originals, and stresses are astoundingly high.
“When we cranked up the superchargers, we
overloaded the connecting rods,” Mike says
of his early-’80s efforts with Dago Red and
Strega. Now, all the fast Merlins use modified Allison rods. They also use heavy valve
springs and pre-oiler setups, to give the
valve train a chance at survival. The bottom
end of many a racing Merlin uses a special
steel main cap design from Roush
Enterprises. There is no consensus here,
though: Many builders are not “believers” in
the steel caps. I’m no authority, but Strega
wins with ‘em.
Modern horsepower comes courtesy of
inner strength and rpm, and lots of it.
Though maximum takeoff rpm during the
war was 3000, racers now run 3400
throughout the entire race. They could go
faster, but there’s another problem: the
speed of sound effectively limits the propeller’s speed and efficiency. Mike explains,
“The engine’s horsepower peak is actually
The Rolls-Royce Merlin engine was built under license by both Packard and Continental during
the war to keep pace with demand.