Ducati uses a 90 degree V. Harley uses less. What is so special about the angle and how does it affect vibration and performance?

 

Harley uses a 45 i think. Aprilia uses a 60 degree and has it patented. the 60 degree on the Aprilia lends itself to give the bike 50-50 weight distribution. So there is the answer on Aprilais part.

The angle is used mostly for weight purposes. If the 2 are built together, then they tend to work better. But if you build a chassis and then fit a motor you have no choices except motor mounts.

Performance is just weight and handling really. The vibration isnt directly caused by the twin engine style.

 

Assuming the engine uses a 180 deg crankshaft-

On a 90 deg V, when one cylinder compresses, the other one is decompressing, sort of balancing things out. So the engine cycle goes like, suck-bang, squish-blow, bang-suck, blow-squish. Very smooth without the need for a balancer shaft.

On a 60 deg V (on Harley's V-rod), the timing is off. When one cylinder is compressing, the other one is done with the final 1/3 of a compression stroke and 2/3 of the way into a decompression stroke and vice versa. Without balancer shafts the engine will vibrate quite a bit though performance doesn't suffer.

Splay angles are a tricky thing.


[Modified by redblues, 8:08 AM 1/4/2002]

 

90 degree V-twins are best for vibration control (for V-twins) as stated earlier. The 45 degree Harley is an early 1900's design so the engine will fit into bicycle type frames. It is very bad for vibration. That is one reason why Harleys can't rev high, have poor horsepower vs. displacement, and need rubber engine mounts on their long range cruisers. Honda and I believe others have used the 45 degree engine for looks, and have addressed the vibration problem using staggered crankpins and balance shafts. I believe they (the Japs) have stopped doing this because the cruiser types like the 45 degree V-twin vibration. I suspect the 60 degree V is a compromise for weight distribution and to get good intake track geometry.

 

I have been told that 90 degree engines can make more torque than engines with less opposing angle.

Might as well talk about boxer engines like the BMW and Goldwings too. I don't know much about how they compare.

 

Boxer engines are the most balanced engines you can get besides a V12. The movement of a piston is exactly the opposite of the other piston. They're huge and don't make much sense to put on a motorcycle unless it's big.

V twins make more torque than their I4 conterparts simply because of its higher displacement. Splay angles don't necessarily affect engine performance, it only serves to compact engine size and affect vibration.

 

Sadly my old BMW had so much side torque from the drive shaft that you could lose balance at low speed if you gunned it. Kinda made the boxer engine moot at that point.