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PostPosted: Sat Oct 05, 2019 12:19 pm 
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We've all heard/read the statement that "...a V12 engine is inherently balanced at any bank angle."

However, a recent discussion on FChat (that went totally off the rails) about whether our 65 degree V12's are even/odd firing piqued my curiosity because odd firing made me remember the odd firing GM V6's, which were well known shakers back in the 80's.

Our 65 degree engines aren't far enough off from the ideal 60 degrees to call them "odd-firing", but I wasn't about to join the mud-slinging contest that went on in that thread, but it turns out there actually are odd firing V12's in existence. The Ryan Falconer odd firing V12 is a 90 degree V with a 120 degree crank, which has a firing sequence of 90-30-90-30-90-30-90-30-90-30-90-30, and apparently it's somewhat of a shaker (http://www.epi-eng.com/piston_engine_te ... ngines.htm scroll almost to the bottom of the page to the graph & discussion of odd-fire V12's).

There are also a few LS based V12's out there as well as a Ford V12, all built by chopping/welding a couple of V8 blocks together and giving them dedicated 120 degree cranks, proper cams, etc.

So these 90 degree V12's seem to contradict the original statement that "...a V12 is inherently balanced at any bank angle."

So what about our Ferrari 180 degree 12's with 120 degree cranks? Are they shakers as well?


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PostPosted: Sat Oct 05, 2019 5:24 pm 
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You can build anything WRONG it turns out ;)

A straight 6 with 1/6 aligned, 2/5 at 120 and 3/4 at 240 is inherently balanced. You can go clockwise or counter clock wise on the angle doesn't matter and ferrari did 1 on the 400 and the other on the TR both are correctly balanced.

Then you can add another set of rods to the journals to make it a 12 cylinder and it will remain balanced regardless of the cylinder angle because both banks are inherently balanced. The piston and rod weights of the 2 banks can be different and it doesn't matter....as long as the rods and pistons are match in each individual bank its balanced.

What will not be "balanced" if you use an angle other than 60 or 180 is the firing pulses and that will start to add some shake as you get further off the ideal angles and in the worst case it acts like a big 6 cylinder at 0 & 120 which is still a pretty smooth engine. My old Lincoln flathead V12 is 75 degress and it was a thing back in the day to show people how smooth it was by setting a nickle on the radiator cad and it just sits there....heavy crank and flywheel and its smoother than a 6 but not quite what 60 degrees would give....but still very smooth. A 90 degree block (or 150 or 30) would be about as bad as its going to get. I remember reading about the 65 and 85 in F1 V8s that they were close enough that there was no measurable difference from the ideal 60 or 90. Interestingly I remember the honda "big bang" 4 cyl 2 stroke GP bikes of the 90s would fire all 4 within 5 degrees or each other, that was about tire grip was better with a single large hit then a recovery for the tire and the 5 degree spread let them not blow the crank out the bottom of the engine :)

The V8 based stuff with 90 degrees between crank throws is not balanced. You can play with bob weights and get it pretty smooth at any particular rpm but its not really balanced.


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PostPosted: Sat Oct 05, 2019 9:00 pm 
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I saw the FChat thread and also thought "No way am throwing my 2 cents in that one." I actually typed a few lines and deleted it. It's hard to have a tech discussion over there.
I am not sure the OP ever got an answer about the firing order, which is what he wanted I think.
Having balanced engine in my race engine building days, it is an interesting area to research. I am just really glad all the Ferrari stuff is flat crank V8 or even inline 6x2. Makes modifications much easier.
I am glad I wasn't the only one running from that post. ;)

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PostPosted: Sat Oct 05, 2019 9:03 pm 
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I just went and looked at the post again and it has been locked by a moderator, crazy stuff right there. I don't think I have seen one locked up before.

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PostPosted: Sun Oct 06, 2019 12:56 pm 
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mk e wrote:
A straight 6 with 1/6 aligned, 2/5 at 120 and 3/4 at 240 is inherently balanced. You can go clockwise or counter clock wise on the angle doesn't matter and ferrari did 1 on the 400 and the other on the TR both are correctly balanced.

I think some equate "inherently balanced" to "even firing" and "smooth running" which isn't the case with these 90 degree V12's, that generate uneven torque pulses with their "odd firing".
mk e wrote:
Then you can add another set of rods to the journals to make it a 12 cylinder and it will remain balanced regardless of the cylinder angle because both banks are inherently balanced. The piston and rod weights of the 2 banks can be different and it doesn't matter....as long as the rods and pistons are match in each individual bank its balanced.
What will not be "balanced" if you use an angle other than 60 or 180 is the firing pulses and that will start to add some shake as you get further off the ideal angles and in the worst case it acts like a big 6 cylinder at 0 & 120 which is still a pretty smooth engine. My old Lincoln flathead V12 is 75 degress and it was a thing back in the day to show people how smooth it was by setting a nickle on the radiator cad and it just sits there....heavy crank and flywheel and its smoother than a 6 but not quite what 60 degrees would give....but still very smooth. A 90 degree block (or 150 or 30) would be about as bad as its going to get. I remember reading about the 65 and 85 in F1 V8s that they were close enough that there was no measurable difference from the ideal 60 or 90. Interestingly I remember the honda "big bang" 4 cyl 2 stroke GP bikes of the 90s would fire all 4 within 5 degrees or each other, that was about tire grip was better with a single large hit then a recovery for the tire and the 5 degree spread let them not blow the crank out the bottom of the engine :)

I always thought V12's with bank angles that are multiples of 60 were not only inherently balanced, but would be smooth running and even firing, which is why the 90 degree V12's, even with their 120 degree cranks, generate uneven torque pulses. But I would expect V12's with bank angles of 60, 120, 180 degrees would all be even firing and smooth running?
mk e wrote:
The V8 based stuff with 90 degrees between crank throws is not balanced. You can play with bob weights and get it pretty smooth at any particular rpm but its not really balanced.

I was trying to find details of some of these V8 based V12's where they claim to have welded/bolted V8 cranks together. I can't understand how a V12 could fire properly with a crank that has 90 degree throws?


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PostPosted: Sun Oct 06, 2019 1:22 pm 
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cribbj wrote:
I always thought V12's with bank angles that are multiples of 60 were not only inherently balanced, but would be smooth running and even firing, which is why the 90 degree V12's, even with their 120 degree cranks, generate uneven torque pulses. But I would expect V12's with bank angles of 60, 120, 180 degrees would all be even firing and smooth running?


The angles that work with common throw crank are 60, 180 because to need to get 60 bank to bank somehow. 60 does that directly 1 is up then 60 degrees later 12 is up, perfect. With 180 it still works but the timing is different....1 goes up, when say 3/4 are 120 past top so at +60 3/4 journals which are also 9/10 are up and that works. 120 can't work because the crank is 120 so 1 goes up then 120 degrees later you would have 2/5 up and 7/12 on the other bank and firing pulse wise you have a 6 cylinder, same problem with 0 degrees.

A common throw crank in a 90 deg block can't make anything like even power pulses....a lot (most) V6 engine use offset crank throws so you could also do that to make a 90 deg block work for a 12 I guess.


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PostPosted: Sun Oct 06, 2019 2:25 pm 
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Here's the billet crank on bottom that the Aussie's had custom made for their version of the LS12. It looks like it has 120 degree throws?

The one on top is a standard LS1 crank.

Attachment:
LS12 Crank.jpg
LS12 Crank.jpg [ 56.15 KiB | Viewed 100 times ]


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PostPosted: Sun Oct 06, 2019 2:36 pm 
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Sure does lot like 120....so mechanically balanced but uneven firing


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PostPosted: Sun Oct 06, 2019 2:57 pm 
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And this guy (Don Groff) goes and cuts up a pair of 1JZ Supra blocks, bolts them to a welded steel crankcase and made a 120 degree V12: https://www.roadandtrack.com/car-cultur ... a-1jz-v12/

Several errors in the article - particularly the ones about Ferrari V12's having a 75 degree bank angle and being odd firing, so I don't know about some of the other claims being made, like it being even firing which would contradict your assertion about 120 degree V12's with common throw cranks being odd firing.

I've looked all over and this is the only photo (from the same article) that shows any part of the crankshaft. Definitely common throws, but are they at 120 degrees? Looks like it.

Attachment:
2x1JZV12 crank.jpg
2x1JZV12 crank.jpg [ 99.95 KiB | Viewed 102 times ]


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PostPosted: Sun Oct 06, 2019 3:42 pm 
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A 120 degree V12 is technically even fire I guess.....but the even number between firings is 120 degrees which means it so uneven 2 cylinders fire at the same time...its a big 6 that revs like a 12.

Do you remember the oval piston honda engine? I was a V8 built to fit rules that required no more than 4 cyl, so they merges cylinders.....each had 2 rods, 2 plugs 8 valve and reved to 20k iirc. A 120 V12 is like that but with round cylinders. Its not a bad engine but won't have the normal V12 smoothness or sound, its a straight 6 as far as those things go.


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