The Slant Six Engine

By Brendan Moore


chrysler-logo-small11960 saw the introduction of Chrysler’s famous Slant Six engine in the Plymouth Valiant with a gross horsepower rating of 101 ponies. The straight-sixes the company used before 1960 were awful, and Chrysler needed another engine for the happening Sixties.

The development engineers leaned the engine 30 degrees to the right, leaned the transmission 30 degrees to the left, and were able to get an approximately even weight balance in this fashion, hence the “Slant Six” name. The 170 cubic inch (round off to 3 litres) production design had extremely large main bearings which meant very low engine stressing, and the Slant Six started setting testing records in performance and durability right away. These results were mirrored in the Chrysler, Dodge and Plymouth customer population, with the Slant Six getting a reputation as being an engine that you couldn’t kill, even if you abused it. Ordinary citizens would run their engines up to 200,000, 300,000 miles with regularity. And by Sixties standards it got pretty good fuel mileage as well.

Increasing the size of the engine to 225 cubic inches and the horsepower rating up to 160 did nothing to decrease its longevity. One thing it couldn’t do, however, was run clean enough (with enough horsepower) to pass modern emissions standards.

The last Slant Sixes were produced for cars in 1984, for trucks in 1987, and, finally, in 1991 for marine use.

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Author: Brendan Moore

Brendan Moore is a Principal Consultant with Cedar Point Consulting , a management consulting practice based in the Washington, DC area. He also manages Autosavant Consulting, a separate practice within Cedar Point Consulting. where he advises businesses connected to the auto industry. Cedar Point Consulting can be found at

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  1. You are misinformed about the slant six. You got the high points right (huge main journals, couldn’t pass emissions in the 80s’) but missed details like the 170 and the 225 were just variants on the same design. The 170 was the LG (low deck G motor) and the 225 was the RG (raised deck G motor). Both were intoduced at the same time. The main differance between the two were that the 225 was the economy motor and the 170 was the even cheeper economy motor (never got a 4-speed). has a good history about the slant six and all its variants (the aluminim slant sixes, the hyperpac, the HEMI slant six from down under).

    Thanks for bringing a good motor to the attention of others.

  2. Well, Kevin, I just want to point out in my defense that I didn’t say anywhere in the post that the 170 and the 225 were different designs. I said merely that Chrylser increased the size of the 170 to get the 225. And I didn’t say the engines were released separately, either – I just didn’t say the engines came out together. I didn’t think that detail was really meaningful to the average reader, although I can certainly understand why you desire more detail in the post. You are obviously a fan of the engine (as I am myself) and want what you view as important data in the story. Hey, I’ve been there, Kevin.

    Guys like you and me have WAY too much information about cars in our heads, and sometimes it’s just gotta come out. But, to the average reader, too much detail makes their eyes glaze over.

    So, for those of you that want more detail about the slant-six, Kevin is pointing you to the right place, which is and they’re open 24 hours, too.

    Kevin, you are correct and thanks for your post.

    Brendan Moore

  3. To the writer:

    I think you got the level of detail right and I’m a car nut. Probably too much detail for the average person, but hen they’re probably not reading this anyway.

  4. OK, here you go, a testament to the slant-six durability: a silver 1975 Plymouth Valiant with the slant-six that did 112,000 miles with me, 79,000 miles with my little sister, 82,000 miles with her husband’s nephew, and is now sittng in my sister’s garage and still used as a spare car occasionally. I think it has just about 300,000 miles on it at this point, and has only ever had the heads re-done. Boy, is it beat inside, but it still runs pretty well.

  5. While I heartily approve of most of what you said on the slant six, I must disagree with the following quote:

    “The straight-sixes the company used before 1960 were awful”

    I have 2 of those motors. One in my 1958 Dodge D100 PU, and one in my 1959 Dodge D100 PU. Both of them run beautifully, 50 years later. All I’ve ever done to them is basic care– oil changes, valve adjustments, etc.,– for the last 20 years.
    So, I don’t agree with the “awful motor” statement.

    I’m obviously a big Mopar fan, but I don’t think everything they did was great. Wiring, for an easy example, was not one of their strong points.

    Anyway, just had to stick up for the mighty flathead.

  6. Came here from the New York Times blog. this is a good overview but short, but it’s all I need to know about an engine I never heard of. don’t know why they didn’t work on it to make it ok for emissions if it was that stout.

  7. The bearings were huge because they were not many of them.
    I think it only had 5 main bearings while most other
    modern designs had 7 main bearings. The key to the motor
    was a great battleship of a crankshaft. Anyone who lifted
    one will attest to this. To be fair Darts/Valiants did
    have terrible brakes. They pulled and one was always working
    on them if you lived anywhere with hills. I bet I can still
    change a water pump in a half hour. Try doing that with a
    front wheel drive transverse engine car. Distributor was
    a pain in the A** but eventually you got good enough that
    it was quicker to pull it out work on it and than put it
    back in as it was tucked under the engine next to the suspention tower. Kept me on the road cheaply for years.

  8. It is sort of amazing that Chrysler couldn’t make it pass emissions even if it was just ten years ago.

    Couldn’t they bring it back now with current technology?

  9. I agree about bringing it back. Modern electronic wizardry should be able to make that engine run cleaner as well as produce MORE horsepower. Should be a piece of cake considering what is does to other engines.

  10. Chrysler used to be innovative in terms of engineering, but that was a long time ago.

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