6 replies to this topic

[marion5drsn]

An explanation of the Bank Angle, Firing Angle
of various engines is a simple rule from ,”The Airplane Engine, L. S. Marks 1922, page # 64”. For a four cycle engine = “360 degrees x 2 = 720 degrees divided by the number of cylinders. = Best Bank and Firing Angle”. 16 cylinders = 45 degrees.
14 ” 51.42 degrees
12 ” 60 degrees
10 ” 72 degrees
8 ” 90 degrees
6 ” 120 degrees
4 ” 180 degrees usually called an opposed 4.
2 ” 360 degrees usually called a vertical twin.

Altho engines have been made using other bank angles this results in one of two undesirable factors,
#1, A rough running engine due to an “odd” firing order.
#2, Using an Offset crankpin or an extra crank arms to achieve an even firing order which results in a weaker crankshaft. Neither of which makes a desirable crankshaft. This being especially true in very high output engines!
#2a, One of the most easily missed virtues of the Vee engine is the shorting of the engine due to the double conrod journal. This is one of the items that using a different Vee configuration than the rule thwarts if the engine uses extra crank arms. Notice also that this is a rule and not a law as many engines have been made in many other configurations, such as “W”, “X” Radials, Rotary radials, Etc. Altho these engines also have there own problems with vibration, shake and so forth. One only has to study the various books on this to see that engines that many people thought ran smoothly were actually very bad shakers and this was hidden by clever mounting and vibration dampers. Also by the fact that the people of that time were possibly not aware that an engine should or shouldn’t be smooth to a certain extent as there wasn’t a good practical measuring device available to most people.
A very good example of an engine that by theory should not of needed counterweighting and vibration dampers was the V-12 Allison and other V-12s made in England and Germany. According to ordinary theory no counterweighting and balancing should be needed on these V-12s. However all of them had these items by the end of WW-2. This was probably due to the transferring of torsional vibrations in the crank at high output.
One can also look at the Ferrari flat 12 crank that in theory does not require any form of crankshaft counterweights but has 12 of them. Likely the customers were upset that the crankshaft put out some very peculiar vibrations for such an expensive car and possibly some conrods thru the block.
A pragmatist would say, “Believe very little of what you hear, possibly some of what you read and then only if is backed up by very well known theory/fact. In other words be very suspicious of all statements. This holds true of engines that apparently are not shakers.
One should very suspicious of engine bank angle other
than these, one example is the 71 degrees of various publications that say the bank angle of a V-10 is 71 degrees. As I can find no real reason for the 71 degrees and have found none in any publication at my grasp.
One engine that really bothers me is the Ferrari Dino V-6 at a bank angle of 65 degrees or at least that is what the books say. This engine was a shaker and why Ferrari’s son wanted this bank angle is a mystery to me.
The engineer that followed went to 120 degrees, a much more logical bank angle for engine balance and crank strength. Altho it, the 65 degree, seemed to be used in later engines. This is a real puzzlement. It may be that someone is testing our credibility. But then again other engines by other companies outdid them. Not an engine that had good engineering logic.
The book,” Ferrari Monoposto”, lists a V-6 90 degree, V-6 65 degree, V-12 65 degree, V-12 75 degree, V-10 75 degrees in such high output engines it boggles the mind to analyze the reason for their adoption. The book lists no reason for the use of such bank angles. At least the Flat 12 seems to have a good reason for the configuration of the banks.
It makes one a little more suspicious of Ferrari bank angles. Some publications giving various bank angles
doesn’t give much faith in Ferrari/Media statements.
Either they have/had some weird theory of bank angles or some vibrations in the power train they were trying to dampen but failed to mention. It would seen to be an unusual way to dampen vibrations by using odd firing spacing.
One of the oddest bank angles that I’ve found is the Ferrari V6 Dino of 65 degrees. After learning of this peculiar angle I made a sketch to see if I could make it work. Only after finding the book Ferrari Dino by Anthony Curtis. Page no. 18, column 4 and some on page 19. This explained the layout and the angles involved. This leaving the 3 left CRANK angles at 0,120 and 240 degrees. But the right CRANK angles at 65, 185, 305. Please note these are crank angles and not firing angles. This also results in 3 extra crank arms.
The next question is, “ Does this produce a crank of superior strength or not?” I for only one would be asking the question, “ Why not use a V-8 if the narrowness was of such importance?”
An investigation of the sketches of the cutaway of the Dino engine reveals the crankpins instead of having two conrods side by side there is a crank arm dividing the ordinarily “double” journal. This seeming to lengthen the engine by the width of this arm by three times its width. This would also seem to be weakening the crank in comparison to a normal “V” engine’s “double journal”.
Did other makers also use this on other V-6 engines? It seems to be an inferior way to make an engine fit into an otherwise narrow car. At least this is narrow by American standards. M. L. Anderson

[Ray Bell]

Peugeot's Douvrain V6 has an included angle of 90 degrees, reputedly because the were perhaps planning an extension to V8. This engine, of course, is the one used in Renault 30, Volvos and the 604.
They had a split journal, that is, the pair of journals for each opposing cylinder were staggered by a small amount. They never seem to lose any strength by it, by the way, standard crankcase, crank and rods being used in the engines of the WMs which ran 245mph at Le Mans with quad-valve heads and dual turbos.
Why, though, are there reports of such horrendous vibrations in the V10s that are running in F1 cars?

[desmo]

I think most of it is attributable to extreme efforts at mass reduction. If you've seen a modern F1 crankshaft it is virtually uncounterweighted. No material that isn't holding the piece together. The bank angles are determined more by packaging considerations than anything else, I believe. Balance and vibration just aren't a priority for the engine designers. The resulting vibrations must be a nightmare for people designing all the other systems that must cope with the horrible buzzing, to say nothing of the drivers.

[Powersteer]

Additional weight and new angles at crankpins will be used as counterbalance for the neighbouring cylinder keeping fibration in check with split crankpins

[Wolf]

Here are some odd angles, according to my literature:
V2 - either 45° or 90° (customary)
V4 - 90° (customary), 15°, 20° (Lancia)
V8 - 60° (Horsch)
V16 - 135° (1938 Cadillac)

They're all pre-war (WWII:)) design.

But I find it ridiculous with VW engines which are clamied to be V5. Who's ever heard of V engine with odd number of cylinders?[p][Edited by Wolf on 10-26-2000]

[Exar Kun]

i've heard that the new renault v10 has a 110degree v.

i know the benefits are lowered centre of gravity but what are the down sides to this configuration and what are the the design difficulties??

[Yelnats]

Volkswagen makes a very peculiar V6 with a bank angle so narrow (20 degrees?) it approaches a straight six in functionality but enjoys the shorter block/crank of the v6. It seems to work quite well and perhaps we can attribute this to computer analysis leading to judicious use of counterweights and harmonic balancers though I have no detailed knowlege of this machine to enforce this view. The point being that modern computer simulations can eliminate many of the fatal harmonic resonances that marred earlier designs.

The biggest shaker in racing that I know of was the Norton single derived four cylinder Vanwall F1 car that Moss drove in the mid fifties. It regularly destroyed trottle linkages and anything else connected to the engine and even managed to froth the fuel in the float bowls and was another reason why Moss never won a WDC.