Whats the difference between Flat 12 and V12?

Sorry to be a pedantic, but the Alfasud was a Giorgetto Giugaro styling, and the project leader was an Austrian called Rudolf Hruschka.

 

I was talking about the front engined Ferrari prototype that Pininfarina made with a BB engine ... not the Sud.

I owned an Alfa Sud so know all about where the engine is, etc. ... and yes just ahead of the front axle (as are Subaru's) but still front engined. From memory the engine bay did not narrow (much if all) AND the engine was only just infront of the axle line so definitely still involved in the turning clearance. I guess because it was FWD due to CV joints, the front wheels did not turn as tight ?

Not so, only about 3/4s of the width maybe.

Pete

 

Pete, nice to see you back, haven't seen you post in a while. Happy Holidays.

 

"Generally" the "V" angle is equally divisable by the number of cylinders, by 720 degrees of crankshaft rotation. So most V-10 engines have 72* bank angles. V-12's either 60*, or in the case of a boxer, 180* bank angles. In the example above however, a Radial aircraft engine has no opposite opposing cylinders, as they are all at equal angles, and ALWAYS in an odd number of cylinders, like 3, 5, 7, or 9. Even numbers wont work. You wont ever see a 4, 6, 8, or 10 cylinder radial. I dont believe a horizontal opposed 180* twin cylinder engine would be called a radial. Also, a Radial engine has all connecting rods sharing one common crank pin, or throw, like a Harley.

I think Ferrari's reasoning for the flat 12, over the V, was as stated elsewhere, for a lower center of gravity, and possibly less weight, and it may be a stronger design being the entire block is behind the thrust of the crank on firing pulses, possibly making more power, whereas a V engine needs a main bearing "cap". Also, it made better packaging, as they could exhaust out the top, and intake off the sides (why you see all those carb throats pointing straight out). Advances in technology, metalurgy, and also as stated elsewhere, aerodynamics, may have driven the V design back onto the blackboard, as its narrower down low where they need their underside verturies.

 

Someone still hasn't explained what the sharing of a crank throw means. A diagram would be useful...

 

I dont know where to find a picture that would explin it well, but if you can imagine a Harley motor. The engine has two cylinders, in a "V". Now imagine that the crankshaft has only one rod bearing journal, and both cylinders connecting rods are sharing that jounal, or crank throw, crank pin, whatever name works. On a V8 for example, the crank has only four throws, and as you look down at it, one cylinder from each side share a throw. So now, when the cranshaft rotates, both pistons go up and down somewhat together.

A radial is just like a Harley, only with more cylinders in the same plane, and all the connecting rods share the same rod throw. That is why it has to have odd numbers of cylinders, so it will fire more evenly as the crank turns twice. It basically skips every other cylinder as the engine turns.

 

It's kinda small, but here ya go. Note how both connecting rods are attached to a single pin on the crankshaft:
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So, can anyone explain why the V12 Ferrari engines have a different firing order to the flat 12's of the same vintage.....

 

I would simply assume that in a V configuration, like in the picture above, one cylinder in a bank could fire, and be followed, 60 degrees later, by a cylinder sharing that same crank pin on the other bank. But because the flat engine is 180 degrees two other cylinders would have to fire before the opposing cylinder could fire. But I dont know thier firing orders to begin with. I thought all 12 cylinder engines fired like two six cylinder inline engines, so 1,9,5,11,3,7 on one bank, 12,4,8,2,10,6 on the other, depending on how they number cylinders. I think that was how a Jag fired. So if that is correct, it should be 1,12,9,4,5,8,11,2,3,10,7,6? But that wouldnt work with a flat 12 engine. I would have to think about that a while. I dont even know how they number a V12. Are they 123.. down one side, 789...down the other? Or are they even on one bank and odd on the other? And is it the same numbering on both a V and a flat? And, are the cranks simular? I am thinking a flat engine would use different throw spacing than a V12

 

Thanks, and happy holiddays to you to

Expanding on krowbars comments ... firing order is determined by which cylinders reach the top sequentially. This drastically changes when you alter the included angle of an engine from 60 degrees to 180 degrees.

Using the front 2 cylinders as an example, on a 60 degree v12 engine the next cylinder to reach top dead centre after number 1 would be its crankpin sharing mate (I assume number 2, but not sure of how Ferrari engines are numbered). Obviously another cylinder also reaches top dead centre along with number 2 as we are talking even numbered, balanced 4 stroke engines. Thus as we have a cylinder firing every 60 degrees with a v12 then one of these cylinders could be the next one to fire ... thus we are developing our firing order.

Now with a 180 degree v12 or flat 12, the crankpin sharing mate to number 1 (using same cylinder numbering sequence as above) thus number 2 would not be the next to reach top dead centre, as we have to wait 180 degrees for it to reach top dead centre and thus the firing order has to be different. Thus even if the heads were exactly the same the camshafts could not be shared ...

Pete

 

Flat 12 is a proper ferrari engine the V12 is not
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LOL ... yeah right

Pete

 

Is not the flat 12 Testarossa the last Ferrari street car who's engine has evolved from a racing engine? 355 550's all came off "clean sheet" for a street car using knowledge gained from racing of course, but the testarossa is a four valve head bb enigne which is a larger 365GTB who's engine is a detuned race car engine. Is that a safe statement?

 

Isn't this thread mixing metaphors? I mean flat (180 degree - opposing cylinders) block and
V block (cylinders that are less than 180 degrees - opposing)
with flat crank which is used by European Exotics 'V' engines compared to
Detriot's norm.
Try this link
http://www.autozine.org/technical_school/engine/smooth4.htm#V8

stephen

 

How about a flat V12? Like the 312PB.
180 degrees 12 cylinders but with firing order like a V-engine.
/Bengt

 

12 cylinder engines do not have 'flat' cranks ... that is a v8 term and means the crank is like a 4 cylinder and thus flat in plane and not perfectly balanced but stronger/lighter.

Are you sure? ... impossible unless very strange and weak crank ??

Pete
ps: I personally think the BB engine had little to do with the F1 3ltr flat 12 ... let alone the Testarossa engine. Completely different requirements.

 

Okay, I did some thinking and looked at cranks from both flat and V 12 engines to refresh my memory. Basically, all the 12 cylinder cranks look like 6 cylinder inline engine cranks. So, with a inline six, you have three sets of throws in the same plane. In other words, if the front cylinder is at top center, so is the far rear. All others are part way in thier bores, two on the way down, two on the way up. All throws are 120 degrees apart. Firing pulses occur at 120 degree intervals. A 12 cylinder has the same basic crankshaft. Each bank fires just the same as an inline six cylinder engine. If we start at the front, calling it #1, and the other cylinders progress to the back as 2, 3, 4, 5, 6, then the firing order for one bank would be identical to all inline six cylinder engines I have seen, 1,5,3,6,2,4.

Now you have another bank of cylinders, either 60 degrees away with a V engine, or 180 degrees away, in a flat engine. That bank would fire exactly opposite, identical to a six inline engine, and out of phase with the first bank by the degrees of bank, either 60, or 180 degrees. Regardless, you will have firing pulses every 60 degrees of crank rotation no matter which engine design. The only advantages of the 180 degree V type flat motor would be lower center of gravity, tighter packaging, and perhaps less weight. Some of the possible advantages with the 60 degree V type could be simple aerodynamics in the case of a Formula car, or fitting the engine between wheel wells in a front engine car.

 

Agree but the OVERALL firing order CANNOT be the same as the cranks for both engine layouts would be identical (like a 6 cylinder and 120 degree throws as you say).

Lets use your 2 bank firing order to explain. Lets start with the v12:

First bank would be: 1, 5, 3, 6, 2, 4
Second bank would be: 7, 11, 9, 12, 8, 10
Note: I am simply stating here that the cylinders are numbered down each bank from front to back, ie. left side 1, 2, 3, 4, 5, 6 and right side 7, 8, 9, 10, 11 and 12. This is probably not correct but useful for my explanation.

Thus the REAL firing order for the v12 would be (using my cylinder numbering system and assuming 60 degree including V angle):

1, 7, 5, 11, 3, 9, 6, 12, 2, 8, 4, 10 ... if they fire like modern F1 engines, or more likely:

1, 12, 5, 8, 3, 10, 6, 7, 2, 11, 4, 9 ... for better balance.

Now a flat 12 using exactly the same INDIVIDUAL bank firing order, overall firing order would be:

1, 9, 5, 12, 3, 8, 6, 10, 2, 7, 4, 11

Each bank would still fire as you said, ie: First bank would be: 1, 5, 3, 6, 2, 4; Second bank would be: 7, 11, 9, 12, 8, 10 (except it would actually start at number 9 and go 9, 12, 8, 10, 7, 11, but same order).

Now this will not probably be a real firing order as I do not believe Ferrari number their cylinders the same as I have, but you have to think about when the next cylinder is going to reach TDC and that is completely different between a 60 degree included V and an 180 degree included V.

Pete
ps: Note FerrariFixer has already correctly informed us that Flat 12 Ferrari engines do indeed have different overall firing orders.

 

Yes, this would be correct, its just difficult to explain it all like you see it in your head in any kind of simple way. But isnt it really interesting, that we are here just trying to understand something that was already created over 70 years ago or more, Like a Cadillac or Packard?? And think of a V16 from way way back when. What great minds have existed.

 

Yes even in a sketch it would be difficult to explain (but still better) ... but I have to admit I had to use a simple sketch to help with this

Pete