Hi folks, wanted to take up for the Hemi design a bit here. There is at
least one form of racing besides NHRA Top Fuel and XXF Class in Speed
Trials (not to mention all the Chrysler Hemis that can speak for
themselves) where the two-valve Hemi is King at the moment, albeit
because of the class handicap system to "equalize" two-valves with four.
I refer to the current NHRA Pro-Stock Bike Champ, Star Racing, rider
Angelle Savoie. The February Cycle World has a nice tech article on the
bike, and we're told the engine is a 1508cc (about 92 cubic inches)
Suzuki two-valve that produces 305 horsepower @ 12,600 rpm. Star Racing
prefers the two-valve 1508cc engine to the 1294cc they could have with a
four-valve, according to NHRA handicap rules, because they can get more
total horsepower with the two-valve bigger engine. The fuel is race
gas.
One interesting item in the article describes the use of three electric
vacuum pumps to scavenge the crankcase to a vacuum of "25 inches"
(inches of what, it doesn't say) which reportedly picks up over 10
horsepower on this engine. This is quite logical, it just reduces the
pumping effort by the pistons on the crankcase air. We could do that,
if anybody wanted to bother with it. Not a new idea mind you,
motorcycle engine designers in England and maybe elsewhere at least 60
years ago were attempting (and sometimes succeeding) to reduce crankcase
pressure below atmospheric by timed breathers in the timing gear train,
that opened as the pistons came down, and closed when they went up.
No-one doubts that today's four-valve head is the best for unblown gas
engines, certainly not me, my '90 Mazda Miata was that way, and an
excellent engine, and my '95 Lincoln Mark VIII is that way, and truly
this is a car with an ideal engine, WAY more power than you EVER need,
more than you hardly EVER dare to use, yet it will give an honest 25 mpg
on a trip, easily. All this using 87 pump gas, yet.
Four valves in a cylinder head goes almost back to the dawn of the
piston engine, both for racing and road use. But today's version, which
I suppose was invented by Cosworth several decades ago, incorporates
highly-refined squish bands which burn all the fuel, give all the power,
have the valuable feature of being almost detonation-proof on low-octane
pump gas, and the four valves have all the gas flow. Cheers Bill
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