.
These engines would be an easy swap since they came installed in the CJs (at least the AMC 304 was in CJs but as I said they are all the same externally)
The problem with that is you'd be better off selling your 2 barrel and getting a 4 barrel. You might be able to get a carb with your V8.
OK so there are no direct bolt ins... I come from the sbc world where you can change the fi out for an intake and a carb. AMC I take it is a whole nother animal indeed.
So in short, rebuild what I have. I know clifford makes performance stuff for the AMC 258 i6 / 4.2l . Looks like it is time to start saving them nickels again!
Thank you all for your informative and insightful postings
1982 Jeep CJ-7 350 Chevy V-8, SM-465 4-speed trans, Dana 300 Twin Stick, Narrowed and locked GM 14 bolt rear, Narrowed and locked Dana 44 front, 38.5" Super Swampers. Fiberglass tub. 6 point roll cage.
OK so there are no direct bolt ins... I come from the sbc world where you can change the fi out for an intake and a carb. AMC I take it is a whole nother animal indeed.
Not really. You can easily go from FI to carb on just about any brand. The AMC V8 engines never came with fuel injection so there is no factory FI to swap away from. The 4.0 straight 6 is not much different from a AMC 258 i6 / 4.2l on the outside at least. They changed to a new head to go with the new fuel injection system. It's not hard to put a carburetor on it if you really want to. A lot of people will tell you you're doing it wrong if you want to do that because they like keeping fuel injection. But it's your rig so I say do what you want with it.
Keeping the 4.0 fuel injection with an older Transmission /Transfer Case combo does require some additional steps but only because you have to keep the fuel injection wiring, crank position sensor, and so forth. It's not rocket surgery but a lot of people are intimidated by it. But it's no more difficult for the 4.0 than it is for most other brands. Putting a TPI 350 into a '72 Chevelle requires similar levels of effort as putting a 4.0 into a CJ.
If you want to swap in a cheap 4.0 and drop a carburetor on it, go ahead and do it. Just make sure you get a pre-2000(?) block. They went to a distributor-less ignition in around 2000 or 2001 or so. I'm not sure if you can use a distributor in a newer block or not. If you can, ignore this part of my advice. But if you can't, you'll be ahead if you get the right block in the first place.
So in short, rebuild what I have. I know clifford makes performance stuff for the AMC 258 i6 / 4.2l . Looks like it is time to start saving them nickels again!
Thank you all for your informative and insightful postings
If I was going to go to the trouble of rebuilding, I'd do a stroker build. If you don't know the history of the AMC 258 i6 / 4.2l /4.0, I'll give you the short version. When AMC designed the 4.0, they took the AMC 258 i6 / 4.2l , bored it out a little (including making room with modifications to the water passages I believe) and shortened the crankshaft. When you put a AMC 258 i6 / 4.2l crank in a 4.0 block you end up with a 4.5 or 4.6 (depending on how much overbore you have in the 4.0 block to clean up the cylinder walls). You have to have a machine shop clearance the block a little but it's no different than putting the SBC 400 crank in a 350 to get a 377-383 (depending on overbore).
I like the idea of a stroker because it gives you good compromise. You get more power, especially torque, without having to do any complicated swap gymnastics. And your fuel economy, assuming you keep your foot out of it, should be on par with your existing setup.
Regardless of whether you drop in a 4.0, rebuild a AMC 258 i6 / 4.2l , do a stroker or swap in a V8 of any kind, there's no problem running a carburetor on any of them. I personally like fuel injection but if you like carburetors, there's no reason not to run them. The idea of a stroker with a 470cfm Holley Truck Avenger or 2bbl Motorcraft 2150 does have it's appeal...
In the end, it's your Jeep. If you want to run a carbureted 4.0, don't let anyone tell you not to.
So I can get the 4.0, hang an intake off the side of it and run my distributor? It bolts directly up to my existing tranny correct?
That is what I was really needing to know. When the thought of crank sensor came up it made me think that no 4.0 had distributor setups in them like my current engine.
Seems to me that is the most economical route at this time. Have been doing some research and these AMC 258 i6 / 4.2l will make decent power when set up with the right valves and cam.
Don't take my word as gospel. I'm a V8 man myself. But I did have an XJ with the 4.0 at one time. Mine was a 2001 with the distributorless ignition that was new either that year or the year before. I did help a friend do a tranny rebuild on his 91 4.0 and while I was in there I helped him do a cap, rotor, wire, plug replace along with a timing adjustment.
The CPS is for the fuel injection. It may help with computer controlled timing but it's more for the fuel injection. If you don't use FI, you probably don't need it.
Double check that a AMC 258 i6 / 4.2l distributor will work in a 4.0, or whether you need a specific distributor. Again, I don't know for sure.
And double check the manifolds. Make sure you can use them between the AMC 258 i6 / 4.2l and 4.0. There may be a difference in port sizes. I don't know for sure. A quick scan of Summit shows that the aftermarket manifolds don't show applications for both the AMC 258 i6 / 4.2l and 4.0. Though a quick google search finds other forums where one guy claims he's running a AMC 258 i6 / 4.2l manifold on a 4.0 head with no problems. But who knows if that's true or not.
