tgg@hou5e.UUCP (06/15/83)
I always heard (read, etc.) that sixes were always better than v-8s on vibration because all of the primary and most of the secondary vibration effects were in balance (not so on v-8s). A guess for the torque increase for 6s is less parasitic drag (fewer pistons, bearings, lifters, you-name-its) and possible better combustion from larger individual cylinders (less quench area, more burn time, larger working area on piston top). Tom Gulvin ABI - Holmdel
jjm@hou5e.UUCP (06/15/83)
As far as V4's are concerned, they are USUALLY not as well balanced as V6's. An exception to the rule is the dynamically balanced design developed by Mitsubishi and used in the Chrysler/Plymouth imports (Colt, Arrow, Sapporo, etc), the Mitsubishis (Cordia, Tredia, Starion) and the new Porsche 944. Are there any V8's that use a dynamic balancing system similar to this? It would seem from this discussion that it may produce a noticeable smoothing... Jim McParland ABI - HO hou5e!jjm
emma@uw-june.UUCP (06/16/83)
One quick note is that all of the 4-bangers you mention are inline, not V. The problem, as I understand it, is not one of balance, but rather that the non-overlapping power strokes set up a lot of vibration. Mitsubishi and Porsche are fighting this with unbalanced shafts set up to introduce a vibration cancelling that from the combustion. My wife's 2.6litre Sapporo is one heck of a lot smoother than my 1.6litre Corolla! -Joe P.
davew@tekecs.UUCP (06/17/83)
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
rs55611@ihuxk.UUCP (06/17/83)
In regard to the question/comment on dynamic balancers used by Chrysler/Mitsubishi in their 2.6 liter in-line 4: 90 degree V-8s, 60 and 120 degree V-6s are inherently balanced by their geometry. In-line 4's, and 90 degree V-6's aren't. (I'm not sure about in-line 6's.) Thus, dynamic balancers help noticeably on in-line 4's (also due to the 4 just having a small no. of cylinders.) The other, related issue is whether the engine firing is evenly spaced. This is a problem for 90 degree V-6s (even-firing on a V-6 requires a cylinder bank angle of 60 or 120 degrees; of course an opposed, or 180 degree six is fine, too, as in Porsche 911's). For example, the first year or two of the Buick 3.8 liter V-6 is an "odd-firing" 90 degree design, with a lopey-sounding idle, and some roughness. This was at least partially solved by incorporating a crankshaft with offset con rod journals, to artificially cause even firing in the 90 degree design. The reason for the 90 degree block is that tight schedules forced the re-use of tooling from the V-8 line, which are of course 90 degrees. The newer V-6 engines from GM, such as the Chevy 2.8 liter (X-bodies, etc.) are designed from scratch, and are 60 degree designs. If I'm blowing smoke here on any of my statements (made from possibly fuzzy memories of magazine articles in Road and Track, etc.), feel free to send flames; I can take it. (I think!) Bob Schleicher ihuxk!rs55611 Bell Labs, Naperville, Ill.