Motorcycle Engine Physics!

[Paulington]

Hey guys, just discussing some stuff in FB chat and thought I'd make a little post, it might interest some of you and I'm sure the videos are reposted!

In this post I will be discussing the physics of the BMW S1000RR engine.

Before reading below, watch these two videos:

Cams & valve springs: https://www.youtube.com/watch?v=8-ymU7ETnnY

Valves: https://www.youtube.com/watch?v=Ed-l2Ot_d9c

Right then, let's get into the nitty gritty, bit of maths to follow!

At 14500 RPM (as far as I know the redline of the S1000RR), the pistons are moving up and down 242 times per SECOND.

This means each valve set is opening 60 times per second.

However!

The most impressive statistic is that per STROKE of each piston in the S1000RR engine (each stroke takes 0.002 seconds or 2 milliseconds, which means that in a blink of an average human eye, a piston has completed a cycle around 100 times!) the piston follows the same timescale:

0 Milliseconds: Bottom dead centre, piston is not moving.

0.001 Milliseconds: Piston begins accelerating.

1.0 Milliseconds: Piston is moving at full speed (roughly 12mph).

1.001 Milliseconds: Piston begins decelerating.

2.0 Milliseconds: Piston reaches top dead centre and has stopped.

WHENEVER the piston is accelerating or decelerating it is moving at 1266G.

1266G Means that for the duration of time the piston is accelerating, it weighs 1266 times its actual weight. The piston on the bike weighs 0.253kg, this means during acceleration/deceleration, it weighs 321kg!

In my opinion, these numbers are astonishing and are a testament to the engineering behind the supersports engines of today. I apologise if I've bored you with a discussion about engine physics but I know some of you may appreciate it.

If there is anything else you would like to know in this kind of area, do let me know and I will do my best!
____________________
"Four wheels move the body, two wheels move the soul."
Current Vehicles: '89 Kawasaki KDX200, '99 Yamaha XV535, '00 Honda ST1100 Pan-European, '08 Suzuki GSX-R1000, '08 Mitsubishi Lancer GS4 2.0 TDCi, '15 BMW 1 Series 116d Sport Turbo.
CBT: 27/08/08. Theory: 04/09/09. Module 1: 16/09/09. Module 2: 01/10/09.

[N cee thirty]

you would have thought that the valves opening that much they would eventually fully overlap,what rpm would it be going for valve bounce?
____________________
'00 Aprilia RS50 > '92 Honda CG > '99 Yamaha Fazer > '91 Yamaha RXS > '79 Suzuki X5 > 01' Honda Cg > 07' Honda Cg > 82' Kawasaki Z200 > suzuki gsxr 400 gk73a > honda vfr 400 NC30 Mod 2 Passed 09/06/2011

Jewlio Iglesias wrote: I actually did vote BNP once

[kestrel]

[Paulington]

[kestrel]

There's no doubt that the S1000RR engine would outlast that of the RC116 but engine longevity was hardly the point of your original post, assuming of course that there actually was a point to it. Also bear in mind that the S1000RR is a modern 21st century machine which make use of modern materials and engineering technology, whereas the RC116 was developed 45 years ago.

[Paulington]

The whole point of the post was to showcase to people the amazing physics at work inside an engine and how incredible it is the engine can do such things for any extended period of time to make it viable for use in the real world.
____________________
"Four wheels move the body, two wheels move the soul."
Current Vehicles: '89 Kawasaki KDX200, '99 Yamaha XV535, '00 Honda ST1100 Pan-European, '08 Suzuki GSX-R1000, '08 Mitsubishi Lancer GS4 2.0 TDCi, '15 BMW 1 Series 116d Sport Turbo.
CBT: 27/08/08. Theory: 04/09/09. Module 1: 16/09/09. Module 2: 01/10/09.

[Billing]

[DrDonnyBrago]

[Frost]

The little bikes have a shorter stroke so the piston speed is lower.

[hmmmnz]

what an exceedingly geekish topic,
i love engines and i love they work but id never dedicate a thread to
how fast a piston moves,

but hey it would be a boring world if we were all the same..
unless all you fuckers were me


____________________
the humans are dead
I kick arse for the lord
Wiring Diagrams BIDNIP it bitches

[DrDonnyBrago]

https://www.youtube.com/watch?v=sEf8va1S7Sw&feature=related


This is cool. An 'in cylinder' view of a 4t engine in slow motion.

[sickpup]

Have they managed to exceed 25metres per second average piston speed?

[Kickstart]

[hmmmnz]

49.7mm stroke
14200rpm redline

so 14200/60=236.666667
236.666667x2 (1 up and 1 down per rev)
473.333334 strokes per second
473.333334x49.7=23 524.6667mm/s
or 23.5m/s or 52.5mph

so no
____________________
the humans are dead
I kick arse for the lord
Wiring Diagrams BIDNIP it bitches

[sickpup]

[Kickstart]

Hi

Yep. Just got the revs by shortening the stroke.

All the best

Keith
____________________
Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[DrDonnyBrago]

What happens at 25ms-1 mean piston speed?


Do we make antimatter?

[Kickstart]

Hi

It is regarded as pretty much the limit of mean piston speed. While revs have increased over the years mean piston speed hasn't massively changed.

All the best

Keith
____________________
Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[Frost]

I think it's likely due to the rate of expansion of the burning fuel inside the cylinder. At > 25m/s the piston is probably travelling faster than the expansion is pushing it, so it'll slow down. So you can get > 25m/s by kicking the bike down a gear when on the redline, but it'll soon slow down

[DrDonnyBrago]

[stinkwheel]

Vaguely relevant object lesson in piston speed, G-force and what that would mean if a piston from a V16 diesel locomotive engine making 4400hp suddenly wasn't attached to the conrod any more.
Clicky

Might be a repost.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[Kickstart]

Hi

Not sure it is flame speed related. It is mean piston speed, so at times it will be travelling a hell of a lot faster (also happens to be close to the times when the con rod is applying the max turning force on the crank).

All the best

Keith
____________________
Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[Ditto]

I was told on my CBT that a more powerful motorbike is easier to manoeuvre at lower speeds as the movement of the pistons gives the bike more 'weight' so to speak.

As in the centre of gravity is lowered by the movement of the pistons.

If you pull the clutch in when you are moving at 30-40mph you feel the bike become 'lighter' so to speak and harder to move around due to the revs dropping.

It feels strange, like you are on a push bike at 40mph and is probably quite dangerous. I guess its the reason motorbikes are so stable at high speeds.
____________________
CG 125 > Bandit 600 > CBR 600 FY > Street Triple R

[Kickstart]

Hi

Don't think that is the pistons, as on a 4 when one pair is flying down another pair is flying up.

However yo do have a crank in there that is acting like a flywheel

All the best

Keith
____________________
Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[Frost]

Essentially a bike has 3 wheels, in terms of gyroscopic stabilisation anyway, with the crank being the 3rd wheel. Revving a bike when at low speed can help stabilise it a bit. Similarly revving can destabilise the bike causing the front end to go light when accelerating hard. To counter this some GP bikes had the crank spin the other way, or had 2 counter rotating cranks to balance out the force.