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 fleet and heavy duty truck/bus service 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).
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’s creators talk about it: Pete Hagenbuch | Willem Weertman
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, continuing to serve in Mexico and possibly South America through (at least) 2003. 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).
This is hardly a complete list, and we would appreciate a chronology of the slant six.
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 1979 (1981 for trucks).
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.).
We have a step by step spark plug replacement guide (with spark plug tube seal replacement) for 1960-1974 slant sixes. Dan Stern recommended Autolite 56 (nonresistor), 66 (resistor), or AP66 spark plugs for pre-1975 SL6. Since that first recommendation in 1997 or so, he wrote:
The Autolite 925 works much better, I've learned in the meantime. It usually has to be specially ordered, but its extra-long electrodes put the spark closer to the center of the combustion chamber and away from a quenchout area. These plugs were originally designed for engines with difficult combustion conditions (stratified charges, extra-lean mixtures, etc.) such as the emission-controlled AMC 232 and 258, and Chrysler's own 1981-83 318 TBI engine in the Imperial.
Ben Deutschman of the Slant Six Club of New York/New Jersey wrote that owners should be careful not to put on spark plugs with the "crush washer" (the loose metal washer at the end), but to take off the washer first, if they have a 1960-1974 engine. After 1974 (starting in 1975), the head was redesigned, the plug tubes were eliminated, and taper seat plugs were used. If you do have a 1974 or earlier slant six, be sure to replace the plug tube seals. (Before 1975, as Ken Mayer pointed out, the tube acted as the washer, so the washer itself should be removed.) As part of the 1975 change, if you plan to replace lifters, you must do it while the heads are off.
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.
Dan Stern provided these standard carburetors used by Chrysler for North American applications (different setups were used outside North America):
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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)
AvailableCompression
RatioHorsepower @ 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 |
|
|---|---|---|
| 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!)
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: Reduced-weight 225 RG engine (hydraulic tappets - engine sold but weight was only cut by 12 pounds).
(Source: A History of Chrysler Corporation's Slant-Six Engine, Volume II)
Notes from 1978, year of the first Super Six
Chrysler wrote: “The 2-barrel carburetor Super-Six has 10 more horsepower than the 1-barrel carburetor version. The 2-barrel carburetor and a 2.25" diameter (Same in the 1-barrel 225) exhaust pipe give the Super-Six improved breathing for better acceleration. A much larger air cleaner distinguishes the 2-barrel Super-Six from the 1-barrel version.
Features of both 225 Slant Sixes include:
- Cast-iron crankshaft-made of cast ductile iron (same material used in all Chrysler V-8 engines)
- Steel-backed aluminum-alloy main bearings (were steel-backed babbitt)
- Long-branch intake manifold with curved pipes
- Deep-skirt engine block gives support to crankshaft and engine bearing areas
- Electronic ignition
- Induction-hardened exhaust-valve seats
- Single exhaust system with catalytic converter
- Aluminized steel exhaust and tail pipe
Specifications for the 1978 slant six 225 show 110 net horsepower and 180 lb-feet of torque, with an 8.4:1 compression ratio (same as the standard slant six). Both standard and Super Six had a single-snorkel air cleaner and single exhaust. Both barrels opened simultaneously.
Slant six engine - Problems and repairs
Spark advance
David Wordinger wrote about changing the spark advance on a 1975 225 engine. Other years are often similar, but we can make no guarantees.
Set the idle and timing according to the specifications (often on a sticker under the hood but available in other 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 you want to 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 /6 I ever owned was a '71, but I think all /6 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.
[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 so you probably can't see them. Note: don't forget to plug the vacuum advance hose after disconnecting it from the distributor.
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 these days, 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 MP sold 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, don't remember where I got mine) 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 pretty much any other ever made for the slant-6, though. Thick gaskets can help here. I just find 'em more hassle than they're worth overall. Seriously, 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, just as with the Aspens and Volarés (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 orginal 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. Sorry, no free power on this one. 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 also. 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. 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! Anyway thanks for letting me share some of my memories at Trenton Engine, Home of the Fire- Eaters."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.
Bob Scott wrote:
My brother George worked in the camshaft and intake research department, so there were lots of interesting things going on. He got to know Tom Hoover very well as the slant six was Tom's first big project.
Early on, Tom came into see George and showed him the flow chart results from the slant six heads. It was purely accidental, but the results were astonishing. The valves performed way better than anything that they had worked on, including the best of the Hemis. Tom remarked at the time that "it looked like we have a racing engine here."
Since the camshafts were part of their department, they were interested in experimenting with variations which might improve performance. Rather than do this hit and miss, they brought in high performance engines from other manufaturers and measured the cams. They were especially interested in the cams that were on the small block Chevys of that time, mainly the legendary Chevy 270 which was the scourge of Woodward Avenue. So they measured the dimensions of that cam and copied them for the slant six and it worked great. I believe that was the cam that was offered with the astonishingly effective hyper kit. Later on, they measured camshafts that were used by Porsche and discovered that Chevy had copied those. So, the engineering game is not always invention, but imitation.
The more I learn about it, the more respect I have for that little 170 engine. Another reason that the 170 was/is great to "soup up" is that the lower end proved to be extremely strong and able to withstand just about anything. George proved that when he put the Paxton supercharger on his and got the boost up to a full atmosphere. Never fazed the lower end of the engine. [Several people have written to tell us that the 225 is most commonly souped up because of the larger chamber size.]Later note: Clifford Performance sells an original specification long runner Hyper-Pak intake manifold for the 170 Slant Six and mentions a certain conventional bodied Six Pack car that turned in 12.34 seconds with their equipment.
Recommended links
- Interview with engineer Pete Hagenbuch
- Interview with architect Willem Weertman
- Other stories of the slant six's development (at Valiant Varieties)
- The Valiant, Duster, (etc) Page
- Dodge Dart
- Slant Six Performance Upgrades (at Valiant Varieties)
- Modifications - one person's experience
- Inliners International
- Slant six.org
- Spark plug replacement guide (with spark plug tube seal replacement)
- Slant Six Club of New York and New Jersey
- Slant Six Club discussion forums