4.0 or 4.2

[Presvjetli]

I am interested in what is better AMC 258 i6 / 4.2l or 4.0 and that 4.0 fits the T-5 on CJ7 82.
For now my AMC 258 i6 / 4.2l is good, but ...

 

[Sasquach]

I am interested in what is better 4.2 or 4.0 and that 4.0 fits the T5 on CJ7 82.
For now my 4.2 is good, but ...

This is a much debated subject but if you have a good running AMC 258 i6 / 4.2l in your Jeep that would be the better engine in my veiw. you can do things to it as you see fit to improve power and driveability.

 

[Cheepjeep85]

the best of two very similar motors, well the answer to that question in my opinion would a mix of each. that's right a stroker motor 4.6. 4.0 block and head, AMC 258 i6 / 4.2l crank and rods.
but yes, if your AMC 258 i6 / 4.2l is running good, no need to swap it out. maybe just some add ons, fuel injection, ignition upgrades, etc.

 

[ThisGuyUKnow]

the best of two very similar motors, well the answer to that question in my opinion would a mix of each. that's right a stroker motor 4.6. 4.0 block and head, 4.2 crank and rods.
but yes, if your 4.2 is running good, no need to swap it out. maybe just some add ons, fuel injection, ignition upgrades, etc.

I agree 4.6 stroker. If you want it to run regular gas you have to have a machinist open the combustion chamber up a bit.

 

[CJim7]

See, now I like the opposite approach

I would take the AMC 258 i6 / 4.2l , install a cam, swap on a 4.0 head. Keep the injection if you want, or carb it. This essentially gives you the stroker that people get by swapping in the crank, and connecting rods from a AMC 258 i6 / 4.2l into a 4.0.
The reason I like this option is you are not messing with the bottom end of the engine (other then swapping a cam if you wish) and in my experience, the less you mess, the more confidence you can have in reliability/durability.

...Plus, that way you can still call it an AMC motor

But any way you go, the inline 6 is just a fun engine to modify.

 

[ThisGuyUKnow]

See, now I like the opposite approach

I would take the 4.2, install a cam, swap on a 4.0 head. Keep the injection if you want, or carb it. This essentially gives you the stroker that people get by swapping in the crank, and connecting rods from a 4.2 into a 4.0.
The reason I like this option is you are not messing with the bottom end of the engine (other then swapping a cam if you wish) and in my experience, the less you mess, the more confidence you can have in reliability/durability.

...Plus, that way you can still call it an AMC motor

But any way you go, the inline 6 is just a fun engine to modify.

Well youd be about .4 to .5 liters off of what everyone is going for

 

[CJim7]

Well youd be about .4 to .5 liters off of what everyone is going for

That's nothing. Really.

 

[Presvjetli]

O.K AMC 258 i6 / 4.2l remains inside.
Thank you very much for your advice. I asked this because I live in a part of the world where not easy to get parts for the Jeep.4.0 is aviable from Cheeroke...and AMC 258 i6 / 4.2l is very hard to find in my country
Tnx once again!

 

[Cheepjeep85]

See, now I like the opposite approach

I would take the 4.2, install a cam, swap on a 4.0 head. Keep the injection if you want, or carb it. This essentially gives you the stroker that people get by swapping in the crank, and connecting rods from a 4.2 into a 4.0.
The reason I like this option is you are not messing with the bottom end of the engine (other then swapping a cam if you wish) and in my experience, the less you mess, the more confidence you can have in reliability/durability.

...Plus, that way you can still call it an AMC motor

But any way you go, the inline 6 is just a fun engine to modify.

Well youd be about .4 to .5 liters off of what everyone is going for

you don't get the same compression ratio either, without changing out the pistons, so hp and torque potential won't be the same. anyone interested in this should check out this thread at pirate (yeah i know its pirate4x4 but still) http://www.pirate4x4.com/forum/showthread.php?t=784954

 

[CJim7]

The only major desireable trait of the AMC 258 i6 / 4.2l is the stroke. Likewise, the only major desireable trait of the 4.0 is the head.

So each motor is lacking one of the other...

Displacement doesnt mean a lot at this point, we're basically looking for the low end grunt provided by a longer stroke and the flow characteristics of the much improved 4.0 head.

I've ran my AMC 258 i6 / 4.2l /4.0 against true 4.6 strokers and the results were very similiar...heaps of low-end torque and crisp power off idle. There was no advantage either way, basically because the engines were pretty much the same when you break it all down.

All that said, It's simply easier to swap a head...then to swap an entire rotating assembly and a different cam to take advantage of the longer stroke introduced by the AMC 258 i6 / 4.2l crank....especially when those things already exist in the AMC 258 i6 / 4.2l block.

 

[ThisGuyUKnow]

you don't get the same compression ratio either, without changing out the pistons, so hp and torque potential won't be the same. anyone interested in this should check out this thread at pirate (yeah i know its pirate4x4 but still) 4.6L stroker racing/competition engine, normally aspirated - Pirate4x4.Com Bulletin Board

That can also be overcome by having the machinist open up the combustion chamber.

 

[Sasquach]

That can also be overcome by having the machinist open up the combustion chamber.

???????Have I lost contact here? but that would reduce compression and lower potential torque no?
Anyway the poster was looking for more basic advice IMHO and not trying to start a race war. maybe you did not notice but he is a bit off the grid being in Serbia and I'm guessing race machine shops are a bit scarce.

 

[Presvjetli]

I was born in wrong country ...

 

[Cheepjeep85]

???????Have I lost contact here? but that would reduce compression and lower potential torque no?
Anyway the poster was looking for more basic advice IMHO and not trying to start a race war. maybe you did not notice but he is a bit off the grid being in Serbia and I'm guessing race machine shops are a bit scarce.

i decided to keep quiet and not say anything else about it, but ahem, your right sasquach.

 

[ThisGuyUKnow]

???????Have I lost contact here? but that would reduce compression and lower potential torque no?
Anyway the poster was looking for more basic advice IMHO and not trying to start a race war. maybe you did not notice but he is a bit off the grid being in Serbia and I'm guessing race machine shops are a bit scarce.

Sorry for some reason i read into that and Was thinking about something else. I had a buddy who did that so he could run 87 in the stroker.