Glenbrook is an online mechanics writer, who enjoys rebuilding and modifying classic Chrysler cars.
The Chrysler Slant Six is my favorite engine. It is one of the most bulletproof engines ever designed, its reliability is unmatched, and it has great potential for power and economy. A Slant Six built for the economy can hit nearly 30 miles per gallon. Build it for speed and it can put a light car in the 12-second range of a quarter mile.
Whatever your goals, building and modifying a Slant Six is a lot of fun. It is the perfect engine for early Mopar A-Body cars, such as a 64 Valiant Station Wagon or a 66 Barracuda. If you’re tired of all the “belly button” V8 powered cars, give the Slant Six a try. You will have fun …
Why build a Slant 6?
The Chrysler 225 Slant 6 probably offers the most fun per dollar of any classic American engine ever made. If your car has a Slant Six, there is almost no reason to convert it to a V8. It is easily the most versatile PentaStar in the Mopar constellation (with the possible exception of 318). If you want fuel economy, the / 6 has it. If you want to go fast, the / 6 can do that too, especially if you put a turbo on it … you can really put a lot of V8 engines to shame. Try one, I know you will like it …
Mopar Slant Six performance improvement
As much as I like the Slant Six, the factory left a lot of room for improvement. In fact, that’s one of the reasons I like it so much. It would be pretty boring if it was perfect out of the box. These are the areas (in no particular order) that will pay the most dividends in terms of reliability, mileage, and performance.
- Pistons and connecting rods, The stock piston and rod assembly on a Slant 6 is heavy, offers a less than optimal ring package, and provides a low compression ratio. For serious performance builds, I recommend replacing the original connecting rods and pistons with K1K1 or Molnar connecting rods and Wiseco pistons. If you are on a budget, you can use 198 rods and Keith Black KB268 Pistons (for a more detailed description of this conversion, click here), although a set of 198 rods can be difficult to find. Either combination gives you a much better piston and ring combination than the stock and increases the compression ratio to about 9.2: 1.
- Exhaust system. The exhaust system on a stock Slant Six is a negligible single pipe. It is suitable (barely) for a series vehicle, but for any kind of performance or economical application it needs to be updated. Options include headings (available in Clifford performance) or Dutra Duals.
- Intake manifold and carburetor. The best Slant Six intake for a street car is the factory Super Six 2 barrel setup. These came with aluminum or cast iron intake manifolds. Although I generally prefer aluminum manifolds to save weight, I have read that the cast aluminum Super Six manifold has quality control issues. I haven’t confirmed it, but until I know something else, I prefer the cast iron version. If you need more performance, Clifford and others offer 4-barrel manifolds. Offenhauser had a nice 4 barrel entry that is no longer in production, but easy to find on eBay. IMHO the ultimate intake system is an Offy dual intake modified to hold a pair of 2-barrel Weber carburettors. Clifford also offers an EFI setup for the Slant Six, as well as a Weber triple side-pull manifold.
- Cylinder head. The Slant 6 is very fond of multi-angle tube work. My old Mopar Performance shows a 5-angle seat, a concept that recently came into vogue for high-performance V8s. The stock valves are downright insignificant and should be replaced with larger Clifford valves for any kind of performance use. The ports might also need some work, the idea is more to straighten them than to oversize them.
- Valve cap. The original valve cover is stamped steel. It is also long, therefore somewhat flexible and prone to dripping. This won’t damage your engine, just make it look dirty. If you don’t want the grunge, you can replace the original cap with a nice cast aluminum valve cap from Clifford or Offenhauser. Cast aluminum is much stiffer than stamped steel, eliminating oil leaks. They look much prettier too, especially the Offenhauser piece from …