How do motorbike engines reliably rev to 14g? Or don't they?
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How do motorbike engines reliably rev to 14g? Or don't they?
Its been stated that the stress on engine components increases exponentially with revs. But also a factor is the weight and also the setup bore/stroke relationship and a million other factors. If you have a car where you are keeping the components the same sort of size and weight, revs will be the main thing working at upping the stress energy. In a bike for high revs they will generally have very contrasting bore stroke relationships, ie 100mm bore and just 50mm stroke or something. This would mean that for the same revs the actual piston would in fact be going slower (covering less distance between top dead centre and bottom dead centre even though high revs) than an engine with a larger stroke. This plays a large part in lowering stress. The other thing though is the size of the pistons and components. Think a 600cc four that revs to 15000revs each piston is fitted in a volume of just 150ml, 3/5 a glass of milk. Take a 2litre four and make it rev at the same rate (even with stroke the same and everything else (which it wont be)) you are moving in something closer to the size of a 600ml coke (500ml). Basically think about the stress that your muscles of your shoulder would go through if you take a tennis ball in your hand hold your arm out and then fling it up and down at say 2cycles a second. Pretty easy but you'll tire after a while. Now get a 4kg shot put, you will more than likely destroy your rotator cuff.Quote:
Originally Posted by gnx1987
Comes down to physics. If you look at a cbr250 they have been revving to over 18k for 15years, a 600cc has only just in recent years hit 15k (and motorbike development and tech has jumped massively recently). Even though the cbr has little technology it has far less weight to throw a far shorter distance for each rev.
But having said that a motorbike still will require a rebuild long before 100k in the sportsbike scene like a cbr600 or something. Some old gixxer 1100 have lasted a long time though.
But yeah thats basically what it comes down to, let us know if i havent explained well.
motor bikes are generally less than a 1000cc will rev higher. Lower capacity engine can rev higher. Also its a 2 stroke in most cases, the ones that rev high, so there is reduced movement inside, not sure how to explain....
Look at Spoon's ek9 it revs high at 11,000rpm but then anything larger is not reving as high.
But as all said before higher revs mean less reliability, you need better fuel, better everything and a little error in the engine will cause major problems due to the speeds involved inteh engine.
That's why high revving cars are found in race cars. Engines are rebuilt every race nearly.
If you want that type of power its easier to boost the car. But even turbos need rebuilding.....
Just to clarify there actually aren't any 'road' motorbikes in 2006 that are two stroke. There was the little nsr150sp honda and the aprilia 125 and 250 a year or two ago but all other motorbikes are in fact 4stroke engines. The aprillia is still made but they dont bring a road registerable one to australia, just track ready as far as i know and im pretty sure the nsr was canned. But yeah no two strokes around in late model bikes. Some off roads still use them but even then any of the slightly larger capacity (above 350 ish) are 4strokes.Quote:
Originally Posted by Limbo
It all depends on what you are going for : if you want the all motor crazyness, then good luck and mucho respect coming your way. Just keep in mind that the money you are required to spend to hit anywhere above 135-140fwkw could be used for boost.
Dont forget, making it go fast isn't everything, try and put some money aside for suspension, BRAKES, gear box re-builds, and any diff modifications, not to mention lsd.
Gets pretty expensive huh, lol!
Nah that's a good enough explanation for me. I kind of figured it was something to do with weight. But in response to the suggestions for shebangs that he might as well go turbo, I know where he's coming from. The ability to beat larger displacement motors with a front wheel drive all motor 4 cylinder is far more impressive than being able to do it with a turbo 4. When you go turbo you're in a different league. And if your turbo 4 beats a car with a larger displacement motor, it's not that impressive because it's generally expected that turbo motors are going to have a lot of power anyway.Quote:
Originally Posted by crx51
Finally someone who knows what they are talking about CRX51 (No offence to ppl in this thread, sick of a couple of other threads here).
I actually have a video with the head engineer at Honda talking about the DC2R when it was built and what they did to it. He mentioned something about the forces inside the engine (the instant and the resulting inertia) reversing at a certain RPM (8000 I think) and from there a exponential increase in force as revs increase. This was something they had to take into account when choosing suitable parts for internals. Interesting though, I wonder if (not taking the valvetrain into account) you keep the overall instant of the rotational inertia the same as the piston reaches both TDC and BDC (i.e. lighter rods and pistons etc at a higher RPM) reliability would be maintained? Obviously the rings are going to wear more, but in terms of throwing a piston etc .. Any thoughts? For Example, titanium rods and super lightweight pistons revving to 10500rpm might be the same as the stock components revving to 9000rpm.
Just so you all know, a DC2r already has higher piston speeds than F1 Cars. Impressed? Now you know why it isn't a good idea to increase the redline too high in a B18C5 or similar. The amazing thing is, having said the above, I have seen these motors going beyond 11,500rpm in an old track video I had. Amazing stuff, but the driver said that he rebuilt the motor every 2 races and had destroyed an engine once when a rod bolt sheered off and sent the piston through the block