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From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
Originally Posted by gkull
in a v12 Ferrari It is treated like two 6 cylinder motors. At least that is what all the older ones did. They run extremely smooth.
I get that. But that doesn't answer my question. Six cylinder engines use a three-plane crank (as it seems that a 12 cylinder engine should also if treated as two six cylinder engines). If a 12 cylinder engine can use a (true) flat crank (ie: no splayed throws/arms), my engineering curiosity would like to know how.
I get that. But that doesn't answer my question. Six cylinder engines use a three-plane crank (as it seems that a 12 cylinder engine should also if treated as two six cylinder engines). If a 12 cylinder engine can use a (true) flat crank (ie: no splayed throws/arms), my engineering curiosity would like to know how.
Ok....stare at the engine from the front and slice the cylinders into 6 V-twin Harley’s....two pistons sharing a common rod pin....but the two cylinders firing 90 degrees apart from each other....
BTW....I have a flat plane crank in my motorcycle
From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
Originally Posted by Jebbysan
Ok....stare at the engine from the front and slice the cylinders into 6 V-twin Harley’s....two pistons sharing a common rod pin....but the two cylinders firing 90 degrees apart from each other....
BTW....I have a flat plane crank in my motorcycle
Jebby
I understand how vee engines and shared crank pins work. My question is how a flat crank can work in a 12 (or six) cylinder engine. Please explain how a flat plane crank can work in your bike there, as I don't see a way that you can get an even firing order without a three plane crank in that engine.
From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
Originally Posted by leigh1322
In theory, It's simple really, 3 go up while 3 go down, or 6 up & 6 down. In a Vee crankpins are not shared, they are all over the place.
In theory that will work. In practice (in a six cylinder) you will have two cylinders firing simultaneously, then 180 crank degrees later you will have one cylinder fire, then 180* later two cylinders will fire, then another 180* you will have the final sixth cylinder fire. Not very smooth or marketable.
Or, for a shaky idle even a Harley can't compete with, you could also have three cylinders fire, then 180* later the other three fire, then nothing for the next 540*, and then the original three cylinders fire again. (Think John Deere two cylinder engine.) Again, not practical in a car or motorcycle.
There's other firing orders possible, but not worth the time to type them out.
My point remains: Satisfy my engineering curiosity on how a flat crank can work (in the real world) on a six cylinder engine, or a 12 cylinder engine.
In theory that will work. In practice (in a six cylinder) you will have two cylinders firing simultaneously, then 180 crank degrees later you will have one cylinder fire, then 180* later two cylinders will fire, then another 180* you will have the final sixth cylinder fire. Not very smooth or marketable.
Or, for a shaky idle even a Harley can't compete with, you could also have three cylinders fire, then 180* later the other three fire, then nothing for the next 540*, and then the original three cylinders fire again. (Think John Deere two cylinder engine.) Again, not practical in a car or motorcycle.
There's other firing orders possible, but not worth the time to type them out.
My point remains: Satisfy my engineering curiosity on how a flat crank can work (in the real world) on a six cylinder engine, or a 12 cylinder engine.
You are right and I retract my Honda statement.....the CBX does not have a flat crank....I was thinking of my DOHC 4 Hondas which did......
Then I sat and thought about it......the third order resonance which would shake it to death..... that said....it would not work on a V-12 either.....and some Googling shows that ZERO 6 or 12 cylinder anything has a flat crank.
I was wrong! (Get your Sharpie out.....LOL)
From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
Originally Posted by Jebbysan
You are right and I retract my Honda statement.....the CBX does not have a flat crank....I was thinking of my DOHC 4 Hondas which did......
Then I sat and thought about it......the third order resonance which would shake it to death..... that said....it would not work on a V-12 either.....and some Googling shows that ZERO 6 or 12 cylinder anything has a flat crank.
I was wrong! (Get your Sharpie out.....LOL)
Jebby
Not a problem. I could not work out a way that a flat crank would work in those applications, but I'm just an automotive enthusiast, not an engine designer, so I was leaving open the option that someone could explain to me how the heck a flat crank could work in that application. I can now stop scratching my head.
From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
Originally Posted by ronarndt
gkull said "the guy that wins is the car with the least amount of pounds per HP". Also, add gear ratio of rear axle, gear ratio of transmission, and a bunch of other racer upgrades. I get a lot of "must be really fast" comments about my 68 convert with NOM 454 with a bunch of internal engine upgrades. I usually reply that my 93 Mazda RX-7 with its little 1.3 liter engine is twice as fast. In addition to its engine upgrades that allow me increase the boost to 15 psi and a 4.10 rear axle, most of the car is aluminum, either from the factory or from parts I swapped out for lightweight replacements. Lighter is better.
I absolutely agree with the "Lighter is better" statement. That is my present philosophy for any mods to my car.
In my youth, I subscribed to the "horsepower can overcome any weight issues". Then, several years ago at a road course track day, I was schooled by some guy in a lightweight little shitbox (an accurate description of his car, but I say this with respect for his choice of that car). On the straights I could outpull him (allowing me to close up on him), clearly showing my car had a better power-to-weight ratio than his, but then through a series of corners and chicanes he would just disappear into the distance ahead of me. After that session I was sufficiently humbled and schooled, as I said, and I walked over to him and complimented him on his car and his driving skills. It was an epiphany.
Since then, I have spent most of my car modification time pulling weight out of the car, and only minimal time trying to add horsepower to the engine.
I'm sure that you might have watched something like this. Ferrari made both apposed cylinder flat crank 12's and the V 12's
I worked on these 5 liter 60degree V 12's in cars know as a 512s and 512m. The flat 12's were just bad ***! These 512 series including the 512 BB were some of my favorite cars. Where ever we went these cars usually won. In those time period groups. Porsche came out with their 930's and 956 turbo cars and that was the end of NA motors competing
From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
Originally Posted by gkull
I'm sure that you might have watched something like this. Ferrari made both apposed cylinder flat crank 12's and the V 12's
I worked on these 5 liter 60degree V 12's in cars know as a 512s and 512m. The flat 12's were just bad ***! These 512 series including the 512 BB were some of my favorite cars. Where ever we went these cars usually won. In those time period groups. Porsche came out with their 930's and 956 turbo cars and that was the end of NA motors competing
I read the first two links, and I didn't see anything mentioning flat cranks in 12 cylinder engines. If I missed it, please point it out.
I fast forwarded through the first video, as it just seemed to be a collection of cars speeding by the camera. No technical information IIRC.
The second video was about flat cranks in 8 cylinder engines. No mention of six or twelve cylinder engines. At 3:50 in this video, the narrator mentions that cross plane cranks are smoother than flat cranks because they fire every 90* instead of 180*. What the hell?
Not a problem. I could not work out a way that a flat crank would work in those applications, but I'm just an automotive enthusiast, not an engine designer, so I was leaving open the option that someone could explain to me how the heck a flat crank could work in that application. I can now stop scratching my head.
The "boxer" engines are flat plane... 6 and/or 12 cylinders
Ferrari /Lambo and my BMW V12 used the 60° blocks- firing every 60°- which makes for a really smooth running engine-
Strange- the new (latest generation) Ferrari run a 55° blocks?
Ok you really got me thinking now too. I see from the pics below (from the prior video) how the flat plane works in a V8. Two pistons are up at a time, one on compression stroke, one on firing. The other bank would fir 90 degrees later, and then this bank again 90 degrees later. So a really even-firing every 90 degrees. Better for intake & exhaust flow etc. Sounds like a "rip" without the "rumble"
I can't even visualize how this would work with 6 cylinders on each side even if it was a flat boxer engine. Wouldn't 2 cylinders have to fire at once with 3 up? Or the crank have to be twisted to fire every 60 degrees (much more likely)?
After watching this video: https://www.carthrottle.com/post/her...lat-12-at-all/
I am even more confused: The Testarosa flat 12 did have flat engine layout but had 4 pistons up while 2 were down on each side.
There is no way that resulted in an even firing order?
It appears even that engine had a 60 degree crankshaft, not flat.
The main high production engine I know of with a true flat crank is the boxer 4. And the two opposed pistons have their own crankpin are are both up at once, resulting in natural balance, no counterweights required and a quicker reving engine. https://en.m.wikipedia.org/wiki/Flat-four_engine
Last edited by leigh1322; Oct 12, 2019 at 09:51 PM.
From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
Originally Posted by leigh1322
Ok you really got me thinking now too. I see from the pics below (from the prior video) how the flat plane works in a V8. Two pistons are up at a time, Remember, there are two pistons up "at a time" with the conventional two plane crank, also. one on compression stroke, one on firing. Just like the stock crank. The other bank would fir 90 degrees later, and then this bank again 90 degrees later. So a really even-firing every 90 degrees.Both crank types will produce 90* even firing sequences. Better for intake & exhaust flow etc. Sounds like a "rip" without the "rumble" The flat crank eliminates the double mass pulse (8&4 and 5&7) that production exhausts have to contend with each 720*, allowing better exhaust tuning.
I can't even visualize how this would work with 6 cylinders on each side even if it was a flat boxer engine. Wouldn't 2 cylinders have to fire at once with 3 up? Or the crank have to be twisted to fire every 60 degrees (much more likely)? Yes, that's why 6 and 12 cylinder engines have a three plane crankshaft, to allow even cylinder firings.
After watching this video: https://www.carthrottle.com/post/her...lat-12-at-all/
I am even more confused: The Testarosa flat 12 did have flat engine layout but had 4 pistons up while 2 were down on each side. If you watch the video, there should be two up, and four partially down/partially up (on each side).
There is no way that resulted in an even firing order? The crank in this picture is a three plane crank. Watching the actual video will show that.
It appears even that engine had a 60 degree crankshaft, not flat. It's a three plane crank. The video shows how the arms are angled
The main high production engine I know of with a true flat crank is the boxer 4. And the two opposed pistons have their own crankpin are are both up at once, resulting in natural balance, no counterweights required and a quicker reving engine. https://en.m.wikipedia.org/wiki/Flat-four_engine
If you look at that assembly, it has counterweights on it. I assume it's because the pistons are on different crank arms, which causes a moment arm that does not allow the piston weights/momentums to cancel exactly. It looks at casual glance that the engine would want to jiggle a bit without the counterweights.
Last edited by 69427; Oct 13, 2019 at 10:18 AM.
Reason: Additional content, grammar correction.
Herb Adams made some 180 degree headers back in the day to help exhaust scavenging. One pipe on each bank crossed over to the opposite side header collector. It had a very similar even firing sound to it, got rid of the V8 stacatto. Heard one once. Sounded more like a Porsche flat six or Ferrarri V12 than a Pontiac V8. Great stuff!
I remember that!
I had a Pontiac T/A, back in those days, and I obtained all of the parts lists, catalogs, and tech sheets that were generated by Herb. He ran a company, for a while, that was called 'Herb Adams VSE". the VSE stood for "very special equipment". He primarily specialized in suspension parts, and even made some items for C-3 Corvettes (and possibly C-4s, too).
That's right... the C8 Z06 and C8 ZR1 ALONG WITH C8R will have flat plane cranks.
The C8R will have a 5.5 L flat plane.
They sound wicked.
This was VERY aparent when the animation of some new chevrolet engine was release a few months ago which had another drive chain off the cam arrangement... knowing engines... it was obviously for a BALANCE SHAFT, which would almost lock in flat plane.
