Production of a Flat Plane Crank Engine
10-19-2015, 04:00 PM
#61
Drifting
It's all a trade off.
Crossplane V8 cranks have excellent mechanical balance at the expense of volumetric efficiency. This compromise makes the crossplane engine smooth and suitable for very large displacements.
Flatplane V8 cranks have excellent volumetric efficiency at the expense of mechanical balance. This compromise makes the flatplane engine capable of a higher specific power output per unit of displacement.
Crossplane V8 cranks have excellent mechanical balance at the expense of volumetric efficiency. This compromise makes the crossplane engine smooth and suitable for very large displacements.
Flatplane V8 cranks have excellent volumetric efficiency at the expense of mechanical balance. This compromise makes the flatplane engine capable of a higher specific power output per unit of displacement.
10-19-2015, 04:19 PM
#62
Team Owner
Pro Mechanic
I asked this earlier. Please explain this. How does the crank affect volumetric efficiency? Both designs draw an intake charge every 90* of crank rotation...
10-19-2015, 04:23 PM
#64
That is correct.The 4 cylinder can not benefit from a cross plane design. The V8 can, b/c the counterweight for one piston can and does weigh about equal to the weight of the piston and rod. THIS mass, when 90* to the motion of the piston (1/2 way up or down the stroke) is cancelled by the adjacent piston that is attached to the same crank pin. This very feature is what makes the "cross plane" V8 so smooth and desireable.
On any inline engine, a crank weight equal to the weight of the piston/rod would cancel vibrations in the vertical plane, but introduce vibrations laterally with equal magnitude as those vibrations created vertically, that we are trying to cancel. It would shake and introduce as much crank stress, as the same engine w/NO counterweights! SO, typically, the counter weights of an inline are ~1/2 the weight of the piston and rod -it cuts vertical vibration in 1/2, and only adds 1/2 laterally (some of which is cancelled by other cylinders' throws, depending on the number of cylinders.
Yamaha motorcycle makes it
www.youtube.com/watch?v=oEXUrO5wYcE
Last edited by Christi@n; 10-19-2015 at 04:27 PM. Reason: Addiction
10-19-2015, 04:55 PM
#65
Team Owner
Pro Mechanic
Yes, I have seen that exception. I don't know that it increased power...that marketing piece extols the virtues of a more even or more manageable power delivery....however little of it makes sense to me. They eliminated an even, 180* firing pattern, with a syncopated one. How can that be more even? Even their graph showed a gap in power. Weird.
10-19-2015, 05:18 PM
#66
Think thatcould be due to the inertia elimination
http://www.yamahapart.com/page/crossplanecrankshaft
This way crank became something like a "without weight" crank
http://www.yamahapart.com/page/crossplanecrankshaft
This way crank became something like a "without weight" crank
10-19-2015, 05:50 PM
#68
Team Owner
Pro Mechanic
IDK....I thought flywheels, (rotating inertia) smoothed power delivery (power pulses)...but what do I know? 
10-20-2015, 12:03 AM
#69
Drifting
The flatplane crank V8 symmetrically alternates the the active (the one firing) cylinder between the two cylinder banks. It's the symmetry of the process that allows the designer to literally tune the intake and exhaust resonant frequencies to obtain the the best power band for the application. This symmetry is absent in a crossplane V8 which compromises the designers ability to tune the intake and exhaust tracts and reduces potential power output.
10-20-2015, 08:11 PM
#71
Team Owner
Pro Mechanic
Cool article.
From the article:
"A flat-plane crank helps take advantage of intake and exhaust resonances"
Still like someone to explain this one. The exhaust, there is potentially a benefit; that is, you go from a syncopated firing rhythm on each side to an even one. Obviously with any equal length exhaust (be it short or long tube) you can not pulse tune the exhaust efficiently when the pulses are un-even. A "work around" for this that is used in NASCAR (among other places) is "180* headers".
But the flat plane crank and it's even bank firing make EXHAUST tuning, much easier. The bizarre thing is, the way that FORD did the exhaust manifolds in their engine, they are not taking advantage of this tuning possibility!
The INTAKE is a different story; we have equal length runners drawing from a common reservoir every 90* of crank rotation...with either crank design. I can't see how crank design has any kind of meaningful impact on "intake tuning".
I think people corralate "flat plane crank" and "high RPM" then assume that the crank = high RPM "tuning" which that though process is folly. As 1analguy already pointed out, the engines which typically use FPC's are displacement limited and MUST rev high to get HP, so they use short runners, larger duration cams, etc. The logic is no different than someone assuming that DOHC = high RPM.
There are TONS of cross plane crank engines that are TUNED to, and do run very high RPM; NASCAR, Drag cars, the Yamaha motorcycle linked earlier and so on.
From the article:
"A flat-plane crank helps take advantage of intake and exhaust resonances"
Still like someone to explain this one. The exhaust, there is potentially a benefit; that is, you go from a syncopated firing rhythm on each side to an even one. Obviously with any equal length exhaust (be it short or long tube) you can not pulse tune the exhaust efficiently when the pulses are un-even. A "work around" for this that is used in NASCAR (among other places) is "180* headers".
But the flat plane crank and it's even bank firing make EXHAUST tuning, much easier. The bizarre thing is, the way that FORD did the exhaust manifolds in their engine, they are not taking advantage of this tuning possibility!
The INTAKE is a different story; we have equal length runners drawing from a common reservoir every 90* of crank rotation...with either crank design. I can't see how crank design has any kind of meaningful impact on "intake tuning".
I think people corralate "flat plane crank" and "high RPM" then assume that the crank = high RPM "tuning" which that though process is folly. As 1analguy already pointed out, the engines which typically use FPC's are displacement limited and MUST rev high to get HP, so they use short runners, larger duration cams, etc. The logic is no different than someone assuming that DOHC = high RPM.
There are TONS of cross plane crank engines that are TUNED to, and do run very high RPM; NASCAR, Drag cars, the Yamaha motorcycle linked earlier and so on.
11-17-2015, 01:23 PM
#72
Pro
Again, missing the point. The example of my '96 GS vs the C4 ZR-1 was just that...an example. Are we capable of moving on to a more modern example? Forget the C4. Forget the C6. Look at the C7...Z51 = better than Z06. Look at the Dodge Hellcat...SRT 392 = better than Hellcat. Get my point now? Balance beats excess...for me. Do whatever you feel you need to do to impress your friends, but at some point you're going to find that a truly balanced car will impress you more than the simple excess of too much power.
"The Corvette Z06 arrived at PCOTY as heir apparent to the Z51 Stingray's decisive win in 2014. Yet about half of us like the standard Corvette more than the special-reserve addition. Blame the supercharger, which endows this car with massive pace yet removes some of the involvement from back-road driving."
It was an interesting test of eight top-notch performance cars. None of the drivers were allowed access to lap times, so their choice was restricted to their subjective opinions about actually driving the cars. They had a clever points system that resulted in an objectively-chosen winner: the GT350R. They voted for the whole car, not just the engine. Their main comment about the engine? It sounds nice at high revs. The only thing they left out of the conclusion was the finishing order behind the GT350R. That would have been interesting. They also said that the only car in the test that felt like it was capable of lapping at ten tenths all day long was the Viper ACR, which was also the fastest car around the track...for all of the drivers.
11-17-2015, 06:57 PM
#73
I would say that world is beautiful why is is diversified, so when i look at american car i say WOW i like very much the v8 rumble... Or sometimes i meet people from your country here and speak a little with them and i say hey they speak american....
Or you when you see ferrari there think say WOW its an italian high rpm singer...
So make a thing that is the same in all the world is not a good idea.
I love to know the local traditions, and think this is a personal enrichment
Or you when you see ferrari there think say WOW its an italian high rpm singer...
So make a thing that is the same in all the world is not a good idea.
I love to know the local traditions, and think this is a personal enrichment
Last edited by Christi@n; 11-17-2015 at 06:59 PM.
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mdull (09-01-2019)
08-27-2019, 03:50 AM
#74
Senior Badass!
Thread Starter
For all the haters that said Chevy would never go the flat plane route. Too funny how I predicted this over four years ago.
https://www.corvetteforum.com/articl...flat-plane-v8/
https://www.corvetteforum.com/articl...flat-plane-v8/
Last edited by JDaniel; 08-27-2019 at 11:01 AM.
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JDaniel (08-28-2019)
08-28-2019, 10:04 AM
#76
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For all the haters that said Chevy would never go the flat plane route. Too funny how I predicted this over four years ago.
https://www.corvetteforum.com/articl...flat-plane-v8/
https://www.corvetteforum.com/articl...flat-plane-v8/
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JDaniel (08-29-2019)
08-28-2019, 10:27 AM
#77
I have no idea why people want this. Flat plane is fine for small displacement...but can you imagine CF when GM goes to a 4L engine...everyone wants their cake...
08-29-2019, 03:03 AM
#78
Senior Badass!
Thread Starter
I am not a fan of big maintenance and I am sure neither is GM. So my guess is that they are going to make the motor reliable and you will still have the traditional 5 year/30,000 mile warranty if not better. I think I am going to hold off on the C8 and see what the price tag is for the C8Z06. I am going to take a guess and say probably $120,000 or better.
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GTS Bruce (11-20-2019)