V12's

Why do today's Ferrari V12's have a 65 degree bank angle?

 

65* is an ideal balance angle for most v-12 firing orders.

Infact, I cannot think of one example of a v-12 with a bank angle other than 65*

 

Incorrect, 60* is the correct angle for perfectly even firing order, but the reason for 65*, I assume, is to allow for wider cylinder heads and inlet manifolds, etc.

Thus the 5* probably does not upset the firing balance that much.

The Columbo and Lampredi v12 Ferrari engines are 60* BTW. It is only recent Ferrari (road) v12 engines that have widened out to 65*.

V angle calculation for even firing pulses:
360* x 2 (as a 4 stroke engine cylinder only fires every 2nd revolution) / number of cylinders, thus:

(360 x 2)/12 = 60* for a v12.
(360 x 2)/8 = 90* for a v8
(360 x)/6 = 120* for a v6 ... but most are 60* or 65* for packaging reasons and I guess the crank modified (i.e opposite cylinders do not share a crankpin?) to correct this.
For fun: (360 x 2)/10 = 72* for a v10.

Pete

 

I stand corrected!

PS: Is vee angle design just firing pulses, or is recripicating mass also taken into account?

 

For engines with possible even firing pulses then I think the reciprocating masses will be balanced too.

By this I mean say a v6 or v12 but not a v2.

The Ducati 90* twin for example is at 90* V to balance the reciprocating mass (I believe) and definitely not for even firing pulses ... but I'm no expert.

I do know (for example) that v8's with a flat plain crank have secondary vibration issues that a normal v8 (ie. normal non-flat crank and thus firing order) does not have.

There was a really good site somewhere that showed (mainly twin engines) balance issues ... I'll see if I can find it.

Pete
ps: Twins: http://www.xs650.org.au/vtwin.html

 

I don't have my copy with me in China, but Ferrari put out a V12 65 degree book in the last year or so that covers all of these engines.

 

Internal Combustion Engine Fundamentals, by John Heywood, has a thorough discussion of V-angle. It has been a long time since I read it, but if IIRC...

There are primary and secondary vibrations within a multicylinder engine. The primary forces are mainly concerned with the instantaneous centers of mass of each cylinder's moving parts, and the shaking forces generated. Other cylinder(s), if positioned at the proper angle and firing sequence, can cancel out this primary vibration from the first cylinder. The two resultant force vectors have equal magnitude but opposite direction and thus result in zero magnitude. There is only one ideal angle for each quantity of cylinders. Vee engines with an odd number of cylinders would never have a solution, in theory.

The secondary vibrations are caused becuase of the offset of each connecting rod. In this case the two vectors mentioned above are no longer colinear, but instead parallel and offset the distance between the two cylinders. A Ducati V-twin, for example, has a couple of centimeters offset between cylinders. Crudely speaking, the result is an engine that tries to rotate back and forth (CW and CCW), if viewed from above.

Hope this helps.

 

My BB512i's V-12 engine has a 180 degree bank angle.

 

60 vs 65 - I think it is to make it sound a bit more rough instead of the super smoothness of the 60 degree 12 cylinder

 

A BB512 is not a V12, it is a flat twelve.

 

Not this again!

Back to the OP -- It's a packaging thing as PSk mentioned -- 60 deg doesn't give much room between the cyl heads (especially at a rather short stroke), and something like 120 deg or more (or even 90 deg) is just too wide. Each bank of a Ferrari 12 cylinder is a perfectly balanced inline-6 so the bank angle has no effect on balance (it's really good regardless of bank angle). The sweetest sound occurs when the bank angle = (2n+1) * 60 deg where n = 0, 1, 2...(which makes the time between all firing events exactly the same), but this only has practical solutions of 60 deg or 180 deg. 65 deg is no huge sin.

 

Pete- V6s are not perfectly balanced, but inline 6s are.

Ferrari introduced the 65 degree V on its F1 engines in the 50s/60s. More room for carburetors and intake manifolds.

 

The somewhat rare Ferrari "Yellow Book" (359/85) has a large fold-out table of the specs for every Ferrari engine from 1946 to 1985. Every V-12 was 60 degrees. There were some flat 12's where the angle was 180 degrees.

 

Bill- Yup, there were later V12 F1 engines with V angles of 65 and 75 degrees, but the first production V12 with 65 degree V angle was the 456 GT from 1992/93. All later production V12s were 65 degree bank angles, including the F50. 333 SP, too.

Those earlier F1 engines with 65 degree bank angles were V6s.