DSB and SS weights changed today.

It's not so much piston speed as it is piston acceleration. I'd venture that the valvetrain is the limiting factor in most all production bikes. If you raise the rev limit, the valvetrain is usually first to fail, not the rods/pins/pistons. Yeah, VE tapers off at high RPMs, but that just means it produces less power. There are actual mechanical reasons why bikes can't rev higher. Twins and fours are bound by the same materials properties, and are bound by the same stress limits of their parts. Those big pistons and valves are heavier and exert more force = can't rev as high = can't produce as much power, cc to cc.

 

exactly on v4 part & the weight & cost factor too .

frictional losses on the twins? i grabbin at straws now......

 

Twins - Bad parts

- Less valve area (only 8 valves)
- Long stroke for a given displacement (not enough pistons)
- Big, heavy engine parts (not enough pistons)
- Big heavy valve train to make up for lack of valves (not enough pistons)
- Long stroke means high piston speed
- High pistons speed means less RPM
- Heavy valve train means less RPM
- Heavy parts mean more frictional loss
- Less RPM means less torque multiplication
- Less RPM makes less power

Simple, cheap solution - More displacement.

 

"Make bigger bangs or more of `em."

-- Jack Wilson, Big D Triumph

 

so by that rational other than the big heavy parts trying to tear themselves apart & the frictional losses associated w/ trying to spin a twin high .......

if the budget was there for the trickest lightest strongest stuff you could build a huge bore , short stroke twin w/ 6 valves per cyl & spin it ? the proverbial grenade w/ pin pulled .

i would assume if this was viable one of the mfg's would have done so in motogp but theory here ?

 

and maybe this is what Ducati is doing with the new Superquadretta......but who knows...

 

...and then again, if you have those materials available for the twin, they're also available to the four.

Just imagine if a manufacturer did a 30,000 rpm, 600cc rotary bike! The AMA would make it's minimum weight limit around 600Lbs!

 

So what you guys are telling me is I should throw my 675 in the trash? There goes my race season...

 

Yep, just let me know where your trash can is!

 

Haha.

It makes up for the 636 you were racing.

 

When is VE not the limiting factor?

Why is all the other things I mentioned not the limiting factor?

Because all of those things are a issue regardless of the number of cylinders and thier effects are worse the larger the bore or stroke. So in reality you are saying the solution to having too large a bore to large a stroke is to allow them to become larger?

There is little differance in the CC/power ratio between the good 600 I4's and good SS 1000 I4's. Are you saying that its not possible to build a 600 cc twin with similar numbers?

The best way would be to start with a more performance oreintated bore/stroke ratio...

It wasn't that many years ago that the 600's had similar cc/power ratio's to the 848, what developments have they seen to bring them to their current levels?

Better bore/stroke ratio, optimized intake and exhaust for higher VE over a narrower range. The VE of a twin(or single for that matter) will never be as good as a inline four With a 180 degree crank due to less efficient scavaging.
but it can be much closer than what the Ducati's is.

 

Ok....then why don't they do that? Why is it that every manufacture since the begining of time with twin cylinder motorcycle asked for a displacement advantage over multi-cylinder bikes?

Why were they given a displacement advantage?

Why did they not win every race by 30 seconds if in fact they can be made equal? Clearly if all is equal then a 200cc - 250cc advantage would be huge right?

Why don't they just build a 600cc twin that is as good as a 600cc inline? If its possible then why don't they just do it?

If I am wrong that a twin cylinder motorcycle of equal displacment to a 4 cylinder motorcycle is not as effcient......then site one example.

 

The hell I don't! Sign me up for that thumper!

 

If that works

You should start building bikes.... You'll be RICH.... RICH I TELL YA!!!

 

What happened to Honda building the smaller V-4's? My first bike was a 1984 Honda Intercepter V-4 500cc. Even in the early to mid 90's, I was still giving 600's fits. The 750 V-4 from the lmid and late 80's was still a good runner. With some good tuning, these were some quick motors. Cam chain tensioners were the biggest killers of these motors...just ask the front two pistons of the poor bike I destroyed.
Honda made the 500, the 750 and the 1100 V-4 motors during the 80's, but dropped the smaller ones into the 90's. How much fun would the new VFR motor be in the CBR 1000 chassis?

 

That answer is easily found in one simple formula: Pi*R^2

Many small circles are better than a few big circles.

(I'm on your side, Chip)

 

Chip has nailed the explanations. It seems like some others are justifying their explanations. I would add another way of thinking about it not mentioned yet, the engine is an air pump. As Chip says, more pistons equals lower piston speeds equals more rpms equals more air. You can get into the nuances of volumetric efficiency I guess, but the main point is that a 600 I-4 can pump about the same amount of air in a given minute as a 750-850cc Twin (I said about so don't counter point the hell out of me here). Of course it is at a higher RPM to accomplish that, but gearing can get that back to the same wheel speed (which by the way multiplies the torque as Chip again mentioned).

The air pump school of thinking also helps one understand why 500cc 2 strokes were matched against 1000cc 4 strokes since the 2-stroke is sucking and compressing twice as much as the 4 stroke. Again there are other minor differences, but displacement and rpm is the driver. It was always funny to read the motocross fans wondering why 450s were competing against 250's. ha.

I was kinda surprised that they let the Ducati compete with an 848, and when they made the EVO version this year, they are finally getting the grunt out of it. Pair with a good (and light) rider, and viola, a competitive platform.

If the Ducati's win by 10+ seconds in most every race, go make a correction. Increasing the spread on weight is probably an okay move because it won't make the Ducati slow down 1 second a lap. Maybe 0.2-0.5? I dunno, but in the range where it still comes down to racing. I have a feeling Eslick and Herrin and maybe some others will have a little something for the Ducatis in future races.

 

But it has 999 Cylinders!!!

NICE!!! :up:

http://www.hordpower.com/gallery/album07/848R

Still, basically running an... illegal... back then 749 = Legal 848... today

Same Stuff

So maybe Ducati should still call it a 749, maybe people will be happier because 848 is such a large number compared to 600, as well as saying the AMA has made the kit for it legal.

Gettn better

http://www.hordpower.com/gallery/album07/848R_001?full=1

SUPERQUADRATA....

 

I'm not sure what any of that has to do with the subject at hand. The old 749R and the current 848 are very different engines. They arrived at the new capacity by adding stroke, it is not a 749R with 999 cylinders. (backwards from what they should have done, IMO) The 848 has much milder camshafts, and lacks all the trick Ti stuff inside. I have no clue what power the Latus bikes are making, but I bet it's nowhere near the old "kitted" 749R's running the good fuel. They don't have as much to work with.

The 749R was legal in AMA FX, when it proved uncompetitive they allowed the bump to 848cc. Then it became somewhat competitive. Now that the rules are more production-based, it makes sense to me that the "new" 848 is allowed to run against the 600's, with performance indexing as needed. People grumbled a lot about the 1125 Buell, (including me) they grumbled a little about the Aprilia 1000's. Now that a good rider is doing the business on a good 848, the bitchfest starts all over again. Whatever.

 

I dunno about you, but I prefer to be with three chicks (4 some) than just one (2 some) ;-)