For some reason, guys keep building these little six-cylinder engines for their daily drivers and even for their race cars. And why not, when they can produce decent power and open the envelope to what is regarded as normal. Just wait, their day of respect is near.
Chrysler's potent little Slant Six definitely gets no respect! Sure, one of them shows up every now and then, but how many of us have thought about building one for racing? If you do, and want a better e.t, you could always bolt on a supercharger or nitrous, but what's the little beast capable of doing in normally aspirated dress? We know you're saying, what's the point, it's still a six-cylinder? The first strike against it is the rotating assembly is known to be rugged, but heavy, limiting rpm. And that intake manifold . . . . If you were a group of air/fuel molecules you wouldn't like making those sharp turns at the base of the carburetor, and then that long run to the cylinder head. Also, no two runners are the same length, and fuel puddling is common. Then there's that cylinder head-beefy, but not exactly free flowing.
Some guys really enjoy racing their Slant Sixes, and we were curious about what more could be done to one. When Romeo Furio started chatting with Mopar Engines West (MEW), the discussion yielded blank looks from the engine builders. Why would anyone build a normally aspirated Slant Six for racing? Since Romeo is a starch proponent of Slant Six racing, he sent MEW a 225 engine for dissection. The base engine for the build was a mess, and soon it became obvious there are some inherent limitations.
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During its lifetime, the Slant Six used two distinctly different crankshafts. A forged unit was used from the '60s into the '80s, but then a lighter cast unit was used. Since we are shooting for 300 hp, the cast crankshaft will work fine. And, it's lighter, an added bonus. | 
With the lighter crankshaft fully machined with an offset grind, the 283 Chevrolet bearings are wrapped around the journals, and the bearing caps tightened up. |
Compress It
The basic Slant Six has always done well with its 7.5:1 compression ratio. But the good news is the head has so much material in it that whacking off 11/410 inch or so from the surface would be possible (We're not kidding). The math said with a flat-top piston, this combination could yield about a 13.0:1 compression ratio by shaving the heads surface and removing about five pounds of cast iron.
The Rods And Slugs
The Slant Six has a long-standing reputation as being virtually indestructible. One reason for this is the pistons, which have such tall skirts they actually look like beer cans. Slugs would be a better name than pistons. Sure you can have a lighter custom piston made, but it would still be a slug because of where the wrist pin is located in order to use a stock rod. The block's deck height and the rod length fix the compression distance. We got to thinking, what if we spring for a set of custom rods, would the change be worth anything?
Since custom pistons and aluminum rods are being used, why not order them any way you want? The rods feature a big end with a smaller journal size to help with clearance at the cylinder bore bottoms. The pistons have special features, such as ring grooves for small millimeter measured rings, a .927-inch wrist pin, and shorter skirts. All told, 100 grams has been shaved from each cylinder's rotating mass. | 
The 283-size Calico bearings feature the required pin-centering hole, and the bearings are narrowed .040-inch on each side, chamfered, and coated with their Calico's CT-1 coating. | 
With one cylinder complete, the rod's clearances and the piston-to-deck measurement can be taken. This is when we found out that we needed to make room at the bottom of the cylinders. |