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

Thanks to Dan Stern! | Slant Six en español

The Slant Six has a legendary reputation for endurance. It also has a hidden secret: strong performance, given the right conditions.

Most slant sixes were given a single one-barrel carburetor; but the optional HyperPak kit, which included a four-barrel, pushed out 196 horsepower, and modern racers have used turbochargers and different carburetion and manifolding to produce far more.

Even with the standard carb, the slant six (so named because it was an in-line six, with all cylinders lined up in a single row, “slanted” 30 degrees) had a nice mixture of torque and economy, with power better than similar, comtemporary GM and Ford offerings.

Aside from a generally superior engine design, the six’s unique slant provided room for an efficient manifold system that provide each cylinder with an individual intake and exhaust tube. Bends had a large radius, and the 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 highly varying lengths.

The "Super Six" with a two-barrel Carter carb compensated for smog controls and increased responsiveness without loss of economy, and with the Feather Duster package, the slant six was capable of 30 mpg on the highway. An export version pushed the tilted engine to 160 bhp, and the fabled HyperPak (an aftermarket package for racing) raised the USA bar to 196 hp.

1960 Slant Six vs GM and Ford	Ford 223	Slant Six 225	Chevrolet HyThrift
	145 hp	145 hp	135 hp
	206 lb-ft	215 lb-ft	207 lb-ft
Choke	Manual	Fast-reaction automatic	Tube-fed automatic

Heavy-duty slant six engines used in industrial and some truck/bus applications used a double-row roller timing chain (but just one 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); Rodger also said some fleet cars had these. You can retrofit the double roller chain and gears into car slant sixes, according to some sources; 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, Rodger).

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

To simplify maintenance and increase reliability, the plugs, distributor, and coil were grouped closely together on one side. Most replaceable parts, including the filters, air cleaner, fuel and water pumps, coil, and dipstick, were relatively easy to reach. In 1960, 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.

The slant six replaced a flat-head design in 1960 models and lasted in US-built cars through 1983, in US-built trucks until 1987, and survived as a marine engine until 1991. After USA production (in Trenton) ended, it was produced at Chrysler's Toluca, Mexico engine plant until the Magnum 3.9 liter V-6 MPI engine was introduced. The next new truck six would be a derivative of the 4.7 V8, and would be introduced in 2001; but the slant six would be 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).

Why the six is slanted

By slanting the engine in the compartment, four distinct advantages were achieved, according to a 1960 press release:

• The center of gravity is kept much lower than in upright engines.
• A low, stylish hood is made possible (in other words, the engine fit into the Valiant).
• Engine accessories are more accessible.
• The water pump can be moved to the side of the engine to reduce the engine's overall length.

While the press release did not mention it, the most important advantage might have been making room for an unusually efficient intake and exhaust manifold. This gave room for wide bends and nearly equal-length tubes going to each individual cylinder, preventing airflow restriction and uneven airflow. But the lower center of gravity would also help the Valiants — the early, more nimble Valiants and Barracudas in particular — to be in the top of their class for handling.

Facts for owners

The slant six gained electronic ignition in 1973 (earlier models could be retrofitted, and many were). The electronic ignition was extremely reliable, and the only component likely to break down was the ballast resistor, which costs about $3 and two minutes. However, most mechanics of the time — and perhaps even now, though most owners are probably aware of the fix — seemed to replace the electronic ignition system instead.

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

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

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 putting weatherstrip foam over the ignition and voltage regular modules. You can get wires and other parts cheaply on-line.

From birth through 1972, the oil filter standpipe was too long to allow for short filters, and long-canister filters, such as PureOne PL30001 and Fram PH8A, must be used. Scott 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 S.).

Owners would be well served by checking our page on slant six spark plugs and spark plug tubes.

 

Dan also advised owners to check for timing chain stretch.

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. In so far as additional sealants are concerned, I don't believe the rubber gasket is intended to have any sealer applied to it.”

Firing order is 1-5-3-6-2-4 (thanks, Ed Friedemann) - note the diagram in this section, sent by DJAlDogg.

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

The standard carb for many slant sixes was a single-barrel. You can increase performance and gas mileage by switching to a good dual-barrel carb, but that requires swapping the manifolds, too. Rodger also suggested an easier swap:

Go to NAPA and ask for a inside diameter 2 1/4 inch muffler with a 2 inch inside diameter outlet. The longer the body is, the better it will sound at the end of the summer. On the original engine, they used a smaller than needed diameter exhaust pipe to the muffler; this saved a production "nickel" every time a car was made. The high performance variations are different.

Dan Stern provided these standard carburetors used by Chrysler for North American applications (different setups were used outside North America): 1960-1971: Carter BBS one-barrel 1962-1972: Holley 1920 one-barrel 1963 only: Stromburg WA-3 one-barrel 1974-1980: Holley 1945 one-barrel 1981-1987: Holley 6145 feedback one-barrel 1976-1981: Carter BBD two-barrel

Walt Ronk wrote about the Lean Burn (the world’s first such computer-controlled system, unless you count 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) was the same as 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 sections on slant six racing and the slant six Hyper-Pak.

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 2 road test mechanics that didn’t know much about engines. The three of us together managed to set up the first two barrel 225. I don’t know if we called it a power pack or not but that was one swell engine for performance anyway. That really turned out to be a winner, in fact my youngest son had one and he just loved it.

All in the slant six engine family

Joseph Newhouse provided the following chart which applies to slant six powered cars from 1959 to 1976. Trucks could be rated somewhat lower than cars (140 hp vs 145 hp gross). These are Federal numbers and could vary in California by 10-15 hp. 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) Available	Compression Ratio	Horsepower @ RPM (see note)	Torque  (lb-ft) @ RPM (see note)
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	8.4 to 1	100 @ 3600	170 @ 1600

Journal Number		1980 3.7-Liter (225 CID) Slant Six
1		2.75' x 0.877"
2		2.75" x 0.877"
3		2.75" x 1.107"
4		2.75" x 0.877"

The engine had four replaceable steel-backed (aluminum alloy on steel) babbitt crankshaft main bearings. Oil grooves were in the upper half of the bearings, and in the lower half of the #1 bearing. The connecting rod bearings were aluminum on steel.

In most years, closed-circuit crankcase ventilation was used; crankcase vapors were routed to the combustion chambers through a PCV valve located in the valve cover. Vapors were burned before being expelled into the air through the exhaust system.

Oil pressure ranged from 35-65 p.s.i. @ 2.000 rp.m.  Crankcase oil capacity was four quarts (one more when changing the filter).

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 dual four-barrel carburetors. He insisted it was not a Hyper-Pack, but a dual quad setup — “We got a tremendous amount of horsepower with it, but it didn’t idle well.”

The beancounters nixed the aluminum RG in 1963, an even larger (246) block with side-fed hydraulic lifters, and, finally, a high-swirl, fast-burn aluminum head in 1978 that could have pushed the slant six on past 1989.

Danield Stern provided the following list of slant six possibilities, most of which were never produced:

• A908, 1958-60: sand-cast aluminum 170 LG engine
• A909, 1958-61: die-cast aluminum 170 LG engine
• A785, 1959-60: Hyper-Pak 170 LG (Sold 1960-61 as a parts package)
• A941, 1962-66: overhead cam 225 RG engine (in 1962!)
• A106, 1964-65: G-RG engines with 180 and 246 c.i.d.
• A227, 1967-68: 246 CID EG engine with hydraulic tappets using added oil gallery in cyl. block
• A294, 1969: 4-cylinder derivative of G-RG engine (Preliminary designs of the 2.2?)
• A396, 1973-74: 225 RG engine with 3rd-valve prechamber [a la Civic CVCC and Mitsubishi MCA-Jet?]
• A420, 1975-80: Diesel version of 225 engine
• A431: 1976-79: Aluminum fast-burn cylinder head for 225 engine
• A463, 1977-78 225 RG turbocharged engine*
• A473, 1979-80: 225 engine with Bendix multi-point EFI
• A489, 1980-83: 2.2 litre 4-cylinder derivative of A420 225 RG diesel engine.
• A497, 1980-83: 2.2 litre 4-cyl turbodiesel version of A489 engine
• A513, 1981-83: 225RG turbodiesel engine (probably a good thing, too!)

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

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

• A826, 1961: die-cast aluminum 225 RG engine (sold from '61-early '63)
• A218, 1966-69: 198 CID RG engine (sold starting 1970)
• A436, 1976-80: Lightweight 225 RG engine (hydraulic tappets); but weight was only cut by 12 pounds.

(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.

Notes from 1978, year of the first Super Six

The Super Six, created by using a special intake manifold and two-barrel carburetor, added ten horsepower and a great deal of responsiveness; the exhaust had the same diameter but better breathing, and a larger air cleaner was used. Like the standard slant six, it used a cast-iron crank, long-branch intake with curved pipes, hardened valve seats, a single exhaust with catalytic converter, aluminized steel exhaust, and, new for 1978, steel-backed aluminum-alloy main bearings.

Specifications for the 1978 slant six 225 showed 110 net horsepower and 180 lb-feet of torque, with an 8.4:1 compression ratio (the same as the standard slant six). Both barrels opened simultaneously.

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.

The newest slant 6 I ever owned was a 1971, but 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.”]

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.]

Driveability

Cold driveability problems tend to stem from poorly adjusted choke and choke pulloff, bad accelerator pump, and sloppy carb rebuilds (Carter BBS one barrel is better than Holley 1920.) Other big driveability problem source is the fact that the vibration damper outer ring tends to slip, which makes the timing mark WAY OFF. Which means timing would never be accurately set. Also check for timing chain stretch.

Check 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. I don't know if this happens on other CC engines. Basically, if your damper has an inner hub and an outer ring sandwiching rubber bonding material, this can happen.

Manifolds

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." (Keep on reading for more opinions on manifold cracks and exchanges.)

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 and you still might be short some parts but the manafolds are bolt on. You might just have to manufacture the linkage [if using a van engine on a car or vice versa] because the vans used a different setup than the cars.

Be sure and put the manifold bolts and washers back in their proper position and follow the torque specs and sequence exactly else the manifolds crack.

Scott Fluke wrote:

I see Super Six intakes chiefly on Diplomats and similar. I've heard (no first-hand experience here) that the iron version is preferable to the aluminum. Rumored casting problems with the aluminum ones making them leak-prone.

Dan Stern added:

The single-piece sandcast aluminum 2bbl intake sold by Mopar Performance is an excellent casting. The 2-piece welded-together "ultra light weight" EB-welded intakes used between about 1979 and 1982 (1bbl and 2bbl) are poor. They were the subject of a few different TSBs and recalls over the short period they were used in production vehicles. Most of them were replaced under warranty (or at customer expense after the warranty had expired) with cast iron manifolds.

There's a good reason why those TSBs were written. That said, they can be made to work reliably. 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-6, though. Thick gaskets can help here. I just find 'em more hassle than they're worth overall. The issue with these manifolds doesn't mean every single one is a piece of junk. It's kind of 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" and did seep fluid.

Because of attrition over the years (the bad ones have mostly disappeared from the roads), the odds are higher of finding a usable 2-piece intake are higher now than they were 10 or 15 years ago. But, I still don't mess with 'em.

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

KOG wrote:

The 1974 and later cars used a smaller 1 bbl carb, the trucks continued to use the original larger carb. The 1973 and earlier cars were all rated at 110 HP as were the 1977 and later 2 bbl "Super Sixes." The trucks, with different emission standards to meet, kept the larger 1 bbl and continued to make 110 HP. The 2 barrel carbs are the same type as 318, but are jetted differently and the stock ones are a smaller bore than 318. The 2 bbl also usually gets poorer mileage in my experience. (Dan Stern noted that other differences include a different choke mechanism, linkage, and power valve calibration - at least.)

Zachary Good wrote about fixing exhaust manifold cracks:

I'd suggest going to a junkyard and pulling an exhaust/intake manifold off any slant 6 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. That's what I have on my 1978 225 Super Six Volare, works great.”

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.

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 ..talk 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.

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.

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.

Recommended links

• Interview with engineer Pete Hagenbuch
• Interview with architect Willem Weertman
• Other stories of the slant six's development (at Valiant Varieties)
• Spark plug replacement guide, with spark plug tube seal replacement
• The Valiant, Duster, (etc) Page
• Dodge Dart
• Slant Six Performance Upgrades (at Valiant Varieties)
• Modifications - one person's experience
• Inliners International
• Slant six.org
• Slant Six Club of New York and New Jersey
• Slant Six Club discussion forums

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