What the 4.0 could have been

Brianj5600

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In my opinion the 4.0 was a poorly thought out engine. The only thing I can think is it was all to do with emissions. There is a calculator on jeepstrokers.com that is pretty handy for working up combinations. I found that with a stock 4.0, zero decking and switch to a 0.040" head gasket gets you 9.3 static compression, 8.0 dynamic compression ratio and 0.040" quench. It should run fine on 87 octane. I'm curious how much power those 2 things would help. Anyone have a horsepower calculator that is some what accurate?

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In my opinion the 4.0 was a poorly thought out engine. The only thing I can think is it was all to do with emissions. There is a calculator on jeepstrokers.com that is pretty handy for working up combinations. I found that with a stock 4.0, zero decking and switch to a 0.040" head gasket gets you 9.3 static compression, 8.0 dynamic compression ratio and 0.040" quench. It should run fine on 87 octane. I'm curious how much power those 2 things would help. Anyone have a horsepower calculator that is some what accurate?

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Is it poorly thought out, or just old? I thought it was just iteratively improved from some old ass AMC design from the 70s
 
Is it poorly thought out, or just old? I thought it was just iteratively improved from some old ass AMC design from the 70s

1963ish from the early AMC Ramblers with the 242, if I recall correctly. It was a very old and highly refined engine by the time the TJs ran it. That doesn't mean it was a good engine for that time, though.
 
Poorly thought out? I don't believe so, not in the least. It is well proven to be one of the best and most reliable engines to have ever come out of Detroit and it has earned a sterling reputation. It's based on an old AMC design and it is extremely well-proven and long-favored engines. To say it has stood the test of time would be an understatement. And if it wasn't a truly great engine it wouldn't have been used in so many Jeep models over so many years. Bad engines don't get used long, look at the 3.8L V6 engine the early JKs came with... it was replaced with the 3.6L 4 years after its introduction.
 
1963ish from the early AMC Ramblers with the 242, if I recall correctly. It was a very old and highly refined engine by the time the TJs ran it. That doesn't mean it was a good engine for that time, though.
Dang, older than I thought. I like the 4.0, it's a good motor reliability wise. Were there better motors out there in the late 90s/early 00s? Forsure. But that's probably more of chrysler cost cutting than anything else. At least we didn't end up with something like the renix version lol
 
It's funny the way historical glasses work in 20/20 vision when looking back. The 4.0L engine is arguably the most successful engine platform ever seen in a Jeep. When looking back now, it seems antiquated. Because. It. Is.

That's how history, and the marching on of technology, works. To appreciate it, you have to look at it in the context of the technological period from which it came. Why was the Wright Brothers' plane so inelegant?
 
It's based off the 1964 AMC 232, which American Motors placed in their 2-door hardtop, called the Typhoon. That little 232 begat the 199, the 258, and the 4.0 (242 cu. in.). Produced for almost 40 years, if the original 232 engine it had been a poorly thought-out design, it never would have survived to become the 4.0.
 
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It's based off the 1964 AMC 232, which American Motors placed in their 2-hardtop, called the Typhoon. That little 232 begat the 199, the 258, and the 4.0 (242 cu. in.). Produced for almost 40 years, if the original 232 engine it had been a poorly thought-out design, it never would have survived to become the 4.0.

As you say, that long history argues the basic design works well for its intended purpose. It is also true that it's a dog in stock form and that it's difficult to make reliable big power with the platform.

I'd be interested to know if there is any longevity data comparing the 4.0L to the SBC, another long lived design of the same era which could be modified to make big power in a pretty reliable manner.

edit: I had a 1985 Volvo 245 DL wagon with a NA 2.3L four. That engine was renowned for its reliability and mine was great well beyond 200K. But it also made about 110hp and I always thought it seemed relatively easy to be reliable with that little stress on it.
 
My first car was a '65 Rambler Ambassador with a 232. My current TJ has the 4.0L. I guess I'm in a 50-year rut.

Huge AMC/Rambler fan, here. Still have a several engines in the garage, including two aluminum-block 196 six-cylinders. Have owned around twenty AMC products. Love 'em!
 
As you say, that long history argues the basic design works well for its intended purpose. It is also true that it's a dog in stock form and that it's difficult to make reliable big power with the platform.

I'd be interested to know if there is any longevity data comparing the 4.0L to the SBC, another long lived design of the same era which could be modified to make big power in a pretty reliable manner.

A straight six vs a V-8...how does one compare the two when seeking but one goal? If the ability to affordably build a powerful engine is the goal (using aftermarket parts, we'll say), then the SBC is king. AMC never had that in mind with their straight six engines, and the aftermarket has never really offered much in the way of performance parts for any AMC engine (at least not compared to the Bowtie offerings). As for reliability, I'd bet on an AMC straight six reaching 300,000 miles long before I'd bet on the SBC doing so. But then again, I will admit to my bias. ;)
 
...As for reliability, I'd bet on an AMC straight six reaching 300,000 miles long before I'd bet on the SBC doing so. But then again, I will admit to my bias. ;)
That's exactly my question. Anecdotally, you see not infrequently on this forum people reporting dead 4.0s before 200K as well as lots of posts citing the 300K+ potential of the motor. Obviously "your results may vary" depending upon a host of factors but I'd like to know what the real longevity numbers are.

Also the hp/liter of the 4.0L and the Volvo 2.3L I mentioned in my edit above are almost identical (i.e. neither is under a lot of pressure so they had better last:))
 
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It's funny the way historical glasses work in 20/20 vision when looking back. The 4.0L engine is arguably the most successful engine platform ever seen in a Jeep. When looking back now, it seems antiquated. Because. It. Is.

That's how history, and the marching on of technology, works. To appreciate it, you have to look at it in the context of the technological period from which it came. Why was the Wright Brothers' plane so inelegant?

About the only accurate positive thing you can say about the 4.0 in the TJ is it is reasonably reliable. It is heavy for what it is, it has a low output per liter, it is not efficient, and it has to run a lot hotter than it could to meet emissions.

It isn't easy to modify for either more horsepower or better mileage. It is just okay, not terrible in a stock rig, but add anything much to move away from stock and boy do the deficiencies start showing up.
 
About the only accurate positive thing you can say about the 4.0 in the TJ is it is reasonably reliable. It is heavy for what it is, it has a low output per liter, it is not efficient, and it has to run a lot hotter than it could to meet emissions.

It isn't easy to modify for either more horsepower or better mileage. It is just okay, not terrible in a stock rig, but add anything much to move away from stock and boy do the deficiencies start showing up.

All true. I've heard two things praised regarding this engine: the reliability, as you noted, and the flat-ish torque curve. Weight, efficiency, power output - not so much. By the time it was in the TJ platform, it was already long in the tooth, and after a decade in that platform, it was as refined as an engine ever gets. In fact, it's been rumored (most likely true, I would guess) that federal emissions standards ultimately killed it. The 3.8L V-6 minivan engine that replaced it was likely responsible for why the 4.0L was so well regarded...
 
I'd be interested to know if there is any longevity data comparing the 4.0L to the SBC, another long lived design of the same era which could be modified to make big power in a pretty reliable manner.

There's a lot going on there, but two things come to mind; 1) There's no replacement for displacement. You need to compare the 4.0 to a Chevy 265 (4.3L), which the standard rating was around 160 hp, and 200 hp (gross) was the top. Those engines are hard-pressed to get 300 hp NA. 2) Engine block nickel content of the SBC changed throughout the 70s, and oils improved, so It'd be hard to find any real apples-to-apples comparison.

The car in my avatar has its original '64 327 with mileage somewhere in the 14x,xxx range. Chrysler generally built a better engine back then, but IDK much about AMC.
 
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All true. I've heard two things praised regarding this engine: the reliability, as you noted, and the flat-ish torque curve. Weight, efficiency, power output - not so much. By the time it was in the TJ platform, it was already long in the tooth, and after a decade in that platform, it was as refined as an engine ever gets. In fact, it's been rumored (most likely true, I would guess) that federal emissions standards ultimately killed it. The 3.8L V-6 minivan engine that replaced it was likely responsible for why the 4.0L was so well regarded...

Two things killed it based on my chat with the engineer. First was emissions and then crash test standards. When we lifted the hood on the first JKs and saw how far back from the grill the engine sat, we asked them if that was done for a future V-8 offering and he said nope, crash tests.
 
Yeah - don't tell Zorba, but due to the 2018 backup camera law, he'll be stuck with a screen in his next NEW vehicle, should he buy one!

That's a curious domino effect from crash safety requirements leading to modern vehicles becoming increasingly thicc and blobby while reducing driver visibility out the windows and mirrors.

The move away from leaded gasoline is interesting because it was becoming very clear in the 1960s that there was a strong correlation between endemic lead pollution from engine exhaust and widespread neurological impairment. The switch to unleaded fuel corresponds to a dramatic decrease in neurological disorders and a reduction in crime. Basically we were poisoning ourselves with lead in conjunction with the proliferation of the automobile. And the automotive and oil industries of the time fought these EPA regulations.