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RFB writes, "I have a 1978 Monte Carlo with 2 valves per cylinder and it's still running well.
I notice these days all cars have 4 valves per cylinder. Does it really make a difference in the
performance, and if so, in what way?"
A great question, RFB, and a wonderful opportunity to talk about some basics in the way the
internal (eco-freaks say "infernal") combustion engine works. My shiny new Webster's Unabridged
(Christmas present from my Editor...is this a comment on my grammar?) defines combustion as "2.
rapid oxidation accompanied by heat and usually, light." Can you say explosion?
The internal combustion engine is an explosion machine. It takes air and gasoline in one end,
lights a fire, causes an explosion and shoves the residue out the other end. Over and over and
over. Of course, it's moving the pistons up and down and turning the crankshaft as a by product
at the same time. It has also been called an air pump. Sucking air in, adding fuel, squeezing
the mixture, lighting it off, burning it and exhausting the leftovers.
What lets the air in and out? Valves, of course. One for intake, one for exhaust. And that's
the way it mostly was until about 15 years ago when Detroit was made to get serious about energy
conservation, fuel economy and emissions control. The race for smaller, lighter, more fuel
efficient and cleaner burning engines began in the early '80s with the imposition of emission
control regulations and CAFE (corporate average fuel economy) requirements.
MIGHTY MITES
What's this got to do with the number of valves? Simple. If the engine must be smaller and
lighter, then the cylinders themselves must be smaller. If the cylinder must be smaller, then
the valves must be smaller. If the valves must be smaller, then the charge of air/fuel mixture
must be smaller. UNLESS. Unless you could add valves to the cylinder head and stuff the same
amount of air/fuel mixture into a smaller space and remove the exhaust faster and do all this at
higher RPMs. If you could do that you could get the same horsepower out of a much smaller chunk
of metal.
So here's what 4-valve engines have that 2-valve engines don't. Greater throughput of air.
Smaller valves mean less weight. Less weight means less energy needed to open and close them. It
also means lighter valve springs to hold them closed. All of which means that the engine can
safely spin at a higher RPM which again, increases the power output for a given engine
displacement.
By the way, it's not true that all current engines are 4-valve. Many are still 2-valve for cost
reasons. At the same time, so-called multi-valve engines are spreading. There are now many V-6
engines with 24 valves and V-8s with 32 valves. Ferrari builds a gorgeous 48-valve, 12-cylinder
engine. And now we are seeing some 5-valve production engines. By the way, this 4-valve
technology is not new. They were building racing engines in the '30s with 4 valves and turbochargers.
HOT TIPS-SURE THINGS AND LUCKY GUESSES
DKH asks, "What would cause my 1989 Mazda 626 to buck or jerk going down the expressway?"
Sounds like you have water in the gas, DKH. This can have two effects. First, if it flows
through the system and into the cylinders it will cause what feels like a "miss" because, of
course it won't burn. It can also clog the fuel filters and prohibit gas flow altogether. Start
by trying some gas treatment (like Drygas). If that doesn't improve the situation then replace
all the fuel filters.
GET A CHARGE OUT OF THIS
Check the purchase date on your battery. If you are nearing the end of the warranty period,
start looking for sale prices now. Don't wait until you have no choice.
David Thompson is President
of Auto Testers, Inc., publishers of The New Driver Car Control
Clinic, a program to help parents make
their new drivers safer drivers.
Questions should be addressed to info@carcontrol.com or:
The Auto Advisor
P.O. Box 99466
Raleigh, NC 27624
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