M3 GTR: Flat plane crank?

[AMOCHOSTO]

Originally Posted by elp_jc

If flat-plane crank V8s sound like Ferraris, I don't personally like that sound at all: too high-pitched and raspy IMO. The S65 is the best V8 I've ever heard, even at idle. Plus it revs as high as a Ferrari. Oh, and it doesn't need freaking BELT changes every 3 years or 15K miles . What else can you ask for?

And that video was great except the poor BMW was being spanked big time . Maybe our S65 engine is better .

I have no idea what a flat plane crank is, but I'd be perfectly happy with the Ferrari sounding engine. Sign me the f\|(k up!

[Robo Squirrel]

Originally Posted by AMOCHOSTO

I have no idea what a flat plane crank is, but I'd be perfectly happy with the Ferrari sounding engine. Sign me the f\|(k up!

cross plane crank, used in most v-8s including our own


uses a counter weight to reduce vibration
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. 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 crank, ferrari, M3 GTR, F1

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.

[gr8000]

Thanks for the info Robo S.

Talking about in-line 4s, do I assume correctly that there must be designs whereby the cranks are at 90 degree angle difference (crank of cyl no. 1 at 0 degrees, no. 2 at 90, no. 3 at 180, and no. 4 at 270) to achieve better balance?

[Robo Squirrel]

Originally Posted by gr8000

Thanks for the info Robo S.

Talking about in-line 4s, do I assume correctly that there must be designs whereby the cranks are at 90 degree angle difference (crank of cyl no. 1 at 0 degrees, no. 2 at 90, no. 3 at 180, and no. 4 at 270) to achieve better balance?

hmmm, i dont know about that. ive never seen one like that

[gr8000]

Originally Posted by Robo Squirrel

hmmm, i dont know about that. ive never seen one like that

I wonder why not... In terms of vibrations is should be super smooth, and I can't think of any issues with such design. Obviously, if there arent any arround there must be plenty of issues I guess

[AMOCHOSTO]

Wow! Thanks Robo! I sure got my learn on this morning!

[gr8000]

Originally Posted by gr8000

I wonder why not... In terms of vibrations is should be super smooth, and I can't think of any issues with such design. Obviously, if there arent any arround there must be plenty of issues I guess

Thinking of it again it maybe it doesnt make sense in the case of 4 stroke engines and here is why: A 4 stroke engine needs 2 revolutions i.e. 720 degrees (2 x 360) to complete one full engine cyrcle (suction, compression, combustion & exhaust). Therefore if you have a 4-cylinder 4-stroke engine, then 720 degrees devided by 4 cylinders = 180 degrees gives you the crank angle difference between the 4 cylinders. Therefore every 180 degrees another cylinder needs to be fired for the engine to run smoothly and evenly balanced (in terms of firing sequence). If each cylinder was placed at 90 degree crank difference and fired accordingly, then there would be huge uneven firing gaps (= vibrations), which would otherwise have to be counter balanced by physical weights probably...

Not sure if I make any sense but at least I think I understand it now!

[Robo Squirrel]

ok so they are out there: http://www.yamaha-motor-europe.com/d...firing%20order

there is a few others i found also. All the 4cyl cranks that I MYSELF have seen are flat plane, but i guess there are exceptions...i would like to hear what a cross plane crank I4 sounds like....maybe like a subaru boxer 4?

[Robo Squirrel]

holy shit they sound like a mini V8

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[mkoesel]

Thanks for all the replies on the differences between flat-plane and cross-plane cranks and the trade-offs involved. I learned something.

I concur that it would be sweet to have a cross-plane crank in the production M3 - would sound more like a F430 or Scuderia!

So who's going to be the first one to do this mod, lol?

[Robo Squirrel]

Originally Posted by mkoesel

Thanks for all the replies on the differences between flat-plane and cross-plane cranks and the trade-offs involved. I learned something.

I concur that it would be sweet to have a cross-plane crank in the production M3 - would sound more like a F430 or Scuderia!

So who's going to be the first one to do this mod, lol?

haha, no problem...i love dorky technical stuff. It would be pretty expensive to convert our motor to flat plane. if only someone could get a hold of the P65 motorsport engine i also found some sweet vids of a TVR 4.5 which uses a flat plane crank.

[vm]

One thing that I want to clarify is that the flat plane cranks both in V8 and 4 cylinder configurations are balanced from the weight distribution point of view. The problem is that the "second order moment of inertia" are unbalanced, which is a more subtle dynamic unbalance. Inline and flat sixes as well a 90 degrees V8 with a well designed crank have their second order vibrations balanced. If you want to learn more in an easy to read article check:
http://www.autozine.org/technical_sc...ne/smooth1.htm

[sehrgut]

Flat-plane crank V8 sounds so nice. GREAT info on this thread, thanks.

Just noticed how old this thread was.

[JCtx]

One more piece of information some folks might not be aware of: The V8 engine started life at the end of the 19th century with a 'flat-plane' crank, and stayed that way for decades until manufacturing technology advanced enough to produce a proper 'cross-plane' crank at the end of the 1930s, I believe (or early 1940s). It's a lot cheaper and easier to build a flat-plane crank. Just wanted to mention this because it's easy to assume the flat-plane crank engine is more 'sophisticated' just because Ferrari uses it, but it's not .

A flat-plane crank engine revs easier (and usually higher) for the reasons Robo and others explained (no counterweights, or minimal), plus its even pulses don't require an elaborate exhaust system, but it'd never last as long due to its inherent internal vibration, so we'd probably never see one on a mainstream vehicle like a BMW. Since a flat-crank is cheaper to produce, everybody would still use it (with active engine mounts) if it was better. I'm happy that old technology is only used on race (and exotic) engines nowadays .

[FredVMI]

Originally Posted by elp_jc

If flat-plane crank V8s sound like Ferraris, I don't personally like that sound at all: too high-pitched and raspy IMO. The S65 is the best V8 I've ever heard, even at idle. Plus it revs as high as a Ferrari. Oh, and it doesn't need freaking BELT changes every 3 years or 15K miles . What else can you ask for?

And that video was great except the poor BMW was being spanked big time . Maybe our S65 engine is better .

The only cars that passed the M3 in the video were LMP cars. No GT cars passed the M3 in the video. LMP cars are spec'd at 650-700 HP with a weight minimum of 900 kg, while GT cars are spec'd at 450-500 HP with a weight minimum of 1145 kg. With this huge power-to-weight ratio disparity, LMP cars will destroy GT cars!

[gemini330zhp]

Wow Great info guys!!!!! I still like the old E46 racecar sounds

[aus]

So could RDSport and Dinan make the stroker engines flat plane crank engines?