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Jeep Straight 6 Long Block in a JT

d k

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Good to know


I bought a prototype aluminum head at a swap meet last year - all-AMC event, races, show, swap meet, etc. It was one of three made. I know one of the others is on a 4.0 in a Grand Cherokee (ZJ or WJ, can't recall) - the guy was wondering about the head. He bought the Jeep for the engine, I think. Anyway, no one could ID it then after I bought mine, I recognized the pictures of his as being one of the prototypes.
Clifford Research had them made but the heads didn't help the low end and torque like they hopes. The power gain was higher in the RPM band than they wanted so they dropped the project.
When I bought the head it even came in the original Clifford Research box.
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5JeepsAz

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I'll be that 'other' guy. I'm 100% with the OP. Just thinking about it today, putting that straight six in there with no goofy tech, into an LE. Actually wondered if how many miles would matter, since the engine I like is 20 years old. They should be cheap enough to swap no problems.

Just as an answer, no harm meant, you go backwards when you went in the wrong direction.
 

ShadowsPapa

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The 4.0 is in pretty high demand these days. A lot of Eagle people are switching to them as well as a fair number of other AMC owners. It's an easy swap - but - not in the cars short of length in the engine bay. It's a long engine.
I don't even have to go into the things you'd run into - the firewall would be in the way, height could be an issue as it's also a fairly tall engine.
I have owned a number of vehicles with the engines in question and as much as I love my WJ and SX4 with the 4.0s, the SX4 having one beefed up a tad, they are pooches compared to the get-up-and-go, fly up that ramp like your life depended on it merging power of the 3.6
My wife's 2018 Grand Cherokee and my JT will both blow my 4.0 equipped vehicles out of the water.
Pulling power down low grunt and torque - I'll take my 4.0, and the 4.0 seems to do a better job pulling a trailer down the highway, but the 4.0 takes longer to wind up. Don't expect the 4.0 equipped vehicle to win any race against the 3.6
But a JT with a 4.0 crawling around the rocks - yeah, I'd like that.
 

ShadowsPapa

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There, it's in the foreground now - much better LOL

(The little SX4 is the car with the 4.0 in it)

Jeep Gladiator Jeep Straight 6 Long Block in a JT 20200425_162330_HDR
 

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brianinca

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I short shift in my YJ at 2000 rpm, 'cause I'm lazy like that. Just a great motor, but the 4.0 is of a different age to the FCA 3.6. Progress is real, I wouldn't want to go backwards.

Heck, I don't mind the RPM's the 3.6 pulls, I've always enjoyed winding up an engine. My Dad let me drive his old Barracuda in high school, 273 Commando with solid lifters and dual points. 6000 rpm was a LOT back then!

Also, adjusting solid lifters sucks. I like NOW engines much better!

The 4.0 is in pretty high demand these days. A lot of Eagle people are switching to them as well as a fair number of other AMC owners. It's an easy swap - but - not in the cars short of length in the engine bay. It's a long engine.
I don't even have to go into the things you'd run into - the firewall would be in the way, height could be an issue as it's also a fairly tall engine.
I have owned a number of vehicles with the engines in question and as much as I love my WJ and SX4 with the 4.0s, the SX4 having one beefed up a tad, they are pooches compared to the get-up-and-go, fly up that ramp like your life depended on it merging power of the 3.6
My wife's 2018 Grand Cherokee and my JT will both blow my 4.0 equipped vehicles out of the water.
Pulling power down low grunt and torque - I'll take my 4.0, and the 4.0 seems to do a better job pulling a trailer down the highway, but the 4.0 takes longer to wind up. Don't expect the 4.0 equipped vehicle to win any race against the 3.6
But a JT with a 4.0 crawling around the rocks - yeah, I'd like that.
 

ShadowsPapa

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LOL - AMC and others were using hydraulic lifters in the early-mid 60s.......... Chrysler/Plymouth was one of the last to move forward.
Normally, you don't need to do any adjusting with solid lifters for thousands of miles unless there's an issue. Mom had a Valiant with solid lifters - I don't recall that car ever having the lifters adjusted.

You do know that you had to set the lifter pre-load on an engine you've rebuilt - even with hydraulic lifters.......... at least you SHOULD.
 

brianinca

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Eh, the Chrysler rocker arms had an adjustment nut for a reason. Still got hot oil on you every 10,000 miles. Sure, there were hydraulic lifters on almost everything by '67, but that 273 was a high rpm engine for the time. At least it wasn't shim adjusted.

Heck, the distributor was also a real son of a gun, one set of points adjusted would throw the other set off. AND the AFB needed adjusting for spring and fall, and and and. I like me some EFI nowadays.

So the Valiant Sport? With the 2bbl and 4 spd Hurst? Buddy of mine had a convertible '64. Good motor.

LOL - AMC and others were using hydraulic lifters in the early-mid 60s.......... Chrysler/Plymouth was one of the last to move forward.
Normally, you don't need to do any adjusting with solid lifters for thousands of miles unless there's an issue. Mom had a Valiant with solid lifters - I don't recall that car ever having the lifters adjusted.

You do know that you had to set the lifter pre-load on an engine you've rebuilt - even with hydraulic lifters.......... at least you SHOULD.
 

Murgatroid

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Specifically something like the Jeep 4.6L 270 HP EFI Turnkey Engine

Could it fit in the engine bay? and allow for all the other necessary components (including the larger alternator, cooling systems, etc)? I can't find any specifications on dimensions of the 3.6L Pentastar
But why all the expense and trouble, have you blown the 3.6? I have enough trouble understanding the guys taking brand new Jeeps and dropping 700 and 1000 HP engines in them but I just figure they are over compensating for some short comings. Just what mountain are you climbing that you need more torque, and if that is it, why not go with factory diesel.
 

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5JeepsAz

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Put it this way. Sure, we make progress and it is good. Generally speaking, engines got better over time. Take your pick of the litter for your own reasons. All good. But consider this. We each have phones in a box that don't work anymore, don't fit anymore into the grid. Does that make them worse than today? No. Just outdated. On the other hand, you can still drive a mechanical Jeep from the first days of jeeps in the forties. I like things that do or can be made to perform the function. These new engines have tech nobody understands and nobody can fix. Just read the threads on any car forum. We make a mistake when we build something according to planned obsolescence, even if the designer of the Gladiator coined the term back in the 60's. My two cents is I want an engine from just before serious tech infected them. That's either the I6 or the one after. In thirty years, still mine will work, and all these new ones will be broke, just like them phones in the box. Outdated and the auto along with it. ESS lasting 30 years? I'll buy a coffee for anyone who lives to see that. My opinions. YMMV.
 

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I get that you guys are talking about strokers with more power output than the 4.0l HO, but did you guys know that Jeep had some JK test mules with 4.0l I6s and they had worse performance numbers than the weak ass 3.8l that everyone (myself included) complained about. IMO, the 4.0l I-6 is one of the most over rated engines of all time. I might be jaded though because the original 4.0l in my 96 XJ had catastrophic failure at 60k miles and the factory long block they replaced it with (goodwill) had bad piston slap after 20k miles. I’ve had a lot of vehicles with different engines and I maintain my stuff, I’ve never had an engine fail, use oil, knock, etc. good engine design for its time, but they were plagued with awful Chrysler quality control. People see the ones around now lasting long lives, those were the good ones, but a lot more than most people realized died early deaths.
 

ShadowsPapa

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I get that you guys are talking about strokers with more power output than the 4.0l HO, but did you guys know that Jeep had some JK test mules with 4.0l I6s and they had worse performance numbers than the weak ass 3.8l that everyone (myself included) complained about. IMO, the 4.0l I-6 is one of the most over rated engines of all time. I might be jaded though because the original 4.0l in my 96 XJ had catastrophic failure at 60k miles and the factory long block they replaced it with (goodwill) had bad piston slap after 20k miles. I’ve had a lot of vehicles with different engines and I maintain my stuff, I’ve never had an engine fail, use oil, knock, etc. good engine design for its time, but they were plagued with awful Chrysler quality control. People see the ones around now lasting long lives, those were the good ones, but a lot more than most people realized died early deaths.
I've owned several and still own two. Most folks I've talked to got crazy miles out of them. I know of a couple pushing 300,000 miles now. My WJ is at about 130,000 and the 4.0 in my SX4 was a VERY abused engine - the owner of that poor ZJ never changed the oil - looked like Texas crude when I got that engine at 100,000 miles.
I now have over 33,000 on the rebuild. Totally trouble-free. My WJ has issues but those are age-related and certainly not engine. It's more related to my father taking it when he owned it to a dealership that didn't know much about Jeeps - go figure.
The internals are pretty much exactly as AMC designed and built them. Even the external parts are - distributor gears and even distributors on the earlier ones interchange, manifolds/headers, the timing cover is even the same and I used the same Kent Moore tools from the 1960s on the 4.0 I built for my Eagle.
I'm running a number of AMC parts in my 4.0 - bearings, for example. So can't say mother MOPAR really did much to ruin the 4.0. There's a ton of 'em still around. The design really didn't change any other than to quiet them down a bit as more families and females bought Jeeps and complained about the noise - especially for the Grand Cherokee. (they do sound like truck engines - but then, that's sort of what they were designed for - Comanche, for example........)
Funny thing - I've never heard anyone ever complain about the 4.0 reliability until tonight. It's the first time I've ever heard a negative!

Now I am not advocating for putting them in anything that is newer than they are! No, I agree with Murgatroid in that it's a hell of a lot of work, effort, money, fabricating, whatever, to get one into a modern vehicle - and why?
Build a more modern engine. Build up the 3.6, or at least go with an engine designed and built in the last decade or so.
But to step back to the 4.0 is not the way to go - maybe in the future if you find one wrecked and in need of an engine and you want to have some fun - yeah, I've taken on projects like that just because I could and I wanted to find out how the story ended.

Putting a 1994 engine in a 1982 car makes a lot of sense - putting a 1990s engine in a 2020 vehicle, not so much.........

Hey, do what everyone else out there is doing with their cars and trucks - put an LS engine in it. Everybody's doin' it! HA
 

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I think you misinterpreted me a bit. They didn’t screw up the design. They had poor quality control. It’s a good design, that’s why the ones that have survived have lived such long lives.
 

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I think you misinterpreted me a bit. They didn’t screw up the design. They had poor quality control. It’s a good design, that’s why the ones that have survived have lived such long lives.
I guess I've never run into the quality control thing. Where I hang out when not here, the 4.0 is pretty much worshipped as one of the longest life engines ever, including the MOPAR years, the 94-96 are really prized. Not sure what you mean by them having quality control issues - I've never actually seen one blown. The Eagle people go nuts over them, and no one has ever commented on finding a bad one or one with any issues - at least not one that had under 100,000 miles.
I must be the most lucky person alive as I've owned a few, one I rather abused - and the only issue with it was the crank sensor! It was a freaky thing how it acted and didn't kick or store a code so the dealership had to get creative to find the issue. They did. They replaced the sensor and I continued to abuse that poor Jeep - hauling a trailer way too big for a Cherokee of the early 90s (boiled transmission fluid)
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