90 degree V6 3 throw crank project

[F1fan01]

V6 90 degree engines have split crank journals for even firing intervals 120 degree for a smoother engine.

However there are success stories like the current F1 V6 with 3 throw cranks with odd firing order.

The benefits of a stronger shared pin (3 pin crank) albeit with an odd firing order makes it a lighter and strong bottom end.

I’ve seen posts suggesting that odd fire shared pin engines not suffering from vibration issues once it revs out.

The new Maserati Nettuno engine is a modern 3 pin v6 90 degree with Odd fire 1-6-3-4-2-5 order.

I am contemplating rebuilding an engine with a 3 pin crank which necessitates an odd fire setup from its original even fire configuration.

Would the valve train or harmonics become a problem with this switch? Assuming the engine will rev from 4000-9000rpm most of the time?

[Tommy Cookers]

V6 90 degree engines have split crank journals for even firing intervals 120 degree for a smoother engine.
However there are success stories like the current F1 V6 with 3 throw cranks with odd firing order.
The benefits of a stronger shared pin (3 pin crank) albeit with an odd firing order makes it a lighter and strong bottom end.
I’ve seen posts suggesting that odd fire shared pin engines not suffering from vibration issues once it revs out.
The new Maserati Nettuno engine is a modern 3 pin v6 90 degree with Odd fire 1-6-3-4-2-5 order.
I am contemplating rebuilding an engine with a 3 pin crank which necessitates an odd fire setup from its original even fire configuration.
Would the valve train or harmonics become a problem with this switch? Assuming the engine will rev from 4000-9000rpm most of the time?

er well ...... and broadly .....

firing order is nothing to do with firing intervals
(there's anyway only 1 firing order with a 3 pin - 2 orders if one bank has internal different order to the other bank)

vibration is to do with inertia forces ie rpm not gas loads ie firing
(the 1960s GM 90 deg 3 pin-ers never had a real vibration problem - people inferred vibration from the uneven sound)
there is no magic bank angle for zero vibration on a 3 pin V6 (a 6pin V6 gets good when the bank angle nears 180 deg)

a 90 deg V twin uses counterweights big enough to cancel primary force vibration (but not the large secondary force)
so a 90 deg V6 could be made with a 'single' pin 'flat' (longitudinally symmetric) crankshaft to use these CWs
and similarly both a 3 pin 'flat' crankshaft (as Laverda 3) and a 3 pin 2 plane @ 90 deg are quite good
but further counterbalances are needed as the basic layout of all these shafts is itself unbalanced
heavy CWs tend to depress torsional vibration frequencies
normal 3 pin V6s (little CW) have force balance but even 120deg bank angles give primary&secondary moment imbalances

most current road V6s are (60 deg) 6 pin with some very slender webs so the engines are no longer than a 3 pin-er
(NOTE to self - this I wrote on p7 of the thread 'engine block aluminium vs CGIron)

[vvillium3]

The safe view on this is yes, the vibrations may become a problem. Key word, being may.

Even if the engine cylinder count and layout results in a perfect first and second order balance. The engine can still have serious vibration issues. The crankshaft, camshafts, timing chains, etc. are just expensive springs. They all bend and stretch in different ways when loaded by different forces that happen in a running engine. The worst being the natural frequency of a component that an engine operates in regularly. Hence the great amount of effort that goes into engine designs to dampen these issues out.

So in short yes, changing a crankshaft layout can affect the vibrations, just not in the way most generally speak. It may not seem like you're changing much, but a little bit may make just enough of a difference.

However, don't let this deter you from the project. You may get lucky and see no issues and the stock damper my work perfectly for your new crankshaft design. Just do your homework and learn about this stuff before paying to have a one off crankshaft machined up. There are tons of great books out there that can be had cheap. It'll be a great opportunity for a learning experience.