What the 4.0 could have been

9.3 cr with 87 octane is going to send the nox through the roof under load. They probably would have had to incorporate an egr valve at that point and possibly a knock sensor to correct the timing curve when some cheapskate put 85 octane in the tank. High 8s cr keeps combustion temps low especially with a cast iron cylinder head and it will run on anything without correction.
 
Poorly thought out? I don't think so, not in the least. It has been one of the best most reliable engines to have ever come out of Detroit and 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.

I’m going to go right along with Jerry on this and make a few comments as somebody that has had this engine in several variations since the 80s-

- First it was something they had the tooling to make , more or less. Or at least know how - it was a known so to speak, and that leads me to the next statement- with a newly acquired vehicle line they didn’t really have a lot of time- When you pull a drowning person out of the water you’re not worried about new clothes, You’re trying to keep him alive. Jeep was not thriving in the mid 80’s.


- that engine was so well respected that it was very important in reviving the jeep to make sure that it had a power plant that was favored by the market- We live in a world today where you can have an all new everything...and technology is so good that it will be a hit. The C8 Corvette testifies to that. Testing an all new platform on wary owners was not a smart strategy in ‘97. And remember test mules are built years before production. It was borne in the 258 era. They had to be able to tell buyers “this is an improved version of the old reliable
straight six”.

The YJ was ok, but was not well accepted- had they simply put round headlights in it it probably would’ve sold 50% more units. The TJ had to look like a Jeep, run forever like a Jeep and drive like a car or modern small truck. The TJ did.


Jeep needed a win, and to get a win they knew an inline
6 close to 258 displacement was important. They were right. An inline 6 was not negotiable. Even today potential owners look for that engine. Remember- jeep was trying to get the easy customer back first- the jeep guy- and make it drive better to attract the customer that wanted more refinement. The success of that thought process has been massive and continues today.


Next, it works. When is the last time...or first time....someone on here has broke an axle due to too much “hit” , which is power all at once. It does not destroy the drive train- it’s tractable power has a lot to do with a TJ’s potency off road- and the mild power to weight ratio has been part of the formula since its’ conception.

Yes, by modern standards, the output is low for what engine designers can yield from that displacement - easily- but in 1997 that was not as common-and a bigger powerplant was not in the cards when past success indicated a fuel injected version of what they had was right.

At the end of the day, it was “if it ain’t broke, fuel inject it and go 10 more years”.

Would 75 more horses be nice- sure with the tires we all want to run- but the ship has sailed and I’m glad to be on it regardless.

Also, as an arguable note, a quicker jeep would instantly make the short wheel bases’ flaws stand out with the best steering sold.

Poorly thought out - I’m going to contend that it didn’t need to be thought about at all.
 
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I’m going to go right along with Jerry on this and make a few comments as somebody that has had this engine in several variations since the 80s-

- First it was something they had the tooling to make , more or less. Or at least know how - it was a known so to speak, and that leads me to the next statement- And honestly with a newly acquired vehicle line they didn’t really have a lot of time- When you pull a drowning person out of the water you’re not worried about new clothes, You’re trying to keep him alive. Jeep was not thriving in the mid 80’s.


- that engine was so well respected that it was very important in reviving the jeep to make sure that it had a power plant that was favored by the market- We live in a world today where you can have an all new everything...and technology is so good that it will be a hit. The C8 Corvette testifies to that. Testing an all new platform on wary owners was not a smart strategy in ‘97. And remember test mules are built years before production. It was borne in the 258 era.

The YJ was ok, but was not well accepted- had they simply put round headlights in it it probably would’ve sold 50% more units. The TJ had to look like a Jeep, run forever like a Jeep and drive like a car or modern small truck. The TJ did.


Jeep needed a win, and to get a win they knew an inline
6 close to 258 displacement was important. They were right. An inline 6 was not negotiable. Even today potential owners look for that engine. Remember- jeep was trying to get the easy customer back first- the jeep guy- and make it drive better to attract the customer that wanted more refinement. The success of that thought process has been massive and continues today.


Next, it works. When is the last time...or first time....someone on here has broke an axle due to too much “hit” , which is power all at once. It does not destroy the drive train- it’s tractable power has a lot to do with a TJ’s potency off road- and the mild power to weight ratio has been part of the formula since its’ conception.

Yes, by modern standards, the output is low for what engine designers can yield from that displacement - easily- but in 1997 that was not as common-and a bigger powerplant was not in the cards when past success indicated a fuel injected version of what they had was right.

At the end of the day, it was “if it ain’t broke, fuel inject it and go 10 more years”.

Would 75 more horses be nice- sure with the tires we all want to run- but the ship has sailed and I’m glad to be on it regardless.

Also, as an arguable note, a quicker jeep would instantly make the short wheel bases’ flaws stand out with the best steering sold.

I will second and third @AndyG and @Jerry Bransford
 
She ain’t even got on a panty.

I bet those boys got a stern talking to before that started.

I’m gonna make another one of my random comments- It is one thing to be successful enough to become a celebrity- But for someone to have the longevity she’s had and make it in television and music and movies... That’s pretty remarkable.

My hat is off to her ....and I’d probably tell her to cover something up with it.
 
Also, as an arguable note, a quicker jeep would instantly make the short wheel bases’ flaws stand out with the best steering sold.
Super true. Speaking as somebody with a 4.7L stroker, well above 9.3:1 compression, a big cam, ported head, etc. a TJ with more than 300hp can be enough of a handful that random 16 year olds would be flipping them over left and right. A sports car the TJ is not. For some stupid reason I enjoy dealing with that handful though.
 
Super true. Speaking as somebody with a 4.7L stroker, well above 9.3:1 compression, a big cam, ported head, etc. a TJ with more than 300hp can be enough of a handful that random 16 year olds would be flipping them over left and right. A sports car the TJ is not. For some stupid reason I enjoy dealing with that handful though.

Well said- a TJ can drive good considering everything it is capable of driving over - But the short of it is when something is faster the handling needs to improve - So that a human being can process what is happening and turn that into input on the controls. The faster things happen the less time you have and the less you can deal with-
 
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It's pretty difficult to make an unreliable straight 6. They're mechanically simple and the inline bearings make most of not all iterations of a straight six practically invincible.

What really kills the AMC design vs. the Toyota 1 or 2JZ or the Barra is the intake and exhaust are on the same side of the head... causing thermodynamic inefficiencies.

What would truly be awesome is someone making an aftermarket head for the 4.0 that moves the intake to the passenger side.

-Mac
 
She ain’t even got on a panty.

I bet those boys got a stern talking to before that started.

I’m gonna make another one of my random comments- It is one thing to be successful enough to become a celebrity- But for someone to have the longevity she’s had and make it in television and music and movies... That’s pretty remarkable.

My hat is off to her ....and I’d probably tell her to cover something up with it.

hey if she doesn't want to wear panties, I'm fine with that !!!!! :love::love::love: I wish we could get REBA to do that too ! you just go clean your windshield and count your ducks :ROFLMAO:
 
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Same basic engine was in my '78 CJ-7. It had a distributor with a hole in the bottom, so every time I hit a puddle, the engine stopped. I had to get out, open the hood, give the dist a squirt of WD-40, close the hood and restart. Always worked.
Also had a carb, an air pump, and about a half-mile of vacuum hose.
I was driving up the highway in the winter of 1979, hit some black ice and was blown off the highway. Hit a utility pole dead between the headlights. Had two failures (?), the front bumper and the battery hold-down clamp. $200 total.
BTW, it ran on leaded gas, although it was difficult to tell 'cause the fuel gauge broke after about a year and the dealer could not find a new sending unit. No internet or Amazon back then. Just guessed from the mileage.
The inside was all steel, no plastic. In the winter if you accidentally let your bare arm touch the door, it would stick to it from the cold.
I much prefer my LJR!
 
Super true. Speaking as somebody with a 4.7L stroker, well above 9.3:1 compression, a big cam, ported head, etc. a TJ with more than 300hp can be enough of a handful that random 16 year olds would be flipping them over left and right. A sports car the TJ is not. For some stupid reason I enjoy dealing with that handful though.

Swing on by so I can test drive a stroker.
 
9.3 cr with 87 octane is going to send the nox through the roof under load. They probably would have had to incorporate an egr valve at that point and possibly a knock sensor to correct the timing curve when some cheapskate put 85 octane in the tank. High 8s cr keeps combustion temps low especially with a cast iron cylinder head and it will run on anything without correction.

Do you think there would be a noticeable difference in performance with those 2 changes? Are the low timing numbers on a stock engine for emissions or very conservative to make sure there are not any abnormal combustion? With stock tune I have seen 17 btdc at 3000 rpm at wot and half throttle to wot made no difference.
 
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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I built a 4.6 stroker in 08, so it’s a solid 240 hp if you get some port and polish with some 5.7 hemi valves… crane cam and 62mm tb.
 
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.

Yet the younger they are the dumber…
 
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.

Man, this would be such a fun conversation to spend a few hours on in real life😃
 
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man she's 68 and still looks good :love: I dont think 10 yrs difference would make her old enough to be my grandmother .....and just her voice can cause my chicken to spring up :ROFLMAO:

Reminds me of the woman who went streaking from the nursing home- Two old men were sitting on the porch and one of them said did you see that?? What was that?

The other one said beats me ... but it sure did need ironing
 
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?

View attachment 425057

Other than striking a nerve with comments I don’t think the conversation moved much In the direction of original question?-, giving this a bump. Curious as well on what happens moving the compression ratio up- no other changes- even if one had to run one of upper tier octanes- what does it give you?

Had a CJ7 with a 2.5- doing The head gasket I took the head to a local old school machine shop, ask them to true the head and take a little bit more
off . Really informal on the request and no clue- other than it was conservative- but the result was a slightly zippier 4cyl. So I always wondered if one addressed this with purpose, what could be had. It’s not just a matter of peak HP/torque- this would should everywhere in the curve.
 
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