Leaning Tower of Power: The Chrysler Slant 6 Story

Chrysler’s Slant 6 of 1960-1987 is remembered today as one of the most rugged and dependable engines in Motor City history. Here’s the story behind the indestructible Mopar six.

 

 

All through the 1950s, the Chrysler Corporation was noted for its engineering leadership and cutting-edge, high-performance V8 engines like the legendary Hemi. But oddly, the automaker’s six-cylinder offerings were antique L-head designs that dated back to well before World War II.

Overweight, bulky, and inefficient, the creaky old L-Head was totally unsuited for the all-new Valiant compact being readied for the 1960 model year. Chrysler’s engine specialists stepped up and designed an equally new and innovative powerplant for the Valiant, the Slant 6, which was then adopted by the company across the board. Along the way, the Slant 6 developed a reputation as one of the most rugged and reliable engines the Motor City has ever produced. Here’s the story.

 

Lead engineer on the Slant 6 project was Chrysler engine wizard Willem Weertman, then the company’s manager of engine design, and he began with a clean sheet of paper, taking nothing from the old flathead sixes. Of course, the engine’s most notable feature was its canted block with the cylinders laid over 30 degrees to the right. This permitted a significantly lower cowl and hood height, a key element in the Valiant’s distinctive styling, and it also made room for long, straight intake manifold runners for improved fuel/air distribution, a traditional trouble spot in inline-six layouts.

While everyone knows the Slant 6 name today, it took a few years to catch on completely, even within the company. Initially, Plymouth branded the engine as the 30-D, referring to the cylinder bank angle—not nearly as catchy, we can agree. Two displacements were initially offered: a 170 CID model for the Valiant with a 3.40-in. bore and 3.125-in. stroke, and the 225 CID unit, which used a long 4.125-in. stroke and a tall-deck block to power the full-size sedans.

 

While the canted block provided an obvious advantage in reduced height, there was another less obvious but equally important benefit. With the cylinders laid over 30 degrees, the water pump could be placed alongside the block instead of in front, shortening the engine’s footprint by a good four inches. Four main bearings also helped to keep engine length to a minimum, while the sturdy, deep-skirted block and short, stiff crankshaft ensured solid reliability and a long service life.

The big DC generator on this 1960 Slant 6 display engine indicates a full-size sedan application. The Valiant was offered from the start with a compact AC alternator. For the initial 1960 model year, the 170 CID version was rated at 101 hp at 4400 rpm, while the long-stroke 225 CID unit produced 145 hp at 4000 rpm.

 

Between 1961 and 1963, Chrysler produced more than 50,000 Slant 6 engines using an advanced die-cast aluminum block. Manufactured only in the raised-deck 225 CID version, this piece proved to be somewhat more trouble-prone than the standard iron block, with cast-in-place ferrous cylinder liners that tended to separate from the aluminium block casting. A special head gasket was also required.

Some of these aluminum blocks also included provisions for hydraulic valve lifters, though they were not so equipped. Sort of an anachronism in this regard, the Slant Six did not adopt hydraulic valve lifters until 1981. All previous versions employed old-fashioned solid lifters that required periodic adjustment.

 

Quickly developing a reputation for ruggedness and dependability, the Slant 6 was soon adapted to all sorts of marine, industrial, and agricultural applications—they could turn up almost anywhere. This Australian advertisement shows a 225 CID, 119 hp Slant 6 paired to a Chrysler Marine outdrive unit. Slant 6 Chryslers are also commonly found powering portable welders, self-propelled combines, and irrigation pumps. Many are still in operation today.

 

While not a performance engine per se, the Slant 6 did find its way into a number of performance applications. Here’s the installation in Tex Smith’s famed XR6 hot rod, winner of the 1963 AMBR Award, which sports three Weber sidedraft carbs and fabricated tubular headers. (Read the feature here.)

Chrysler offered the Hyper-Pak, an over-the-counter performance package sold by Dodge and Plymouth dealer parts departments. The setup included a long-ram intake manifold, special exhaust manifolds, domed pistons, and a special camshaft, boosting the output of the 170 CID Slant 6 to 148 hp or more. Updated versions of the trick pieces are now available in the performance aftermarket.

 

The Slant 6 was continually updated throughout the ’70s and ’80s—this later version sports a thermostatic air cleaner, air injection pump, EGR valve, and other familiar hardware of the Detroit emissions era. The venerable engine handled the modifications well, though they didn’t do the net output any good. In 1974 a 198 CID version (destroked for fuel economy) was introduced, and in 1977-78 there was a 225 CID Super Six variant that boasted a Carter two-barrel carburetor for a little extra punch.

One of the longer-running engine families of the era, the Slant 6 remained in production until 1983 in passenger cars and until 1987 in trucks, and not until 1991 was the engine finally discontinued in industrial applications. Thus closed the book on one of Detroit’s most beloved engines.

 

An interesting footnote to the Slant 6 story: Not many Detroit concept cars are motivated by a new engine design, but in 1960, Chrysler vice president of styling Virgil Exner created the Plymouth XNR prototype sports car. The concept’s unusual asymmetric design elements were directly inspired by the Slant 6’s offset engine configuration. This photo, as well as the photo of the XNR’s engine that leads this feature, are courtesy of RM Sotheby’s.

 

20 thoughts on “Leaning Tower of Power: The Chrysler Slant 6 Story

  1. I think everybody has had some connection to the slant 6. Aside from the “hemi”, it was probably one of Chrysler’s more popular engines. I, myself, have had several, and while I never thought of them as any kind of powerhouse ( dump enough gas in any motor and it will go) My 2nd car, a ’63 Valiant had a 170 slant 6, and I put a 2bbl. carb on it, but a friend’s Mustang, with a 240/6 always beat me. Truth be known, the slant 6 was a leaky, ( spark plug tubes, like the hemi) noisy, ( lifters and piston slap), hard to get at the distributor, (which was usually covered with oil) not very fuel efficient and as stated, not a very emission friendly motor, but usually chugged on and on, despite lack of maintenance, as the vehicle it was in, slowly disappeared around it. In line sixes are almost extinct now, ( except in semi’s) but there was a time when these motors were king. Thanks, MCG.

    • I owned five of those slant sixes, one small one and four large ones. The spark plug tube orings did need replacing every so often but in the 70;s they eleminated the tubes and went to a conventional design. The valve lifters did not require adjustment very often, probably every 30K or so. No piston slap on any I ever owned and they were very fuel effecient. My 1974 Dodge pickup without overdrive would get better than 20 mpg in a time when 6 cylinder Chevy trucks were lucky to get 15. I will agree that the distributor was hard to work on. It was much easier to remove it for service. One 7/16 head bolt and one wire, one minute.

  2. It also had a short lived NASCAR stint in a newly formed compact class, which was curtailed after Lee Petty and his Valiant dominated the class, winning all of the races, and surpassing all the other compacts entered.

  3. The first Slant Six we had at our place was in ’61 when Dad picked up a Valiant station wagon. Mom liked the ease of handling and maneuverability but wasn’t all that fussy about the manual transmission. Besides the gravel roads didn’t help the car’s longevity. It was replaced with a V8/auto model a couple of years later. After that we only had (2) more of those motors over the years: I got a Revell model (1/4) scale for my 9th birthday in ’62, and we had a John Deere swather with one in the early 70s. I worked on several during my years in the GM/John Deere dealership. My ex- father-in-law had a couple of Case 960 combines powered by them and he put them through the mill. I remember the fans in both losing blades and he simply welded them back on because a new fan was so ‘damned expensive.’ Muttered incessantly about the ‘cheap’ bearings in the water pumps after that. I drive past a power unit on natural gas running an irrigation pivot every day on my way to and from work. It’s been there for 30+ years and still going; drove past it this morning…

  4. Curiously perhaps, I have in my possession a 1962 Dodge Lancer with an aluminum block 225 slant six, and the book Wim Weertman wrote covering decades worth of Chrysler engine designs including. Both the book and the car I have are actually the property of the friend who did a lot of editing for Weertman on that book.

  5. The big old engine that got drunk and fell over was used here in Oz from 60 [R series] until 69 when it was replaced by the 6 cyl hemis. All 225s

    In reality it was archaic when released with 4 main crank and solid tappets. BUT because it was 225ci compared with 138 in Holdens and 144/170 in Falcons it was king,, until about 63 when Holden got a 179 that was quicker and Ford had the 170 working.

    We had 3 distinct versions, yellow truck, a torquey thing but slow, red 145hp single barrel engine and blue 160hp 2 bbl engine. There was sub versions right through those 9 years. Reputedly the late 68 69 block was the best
    Plenty of people made very good power from modified ones but you had to be carefull, 6000 rpm and they broke cranks! Though that big long stroke was part of that. But made them very torquey.
    Last one I owned was a US body [Oz assembled CKD] AP5 with mild cam, some headwork and triple SUs and extractors. 120mph car and dangerous over about 90!

    Surprisingly early Vals are not that popular here, the later 70 on cars with the hemi are far more popular. Personally I like the quirky early cars, R, S AP5 with typewriter trans and ball and trunnion tailshaft etc. 65 on were more normal mainstream and I suspect a lot more Oz made parts. From about 64 they were pressed here, some AP5s [63 64] have the wipers sweep to the LEFT pillar US fashion and later ones to the right,,, where the driver is!

    • Ah Grasshopper, you’ve missed a few local variants.. Shall we let the yanks know what they missed out on? 😀
      There were 6 Q’s imported with 170’s, to test the waters before R’s arrived, everything else was 225.
      R, S, and AP5 all had the ‘If it’s not rockin’, it’s not runnin’ cam, which was swapped out for the early AP6’s, until customers complained they were slower.
      VC’s (like mine) had the 145hp in manual and auto versions, with single barrel.
      VE’s had four versions – the same as the VC, plus a slightly higher compression unit with two barrel for the ‘160hp’ edition.
      VF’s also got a ‘Pacer’ edition, at around 195hp, before the Hemi 6 arrived. The Pacer V7F unit had a different head with better gas flow.
      VE also marked local production of the blocks – my daily driven VC currently has an ‘LVE8D’ casting – Lonsdale plant, VE high compression (160hp).
      When I got the car, it had an ‘AT2’ spec, which is the lower compression, wider torque band, for use in trucks – wouldn’t rev, but would spin the tyre on the white lines leaving every traffic lights, regardless of how light you pressed the gas pedal. 🙂
      The LVE8D in the daily driven ’66 VC Valiant (by Chrysler here in Oz, not Plymouth) wears a HyperPak, tuned headers, four barrel, Electronic Ignition,… and picks on heavy Commodores for laughs.

      • Yeah, I forgot the Racer Pacer slopey. A rorty torty thing,, still with a 3 speed box!
        The local blocks were reputedly better.,,, if you wanna buy and engine plant it is for sale!
        A friend had a VF with a decent bottom end and triple Webers, that was QUICK,, or until the 6 pack hemi [265 with triple Webers factory] arrived, the E49 was a high 13 sec car and had enough gears for a road race track. Off the showroom.

  6. I owned a Valiant but I forget what year it was. It was Green and White, which was a standard color. What I liked the most about the slant 6 was the ease in making repairs when needed on the electrical components on the engine, such as the alternator and starter motor. Everything was housed on top of the engine for easy access ability. I wish I still had it today. It was one of the best cars I ever owned.

  7. my mom had a ’64 Plymouth Valiant 225 (with fuel injection!) when i was a kid, a ’68 Valiant (to replace the ’64 destroyed by my drunken stepfather), and i had a ’69 Dodge A-108 van while in college (that i drove 750 miles from Birmingham AL to Ft Pierce FL with a BROKEN BLOCK that had been caused by a mechanics forgetting to refill the radiator after a cooling system flush – i had no choice but to attempt the trip… but I MADE IT! although i had to stop every 20-30 miles to put water in the damn thing) and a ’78 Dodge Aspen that i reluctantly sold when my mom offered me her ’84 Ford “baby” LTD – i should have kept the Aspen…

    ALL the Slant Sixes were amazing, reliable engines. Wish they were still available; i’d buy another in a heartbeat.

      • true. but my first stepfather was a powerboat racer (owned the hydroplane U-45, the Yellowjack, in SW Florida 1964-66) and he and his mechanic decided to see if they could make a conversion on the Valiant. it worked.

  8. I have owned probably 20 or more Valiants, Lancers, Darts and B bodys with slant sixes in the last 50 years. I presently have a 62 Lancer with a blue printed 225–Cam-Headers-Edelbrock 4 BBL manifold and a 450 Holly Carb–4 spd with the old trunion and a 7 1/4 rear. Estimated H P is 200 to 225. Runs good but gas mileage really suffered when I put the modified motor in.

    • The 450 Holley is a poor performer on a slant six. Try an Edelbrock 500 and you should see a nice fuel economy improvement with no loss in power and probably even a nice increase. If you really want a Holley the 390 is better, but not as good as the Edelbrock/AFB.

  9. I had good luck with all the slant sixes from the forklift on propane in a wire manufactor but best was in the 60’s Curly Allison a cousin of Bobby & Donnie had a 39 plymouth that blew a lot of doors off competition here in Georgia

  10. One significant slant six deature that goes totally ignored is its phenomenal performance capability when forced induction is utilized. I know of two examples here in the U.S. that make over 500 horsepower and one fuel-injected model in Australia that makes over 600. That will push an early A-Body down into the ten-second bracket in the quarter mile with speeds closely approaching 130 mph. Here is one such example: https://www.youtube.com/watch?v=7QzUfV8iTpQ

    What makes this motor especially suitable for turb9- or supercharging is its unusually robust architecture. Its short, forged steel crank and almost Diesel-like block and head make it a suvivor where other engines would be turned into scrap metal. That car in the video is running twenty-eight poinds of boost from a turbo and has experimentally run as much as 37 pounds wth no apparent damage.

    This is a too-well-kept secret and needs to get more exposure. The car in the pictue has a flat-tappet cam, no fuel injection, and a 5,500 rpm red line. All basic stuff; no high-tech.

    It makes swapping in a V8 when Granny donates her Duster, a questionable choice.

  11. Right, there aren’t many six cylinder engines made anymore, if you don’t count the ones in BMWs- maybe the best in-line sixes ever made by anyone, anywhere. And until fiarly recently, Jaguar made in-line sixes as well.

  12. My mom had a ’73 Plymouth Scamp and I’m pretty sure it had one of these engines. All I remember about it was turning up the idle so the car would run and turning it back down so it would pass NJ state inspection. She had the car about 14 years, before she was forced to junk it. The rear end and frame were beyond repair after it was creamed by a city plow truck one snowy winter morning.

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