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

[MikeWa]

Are these aluminum pistons or cast iron? I mean something makes this bike so heavy don't ya know.

 

Mike

[cowpuc]

Are these aluminum pistons or cast iron? I mean something makes this bike so heavy don't ya know

Mike

 

Back at cha Mike = 100%!! That is an EXTREMELY profound statement when ya consider what Honda just revealed, an 850 pound 6 CYLINDER world class full touring bike with all the same goodies (parking assist, reverse ect.. = and then some) all at 150 pounds LESS in curb weight than the Yam? Plus the Honda is water cooled and shaft drive = one would TOTALLY think those weight numbers would be the other way around!!

Maybe,, just maybe,, there is some actual justification for my "OHH POOP" comment when that new Venture was unveiled after all

[cowpuc]

 

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

 

:sign yeah that::sign Rock On::sign Rock On:

 

 

[cowpuc]

Look what I just found!! This guy may be as far out in left field as I am in my debate theory platform but he is stating exactly,, and in a whole lot easier fashion to follow,, what I am saying... Definitely a simplified method of understanding compared to the other stuff we have been watching/reading while debating this BUT - IMHO,, very well done and very supportive to my case !! Besides,, he is using actual parts n pieces = I LOVE pictures!!

 

 

 

[Flyinfool]

Look what I just found!! This guy may be as far out in left field as I am in my debate theory platform but he is stating exactly,, and in a whole lot easier fashion to follow,, what I am saying... Definitely a simplified method of understanding compared to the other stuff we have been watching/reading while debating this BUT - IMHO,, very well done and very supportive to my case !! Besides,, he is using actual parts n pieces = I LOVE pictures!!

 

 

 

 

Yup that guy is almost as far out in left field as you are. ALMOST.

If you go back to that vid at the 5:23 mark he lets your cat out of the bag when he says unless the engine is designed to spin faster.

That whole vid is about taking a stock car engine that was designed to turn slow and why you can not turn it faster. He is also making some other assumptions that mathematically do not hold water unless you do a LOT of assuming and rounding off. My point all along has been that Yamaha did not have to design this new engine to turn as slow as possible. they could have just as easily designed it to spin up and make some power. Yamaha made a conscious choice to make an engine that was all low end torque and to heck with Horse power that comes in as you wind it up. It is not difficult to make an engine that will spin up, the size of the Yamaha is not the deterrent as is proven by many other manufacturers that have an even bigger stroke that spin up a lot faster in a PRODUCTION engine. Your whole theory is based on this random 4000 FPM for an engine with cheap cast rads and pistons that will grenade at high revs. it is not much of a stretch to put in better pistons and rods that can take the stress of the higher RPM all day long and never break a sweat. You are wanting a higher performance motor in your touring bike, why do you insist on thinking like Yamaha did and use crappy parts that are not much less cost that good parts that will get the job done.

 

I keep hearing this 4000 number thrown about. but in every case it is being used in reference to a stock economy motor like your horizontal shaft minibike motor that was designed to red line at 3600 RPM, or a stock cast iron car engine from 20 years ago. never yet heard that 4000 number used in the same sentence with performance.

 

Do you want a motor to tun the world upside down or a grocery getter?

If you want a grocery getter then by all means design for that 4000 number, If you want a world class motor then throw that antiquated 4000 number out the window.

 

Until someone can explain the "scientific" reason for 4000 which the makers all seem to ignore, I aint buyin it. I want to know WHY that 4000 is the limit and then I want you to explain why all of the current real life current examples all exceed it in production engines?

 

Sorry but I have shown proof positive with solid math that the 4000 max is a myth, and in my book that will trump cuz I said so every time.

[bongobobny]

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

Ummmm, usually a shattered piston and a bent valve stem for starters. Also, it can lead to a broken crank or at least a damaged journal for starters. A rod can penetrate the side of a block...

[Flyinfool]

Ummmm, usually a shattered piston and a bent valve stem for starters. Also, it can lead to a broken crank or at least a damaged journal for starters. A rod can penetrate the side of a block...

 

Translated......

BOOM!!!

[RedRider]

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...

 

I'll jump in here for this one.

 

The reflected moment of inertia (to the crankshaft) of the piston and rod have to stop and reverse direction is ......

 

ZERO!

 

There is no moment when all the components are lined up. Therefore, no moment of inertia either.

 

RR

[Flyinfool]

:sign yeah that:

In the last vid that Puc posted the guy spends time talking about the dwell time that the piston and rod spend motionless, they are never truly motionless. except at the very point of top or bottom dead center, there is no dwell time where the piston is motionless and the rod is still moving at the speed or crank rotation, just most of that movement is sideways to the direction of piston travel.

 

This was another nail in the coffin of that vid.

[Dragonslayer]

On the sultry days of summer when I am basking in the shade sipping on a mint julip I may be entertained by such dialogue, banter and debate. But on those days more on the pace of a rat race, such as today, my thoughts lean more towards," who has time for such immaterial conflict motivated dissertations"

So my vote today is, they should go to their corners and spend some quite time.

 

Tomorrow I may feel differently.

[bongobobny]

I'll jump in here for this one.

 

The reflected moment of inertia (to the crankshaft) of the piston and rod have to stop and reverse direction is ......

 

ZERO!

 

There is no moment when all the components are lined up. Therefore, no moment of inertia either.

 

RR

Very astute of you, RR!

Ummm, however, there are some very educated engineers who might disagree with you...

 

http://journals.sagepub.com/doi/abs/10.1177/2041299110394918

 

https://www.google.com/search?rlz=1C2CHBF_enUS719US719&source=hp&ei=6JTzWbCOGafRjwTVurToDA&q=inertia+in+internal+combustion+engine&oq=inertia+in+an+internal&gs_l=psy-ab.1.0.0i22i30k1.6433279.6444225.0.6448246.23.22.0.0.0.0.197.2788.0j20.20.0....0...1.1.64.psy-ab..3.20.2787.0..0j35i39k1j0i131k1j0i20i264k1j0i22i10i30k1j33i22i29i30k1.0.6U_R3NXhUrk

 

https://www.google.com/search?rlz=1C2CHBF_enUS719US719&ei=HK7zWabGGIijjwTv0aO4Ag&q=moment+of+inertia+in+internal+combustion+engine&oq=moment+of+inertia+in+internal+combustion+engine&gs_l=psy-ab.3...73312.77062.0.79170.10.10.0.0.0.0.127.1107.2j8.10.0....0...1.1.64.psy-ab..0.1.127...35i39k1.0.fYasbTr6wa8

[RedRider]

Very astute of you, RR!

Ummm, however, there are some very educated engineers who might disagree with you...

 

http://journals.sagepub.com/doi/abs/10.1177/2041299110394918

 

https://www.google.com/search?rlz=1C2CHBF_enUS719US719&source=hp&ei=6JTzWbCOGafRjwTVurToDA&q=inertia+in+internal+combustion+engine&oq=inertia+in+an+internal&gs_l=psy-ab.1.0.0i22i30k1.6433279.6444225.0.6448246.23.22.0.0.0.0.197.2788.0j20.20.0....0...1.1.64.psy-ab..3.20.2787.0..0j35i39k1j0i131k1j0i20i264k1j0i22i10i30k1j33i22i29i30k1.0.6U_R3NXhUrk

 

https://www.google.com/search?rlz=1C2CHBF_enUS719US719&ei=HK7zWabGGIijjwTv0aO4Ag&q=moment+of+inertia+in+internal+combustion+engine&oq=moment+of+inertia+in+internal+combustion+engine&gs_l=psy-ab.3...73312.77062.0.79170.10.10.0.0.0.0.127.1107.2j8.10.0....0...1.1.64.psy-ab..0.1.127...35i39k1.0.fYasbTr6wa8

 

What I could tell of these articles (not going to pay for the complete download) is they apply to the complete crankshaft/multi-piston engine inertia. My comment was directed at the very specific scenario presented:

 

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...

 

I've had to do the inertia calculations for a system similar to a crank/piston (actually a Scotch yoke). Single piston. No reflected inertia when all is lined up.

 

All in good fun.

 

RR

[bongobobny]

Yup! Overall there is very little if any effect on maximum RPM's. The real limiting factor is the sheer mass of the piston and rod as well as the stroke and bore. Of course, friction also plays a role as does many much more minor factors.

 

I also wanted people to think about the role of the crankshaft and what drives what! Do the pistons drive the crank or does the crank drive the pistons or is it both?!!? Ahh! There's the rub! Gee, can the crankshaft limit RPMs too?? More points to ponder...

 

I was just adding fuel to the fire for the great debate going on between Pucster and the Fool...

[cowpuc]

Yup! Overall there is very little if any effect on maximum RPM's. The real limiting factor is the sheer mass of the piston and rod as well as the stroke and bore. Of course, friction also plays a role as does many much more minor factors.

 

I also wanted people to think about the role of the crankshaft and what drives what! Do the pistons drive the crank or does the crank drive the pistons or is it both?!!? Ahh! There's the rub! Gee, can the crankshaft limit RPMs too?? More points to ponder...

 

I was just adding fuel to the fire for the great debate going on between Pucster and the Fool...

 

Some really good ,, ,,, material right there Bongo!! Using my 8 fingers, 2 thumbs and 10 toes to do some figuring here,, I think the system works both ways. Hit the starter button, battery discharges into the starter windings which spin the armature which spins the crank which pushes the pistons up and down to get her lit so, in that case,, the crank is powering the pistons.. Once its lit though,, all that boomin going on in that combustion chamber is forcing the pistons down on the power stroke and the pistons are spinning the crank to put power to the ground to make ya move..

All that said,, here is point when it could get interesting.. Say,, you get to the top of a big hill with your bike.. Start to coast down, drop er in gear and dump the clutch with the key off.. Nice steep hill,, like the +10 degree one coming down out of the Big Horns on 14A North east of Cody = you know the one,, the hill that took over 30 years for the road guys to complete (WOW IS GORGEOUS - BUT I DIGRESS). Your motor is SCREAMING at cha that she is wayyyy over revving.. Now,, IMHO,, partially because of what my platform is here in this debate,, the rods and pistons are in jeapordy of coming unglued because it dont make no difference how you obtain max speed on those piston's = thru the piston's driving the crank or the crank driving the pistons = over rev is over rev...

 

Boom,,, clack, clack,clack, crunch,, skidderrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrr

[Oldodge]

All this piston speed, versus stroke length, versus load weight, is what drives guys to play with their Wankel! Sorry..... I will kick myself now

[RedRider]

All this piston speed, versus stroke length, versus load weight, is what drives guys to play with their Wankel! Sorry..... I will kick myself now

 

It does seem to be a rotary argument.

 

RR