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V8 vs I6 swap options

V8 vs I6 swap options
M

MayberryF3

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Knoxville
Vehicle(s)
1983 CJ 7, 1942 Willys MBT
I'm spitballing here so stand by,

I've been doing lots of reading (that's dangerous) and I see tons and tons of write ups for V8 swaps. How come there aren't more swaps to newer I6/4.0 motors? I assume if you are doing a swap that it doesn't make sense dollar wise to do a I6 instead of a V8.

But...here's my deal, my CJ sees mostly road and DD duties, and I don't really think I need a V8 swap, but is it dumb to go through the trouble of swapping to a newer I6 (maybe TJ 4.0 so 02-06) instead of going V8?

I have the AMC 258 i6 / 4.2l with a 4.0 head, T-5 Transmission , and a Dana 300 . Everything I read says the Dana 300 should be good to go, even if I go V8, but that the weak link is my T-5 . So I assume if I can find a TJ 4.0 and Transmission for sale I'd be better off in the motor and Transmission department than what I have now. Better yet if I can find a wrecked TJ I can pick and pull all the parts I would want regarding the wiring harness etc.

The physical swap also has some questions that I can't seem to find. Such as, If I go AMC 258 i6 / 4.2l to 4.0 would it require new motor mounts? Fuel pump? Etc

I'm sure I'll have more in few minutes but that's what I just thought of.
 
First let address the V8 vs. the I6: I6 - better gas mileage, more room in the engine compartment for other goodies, will work with current Transmission and Transfer Case . V8 - more horse power and torque, depending on the size tire you run will need a better rear end, less fuel mileage. Probably a lot more things, but that will do for now. Oh if you don't go with an AMC V8 other problems come into play with Transmission and Transfer Case .

Lets talk about current setup. You have a AMC 258 i6 / 4.2l with a 4.0L head.....dang all you need is the fuel injection system and you have a stroker AMC 258 i6 / 4.2l . Need a different fuel pump too. Heck of an engine combo that works with everything you already have.

A drive train from a TJ has enough differences that you will need an adapter for the Dana 300 (expensive). Different motor mounts will need to be swapped in. With the exception of the Transmission you will have a setup very similar to the above setup.

So the really big question here is what tire size are you running or will you be changing to a different size? To me tire size will determine almost everything you do to your Jeep. So maybe now you feel like your not getting enough power from your current setup. Is this due to tire size, gearing, Transmission , or maybe the engine needs some help. Just a guess, but what other reason would you want to swap to a different engine.

So let's first talk about the reason why you're looking at an engine swap. Also do you plan to run a different size tire? Do you know what the gearing is in the axles? If you would please answer some of these questions, I think we could all come up with some good answers, instead of the shot in the dark I just gave you.

Try searching this forum for fuel injection and 4.0L head swap. You might find some interesting stuff. Several people have done a lot of research on this and the details of how to do it.
 
PB- engine has the Mopar FI system. (At least that's what the receipts show). Which seems to be doing alright

Reason for the swap consideration was just that consideration. I didn't know if swapping to something newer maybe something I should look into. And seeing all the V8 swap threads got me thinking about it.

The only issue with the current drivetrain setup is that it has lots of noises. I think either the fuel pump or fuel injection hums loudly. Like hear it in the cab riding down the road loudly. And you mentioned fuel pump, or not having the right one, how do I know? There is also a tapping sound that to me sounds like an exhaust leak. And while none of the noises seem to affect performance, as I can roll down the road at 70-75 all day and have a little power to pass when needed. I'm not winning any steep interstate hill climbs if that is a comparison at all.

My biggest concern is how long this combo will last and how reliable is it. It's one thing to use the Jeep as DD where my wife can come and get me if it breaks down. It's another to be off on a backwoods fishing/camping trip with mini-me, to have the Jeep decide that is the right moment to give up the ghost. So maybe this is more of a "what should I be planning for" discussion

Along those lines it is good to know on the motor mounts, so either swap would need those changed. Either swap would also need some sort of adapter for the Dana 300 as well.

As far as current tires, they are 33x12.5x15 and I plan to stay with those or if I remove the body lift drop down to 31s. I'm not a huge fan of the body lift, but the tires are pretty new so I hate to swap them at the moment. I have no plans to go to anything bigger than 33s. Dana 20 in the rear. I don't know the gears. It does have a lunchbox locker, but I don't know the make of it.

Plans for the Jeep? Like I said mostly DD duties. Fishing, camping duties, and it pulls a small Willys MBT trailer. That's about it.
 
Your current setup is a good reliable setup if maintained properly. Noises can be really hard to nail down. The hum sounds like the fuel pump. it should be located as near to the gas tank as possible and lower than it. Could it be located inside the compartment area? If it hums while driving you may need help finding it while standing still. The injection parts on the engine shouldn't make any noise. If you find the fuel pump take a picture of it. There are guys on here that know that stuff better than I.

The tapping noise concerns me. It's either something lose or the engine. Does it change any as you increase speed? Is it present while standing still and idling? Tray to track it down. You really need to find it and eliminate it.

33x12.5x15 are large tires. They require some changes in a stock Jeep. Make sure your steering linkage is all in good shape. Your AMC20 rear axle needs to have one piece axles. If not do that soon.

You locker could be making noise to. If you pull the differential cover and take a picture, the guys on the forum can identify it. Knowing that they can tell you how to maintain it, and what noise it may make.

Swapping in a different engine is costly. Little stuff will eat your pocket book big time. I'd stick with the current setup. It's a good one. If you start having engine problems, fixing them will be cheaper than putting something new in.

Reliability, your driving a 30+ year old Jeep, anything can happen at anytime. Proper maintenance is the biggest factor in reliability.
 
PB- thanks

I am hoping maybe mine is just due for some long over due maintenance. From my other thread you know I have wiring issues.

Steering seems find, no binding or noises. I will try and get a video of the humming next time I crank it.

Here is a pic of the rear AMC20 . I was told it was a lunchbox locker but no idea on which one or ifnitnis even working right.

IMG_2454.webp
 
no locker there
 
Biggest reason I could think of keeping an I6 is for the torque curve, it starts so much lower than the average v8.

face it jeeps go slow, kind of scary driving one fast even on the freeway, short wheelbase and ancient brakes and steering.

but some guys have to have that power. I just think that when wheeling most of the time you are at near idle, where that I6 owns the v8
 
Jeep AMC 258 i6 / 4.2l to AMC v8 is a bolt in deal. Others 8's-Lots of custom fab'n.
Your T-5 will not live long behind the weakest of 8's.
In your picture of the R&P. That's a std open carrier No LSD or such.
Sounds like you're try'n to fix somedangthing that hasn't broke. :confused:
What R&P ratio do you have? Do you have 1 piece axles in that '20'?
LG
 
No idea on R&P, I looked for the tag like I've seen on other axles but couldn't find it.

No idea on axles.

I only got the Jeep in October so "I don't know" may be the answer to most questions. Lol.
 
Count the teeth on the ring gear and post up.
On the rear flat of the housing near the diff. cover at the 2-3 o'clock position will be a letter(s)stamp. What is stamped?
Post a picture of the rear axle brake drum area with the wheel off. We can let you know.
LG
 
Comments about a V8. I have a V8 jeep, it started life as a AMC 304 which was tired when I got it so a 360 was installed. The jeep certainly does have considerable "hop", but the mileage is awful. Quite frankly the CJ isn't a good candidate for a serious horse power upgrade. It's meant for relatively slow bobbling around in the back country with enough power to help pull your buddy out. It's a representation of a slower life style. You can dig deeper and go faster in a side-by -side ATV. A pick-up truck will carry a bigger load and run the interstate at speeds that would leave a sane person screaming in a CJ. Your I6, especially with a fuel injection will serve you for many years. I would find the extra noise makers and fix'em. You might need tub spacers, engine and Transmission mounts, maybe shocks. Those are relatively easy and inexpensive to repair.
 
Well-After put'n a built 401 Interceptor engine in my son's CJ5 I will say this.
Haven't seen a sand dune yet he can't conquer.
Horsepower is fun-LOL
BTW, this Jeep is his DD
LG
 
What I said, with the exception of sand dunes. Sand takes a lot of raw power to do well. :) The problem with big horse power, combined with paddle tires is keeping a Transmission and rear end intact. There is no stock rear end, even the Dana 44 that can stand up to that combination.

Okay, I can see it coming, how do I defend that statement? Rob at Willys Works talked to me about this very scenario. With paddle tires there is a lot of what I call snatch and grab in sand. I.E. tires spin and the paddles grab a bunch of sand shoving the jeep forward ....over and over and over again. He's had several friends that did just that, they couldn't keep from tearing up their rear axles until they moved on up to a big Ford axle. Don't ask which one, I don't really know axles very well.
 
Ford 9", is very popular in the back of Jeeps. I run one and never regretted the cost.
I will say that 401 is a handful in my son's CJ5 , and not for some 'kid/novice' who 'thinks' he can drive.:eek:
This Jeep is for someone WHO can drive.;)
:chug:
That said-My 6cyl has served me well for over 32yrs now.:cool:
LG
 
Take the engine belts off-See if the noise stops.
LG
 
Your ring and pinion gears should have some stampings on them. Looks something like this:

baaa0f9e-b6a4-4b09-973e-c5d52569cacb_zps100009ae.webp

Look at the very far right numbers. Mine is 46 and 13. That's 46 teeth on the gear and 13 on the pinion. Divide 46 by 13 and you get 3:538 when you round up 3:54. That's my gear ratio.
 
Hedgehog said:
:) The problem with big horse power, combined with paddle tires is keeping a Transmission and rear end intact. There is no stock rear end, even the Dana 44 that can stand up to that combination. .
Click to expand...


WOW that's quite a statement. You probably need to come to the Oregon Dunes National Recreation Area and see for yourself how it really is.
It does take good equipment but nothing like your describing ..Not trying to put you down just that there is entry level to all out and a lot in between.It is very popular for Oregon/Washington residents . A 9" ford or Dana 60 is a great addition for the hardcore hill climbers but most do just fine with less.
 
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