Fastest/ most powerful slant six?
I was little off on the Ramchargers thing but they were definitely involved. I cut and pasted the following from an interview with Chrysler engineer George Scott on AllPar. The formulas are included:
I worked for a year on the fuel injection program and during that time I was involved with the single cylinder testing I was telling you about. The single cylinder test stand was a 354 ci Chrysler hemi that had all but one piston, rod and valve set removed.
It's really too bad that the voluminious research conducted "back then," was done on an engine that was the unintended victim of a cylinder head that was so mis-matched (in flow capability) to the 225 motor, that it never had a chance. That head was designed for the 170 and was an appropriate piece for that application with total flow numbers that made the 170 a holy terror. It dominated the compact race at Daytona to the extent that NASCAR cancelled the series.... that's how lopsided the results were, in Chrysler's favor.
NASCAR couldn't abide seeing G.M. being embarrassed like that, again...
But, then they (MOPAR) needed a bigger motor for hauling around B-bodies, which were a lot heavier than the Valiants. So, they stroked it a full inch, which was good for the low-end torque, but strangled the upper-rpm breathing, horribly. All of a sudden the high-revving, powerful-for-its-size, 170 became the asthmatic, strangulated, 225, which struggled to get out of its own way.
No amount of exotic intake/exhaust manifolding could be designed/configured to alleviate the problem that was IN THE HEAD; small bore centers, and small valves were the unavoidable result of the ( front office) dictated smallish bores (3.4") and there was no fixing it without designing a completely new head with either 4 valves per cylinder or some sort of Hemi chamber with canted valves with, maybe, a crossflow design that would allow for significantly better breathing.
So, they did nothing. For many, many years. 'Til the end of production, in fact, for that engine.
The 225 slant six
never got a cylinder head with the kind of flow it needed, for true, N/A high-performance. It was stuck with that 170 head.
BUT...
The aluminum infrastructure the 225 had early on, was carried over to the cast iron version, which made for an unusually strong, almost Diesel-like, (construction) engine. Thick main bearing saddles, a forged crank with outsized bearings, a thick deck, and hefty, thick cylinder walls were used, along with NO "thin-wall" castings....
This robust block, head and crank, made for an engine that could withstand stresses that other, lesser engines were incapable of surviving. It made it possible to fully utilize forced induction (or, N2-0,) to the extent that when properly tuned, it was not much of a "trick" to obtain 500 horsepower from this boosted, little six.
Not many people know that, so the number of turbo and supercharged slant sixes that exist, is small, but growing.
It is just a shame that the wealth of research that was done on the naturally-aspirated version of the 225, back in the Ranchargers' day, wasn't spent on turbo versions of this motor, because I think nearly everything available now, was available, then.
No telling what the Ramchargers could have accomplished with their formidable talents, back then... Six-hundred horsepower turbo slant sixes might have been in abundance, when 500 horsepower naturally-aspirated 340s were considered the ultimate...
Maybe that's why it wasn't done... I have been privy to some tersting done on the slant six motor with up to 37 pounds of boost... and, there was no damage.
That's how tough these motors are...
What a shame it's such a well-kept secret...