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The Chrysler Slant Six Engine (170-198-225)

The Slant Six became a legend for its endurance, but for a few brief, shining moments, it was a true performance engine as well.

Nicknamed for its 30° slant when installed, the slant six had a better mixture of power and economy than contemporary GM and Ford sixes. The slant was needed to fit under the compact, low-slung Valiant’s hood; it made room for efficient manifolds, which is one reason why they kept the slant when it was used in bigger cars and trucks (the other was the cost of changing it).

1961 aluminum slant six engine

The slant six manifolds’ bends had large radii, and intake tubes and exhaust tubes were nearly equal in length. The design assured that each cylinder got the same amount of air and fuel at the proper time, and that exhaust gases were fully, equally vented. Competitive designs made some cylinders “double up,” or had sharp bends or tubes with very different lengths.

The 1960 HyperPak option, added a four-barrel carburetor and other parts to push out a V8-like 196 horsepower. Modern racers have used turbochargers and different carburetion and manifolding to produce far more.

An export version, used in Australian cars, pushed the engine to 160 bhp by using a two-barrel carburetor; and the 1977 “Super Six” used a two-barrel Carter carburetor to increase responsiveness without loss of economy. On the other end, the 1976 Feather Duster package let the 1976 slant six achieve 30 mpg on the highway.

Ford 223

225 Slant Six

145 hp 145 hp 135 hp
206 lb-ft 215 lb-ft 207 lb-ft

Heavy-duty slant six engines used in industrial and some truck/bus (perhaps fleet as well) applications used a double-row roller timing chain, chrome-plated upper piston rings, and other features depending on service duty (polyacrylic valve stem seals, positive valve rotators, stellite-faced exhaust valves, and/or a high-volume oil pump). Some say you can retrofit the double roller chain and gears into car slant sixes; the double row timing chain is NAPA part 9168, used from 1962 to 1975 on the slant six; the sprockets are part S338 and S339 (thanks, Bob Rodger).

slant six

The slant six’s creators talk about it: Pete Hagenbuch | Willem Weertman

The plugs, distributor, and coil were grouped closely together on one side. Most replaceable parts, including the filters, air cleaner, water pump, coil, and dipstick, were relatively easy to reach.

At launch, the pistons were a tin-plated aluminum alloy, with cast-in steel struts for thermal control; the top ring was chrome plated, the second ring was tin-plated, and a sectional oil control ring had chrome-plated steel rails.

engine torqueThe slant six replaced an old flat-head design starting in 1960 models, and lasted in US-built cars through 1983, in US-built trucks until 1987, and as a marine engine until 1991. After leaving its original plant in Trenton, Michigan, the six was produced at Chrysler’s Toluca, Mexico engine plant. It was the last in-line Chrysler engine with more than four cylinders.

Charlie S. noted that you can tell the difference between the 170 and 198/225 engines by looking at the rubber hose that goes from the water pump to the underside of the head: if it is about 1 1/2 to 2 inches long, it’s a 170 block (G engine). If it’s about 3 inches long, it’s a 198/225 (LG engine).

The aluminum slant six

This section by Warren Steele, retired cost estimator

The aluminum six grew out of the original Valiant car development.

A 170 cubic inch, six-cylinder engine was planned for this car, but it was too long to fit in the engine bay. As a result, the engine was laid over at a 30° angle and the water pump was moved beside the block, which shortened the assembly.

slant six enginesIntake and exhaust manifolds were made level, which resulted in a “bunch of bananas” intake manifold said to be “tuned!” Many of us never liked this entire arrangement, as it severely restricted access to spark plugs, the distributor, and the starter. This was something we had to live with forever! We did look at straightening up the engine but costs were too high.

At about this time, the Chevy Vega was coming along with an aluminum block engine, so of course we had to have an aluminum engine; a few made it into production. Thankfully, not many serious problems developed (they included overheating, cylinder bore cast iron liners shifting, and water leaks), but that operation was shut down. One of my estimators bought a car with this engine, but it was recalled. GM’s aluminum engine program was a disaster and was cancelled.

It was said there was never to be anything larger in the Valiant than the 170 cubic inch engine, but that edict was rescinded. Soon the 225 engines replaced the 170 and eventually we even put 340 and 360 in — V-8s in that engine bay! So much for “we never will need anything more than a 170 engine.”

Why the six is slanted

A 1960 press release named four reasons for slanting the engine, one of which is the real reason, according to Warren Steele:

nodular crankshaft

The change also made room for an unusually efficient intake and exhaust manifold with wide bends and similar-length tubes going to each cylinder, reducing restrictions and uneven airflow. The lower center of gravity would help the early, more nimble Valiants and Barracudas to be in the top of their class for handling.

Facts for owners

slant six firing diagram The slant six gained electronic ignition in 1973, a strong, reliable system over the long haul — though the ballast resistor tends to fail, making starting impossible. Replacing the ballast resistor costs about $3 and two minutes, but many mechanics then and now replaced the entire electronic ignition system when it failed.

Valves needed to be adjusted manually until hydraulic lifters were used, starting in 1981 (a small number of earlier fleet vehicles had hydraulic lifters).

Once a year or so, a couple of drops of light oil need to be placed onto the felt pad under the rotor in the distributor. The factory recommended engine oil for this.

The crankcase inlet air cleaner was supposed to be cleaned annually, though often owners and mechanics simply ignored it, resulting in blue smoke from the exhaust as it clogged.

Wet weather stalling can be fixed by using a high quality distributor cap and rotor (e.g. Mopar or Bluestreak), high-quality wires, a distributor cap gasket (Standard PN AL-483G), and, in some cases, putting weatherstrip foam over the ignition and voltage regular modules. You can get wires and other parts cheaply on-line.

Trenton Engine

Until the end of 1972, the oil filter standpipe was too long for short filters, so long-canister filters, such as PureOne PL30001 and Fram PH8A, must be used. Scott Sigethy recommended using Ford filter FL-30001 (made by Purolator) because its double seals, which prevent the engine from being starved for oil. Starting in 1973, shorter filters such as the STP S-16 become more advisable since the tall filters won’t fill all the way, and the engine will get oil a little later on startup (thanks, Scott).

See our page on slant six spark plugs and spark plug tubes.

Daniel Stern advised owners to check for timing chain stretch.

slant six engines

Ben also suggested using a composite rubber/cork gasket: “I’ve found the rubber ones tend to harden up too quickly, and then leak, and pure cork isn’t much better. I don’t believe the rubber gasket is intended to have any sealer applied to it.”

The firing order is 1-5-3-6-2-4.

A common problem is manifold cracking - see below for a discussion.

Slant Six Hyper-Pak

In most years, the slant six used a forged steel crankshaft, moving to cast nodular iron in the middle of 1976 model-year production, as a running change. Daniel Stern wrote, “The forged crank is stronger in theory, but the cast crank is still plenty strong for all but the hardest-core builds. There isn't really any practical reason to think you're unlucky if you have a cast crank.”

The standard carburetor for most slant sixes was a single-barrel. You can increase performance and gas mileage by switching to a good dual-barrel, but that requires swapping the manifolds, too.

Rodger claimed it was easier to get a muffler with an inside diameter of 2.25 inches, and a two-inch inside-diameter outlet, recommending a long body. He wrote, “On the original engine, they used a smaller than needed diameter exhaust pipe to the muffler; this saved money. The high performance variations are different.”

Slant Six line drawing

Dan Stern provided these standard carburetors used by Chrysler for North American cars:

Walt Ronk wrote about the Lean Burn (the world’s first such computer-controlled system, except the electronic fuel injection used on some 1958 Chryslers). He said that, according to the Mitchell guide, there was no difference between 1979’s Electronic Spark Control ignition (ESC) and Electronic Lean-Burn ignition. The ignition box is mounted on the air cleaner. There was an early style with two pickups in the distributor and a later version with a single pickup.

Slant six performance

We have moved the performance section to our Valiant site and have a section on the slant six Hyper-Pak.

super six

As for the Super Six, Pete Hagenbuch said:

Here I was [in 1975], the head of the valve group working in the road test garage with two road test mechanics that didn’t know much about engines. The three of us together managed to set up the first two barrel 225. That really turned out to be a winner, in fact my youngest son had one and he just loved it.

cutaway diagram

... The first and most important thing was the carburetor; it had 2 holes in it. Oh, there is so much you can do, Dave, that doesn’t even show. We messed around with the spark advance schedules and did a super calibration job on the carburetor. We had a low restriction air cleaner. Improved exhaust system but still single of course. I wanted in the worst kind of way to have a twin exhaust system because, man, will that do wonders for a six. You put one, two and three, and four, five and six together and you run ’em down about 6 or 8 feet and bring them together in one tailpipe and you’ve added great huge gobs of output.

Engines, especially engines that are low output, the things you can get for just a little bit of effort are just unbelievable sometimes. But to turn that 225 from what I always thought was a real slug, but a dependable, durable slug, into one hell of a nice engine, that was a fun program.

super six carburetors

Like the standard slant six, the Super Six used a cast-iron crank, long-branch intake with curved pipes, hardened valve seats, a single exhaust with catalytic converter, aluminized steel exhaust, and, starting in 1978, steel-backed aluminum-alloy main bearings.

Bill Cawthon wrote: “The first Bricklin concept car, built by Bruce Meyers of Meyers Manx fame, had a Slant Six under the hood.” (The first production engines used 220HP AMC 360 V8 engines.)

Slant six camshafts

Gene Yetter wrote that the Direct Connection racing manual lists a hotter camshaft as part number 3512639. It had a 244° duration, 26° overlap, 0.406” lift on intake, and 0.414” lift on exhaust. Valve lash was 0.010” on intake; 0.020 on exhaust. Settings are “hot,” and it’s recommended as being “best for 1971-77” engines.

Gene also wrote that, according to Daniel Stern, there is a new Dutra/Erson RV10-RDP cam. “Anyone can now have their solid-lifter Slant-6 cam reground into an RV10-RDP by requesting Grind #2106. The RV10 and RV15 cams use Erson intake profiles, the Mopar 244 exhaust profile, and non-standard (not 110) lobe separations to approximate the Mopar 244 cam lobe separations.”

Dan continued that it was not important whether one used a forged or cast crankshaft, but...

The basic engine hard-parts factor that directly constrains camshaft selection is whether you're running a 1960-1980 solid-lifter valvetrain or an 1981-1987 hydraulic valvetrain. Either type can be run in any Slant-6 engine, but you have to have all the pieces: camshaft, lifters, pushrods, rocker arm assembly. Camshaft selection is much wider for the solid-lifter setup.

There are still many other variables in the cam choice, such as how the engine is configured (compression ratio, induction and exhaust systems, etc), vehicle weight and drivetrain specifications, intended usage, etc.

All in the slant six engine family

Joseph Newhouse provided the following chart for slant six powered cars from 1959 to 1978; it does not include trucks, which could be rated somewhat lower than cars as they had changes for higher durability. These are Federal, not California, numbers. The slant six continued in use through to 1987 in Mexico, where, with a rejetted Carter YPF two-barrel carburetor and recurved distributor to reduce emissions by 30%, it was rated at 98 hp net.

Engine Year(s)
(red = gross)
Torque  (lb-ft)
170 1959-1963 8.2 to 1 101 @ 4400 155 @ 2400
170 1964-1966 8.5 to 1 101 @ 4400 155 @ 2400
170 1967-1969 8.5 to 1 115 @ 4400 155 @ 2400
198 1970-1971 8.4 to 1 125 @ 4400 180 @ 2000
198 1972 8.4 to 1 100 @ 4400 160 @ 2400
198 1973 8.4 to 1 95 @ 4000 150 @ 1600
198 1974 8.4 to 1 95 @ 4000 145 @ 2000
225 1960-1962 8.5 to 1 145 @ 4000 215 @ 2800
225 1963 8.2 to 1 145 @ 4000 215 @ 2400
225 1964-1971 8.4 to 1 145 @ 4000 215 @ 2400
225 1972 8.4 to 1 110 @ 4000 185 @ 2000
225 1973 8.4 to 1 105 @ 4000 185 @ 1600
225 1974 8.4 to 1 105 @ 3600 180 @ 1600
225 1975 8.4 to 1 95 @ 3600 170 @ 1600
225 1976-78 8.4 to 1 100 @ 3600 170 @ 1600
225-2V1977-788.4 to 1110180

Lost slant six performance potential

Auto Trader’s Neil Newman (as interviewed by John Gunnell) said there was a slant six in the Engine Development Lab with a special intake carrying a pair of four-barrel carburetors. “We got a tremendous amount of horsepower with it, but it didn’t idle well.”

aluminum slant six

The aluminum RG version was dropped in 1963, and executives rejected an even larger (246 cid) block with side-fed hydraulic lifters, and a high-swirl, fast-burn aluminum head (developed in 1978) that could have pushed the slant six on past 1989 by increasing power and cutting emissions. Other possibilities (provided by Daniel Stern), most of which were never produced, were:

* Chrysler engine tester Marc Rozman remembers seeing a 1975/76 Dodge Monaco with the turbocharged slant six — it ran very well.

Revell kit

Jim Grundy wrote, “I was an engineer at Chrysler from 1967 to 1971. I designed an overhead cam slant six while I was at Chrysler, and built it in 1971 - 1972 (170 cubic inch). I installed the engine in a Dart. I wanted to use the engine as an example so I could convince someone to help me create an OHC conversion for the 392 HEMI. I was unable to find interest for this project, so I sold the car in 1973. Then, in 1992, a friend of mine saw my engine at the MSU engine laboratory. I purchased the engine from MSU and it has been stored in garages ever since.”

Some that actually made the cut but are not well known include:

(Source: A History of Chrysler Corporation’s Slant-Six Engine, Volume II)

Revell made a model of the slant six for a brief time; it included a book by Willem Weertman on engine design.

slant six engine

Slant six engine - Problems and repairs

Spark advance

David Wordinger wrote about changing the spark advance on a 1971-76 225 engine. Other years are often similar.

Set the idle speed and timing according to the specifications (often on a sticker under the hood but also available in reference books.)

[If you have problems setting the timing], remove the spark plugs so the engine rotates freely. Pull the cap off the distributor. Now rotate the crankshaft back and forth a few degrees in both directions. The easiest way to do this is probably by turning the fan. Watch the rotor in the distributor. If you can turn the crank without the distributor moving, you probably have a bad timing chain.

slant six engine

I think all slant six distributors have two places to adjust timing. Looking down from above, there is a slotted plate that bolts to the engine that you have been using to set the timing. The other end of this plate has a similar slot that bolts to the distributor housing from the bottom. You can’t see it with the distributor installed, but this will give you more adjustment.

[Warning: this second bolt should only be used in extreme cases. As the Slant Six Club’s Ben Deutschman wrote, “That other bolt is set in the correct position by the factory, and should not be played with. Remove the distributor from the engine, making sure to note where the rotor is pointed, before touching the hold-down bolt. Once the distributor has been removed, the other bolt can be loosened with a 7/16 socket or wrench. Since the distributor is gear driven, great care needs to be taken when removing it, to not damage the nylon drive gear, which is no longer commonly found in auto parts stores.”]

slant six

Don’t forget to plug the vacuum advance hose after disconnecting it from the distributor. Even when the vacuum advance hose is disconnected, the advance changes as the engine revs. It’s normal. The weights for the mechanical advance are under a plate in the distributor. [That’s why you need to adjust the engine speed first, then the timing.]

Again, the felt pad under the rotor must be lubricated once a year or so.

hot testing slant six engines in Trenton Engine


Cold driveability problems tend to stem from poorly adjusted choke and choke pulloff, bad accelerator pumps, and sloppy carburetor rebuilds (Carter BBS is better than the Holley 1920 or 1945.) Another problem is the fact that the vibration damper outer ring tends to slip, which makes the timing mark far off, so timing would never be accurately set.

Also check for timing chain stretch by putting the engine at #1 TDC - top of compression stroke (both valves closed) and see where the timing mark is. There are companies that re-bond dampers with new silicone material. I think one is called Damper Dudes, out of California.


One of the more common slant six problems, decades after their creation, is cracking manifolds. Dave B wrote, “POR15 makes manifold repair kits which would fill a hairline fracture if you don’t feel like replacing the whole thing.”

slant six engine with carburetor and air cleaner

stevem wrote:

I believe that all the heads from all the slant sixes are interchangable. The carb and choke linkages need to be taken from the donor car. You might just have to manufacture the linkage. Be sure and put the manifold bolts and washers back in their proper position and follow the torque specs and sequence exactly or the manifolds are likely to crack.

Dan Stern added:

Chrysler wrote in 1979: “Two-piece aluminum die cast intake manifolds ... are electron beam-welded as an assembly, and have a common bottom casting and unique upper castings for the one barrel and two barrel versions. Use of the electron beam welding process [is] an industry first for commercial welding of aluminum die cast manifolds on a high volume basis... the manifolds are welded by an automatic non-vacuum electron beam welder with a capacity of 450 inches per minute. Use of this manifold results in a 14 to 15 pound savings per car.”

The single-piece sand-aluminum two-barrel intake sold by Mopar Performance is an excellent casting. In contrast, the two-piece welded-together “ultra light weight” electron-beam welded intakes used between about 1979 and 1982 were the subject of a few different TSBs and recalls over the short period they were used. Most of them were replaced under warranty with cast iron manifolds.

You can greatly reduce the likelihood of porosity problems by having one of these manifolds powder coated to seal the casting. Or, after proper cleaning, you can use several coats of epoxy paint (tough to find in Chrysler red) to do the same thing.

Warpage at the head sealing surface and the exhaust manifold junction are still much bigger issues with this manifold than with any other made for the slant six. Thick gaskets can help here. The issue with these manifolds doesn’t mean every single one is a piece of junk. It’s like the porous castings in the 1975-77 aluminum-case A833OD transmissions. Many of them were fine and never seeped a drop of fluid, but many of them were “not-fine.”

Because the bad ones have mostly disappeared from the roads, the odds are higher of finding a usable 2-piece intake are higher now.

While all exhaust manifolds had the same two inch outlet, the headpipes on the super six engines differed.

aluminum manifolds

Zachary Good wrote about fixing exhaust manifold cracks:

I’d suggest going to a junkyard and pulling an exhaust/intake manifold off any slant six around the same year (Valiant, Dart, Aspen, etc.) and replace the whole assembly. It’s easier than pulling the two apart on both cars. Just make sure the new intake manifold is set up for your carb. It’ll be worth it, repair kits last at best a few months.

Todd Johnson added: "You can also find a competent welder...he can weld cast iron."

Wes Moeller wrote: “Dutra Duals are another option. Depending on where the crack is on the exhaust manifold, you can cut off the front ‘leg,’ and then cap off the hole. Then this modified exhaust manifold would be for the rear three cylinders, and the new casting from Doug Dutra would be for the front.”

Development stories

Gerard Duchene noted: "I remember when we first started running hydraulic cams on the 225 and did we have problems in the hot test area! I am pretty sure it was in 1978 [though they were not released in that year]. We shipped the 225 to Mexico in 1979.

As you can imagine, going from a solid lifter to a hydraulic lifter is no small feat. At the beginning 50% would not start or had pounding lifters. I guess there were some bugs they didn’t see coming.

slant six

I also spent a few years on the Merry-Go-Round, a huge revolving 100 foot diameter wheel with stands where we hot tested the 400 and 440 CI engines, man about a loud place to work! Nothing like listening to 20 440s running at the same time at 5:00 am with almost no exhaust!"

Dan Stern wrote:

The hydraulic lifter setup was designed and developed at WEP (Windsor Engine Plant, Chrysler Canada) and a small number were produced in 1978, and placed in fleet service to monitor in-use durability. No other hydraulic-lifter slant-sixes were produced until the 1981 model year, when all were so equipped.

No oil galleys were added to the engine block. Instead, the rearmost camshaft bearing was fully grooved to feed high-volume oil up through the head to the rocker shaft, through the rocker arm bodies, and down through hollow pushrods to new top-feed hydraulic lifters. This unique and innovative method of feeding the lifters eliminated the need to rework the block.

slant six

Pete Hagenbuch wrote about an early development problem with oil passing across the rings:

Aside from the “slant,” the only other unusual features were its stamped valve rockers and the steel-rail oil rings, the latter resulting from a thorough investigation into all the factors affecting oil usage past the rings. In six months I was the oil ring guru or expert (we always said an expert was anyone more than 25 miles from the home plant) or something.

We looked at the finish of the cylinder bores, twist properties of the compression rings, clearance between the ring lands and the bores, the results of using chromium plated ring faces and their effect on run-in oil economy, and we evaluated oil ring designs from all out ring vendors. On the 170 we left everything alone. On the 225 we released the first steel rail oil ring in Chrysler history, the Sealed Power SS 50 with chrome. We eventually released a chromium plated top ring and a reverse twist second ring. If I remember correctly, one of the vendors came up with a process to give the chrome plating an initial surface with an abrasive treatment just like we’d want it after run-in.

slant six

The entire package didn’t get into the 1960 model year, but it did in 1961, and the problem went away. Once the SS50s got into production it was no longer a panic, but we needed the chrome for long-term. The reverse twist ring was nearly immediate, all the vendors had to do was put their “top” mark on the other side. Why? Because most compression rings were made with positive twist, which was produced by cutting a chamfer on the top inside corner of the ring. Reverse twist merely moved the chamfer to the bottom.

More development stories are told by Bob Scott, Willem Weertman, and Pete Hagenbuch.

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