I really like the Mopar Slant Six, so my next project will be building one to put into my Valiant station wagon. I found one on Craig's List complete with bellhousing, 4 speed transmission, etc. for $200 so I decided to go for it. It's a 1970 block but I'm not sure if it's a 198 or 225 - whatever it is now it will end up as a 225. It's really easy (for me at least) to get carried away on these sorts of things, so it's important to come up with a realistic plan and then stick to the plan. In my case, the 2 most important considerations are that (1) it's my first ever engine build and (2) it's going into a car (automatic transmission) that is somewhat rough and won't be restored for quite some time. Because of this, I'll be doing a rebuild that is on the simpler end of the spectrum, but I will use a few "special" parts. All of the information here was gleaned from slantsix.org and I'm not trying to take anything away from them - they are the best source of information on the Slant Six, bar none. I'm just putting the info where it's easier for me to find.
Overall Plan for the Build
This will be going into a driver, not a street machine or racer. This means I want good gas mileage, decent performance, and it has to run on 92 octane pump gas. I don't need anything fancy (like stuffing a 198 crank into a 170 block), but I do want as many cubes as possible. A fairly stock 225 should easily meet those goals and not challenge my mechanical skills too much.
Slant Six Blocks
According to Doug Dutra at slantsix.org, the 2nd generation RGFC blocks (casting number 2806830, 1968 – 75) are the strongest Slant Six blocks available. If you're building a high performance or racing Slant Six, it's probably worth your while to search out one of these blocks. For a daily driver, it probably doesn't matter. I'm glad that my block is in fact a 2806830, but I woudn't sweat it if not.
Slant Six Crankshaft
All Slant Sixes have the same 3.40" bore. The different displacements are acheived by changing the stroke of the crankshaft. The 170 has the shortest stroke at 3.125", the 198 stroke is 3.64", and the 225 has a stroke of 4.125". Early versions used a forged steel cranshaft; engines built after mid 1976 used a cast crank (the cast crank engines also used a different block, bearings, and connecting rods). The 170 crankshaft fits the "low" block while the 198 and 225 crankshafts fit the "raised" block. A 198 can be converted into a 225 (and vice versa) by swapping the crank, rods, and pistons. For my build, I'll be using a 225 forged crank (hopefully that's what is already in the engine).
Slant Six Pistons and Rings
Stock Slant Six pistons are big and heavy. As one magazine article put it, they could almost be beer cans. Because of this, I'm going to run a set of, ahem, non standard pistons. Keith Black makes a set hypereutectic pistons for the Mopar 2.2 turbo engine that just happen to fit the Slant Six, and that is what I'll be running. (For details, scroll down towards the bottom of this article). Rings will be Total Seal gapless.
Slant Six Connecting Rods
Each Slant Six also has a unique connecting rod. Because the compression height on my "special" pistons is much shorter than the stock 225 piston, the stock 255 connecting rod is also much too short. Fortunately, the rod from the 198 is exactly the right length for these pistons. If I was on a really tight budget, I'd spend some time and hunt down a set of 198 rods. However, I'm probably going to run K1 rods instead. They're the same length as the stock 198 rods and I think lighter. The main reason I want to run them though is for piece of mind. If I find a set of 198 rods I'll have no idea how hard they were used or abused before I get them. The K1's are barnd new. Used 198 rods go for about $150 to $200 a set, then you have to buy rod bolts and have them reconditioned. Figure about $300 to $350 total. The K1's cost $500 and you just bolt them in and go. To me, the higher cost is worth it.
Slant Six Cylinder Heads
This is another area where I lucked out. According to this article, Slant Six heads made from 1968 on are better for both power and fuel economy, and mine is a 1970 head. This is one item I would take the time to look for if my engine had an earlier head. Even for a daily driver the extra mileage potential makes the later head worth the time and money to track down. Since I'm trying to keep my build fairly simple I'm going to leave the heads mostly stock - no fancy (and expensive) porting. I may install larger valves from Clifford if I can afford them but I won't sweat it if I can't.
Slant Six Camshaft
more to come soon...
Slant Six Intake Manifold and Carburetor(s)
more to come soon...
Slant Six Exhaust
more to come soon...