Slant Six

The slant six started life as a 170 cubic inch replacement for the old flathead Mopar six in 1960.  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.

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.

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.

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, 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, and was advertised at 198 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.  The last service was in the truck line. The economy of the engine was demonstrated in the 1975 Feather Duster, and the Dart Light.  These cars featured aluminum front panels and pieces, a four speed overdrive transmission, 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.  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.  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