Another VR Poll: Friendly debate between Fool and Puc about Piston Speed Limits!

[cowpuc]

@Flyinfool and I are continuing our debate concerning the concept of terminal (meaning at a certain speed pistons and rods come unglued) Piston speed limits. At present time the debate is centered around whether or not there is such a thing and whether or not piston speed is relevant to the maximum RPM a motor can spin up without self destructing..

In another thread, where Fool did everything he could do to get me to commit another heinous act of with his comment and it didnt work, FlyingFool posted:

 

""Puc I still have to disagree with you on the "physics" of max RPM. There are engines out there that have a bigger bore and a longer stroke than the Yamaharley that will spin well over 5K"" - To which I started to reply but then decided to defer our debate to this thread as I have developed an allergy to club probation..

 

In posting this thread, Fool and I would like to invite any and all of our other club members to feel free to participate = we welcome your thoughts, theories and philosophies on this subject. For those of you who may be nervous about letting your true feelings about such a sensitive subject known = we would like you to feel free to participate in the Poll. Your response will remain anonymous to protect the innocent - as if I know any members wh,,,, sorry,,, you integrity will be protected..

At this time I am cooking my debate platform on You Tube so the few people who actually follow my You Tube channel (my Grandson in California LOVES this stuff!!) can also participate if they so desire.. I will post my actual debate response as soon as it is done cooking..

I am thinking Fool will probably want to update his response from that of above but if not,, that's OK,, we know enough about his stand already to know his side of all this (Engineering brain against a back yard mechanic (ME) "has been") and you varmints can decide a debate winner from that!!

LET THE DEBATE BEGIN!!!

Edited October 24, 2017 by cowpuc

[cowpuc]

My debate platform presentation :

 

[XV1100SE]

Maybe settle the debate without having to take sides.....

http://thefirstgensite.com/code/maxrpm.htm => max rpm calculator

 

https://www.carthrottle.com/post/engineering-explained-why-some-engines-rev-high-and-their-benefits/

 

From https://en.wikipedia.org/wiki/Rev_limiter

"Physical Limiters

The maximum RPM of an engine is limited to the airflow through the engine, the

displacement

of the engine, the mass and balance of the rotating parts, along with the

bore

and

stroke

of the pistons.

^[3]

Formula One engines can rev up to 15,000 rpm as per Formula One rules

^[4]

because of their smaller displacement, low mass, and short stroke.

Engines with

hydraulic tappets

(such as the

Buick/Rover V8

) often have in effect a rev limiter by virtue of their design. The tappet clearances are maintained by the flow of the engine's lubricating oil. At high engine speeds, the oil pressure rises to such an extent that the tappets 'pump up', causing valve float. This sharply reduces engine power, causing speed to drop

 

Racing Uses

The RPM level that results with the spark timing being arrested can be a constant level, or, with the proper ignition control modules, variable. Variable rate ignition modules can be adjusted quickly and easily to achieve the appropriate RPM limit for different situations, such as street racing, drag racing, road course racing and highway driving.

Multiple stage ignition modules offer greater RPM limit control. The first stage can be used to limit RPM levels when launching a vehicle from a stationary position, providing maximum power and traction. The second stage is activated after launch to set a higher RPM limit for

wide-open-throttle

acceleration."

 

Discussion on Corvette forum :

https://www.corvetteforum.com/forums/c4-tech-performance/753988-anyone-know-how-to-calculate-max-rpm.html

[RandyR]

More info. good reading.

 

http://www.enginebuildermag.com/2017/10/assembly-fastening-lubes-dont-underestimate-importance-proper-lubrication/

 

[bongobobny]

Yup! One of the SEVERAL maximum RPM factors is the MASS of the piston, not just the size...

 

My vote is E. None of the above...

[luvmy40]

I would have to assume that the compression ratio is going to effect the max piston speed as well. At least from a long term stress view. A dragster engine that gets rebuilt between runs is going to be able to have a higher compression ratio and max piston speed than an engine designed to go 100k miles before needing a rebuild.

[venturesome]

Never argue with math and physics! There are so many variables in this issue that I would have to vote with Flying Fool, however from a common sense approach to engine design based on today's norms and standard manufacturing methods and economic considerations, I certainly lean toward Puc's ideas.

Besides, who wants to upset either one of these varmints, when you consider that one can cut off the supply of hot dogs and the other can dust you off with some gold danged winter machine!

I aint votin!!

[cowpuc]

I would have to assume that the compression ratio is going to effect the max piston speed as well. At least from a long term stress view. A dragster engine that gets rebuilt between runs is going to be able to have a higher compression ratio and max piston speed than an engine designed to go 100k miles before needing a rebuild.

 

For sure but I gotta a hunch that it's actually the metal structure/alloy of the high compression piston that creates a more durable piston/rod assembly that allows for the piston to be able to go faster without grenading.. If you look at this calculator that XV came up with (NICE = thanks XV) (calculator is found here: http://thefirstgensite.com/code/maxrpm.htm ) and play with it a little bit you may notice the different catagory's for determining max revs will go up as you change into non stock catagories = VERY interesting little calculator IMHO!! The first catagory in that calculator actually is saying that with stock motors, the max safe piston speed is 3500 feet per minute.. Get up above that and ya start needing to think forged pistons, peened rods (like you mentioned = often found in High Compression Pistons..

[cowpuc]

Another VERY interesting thing about that calculator is that if you plug in the stroke of the new Venture (4.7) into the Stock components category = the calculator will return just under 4500 RPM to max rev's or where the rev limiter should be set.. Interestingly enough - that is exactly where Mom Yam set the rev limiter on the new one....

[Flyinfool]

OK, here we go.

 

1. You used the example of the little 5 horse motor that you kept over revving and snapping rods. I would be surprised if the parts in that engine could even get to 4000 Feet Per Minute (FPM) piston speed.

 

You also want to use a very modern example. How about the new Yamaharley since that is what started this whole thing in the first place.

the Yamaharley has a stroke of 4.7 and a red line of 4750. Now lets apply a bit of math to those numbers. CUz we know I like numbers and you started with your math.

 

First you need to get all of your units the same, so stroke ÷ 12 to get feet.

Then you take your stroke in feet X Pi to get the distance the crank pin travels per revolution.

Then you take the circumference the crank pin travels X RPM gives you the speed in FPM that the crank pin will be moving at.

When the crank pin is at ~90° is when it is moving fastest in the direction of piston travel and that number is equal to the speed in FPM that you just calculated.

 

so, 4.7 ÷ 12 X 3.14159 X 4750 = 5844 FPM

 

So the Yamaharley has a piston speed of 5,844 FPM. OK so much for your 4000 FPM max piston speed theory.

 

Lets take a look at Tweeksis

2.6 ÷ 12 X 3.14159 X 7500 = 5105 FPM

Interesting, 35 year old technology seems to have a lower piston speed than newer, but still well over 4000.

 

How about we try your little liter engine sitting in Maggi. Surely that is an example of using a small stroke to keep piston speed down.

2.1 ÷ 12 X 3.14159 X 11750 = 6460 FPM. Oh rats that sure verifies the 4000 FPM max theory.......

 

This is for stock production street engines that are expected to, and do have a long service life.

If you start applying race part technology to get the revs way up there, then even these numbers look pretty small.

 

Now in your defense just cuz I am a nice guy. What you are remembering is from a half century ago. I would not fault your rememberer, it is just that technology has changed a smidgen in the last 50 years. That 4000 number you are remembering probably made a lot of sense back then. Metallurgy was no where near what it is now, and they did not have the modern methods of manufacturing the parts out of these new and wonderful alloys. Then we have newer and better lubricants to keep the metal parts from touching each other so that these higher speeds can be safely achieved.

I did not know much of anything about engines back then I did not start to learn about such things until I was in my late 20s so I have a more recent frame of reference than you.

 

You are also pretty close on what you have noticed about where torque and HP curves cross. The actual crossing point is 5252 RPM in a well tuned engine. That is a real number, somewhat irreverent to the discussion but none the less a real number. Does that mean that that should be red line and there is no reason to take the RPM any higher than that? Heck no, For sure don't try to tell Maggi that, she will hurt you if you try to keep her under 5252 RPM, so will Tweeksis.

 

Here is an interesting read on torque vs HP.

http://www.lainefamily.com/hp.htm

[Flyinfool]

Another VERY interesting thing about that calculator is that if you plug in the stroke of the new Venture (4.7) into the Stock components category = the calculator will return just under 4500 RPM to max rev's or where the rev limiter should be set.. Interestingly enough - that is exactly where Mom Yam set the rev limiter on the new one....

 

Another interesting thing about that calculator is that they picked the arbitrary number of 3500, 4000 and 5000 FPS for max piston speeds in each of the categories. The listed red line on the new venture is 4750 rpm so it falls between stock and Heavy duty.

[cowpuc]

Another interesting thing about that calculator is that they picked the arbitrary number of 3500, 4000 and 5000 FPS for max piston speeds in each of the categories. The listed red line on the new venture is 4750 rpm so it falls between stock and Heavy duty.

 

AHAAAAA!! Now we got it happening!! I contend that those numbers of 3500, 4000 and 5000 are far from arbitary.. Those are, as matter of scientific fact, speed limit numbers for the components listed in the categories they correspond with = you cross those speed limits and you risk BOOM = GRENADE TIME!!

That understood and accepted = go back and plug in the new Venture's stroke = 4.7, now hit calculate on the "stock" category and see what you come up with for max rpm to stay safe with that motor = set your rev limiter at 4468 (4500)..

Of course,, that rev limit is gonna go up as you mod the motor with forged parts or other stronger ways like peening rods as clearly mentioned in the other categorys in that calculator..

It is interesting here, IMHO, to see that this calculator actually is saying that I am wrong in my understanding of 4000 FPM being the magic number.. I know I was told 4000 years ago but according to this = the safe opporating speed for stock engine components has actually dropped to 3500 FPM!! NAHHHHHH NAHHHHH DEEEE BOOOO BOOO!! :moon:

 

Also,, you bringing up torque vs HP sets up a whole nuther round of debate!! Gonna need a whole new batch of Hot Dog's for that one cause, IMHO,, once you cross that 5200 RPM line = torque becomes a non issue (even though HP is actually a function of Torque) and irrelevant and it all becomes about HORSEPOWER - BUT, ya gotta be able to spin em up to get there,, the farther beyond that 5200 R line ya get without grenading due to excessive piston speed (controlled by stroke length) = the more exciting life gets cause high horsepower ROCKS!!

 

****** Is it obvious? = I am more of a MOTO GP, Motocross or Formula One racing lover than an All Harley Drag or Tractor Pulling kind of guy:banana::banana::banana::guitarist 2::guitarist 2::rasberry:

Edited October 24, 2017 by cowpuc

[cowpuc]

Ya know,, this is really turning into something I never considered before - stretching of the brain,,,,, I am beginning to understand a little more of why modern scoots have rev limiters = that "need" is starting to come clear to me.. If a person looks at what I am talking about as a scientific means to determine where your max R's should be, or where your engines rev limiter should be set to protect your engine from destroying itself = pretty interesting.. I wonder if engineers who work for corporations use this very math to make those factory settings??

Funny,, I always thought mounted tach's were for those who couldn't "feel" the horsepower running out by the seat of their pants and know by that feel when to shift so ya win the race = you know,, let the tach tell ya when to shift..

[cowpuc]

Maybe settle the debate without having to take sides.....

 

https://www.carthrottle.com/post/engineering-explained-why-some-engines-rev-high-and-their-benefits/

 

Another GREAT one XV!! Thanks for participating in this debate brother!!!

 

OK, here we go.

 

1. You used the example of the little 5 horse motor that you kept over revving and snapping rods. I would be surprised if the parts in that engine could even get to 4000 Feet Per Minute (FPM) piston speed.

 

You also want to use a very modern example. How about the new Yamaharley since that is what started this whole thing in the first place.

the Yamaharley has a stroke of 4.7 and a red line of 4750. Now lets apply a bit of math to those numbers. CUz we know I like numbers and you started with your math.

 

First you need to get all of your units the same, so stroke ÷ 12 to get feet.

Then you take your stroke in feet X Pi to get the distance the crank pin travels per revolution.

Then you take the circumference the crank pin travels X RPM gives you the speed in FPM that the crank pin will be moving at.

When the crank pin is at ~90° is when it is moving fastest in the direction of piston travel and that number is equal to the speed in FPM that you just calculated.

 

so, 4.7 ÷ 12 X 3.14159 X 4750 = 5844 FPM

 

So the Yamaharley has a piston speed of 5,844 FPM. OK so much for your 4000 FPM max piston speed theory.

 

Lets take a look at Tweeksis

2.6 ÷ 12 X 3.14159 X 7500 = 5105 FPM

Interesting, 35 year old technology seems to have a lower piston speed than newer, but still well over 4000.

 

How about we try your little liter engine sitting in Maggi. Surely that is an example of using a small stroke to keep piston speed down.

2.1 ÷ 12 X 3.14159 X 11750 = 6460 FPM. Oh rats that sure verifies the 4000 FPM max theory.......

 

So I clicked on the link the link that XV posted above,, about 1/4 page down was a You Tube vid linked inside of that article.. Clicked on it and below is what appeared.. Made me wonder if the viewing audience toF this debate would like to see Fool produce a video like this? I know I sure would!!! WOWZY = look at the math!!!!!!

 

 

[bongobobny]

OK, you wanna be scientists, here's something else for you to ponder, the moment of inertia when both the piston and rod have to stop and reverse direction...

[XV1100SE]

Glad you like the calculator and video in the link. Here are more videos by the same guy (Engineering Explained) - https://www.youtube.com/channel/UClqhvGmHcvWL9w3R48t9QXQ

 

F1...amazing that they got the RPM up over 21,000 and considering the distance per race, the power demands.... the auto companies that thought they could just jump in and have an engine that could compete out of the box (Honda, Toyota)...they both threw a lot of money into F1 and didn't get anywhere (Honda in their current form). Still, would be nice if the engines were closer in performance (and more teams had the "magic mode"/"button").

 

You two still haven't convinced me who should get my vote....

[cowpuc]

OK, you wanna be scientists, here's something else for you to ponder, the moment of inertia when both the piston and rod have to stop and reverse direction...

 

Actually you missed that part of this little debate,, thinking back,, this may have even before this turned into a full blown camp fire, hot dog roasting debate with the Jeff popping the lid on the rum balls to calm his nerves = wayyy back somewhere in this discussion, probably 10 threads ago (maybe while you were playing in Mexico) that was talked about some.. I think when that force where the piston is trying to keep heading in the direction it is heading in (whether its up the stroke or down the stroke) becomes so great that the piston actually comes apart in it's effort to keep going in the direction it is heading is directly related to piston speed...

Now that cha got me thinkin again about that though Bob, another part of that changing direction inertia thing to think about, at least in my pea brain is the increase or decrease of piston speed along the rotational area of the wrist pin and crank pin as the rod moves back and forth just before the piston comes to a dead stop and heads the other way..

There is a LOT going on there and I think this piston speed according to stroke length may end up being just a real easy way to determine rev limits without having to go thru a whole bunch of math... Since seeing that calculator,, my resolve in thinking my thinking is correct has actually getting stronger

Edited October 25, 2017 by cowpuc

[cowpuc]

Glad you like the calculator and video in the link. Here are more videos by the same guy (Engineering Explained) - https://www.youtube.com/channel/UClqhvGmHcvWL9w3R48t9QXQ

 

F1...amazing that they got the RPM up over 21,000 and considering the distance per race, the power demands.... the auto companies that thought they could just jump in and have an engine that could compete out of the box (Honda, Toyota)...they both threw a lot of money into F1 and didn't get anywhere (Honda in their current form). Still, would be nice if the engines were closer in performance (and more teams had the "magic mode"/"button").

 

You two still haven't convinced me who should get my vote....

 

Suite yourself but as for me,, I aint skeerd of no Wisconsin White Washer so I know who I would vote for if I was you.. Of course,, I do have to admit,,, it has been raining SOLID since this debate started and I also noticed on our weather radar that there is a HUGE area of rain clouds rotating above our house AND my house looks like it is the axle of the wheel of rotation those clouds are forming = funny cause it looks like a Hurricane but never in history have we ever had a Hurricane off Lake Michigan...

Perhaps,,, maybe,, I should stop with the that lop eared FlyinFool BEFORE the temps start changin

[Flyinfool]

AHAAAAA!! Now we got it happening!! I contend that those numbers of 3500, 4000 and 5000 are far from arbitary.. Those are, as matter of scientific fact, speed limit numbers for the components listed in the categories they correspond with = you cross those speed limits and you risk BOOM = GRENADE TIME!!

That understood and accepted = go back and plug in the new Venture's stroke = 4.7, now hit calculate on the "stock" category and see what you come up with for max rpm to stay safe with that motor = set your rev limiter at 4468 (4500)..

Of course,, that rev limit is gonna go up as you mod the motor with forged parts or other stronger ways like peening rods as clearly mentioned in the other categorys in that calculator..

It is interesting here, IMHO, to see that this calculator actually is saying that I am wrong in my understanding of 4000 FPM being the magic number.. I know I was told 4000 years ago but according to this = the safe opporating speed for stock engine components has actually dropped to 3500 FPM!! NAHHHHHH NAHHHHH DEEEE BOOOO BOOO!! :moon:

 

Also,, you bringing up torque vs HP sets up a whole nuther round of debate!! Gonna need a whole new batch of Hot Dog's for that one cause, IMHO,, once you cross that 5200 RPM line = torque becomes a non issue (even though HP is actually a function of Torque) and irrelevant and it all becomes about HORSEPOWER - BUT, ya gotta be able to spin em up to get there,, the farther beyond that 5200 R line ya get without grenading due to excessive piston speed (controlled by stroke length) = the more exciting life gets cause high horsepower ROCKS!!

 

****** Is it obvious? = I am more of a MOTO GP, Motocross or Formula One racing lover than an All Harley Drag or Tractor Pulling kind of guy:banana::banana::banana::guitarist 2::guitarist 2::rasberry:

 

Ya see now Puc this is where you are cornfusing your self. If the piston speed was a scientific constant then it would be the same in all cases. In this calculator they arbitrarily picked 3 speeds as reference points, You can prove this to yourself by entering the info for known sources, 4.7 does not get you the red line that the New venture really has, entering 2.6 does not match the red line of Tweeksis, and entering the 2.1 does not match up with Maggi. This proves that the calculator is just using arbitrary numbers as reference.

 

There is no magic number for piston speed vs red line. All of these examples all prove out that it is all dependent on the design and construction of the engine. Going way back a few Hi-Jacks, you made the comment that it is mathematically impossible for an engine the size of the venture or a big Hardly to turn over 5000 RPM. My point was that built properly it is very possible to wind up a bigger engine AND have it live a long life. There are a few little no name companies that have figured out how to do it, You know the little places like GM, Ford, Dodge, Porsche, BMW...........

 

As confirmed by all of the links so far, the piston is rarely the weak link that will break at High RPM, it is usually the Connecting rod or valve train that lets go first. But yet the discussion seems to focused on the piston and not the actual weak links. As you learned at an early age, the rod usually goes long before the piston fails.

 

And then Mr Bob brought up Inertial reversals. Your right, that one will take a whole nuther case of Hot dogs and another chord of campfire wood.

[cowpuc]

Ya see now Puc this is where you are cornfusing your self. If the piston speed was a scientific constant then it would be the same in all cases it does remain constant as long as we are talking "stock" pieces and parts, as noted in the calculator = its when those pieces and parts are upgraded to forged steel, ect, ect. that the constant piston speed changes because the modifications can support the faster piston speeds. In this calculator they arbitrarily picked 3 speeds as reference points, You can prove this to yourself by entering the info for known sources, 4.7 does not get you the red line that the New venture really has, entering 2.6 does not match the red line of Tweeksis, and entering the 2.1 does not match up with Maggi. This proves that the calculator is just using arbitrary numbers as reference. I think those red line numbers produced in each catagory are not excact numbers, i.e. = if the chart produces 4348.4867 as a suggested red line it is not saying that is exactly what you should set your rev limiter at. Gotta be a small amount of elbow room in there as there are other forces at play too. It is just a guide line but still, one to be highly considered when determine Max R's.

 

There is no magic number for piston speed vs red line thats the debate = my platform is there is. All of these examples all prove out that it is all dependent on the design and construction of the engine. Going way back a few Hi-Jacks, you made the comment that it is mathematically impossible for an engine the size of the venture or a big Hardly to turn over 5000 RPMno,, thats not what I said, I said that a v-twin reguires a longer stroke and bigger bore to accumulate the same Cubic Inch/CC as a multi cylinder bike with more cylinders - therefore, the motor's can be the same size but the shorter stroked engine with more cylinders can be spun up faster because of reduced piston speeds . My point was that built properly it is very possible to wind up a bigger engine AND have it live a long life. There are a few little no name companies that have figured out how to do it, You know the little places like GM, Ford, Dodge, Porsche, BMW...........

 

As confirmed by all of the links so far, the piston is rarely the weak link that will break at High RPM, it is usually the Connecting rod or valve train that lets go first. But yet the discussion seems to focused on the piston and not the actual weak links. As you learned at an early age, the rod usually goes long before the piston fails. Yes but the piston speed measurement is just a way of determining where parts like the rods (and pistons) will probably come unglued = it's the zone to stay under,, its the goal posts on the foot ball field...

 

And then Mr Bob brought up Inertial reversals. Your right, that one will take a whole nuther case of Hot dogs and another chord of campfire wood. INDEED!! That will be a fun subject consisting of flat top pistons with no skirts,, titanium valves and all that fun stuff!!

 

Pass the hot dogs will ya Fool,,,,,, AND,, could you unplug that formidable White Washer when ya step back inside for more dogs = PLEASE! We are getting SOAKED over here

[Air Ready Auto]

[XV1100SE]

Lets throw in a couple more calculators...

Piston speed - http://www.csgnetwork.com/pistonspeedcalc.html

 

Multiple - http://www.bgsoflex.com/auto.html

 

Every calculation you could ever want in one place - http://www.wallaceracing.com/Calculators.htm

 

Crank up the volume for this one - 21,000 rpm Honda F1 engine -

 

- Ferrari motors - 12/10/8/6 cylinders (over 2 decades) -

 

Car and Driver - Physics of Redline - https://www.caranddriver.com/features/the-physics-of-redline-feature

 

Hmmmm.....forget the calculations .... just keep replaying the F1 engine at 21,000rpm and crank up the volume even more !!

[RandyR]

OK, you wanna be scientists, here's something else for you to ponder, the moment of inertia when both the piston and rod have to stop and reverse direction...

 

how does a slightly stuck open valve intersecting the crown of the piston factor into the equations?

[Flyinfool]

how does a slightly stuck open valve intersecting the crown of the piston factor into the equations?

 

 

 

boom!!! :225:

[luvmy40]

Just a tiny thread drift that I think all would find interesting.

 

Related to the advance of machining and measuring processes; I read a book many years ago about the Wright Brothers and their road to designing the Wright Flyer. In the process they corrected many erroneous data points that had been taken as gospel for years. Data like the coefficient of lift and the drag coefficient when designing a wing surface. They also pioneered the wind tunnel testing and invented new measuring devices and methods still used today.

 

Anyway, sometime in the recent past a group of college students(MIT, I believe) embarked on a trip to reproduce the Wright Flyer from the original plans of the Wright Brothers. Everything went well except for the engine. They could not get it to run at all.

 

It was determined the problem was one of precision. When they built the engine to the Wright Bros. specifications with modern tooling and measuring devices, it would not work at all. When they used period correct machining tools and measuring devices it worked perfectly.

 

I believe the book was "Visions of a Flying Machine (The Wright Brothers and the Process of Invention)" by Peter L. Jakab