15 replies to this topic

[hydra]

Hey all,
have there ever been any 120 degree v-12s used in racing? If so why not? I know of a few vintage aero engines used the layout, but that's about it. If I'm not mistaken a 120 degree V12 should have even firing intervals...

[hydra]

Actually, I AM very much mistaken...
a 120 degree V-12 engine is the worst possible configuration for a V12 as far as uneven firing intervals are concerned. My bad yo

How about a 144 degree V10 then? To the best of my knowledge an engine with that layout has never been commercialized...

[marion5drsn]

After making a layout of this firing pattern and the bank angle I have come to one conclusion, it would fire as a six cylinder engine, that is it would still work, but two cylinders would fire at the same time. Just not an ideal layout. M.L. Anderson

[Powersteer]

Marion, you mean there would be four cylinders on TDC at the same time? If its two then one could be on the power stroke and the other on intake.

[Engineguy]

Originally posted by Powersteer
Marion, you mean there would be four cylinders on TDC at the same time? If its two then one could be on the power stroke and the other on intake.

You are correct sir. An inline six fires every 120° of crank rotation. Only 2 pistons can be at TDC at any time on a six rod journal 120° V12... one firing, one not. So it will fire one cylinder every 60° of crank rotation.

[marion5drsn]

If you people are trying to confuse me you have thoroly succeeded! I must now do a complete layout and see if I messed up. Remember a V-12 engine crankshaft has the journals laid out at 120-degrees. Well back to the old drawing board and the 120-degree vee and the 120-degree crankshaft.
Yours, M.L. Anderson

Be back in a couple of days.

[hydra]

I've been doing some preliminary sketches on ProE, and I've hit a brick wall. How the hell do you design a wide angle (i.e. >120 degree) V engine and still have the block in 1 piece? Long rods and short strokes help, but that's not the solution I'm looking for

[hydra]

Brainfart yet again! The secret is to include some form of detachable bedplate of sorts, which I believe was done on certain boxer engines (lancia and/or alfa maybe?) If anyone would provide further specific examples then I would be most grateful

[marion5drsn]

I just finished and still believe I am correct. Using the same style of crankshaft as the 1930s Lincoln Zephyr V-12 and also the 1935-1937 Cadillac V-12 firing order of # 1-4-9-8-5-2-11-10-3-6-7-12, this puts crank journals # 1,2 and 11-12 directly inline with one another, #3-4 and 9-10 in ,in line with one another, # 7-8 and 5-6 in line with one another. At one hundred and twenty degrees block angle this means that four pins are lined up each time that any one piston is at top dead center. Example: # 1 and 11 on the left and 4 and 10 on the right. This does not happen when the block is at 60-degrees as the block and crankshaft pins are out of line 30-degrees.
Yours, M. L Anderson

[Engineguy]

Originally posted by marion5drsn
...Using the same style of crankshaft as the 1930s Lincoln Zephyr V-12...

Why are you doing that? It was not a 120° VEE.

Six journals at 0, 60, 120, 180, 240, and 300 works for a 120° VEE... only two pistons at TDC at a time.

[Engineguy]

Originally posted by hydra
I've been doing some preliminary sketches on ProE, and I've hit a brick wall. How the hell do you design a wide angle (i.e. >120 degree) V engine and still have the block in 1 piece? Long rods and short strokes help, but that's not the solution I'm looking for

A 120° Vee block is not very difficult... just have to make sure you can get to the con rod bolts/nuts at some point in the crank rotation (shorter rods & longer stroke actually helps with that)... so if you have a really deep skirt block you may have to space the pan rails out a little at some point. But it's not a problem unless you go to an extreme.

Here's a 120° V6 Ford F1 block by Cosworth (1986 1.5L Turbo)... surprisingly conventional Vee block configuration with individual 2-bolt main caps (plus side bolts).

[hydra]

Awesome pic Engineguy, thanks!
Since you seem to be a big fan of 120 degree V6s, I couldn't help but wonder if you've got more pics like that...
Another question, how much if at all can the piston skirt be permitted to stick out of the bore at bottom dead center, i.e. how deep do you make the bore in relation to the stroke?


P.S. What are the roller bearings on the front face for?

[david_martin]

Originally posted by hydra
P.S. What are the roller bearings on the front face for?

Primary drive gears for the valve train would be my guess.

[Engineguy]

Yes, the 2:1 ratio reduction for the cams is done there, then it's chain drive up to the cams... since the redution is already taken care of, the sprockets on the cam don't need to be large. The rectangular projection the chain straddles is a water passage to the cylinder bank.

On the subject of how far a piston can be pulled out of the bore, I recalled that the production 4.6L Fords do this...

"One of the challanges of the 4.6-liter engine is the fact that the piston is pulled so far out of the bore at the bottom of the stroke. The largest piston diameter comes clear out of the bore, allowing the piston to contact the cylinder wall on change of direction, creating noise when cold."

AND...

"The 4.6 suffers from the fact that the area on the piston that is the largest in diameter is withdrawn from the bore at BDC, leaving an area that is .002-.004 inch smaller in OD than the measuring area of the piston.
...until the engine is at operating temperature.... excess clearance allows the piston to rock excessively at BDC, which causes piston clatter." (Both quotes from Sean Hyland's book)

Sounds like this engine is about the max in this regard...

The deck height is 8.937, stroke is 3.543, rod length is 5.933, piston pin dia is 0.866. Just need to find out how long the cylinder sleeve is to know where the pin is relative to the bottom of the sleeve at BDC... can't find it in the book or on the internet.

[Powersteer]

Engineguy, the pic of that 120° V-6 is from what vehicle? I think a 120° V-6 should sound a bit like an in-line 6, so i imagine what a 120° V-12 would sound like, two in-line 6's or a flat-12 which is known to produce the best ochestra.

[Engineguy]

Originally posted by Powersteer
Engineguy, the pic of that 120° V-6 is from what vehicle?

It is the Ford F1 engine (1.5L twin-turbo ~1000HP) used in 1986 by Haas/Force (Carl Haas/Teddy Mayer/Tyler Alexander/Ross Brawn/Neil Oatley/Adrian Newey) and used in 1987 by Benetton.