Kind of OT: Moto GP

[jrt]

So I was watching 'Faster' last night (thanks Wife!)...actually, she enjoys it as much as I, but that's a different discussion. Anyhow, one of the recent changes is that all the machines are going from 500cc 2 stroke to 990cc 4 strokes. The 4 strokes are apparently significantly faster.

So why is this? I would have guessed the 4 strokes would have been slower. From just size, then they both fire 1 L (approx) every four cycles. The 4 stroke requires more moving hardware (valves) that I would expect to slow them down. Does the 4 stroke benefit from a scaling factor? Less piston friction per cc or something like that? Or does it have better compression?

Jason

[Steve G.]

The movie "Faster" is in fact about 2 yrs in the past. All Moto GP bikes are 4 stroke now, albeit with many different engine design layouts, most approaching the 990cc capacity limit, vs 500cc with the 2 strokes. .

2 stroke engines do have an advantage simply because they fire on every top dead center of the piston. But it is not double the advantage, as the engine capacity would indicate, as well, 2 stroke technology has basically hit a plateau, as a result of lack of effort with R&D at the race shops, and that 2 stroke technology has pretty well topped out. 4 strokes are sort of in a new frontier of sorts. Remember they used to rule the roost on GP bikes until the mid seventies when 2 strokes came along. New technologies, metalurgy [extremely lightweight metals allowing quicker, higher revs], electronics, and mind set mean that now we can see a new horse power war happening.

As well as having more power now, 4 strokes have significantly easier power bands to deal with, so riders are able to get much closer to that elusive edge of adhesion. 2 strokes have almost the same power, but deliver it in a much smaller 'power window', and it hit hard, and the last generation 2 strokes were the nicknamed "screemers" which had more power than the "big bang" 2 strokes [different firing order engines] which were used because they had a more managable power band. These fell out of favour in the last years of the 2 stroke, when they banned leaded fuels, which made the big bang significantly less powerfull. The last years as a result were the screemers.

Ciao, Steve G.

[Guzzirider]

Another good reason for the manufacturers switching to 4 strokes is that they can recoup some of their R & D costs by transferring some of the new technology onto road bike engines.

 

With the death of large 2 stroke road bikes due to emission laws, this was not possible before the switch.

 

The change also allowed Ducati into GPs!

 

Guy

[gthyni]

Another good reason for the manufacturers switching to 4 strokes is that they can recoup some of their R & D costs by transferring some of the new technology onto road bike engines.

 

You means recoup some cost in marketing <_>

 

In motocross where they compete 450cc 4-stroke vs 250cc 2-stroke

the jury is still out. The main reason for 2-stroke 500GP bikes not

being competetive IMHO is that development stopped. Refinement to

engines AND chassis are a comtinuing process, 2-3 years old bike is

not competetive at all.

 

The nice things with the 2-strokes were lower weight gives higher curve

speeds and lower development costs - meaning more teams could compete.

[Guzzirider]

The 2 stroke 500s also smelled lovely leaving the starting grid at Donnington!!

[TX REDNECK (R.I.P.)]

The 2 stroke 500s also smelled lovely leaving the starting grid at Donnington!!

40283[/snapback]

 

I too love the smell of castor bean oil