The I6 Sacred Cow

Anyone care to explain what's so hot about an I6 engine, and why everyone rushes to suggest them over a V6?

I know that they were "special" enough for AMC to strech the CJ-5 and 6 front clip to make room for one, but that's about it. But what I don't know is really why. Best I can figure is that they're a relic from the bygone age of gas-hogging muscle cars, and everyone gets all dreamy thinking about them.

 

Bullet proof. Reliable. Great power to weight ratio for that era of Jeep. Good gas mileage for that era. Easy to work on. Parts are plentiful and relatively cheap. Wether you're talking about the 4.2L from the 70's and 80's, or the 4.0L from the 90's, they are great engines for the CJ, Wrangler series!

 

The original Rambler American straight six was designed for economy and duribilty. All AMC and Chrysler ever did was improve on the design and make it more reliable IIRC.

 

"My personal recommendation would be a Merlin V12"

Supercharged...?

 

The best way to make your Jeep FLY!
Just throw a Trent 1000 in while you're at it.

I have a straight 6 and contemplated throwing a v6 in just for it's size and the looks with the carb and air cleaner on top but I think I won't get rid of it at all. I am currently tearing it apart to rebuild and put a 4.0 head conversion on.

 

X2 on good engine for jeep . but none where good on gas them days . not even our jeep V6 . but that was simpler times :tea: :AMC:

 

Had one, a 258 in a '73 CJ. Makes a better highway vehicle than the f-head. But most of my jeeping is on old woods roads, and I often felt the straight-6 was much more engine than I needed or wanted. My F-134s are better for crawling the trails, and exploring unpaved back roads.

 

The inline 6 is the fewest number of cylinders that has both primary and secondary mechanical balance. http://en.wikipedia.org/wiki/Straight-six_engine#Balance_and_smoothness

They are very smooth. The Rambler sixes in particular were very smooth - I know from personal experience that, inside the car, you could not tell that their cars were running at idle. Rambler, and then AMC, were known for their excellent inline sixes, which were reliable, durable, economical and smooth.

Inline fours and V6s cannot be as smooth, due to their inherent design characteristics. Indeed, vibrations with the Buick odd-fire V6 were particularly bad, so Buick used very soft motor mounts to try and damp out some of the vibration. They gave up on the V6, then reconsidered in face of the '70s oil crisis, and bought the design and tooling back from AMC.

For AMC, changing to their own engines must have seemed an obvious move. They could shut down the V6 engine line, and sell everything back to GM. Just like today, the car manufacturers try to vertically integrate their engines, using as few engine types as possible.

 

That's what I was going to say.... the I-6 are a very well balance design.
And yes the AMC 258 has a great reputaion concerning DEPENDABILITY.
The AMC 232 and 258 develope maximum torque at a very low 1600 to 1800 RPM.
That number strongly effects the choice for optimum final drive ratio.
It mandates that one should run high final drive ratios for optimum on road fuel efficiency.
Main problem is that the high final drive ratios are a poor choice for offroad use.
So in essence it can be geared either for road use or for offroad use yet the optimum RPM range is not ideal for type both uses.

 

"Main problem is that the high final drive ratios are a poor choice for offroad use....So in essence it can be geared either for road use or for offroad use yet the optimum RPM range is not ideal for type both uses."

That may explain why I always felt it was "pushing" me too much on slow trails.

 

Lest we not forget the Dodge slant six (225?) and the Ford 300 six.

I6s, regardless of manufacturer, just seem to be great engines, for all the reasons listed above.

If ever there was an engine that deserved the name, "Dauntless," I would say it would be the I6 rather than the V6. (ducking fast).

 

There was a 170 and a 225 slant six. The 300 was first released as a 240, and used as the standard engine in Ford's big passenger cars, as well as pickup trucks. Ford, Chrysler and GM all had very good inline sixes. It's probably not fair to single out the 258, 225 or 300 as exemplary - the inline six has a long and distinguished history. How about the 230 Continental six? Bulletproof and durable, it appeared in a lot of different cars, including Jeeps and Checker cabs. IMO the Chevy 230 and 250 are also great engines and don't get the recognition they deserve. And how about the exotic sixes from European car makers like Jaguar, BMW and Mercedes? Plenty of inline six lore to draw from...

 

also you can stroke out the I6 amc to be an even better engine. like tim and everyone else said these I6 engines are bullet proof. heck back in the 80's a friend had a plymouth volarie with a slant six in it and ran it out of oil, made it to the gas station by pushing it in and put oil in and ran it for another year. i mean it locked up.

 

I had a mustang back in the day with the 200 I6 not allot of power but I ran it over 200 thousand miles.

 

Agreed, Tim. I, too, believe the general design qualities if the I6 engine, regardless of manufacturer, make it a great engine. There are many. Makes me wonder if, the reason for not offering them in current production vehicles, has something to do with their dependability. I'm sure modern emissions constraints and overall vehicle design (with limited space for a long engine) also can be regarded as reasons but.

Leads me to wondering about the straight 8 engine. Old feller once told me that he had owned a, maybe Buick or Olds, with a straight 8 in it. He claimed it was theeeeee smoothest running he had ever driven. Bet the head on one those things is HEAVY. I'd like to drive one, though. Just to see how it runs.

Side note: I had a '70 F100 with the 240 in it. Good little engine. Also owned a '83 F150 with a 300. Never owned any of the others, with exception of the 4.0 which, as we all know, are just as durable as the others and well known as 200k plus engines. Straight six. Yea, I like them.

 

I suspect that the compact and lighter configuration of the V6 has much to do with it. The V engines share more block material through the valley, which could make them stronger with less material. And they have shorter cranks. And the compact engine configuration likely affects the body and chassis design, and possibly aerodynamics. Fuel distribution is likely easier - in the days of the carburetor, long inline engines had difficulty evenly distributing fuel to the cylinders. Multiport fuel injection may remove that as an issue today... don't know. An automotive engineer could comment on this. <edit> Wikipedia suggests that assembly line logistics has something to do with preference for V6s today. V8s and V6s derived from the same design that share important dimensions can share tooling and equipment on the line. And they claim it costs less to lop off two cylinders from an existing V8 design, than to design something new.

Re the straight eights, they too have primary and secondary balance, and are very smooth. I'm guessing the crankshaft length and cost was the main issue there, aside from the stylishness/practicality of the very very long hood required. I don't think there were ever any 9 main bearing straight 8s - they were all 5 main bearing, and required an expensive forged steel crank. The 170/225 slant six was the only 4 main bearing inline 6 that made it into the "modern" age, AFAIK. Even those were compromised with a cast iron crank later in the run - supposedly the early engines with steel cranks are the ones to have. The "modern" inline 6s (ie AMC 199/232/242/258, Chevy 194/230/250/292 and Atlas engines, Ford 170/200/250 and 240/300) all have 7 main bearings, and a cast iron crank, which is a lot cheaper to produce than the steel crank, and preserves the durability associated with the earlier engines.

 

"engine configuration likely affects the body and chassis design..."

I once had a 1951 Pontiac Straight-Eight. Had an interesting 6V battery, narrow with "in-line" cells to fit alongside the engine.

It was extremely smooth.