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From: davew@tekecs.UUCP
Newsgroups: net.auto
Subject: Re: "v8, sixes and torque"
Message-ID: <1434@tekecs.UUCP>
Date: Fri, 17-Jun-83 11:44:48 EDT
Article-I.D.: tekecs.1434
Posted: Fri Jun 17 11:44:48 1983
Date-Received: Sat, 25-Jun-83 22:07:16 EDT
References: uw-june.482
Lines: 24


   The problem with 4 bangers is two fold. The first problem is power
overlap, as you mentioned. This usually can be dealt with by using a
heavier flywheel to smooth out the power pulses. The second problem is
acceleration/deceleration of mass. In a four cylinder engine the center
two piston/rod assemblies reach top dead center at the same time as the
outside two reach bottom dead center. The mass of all the reciprocating
parts are accelerated and decelerated at the same time leading to an
inherent vibration. A six cylinder has less vibration since it fires at
120 degrees of crankshaft rotation, 2 pistons at tdc, 2 at 120 degrees
ahead going down their cylinder and 2 lagging at 120 degrees going up
their cylinders. A V8 has a 270-90 firing order with 2 pistons at tdc,
2 at bdc on the opposite bank and 4 half way up their respective
barrels, 2 moving up and 2 moving down. This means that while 4 pistons
are either accelerating or decelerating 4 are at their maximum linear
velocity and thus help dampen the vibration. In the late 1930's Ford
built some experimental engines including straight 5,7 and 9 cylinders
and V10 and V12. They found the smoothest running engine to be the
straight 9, but felt no one would buy a car with an odd number of
cylinders (marketing strikes again), so they went with the V-12 in the
Lincoln Zephyr and Continental. I hope this helps.
					   Dave Williams
					   Tektronix, Inc.
					   ECS