Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!linus!wivax!decvax!harpo!floyd!vax135!cornell!uw-beaver!tektronix!tekecs!davew 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