flat plane crank??

[cikay1]

Anyone care to explain to me what a flat plane crank engine configuration is?? Apparently thats what make the ferrari engines sound so racy. Pictures will be good. Thanks! :

[coombsie66]

I take it u know what a crank shaft is yes?
Well the rods in most engines connect to the crank on mountings that are 90 degrees from each other. In a flat plane crank, the mountings are 180 degrees apart. So the crank looks 'flater'.

[coloradosilver]

What's the performance value to thsi configeration? Is it because having the 180 degree plain makes it perfectly balanced so It can rev smoother and to higher RPMs?

[coloradosilver]

What's the performance value to this configeration? Is it because having the 180 degree plain makes it perfectly balanced so It can rev smoother and to higher RPMs?

[coombsie66]

Im really not sure, im sure that must have something to do with it, but it might be due to the angle of V that ferarri use in their engines that you can get higher power levels with that firing order.
Its an area i have never really looked into, mite give it a look now!!

[XTwinTurboVR4X]

OK, here it is, single-plane("flat-plane") engines use a crank that when you lay it on a bench, it lays flat. With a twin-plane crank, you get this whole wobbly thing sittin on your table. Flat-planes are good for higher power engines, as they can rev far higher, and you can use exhaust tuning techniques(great sound - think IRL and CART race cars) and also more power Also the 60 degree V design incorporated also changes the sound, because instead of the normal 90+90 degree firing intervals, you have 60+120 degree firing intervals.

[zevolv]

An engine with a flat-plane crank or the pistons at 180 degrees rather than at 90 is called a boxer engine or an opposed engine. they are used in porsches and subarus they actually idle somewhat less stable than other engines. the real advantage of such engine is that there is no mechanical loss form the cylinder to the crank since the pistons don't have to push the otherside back up they just push the other cylinders in the direction they were already going. there are algebraic equations to show this but I don't remember them I will try to find them. The engine really can't rev any higher than an engine of similar size in a 4 or 6 cylinder setup. the engines aren't any better balanced than a V engine the V setup is actually alot stronger.

[hotgemini]

BAHAHAHAHAHAHA, no offence, but this is like listening to a bunch of blind people sitting around and having a colour guessing competition.

zevolv: The angle of the cylinders relative to each other and the angle of the crank journals relative to each other are two completely unrelated things.

TwinTurboVR4: You're basically on the mark, but the science of exhaust resonance applies to all engines, not just those with 180 degree crank journal intervals.

ColoradoSilver: They aren't smoother, 90 degree cranks have less harmonic problems and in a 90 degree V8 give a 'smoother' power output (more regularly spaced firing intervals).

Flatplane cranks are lighter, when you've got all of the offset reciprocating mass offset in one plane, it requires less additional mass to balance it, when you've got half as much mass in each of two planes, it requires greater mass to balance it.

[takata]

extracted:
1st of all, all V8s are 90°. I haven’t heard any non-90° V8. 90° is the only configuration achieving good balance for V8. However, there are two types of crankshaft arrangements, which delivers very different characters. They are cross-plane crankshaft and flat-plane crankshaft. Most of the world’s V8s are cross-plane V8, including all American V8s and all sedans’ V8s. However, the most exotic European sports cars, including Ferrari, Lotus and TVRs, employ flat-plane V8s.

No matter which kind of V8s, they have 5 main bearings. A cylinder in bank A shares the same crank pin with the corresponding cylinder in bank B, therefore the crankshaft of V8 is actually simpler than V6. Both V8s generate no vibration in vertical, transverse directions or between bank and bank.


Flat-plane V8 (left) and Cross-plane V8 (right)

Cross-plane V8

However, for cross-plane V8s, there is vibration from end to end of the engine, this is because the first piston of bank A is not in the same position as the last piston of bank A (the same goes for bank B), unlike an inline-4 engine. No problem, the 90° V8 solves this problem by introducing an extra-heavy counter weight to every cylinder. The counter weight is heavy enough to balance the weight of crank throw, con-rod and piston of that cylinder, thus resulting in lack of vibration.

Now you must be wondering why such counter weight is not used in other kinds of engines. It is because this counter weight must be used in 90° V-type engines which have shared crank pins. It our previous study, you’ll find only V8 fulfills all these requirements. Why are there such requirements? good question. As you know, all engines have counter weights just enough to balance the weight of crank throws and part of the connecting rods, leaving the remaining weight of connecting rods and the whole, all-important pistons unbalanced. This is because the rotating counter weight can only balance rotating mass. Unluckily, the whole piston moves vertically rather than rotates about the crankshaft, while the CG of con-rod is somewhat rotating but also somewhat going up and down. If we insist to use heavy counter weight, it will cause side shake.
Considering the illustration. Assume the counter weight in vertical position is heavy enough to balance the crank throw, con-rod and pistons. When the crankshaft rotate 90°, the counter weight is repositioned to the right, but the piston doesn’t go to the left, and the con-rod just partially moves to the left. Only the crank pin moves completely to the left. Now you can see the system is not balanced. The counter weight will generate a net force towards the right.
However, for 90° V8, when such a heavy counter weight moves to the right, the piston from another bank will cancel it completely, because their movement are exactly opposed at this moment. (see illustrations below) The same result can be found for the counter weight moving to the left. Therefore 90° cross-plane V8 employs full-weight counter weights can achieve near perfect smoothness.


Flat-plane V8 for high performance cars
However, the disadvantage of cross-plane V8s is also about the counter weights - not only increase the weight of engine, they also contribute to rotational inertia, thus making the engine less responsive and less revvy, dropping upper rev limit and top-end power. Moreover, the larger counter weights usually requires a larger crankcase to house them, thus raising the height (and more important, center of gravity) of the enigne. Therefore Ferrari all V8 models, TVR Cerbera AJP V8 and Lotus Esprit V8 employ flat-plane V8s instead.

Flat-plane V8 is named according to the shape of the crankshaft, which is in a flat plane. It is very much like two inline-4 engines mated together. In particular, it achieves end-to-end balance because the first piston and last piston of a bank is exactly in the same position, so are the center two pistons. This is just the same as straight-four engines, therefore the sound of flat-plane V8 is usually somewhat like a pair of four-pot engines screaming simultaneously, unlike the rumble-bumble of cross-plane V8s.

As both banks run like an inline-4 engine, there is second-order vibration. For a 90° flat-plane V8, the sum of second-order force generated in the 2 banks is - by simple vector analysis - 1.41 times (root-2) of the force generated by each of the inline-4 it consists of. And the direction of vibration is left-right instead of top-down. In other words, while displacement increases 100% compare with the inline-4, the second-order vibration increases just 41%. That makes the flat-plane V8 more refined than an inline-4 although it is not as smooth and quiet as cross-plane V8.

To exotic sports cars, less refinement is not a big problem. Especially they usually employ short stroke and light weight pistons / con-rods, the second-order vibration is greatly reduced.

[hotgemini]

What he said.

[coombsie66]

takata, thankyou for the very informative and interesting post. What did you study and specialise in at uni??

[takata]

i'm a uni drop-out

:roll: