Manifold Mystery Tour – Dodge Exhaust Manifolds on Trial – Slant Six
7 years ago
Heritage
The Slant Six Was a Legend of Efficiency and Durability: What Happens When We Add a Bigger Carburetor and Cast Headers?
So far in the Manifold Mystery Tour exhaust manifold vs. header dyno comparison series, we’ve examined the impact of exhaust headers on a 392 Chrysler HEMI®, 426 Street HEMI and 340 Six Pack. But what about the millions of Slant Sixes that powered the Darts, Challengers, Chargers and Coronets on the lower side of the performance curve, is there hope for added scoot? You bet!
Even though it’s been nearly three decades since the last Slant Six-powered Dodge rolled off the line, restorers, hot rodders and tinkerers still embrace the so-called “leaning tower of power” for its nifty looks and low cost. Rebuildable core engines can be purchased for next to nothing and there’s a ton of aftermarket support, so, why not?
About the “leaning tower” part, the Slant Six gets its name from the way its designers decided to set the engine block over at a 30-degree angle from vertical. By laying the engine over to the right-hand side of the engine bay (that’s the passenger side in the left-hand-steer cars we’ve got here in America), several benefits were achieved. None of them were accidental.
First, the overall height of the as-installed engine was reduced several inches. This allowed body designers to use lower, sleeker cowl and hood surfaces. The extra distance between the cylinder head and the left-hand side of the engine compartment added room for much more efficient intake and exhaust plumbing.
And finally, the 30-degree slant made extra room for the water pump to move from its traditional location – at the nose of the engine block – to a more compact location at the leading end of the left-hand side. This reduced engine length by critical inches, all the better to fit thicker radiators for improved cooling.
Introduced in 1960 with 170 or 225 cubic inches, early marketing materials referred to the new engine as the “30-D Economy Six”, the numeric nomenclature number being a reference to the 30-degree slant of the block. Though a catchy name, consumers quickly called it what it is, the Slant Six. In this article, lets watch as Donnie Wood and the team at R.A.D. Auto Machine (Ludlow, MA 413/583-4414) grab an extra 32 horsepower and 22.8 lb.-ft. of torque by switching carburetors and exhaust manifolds.
The majority of the 12.5 million Slant Sixes had regular cast iron engine blocks. Ours is one of about 50,000 1961-62 engines with die-cast aluminum blocks for weight savings. Aside from the 66-pound weight savings (64 versus 130), mechanical specifications were identical. The factory charged a mere $47.35 for the aluminum block option. Ours is number 37,415 and came from a 1962 Dodge Lancer GT.
The completed test engine is mounted to the R.A.D. dyno with the stock Carter 1-barrel carburetor and log-style exhaust manifold in place. For enhanced performance in our rebuild, we used a solid, flat tappet cam with 0.474 / 0.483-inch lift and 206/210 degrees of duration. We also milled the cylinder head 0.100-inch to bump the compression ratio from 8.4 to 9.2:1.
Dodge rated the 225 Slant Six at 145 hp at 4000 rpm and 215 lb.-ft. at 2800 rpm. But those figures were taken using the old industry-wide “gross” testing system, which was generally 20-percent optimistic. Our 130.2 hp at 4300 rpm / 192.3 lb.-ft. at 2700 rpm measurements are about right considering the mild modifications.
Okay, let’s move up to the Carter 2-barrel carburetor. Though used on Australian Slant Sixes as early as 1967, Dodge waited until 1977 to equip U.S. spec 225s with the larger 260-cfm carburetor. Junkyard shoppers know these are typically found in 1977-80 Dodge Aspen station wagons. The exhaust manifold remains unchanged.
Nice! The improved breathing afforded by the 2-barrel carburetor bumped output to 151 hp at 4700 rpm and torque to 204 lb.-ft. at 3300 rpm, gains of 20.8 hp and 11.7 lb.-ft.
Since every reciprocating internal combustion engine is essentially an air pump that inhales and exhales, improvements to the intake side (carburetion) are only fully utilized when similar attention is given to the exhaust side (manifold). The stock cast iron manifold (bottom) is fairly efficient but could be better. California Slant Six enthusiast Doug Dutra offers the much more streamlined, two-piece Dutra Dual manifolds as an alternative (bottom).
Mounted to the test engine, the added exhaust capacity bumped output by an extra 11.4 hp and 11.1 lb.-ft. over the center-dump factory log. The rearmost exhaust manifold is configured with a horizontal outlet to clear the factory starter motor location (not present). R.A.D.’s Land & Sea engine dyno has its electric starter motor meshed to the flywheel at the end of the engine.
So here it is folks, with the bolt-on 2-bbl and Dutra Duals, the 225 Slant Six makes 162.4 hp at 4200 rpm and 215.1 lb.-ft. at 3300 rpm, total gains of 32.2 hp and 22.8 lb.-ft. over the stock 1-barrel carburetor and single-outlet iron exhaust manifold. No, the Slant Six may not lay rubber for a hundred feet or strike fear into the hearts of Corvette drivers, but if you’re just as impressed by innovative engineering as brute power, the Slant Six deserves a second look.
