flat plane crank ?

[yvon_la]

ok! just viewed info on the new mustang 350r etc ,basicly they followed tried and true formula of cadillac ferrari etc ,

my question: are there inline 6 that exist with flat plane crank?

 

[ARCOgraphite]

I hope not.

 

[A_Harman]

Not that I know of, but people have tried some pretty weird stuff over the years. The engine wouldn't be even firing. And it would have primary imbalance of the reciprocating masses.

Cadillac doesn't use flat plane cranks in their V8's.
Ferrari does. McLaren does.

 

[CT8]

I am almost positive that all inline engines have flat plane cranks except for the Yamaha cross plane inline engines. Please any one correct me if I am wrong,

 

[yvon_la]

http://www.caranddriver.com/features/the-physics-of-engine-cylinder-bank-angles-feature

i was reading this and they mentionned 720 degree for each explosion divided by number of cylinder
and yet mustang use a 180 degree configuration ( a 4 cylinder territory) for a v8
and in theory a 120 degree would be best for inline 6
so this brought a lot of question into the why and all

 

[d00df00d]

Originally Posted By: yvon_la
ok! just viewed info on the new mustang 350r etc ,basicly they followed tried and true formula of cadillac ferrari etc ,

Sorta-kinda.

There's more than one way to do a flat-plane crank in a V8: the way Ford did it in the GT350, and the way everyone else (Ferrari, McLaren, etc.) does it.

The way everyone else does it has 3 main benefits: It weighs less, it's more compact, and the firing pulses are evenly spaced.

Unfortunately, doing it that way requires intake and exhaust manifolds that Ford couldn't fit in the GT350's engine bay. So, they had to tweak the design a bit. Their version still has evenly spaced firing pulses (which is why it makes so much power), but it weighs just as much as a normal cross-plane crank V8.


Originally Posted By: yvon_la
my question: are there inline 6 that exist with flat plane crank?

A flat-plane crank only works with 2, 4, 8, or 16 cylinders. With any other number, it'd make hideous vibrations for no real benefit.

An inline-6 already has evenly spaced firing pulses and minimal excess weight anyway, so it has many of the same benefits as a flat-plane crank in a V8 -- plus perfect natural balance (i.e. minimal vibration).

 

[yvon_la]

Originally Posted By: CT8
I am almost positive that all inline engines have flat plane cranks except for the Yamaha cross plane inline engines. Please any one correct me if I am wrong,


from what i read i6 are 120 degree http://www.burnsstainless.com/V-12ExhaustDesign.aspx
if they are ? how come their rev limiter is so low?

 

[yvon_la]

ty for feedback! ya i assumed as much ( being a trucker in america) but i always wondered why i6 were so uber!

 

[d00df00d]

Rigidity can be a problem for an inline-6 because it's so long. That's a big concern for high RPM applications.

However, there are definitely high-RPM inline-6 engines. Nissan's RB series, BMW's S54 engine (e.g. in the 200-2006 M3), etc.

 

[d00df00d]

An inline-6 is perfect for a truck because of its inherent balance. No matter which way any piston moves, its motion is always canceled out by the motion of another piston. So, as long as all the parts are rigid and properly machined, there is virtually no vibration. Other engine types need big counterweights just to come close to that level of smoothness. All else equal, the only thing smoother than an inline-6 is a V-12, which is... two inline-6s.

That smoothness is VERY important for durability. Plus, it's relatively easy to make power with an inline-6 because you have evenly spaced firing pulses. At the same time, it's better than a V-12 because it's simpler.

So basically, an inline-6 is the best balance of simplicity, power, smoothness, and durability. The only problem is how big it is, which isn't much of a concern in a big truck.

 

[OneEyeJack]

Don't forget that even with a 90 degree crank on a V8 you still have options with the firing order and that can have an effect on balance and vibration especially in light weight engines in a light chassis.

Nissan VK 1-8-7-3-6-5-4-2
GM, Toy UZ 1-8-7-2-6-5-4-3
Older GM 1-8-4-3-6-5-7-2
Cad, BMW 1-6-2-5-8-3-7-4
Ford Mod 1-5-6-3-4-2-7-8
& flathead 1-5-4-8-7-2-6-3
Ford sm bk 1-5-4-8-6-3-7-2
& bg blk 1-5-4-2-6-3-7-8
Porsche 1-3-7-2-6-5-4-8
& Fd Wind 1-2-7-8-4-5-6-3
Cad NS 1-2-7-3-4-5-6-8

Understanding this depends on how the cylinders are numbered

Cyl bank Ferrari Audi Ford GM & Chr GM (Northstar)
Right side 4321 1234 1234 2468 1357
Left side 5678 5678 5678 1357 2468

 

[440Magnum]

An inline-6 will never have a flat-plane crank. It doesn't work that way.

An inline 4-stroke engine can only have a flat-plane crank if it has 2 or 4 cylinders, unless you allow it to fire more than one cylinder at the same time, which is useless.

A v8 can have a flat-plane crank IF its a 90-degree bank angle, and IF you can tolerate the high level of 2nd order imbalance, or mitigate it with long connecting rods.

The big advantages of a flat-plane crank in a v8 is that it allows the crankshaft to be far, far lighter than a 90-degree crank because it has much smaller counter-weights. That lets it accelerate faster. A secondary advantage is that it allows exhaust pulses to alternate bank-to-bank, which a 90-degree crank does not. Because it has less weight and inertia, it is desirable for racing but because it has 2nd order imbalance worse than an inline-4, its not desirable for much else.

The advantage of the 90-degree crank is that it has much better balance characteristics and results in a much smoother-running engine.

https://en.wikipedia.org/wiki/Engine_balance

 

[FCD]

Ford made a flat plane V4, now that's odd

 

[440Magnum]

Originally Posted By: OneEyeJack
Don't forget that even with a 90 degree crank on a V8 you still have options with the firing order and that can have an effect on balance and vibration especially in light weight engines in a light chassis.



I think its true that if you convert everything to a common cylinder numbering system, there are only two truly unique firing orders for a 90-degree crank v8: the old GM/Chrysler order (1-8-4-3-6-5-7-2 by GM/Chrysler numbering), and the Ford Modular/ GM LSx firing order (1-8-7-2-6-5-4-3 by the same numbering system). The latter has a very slight theoretical advantage in torsional vibration induced in the crank, but its so small as to (obviously) not matter since production and racing engines of both types produce power to the same levels and same reliability.

 

[punisher]

My go to site for explaining engine vibration/crank layouts etc.

http://www.autozine.org/technical_school/engine/smooth1.htm

With inline 6s, you always have that inherent balance with 120° throws. That's the good thing. The bad is there is always a trade off. Inline 6s have long cranks that have to be heavier/thicker to control harmonics. In a big diesel, no problem as the RPM limit is quite low. When the RPMs climb you get all sorts of harmonics that have to be dealt with. Example is the guys running stock classes with inline 6s. You saw wild and weird harmonic balancer setups to keep the valve train together.

 

[440Magnum]

Originally Posted By: punisher
My go to site for explaining engine vibration/crank layouts etc.

http://www.autozine.org/technical_school/engine/smooth1.htm

With inline 6s, you always have that inherent balance with 120° throws. That's the good thing. The bad is there is always a trade off. Inline 6s have long cranks that have to be heavier/thicker to control harmonics. .


And that's not all. Like all inline 4-strokes, there are always pairs of cylinders that move exactly in-phase, in the same plane. When that happens, there is 2nd order imbalance due to the length of the connecting rod making the piston motion non-sinusoidal, and that makes the block want to "bounce" up and down at the frequency of the crank rotation for each pair of cylinders, so 2x crank rotation speed in a 4-banger, and 3x crank rotation speed in a six, 4x in an inline-8. The higher that frequency becomes, the less obvious it is to the outside observer so an inline 8 is better than a 6 is better than a 4 in that regard. But the main thing that helps is making the connecting rods as long as possible relative to the stroke (a greater "rod ratio" in other words.) It also comes into play in v-type engines , but in that case the "paired" cylinders are usually on opposite banks and moving in different planes, so the vibrations partially cancel and are less noticeable than an inline.

 

[440Magnum]

Originally Posted By: d00df00d
Originally Posted By: yvon_la
ok! just viewed info on the new mustang 350r etc ,basicly they followed tried and true formula of cadillac ferrari etc ,

Sorta-kinda.

There's more than one way to do a flat-plane crank in a V8: the way Ford did it in the GT350, and the way everyone else (Ferrari, McLaren, etc.) does it.

The way everyone else does it has 3 main benefits: It weighs less, it's more compact, and the firing pulses are evenly spaced.

Unfortunately, doing it that way requires intake and exhaust manifolds that Ford couldn't fit in the GT350's engine bay. So, they had to tweak the design a bit. Their version still has evenly spaced firing pulses (which is why it makes so much power), but it weighs just as much as a normal cross-plane crank V8.



You're referring to Ford using an "up-down-up-down" crankpin configuration instead of the "up-down-down-up" crankpin configuration of an inline 4 (or Ferrari v8). I'm not sure why they did it, but probably to improve scavenging in the exhaust system or something similar. But its not "just as heavy" as a comparable 90-degree crank. It needs counterweights that are about half to 60% as heavy as the counterweights of an equivalent 90-degree crank, so there's still a pretty big weight savings. Its also why the Voodoo v8 sounds very different than the brappy screech of a Ferrari v8. It retains some of the lower rumble of an American v8, but without the left-right 'thumping" of the exhaust when heard through dual exhausts. Honestly, its sound reminds me most of a Ford GT, which was a traditional American v8 but with the "nest of snakes" exhaust plumbing to even out the scavenging pulses.

 

[CT8]

Originally Posted By: yvon_la
Originally Posted By: CT8
I am almost positive that all inline engines have flat plane cranks except for the Yamaha cross plane inline engines. Please any one correct me if I am wrong,


from what i read i6 are 120 degree http://www.burnsstainless.com/V-12ExhaustDesign.aspx
if they are ? how come their rev limiter is so low?
The long length of the crankmaybe I don't know about the BMW cyls revs thought . Most inline sixes aren't hi performance to begin with

 

[SwampSurvivor]

High speed inline sixes are music to my ears

 

[d00df00d]

Originally Posted By: 440Magnum
You're referring to Ford using an "up-down-up-down" crankpin configuration instead of the "up-down-down-up" crankpin configuration of an inline 4 (or Ferrari v8). I'm not sure why they did it, but probably to improve scavenging in the exhaust system or something similar.

As I understand, it's because they couldn't make dual intake plenums work, and UDUD works better than UDDU with a single manifold -- something about resonances.

Also, I goofed when I included exhaust manifolds as part of the explanation. Sorry.



Originally Posted By: 440Magnum
But its not "just as heavy" as a comparable 90-degree crank. It needs counterweights that are about half to 60% as heavy as the counterweights of an equivalent 90-degree crank, so there's still a pretty big weight savings. Its also why the Voodoo v8 sounds very different than the brappy screech of a Ferrari v8. It retains some of the lower rumble of an American v8, but without the left-right 'thumping" of the exhaust when heard through dual exhausts. Honestly, its sound reminds me most of a Ford GT, which was a traditional American v8 but with the "nest of snakes" exhaust plumbing to even out the scavenging pulses.

Isn't the new Chevy small block's crank about the same weight?

Regarding the sound, the configuration is one influence; the other is that it has unequal-length exhaust manifolds because that was the only way to keep the cats close enough to the ports in that engine bay.