(HMCC Web Editor's note: One of the best things about the Web is it allows people to work together across time and geography. Dan Stern wrote to add some details to Bob's original article. I've included Dan's comments using a * symbol and italic text.

MotorTraxx Techline

Slant Six

...This [article] will deal with the venerable slant six, and its history. My friend Howard Fischer describes the slant six as the 300,000 mile motor. The machine shops don't see many of the engines because they run forever. Most of you who know me, know that I lean toward the musclecars. Most of you don't know that my daily driver is a 1963 Dart GT. There was no V-8 option in the A-body until 1964. That makes mine a 225 cubic inch slant six. It was found in a shed in Sebastian, TX. It had not been started in 5 years. Gas down the carburetor, new battery, and light the fire. After removing the gas tank, and cleaning the sludge, new front brakes, set of used tires, over 10,000 miles have been put on the car/engine with only new plugs. No rebuild, no oil burning, no leaks no trouble.

The slant six started life as a 170 cubic inch replacement for the old flathead Mopar six in 1960.
* [T]he 170 and the 225 were both released simultaneously in late 1959 for the new 1960 cars.
New overhead valves, rocker shaft setup, solid lifters, individual porting for each cylinder, gently curving exhaust and intake manifolds, and a somewhat strange 30 degree slope to the passenger side. Everyone who looked at the engine said that it looked like it was slanted to the side. It was a name that stuck the slant six.
* Chrysler Engineering came up with the term in early 1958 during preliminary design of the Slant-6.
The 170 cubic inch version had a bore of 3.40 inches and a stroke of 3.125 inches. The rod length was 5.7 inches. The main reason that the engine was tilted to the side, was to allow the water pump to be positioned to the side of the engine. This made the overall length shorter. You can run outside and look at yours to confirm this after reading [this]. another bit of trivia, the first production car to receive the slant six was the Valiant prototype.
* The first production cars to receive the Slant-6 were the 1960 Valiant, the 1960 Plymouth, and the 1960 Dodge Dart series. Again, this was all simultaneous. Also note that the '60 (and '61) Dart was not the compact, but was an “intermediate” car.
This was not a Plymouth Valiant. The original Valiant was proposed as a separate car line. The prototype Valiant also received the first alternator in the entire auto industry.
* “Prototype” means it's not a production car. The 1960 Valiant was not a prototype. It was a Valiant (“by Chrysler”), and not a Plymouth Valiant, but it was not a prototype. In addition, it wasn't the first alternator in the entire auto industry. It was the first use of the alternator as standard equipment in a regular-production automobile. Alternators had been used for several years prior in heavy-duty (police, emergency, etc.) vehicles as an option.

In 1961 Dodge brought out the Lancer. Along with the Lancer, came a somewhat useful item. The 225 cubic inch slant six from the big car line of 1960. This engine featured a one inch stroker crankshaft. This made the bore the same 3.40, but the stroke was increased to 4.125. Talk about torque. There is also a third version introduced in 1970 that displaces 198 cubic inches. The bore again remains at 3.40, with the stroke at 3.640.

I can't tell the whole story, without mentioning the performance aspects of the dependable engine. In 1960 NASCAR sanctioned a race for the new compact cars coming out of Detroit. Chrysler had developed a Hyper-Pak version of the 170 cubic inch engine. It featured a four-barrel aluminum manifold, cast headers, milled head,
* The head was not milled. The full-race version of the Hyper-Pak featured pop-up pistons.
and hotter cam. The advertised horsepower on the Hyper-Pak 170 was 148 ponies. Seven Valiants were entered in the race. They finished 1,2,3,4,5,6, and 7. Not bad for a first showing. Oops! I almost forgot to mention that the lap speeds at Daytona International Raceway exceeded 130 MPH. Next time you get close to a Valiant, look at the frontal area. Imagine the power needed to push this thing 130 MPH! The calculations work out to almost 200 horsepower from 170 cubic inches. The 225 received the Hyper-Pak treatment in 1961,
* The Hyper-Pak was never a factory installation; it was sold as a parts package over the parts counter from Day One.
and was advertised at 198
* 196
horsepower. The intro two barrel 273 had an advertised rating of only 180 horsepower, when it came along in 1964.

The dependability and economy role of the slant six continued for many years. It was the six cylinder engine up until 1984.
* 1986 in domestic trucks
The last service was in the truck line. The economy of the engine was demonstrated in the 1975 Feather Duster, and the Dart Light.
* 1976 only.
These cars featured aluminum front panels and pieces,
* Aluminum hood and trunk inner bracing and bumper brackets, only. All the other sheetmetal and parts were stock steel items.
a four speed overdrive transmission,
* or Torqueflite automatic, per customer choice
and a 225 slant six engine. The EPA rating on these cars was 36 mpg highway. This is the highest rating ever achieved by an American six cylinder compact car.

For those readers who want the swap information, here it is. The 225 crank can be put in the 198 block with the 225 rods. The 225 crank WILL NOT fit the 170 block.
* Not without modification to the crank and block, anyhow, but it has been done.
The stroke increase hits the block. All three engines share common pistons. All three have different rod lengths. The last forged 225 crankshaft was produced in 1976. The displacement identification is on the top right side (passenger) of the block, near the front. The number is clearly marked ... 170, 198, 225 etc., just below the head.
* This numbering system is only used on later (sometime in the '70s and later) Slant-6s, and this location for the number was only used until about '78 or so, when it was moved to the rear of the block. Other numbering systems were used from '60-'7x, and the '60 engines were stamped in one of three different places.
Any cast crank will be indicated by the letter E, following the displacement (225E). Any reader needing more information is welcome to call or write. Thanks for the time.

Bob Doty

Gary Hamel, HMCC Web Editor
July 12, 1997
Updated, November 11, 1997; April 16, 2006

Return to the HMCC Tech Page

Return to HMCC Home Page