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To help keep a cap on power and, hence, speed, the MSMA has decided to propose a reduction in engine capacity from 990cc to 900cc. "The intention is not to reduce performance but to prevent a continuous improvement in speed and lap times," according to the press release.

2004 2007 weight changes
2 Cylinders 135 Kg 133Kg - -2Kg
3 Cylinders 135Kg 140.5 Kg +5.5Kg
4 cylinders 145 Kg 148Kg + 3Kg
5 cylinders 145Kg 155.5 Kg +10.5 Kg
6 cylinders 155Kg 163 Kg +8Kg

The proposed changes to the rules also affect the minimum weight standards, adding more weight to engines with more than two cylinders from 2007.

The proposed changes above may indicate the technical direction that some manufacturers are pursuing for the future. As Honda is the most powerful voice among the companies, it is interesting that the proposed minimum weight for five-cylinder machines, such as the Honda RC211V (and Proton KRV5), has been increased the greatest amount. This may indicate that Big Red is already working on new engine configurations and is looking to abandon the V-5.

And, as two-cylinder bikes are the only ones to get a minimum weight decrease, might we see the introduction of a 900cc MotoGP V-Twin? If so, it wouldn't be as powerful, no doubt, but it would enjoy nearly a 50-pound weight advantage over a V-5-powered machine. And, as a Twin would have a 66-pound advantage over a six-cylinder-powered bike, it looks like the rumors of a Honda V-6 will not be fulfilled.

The MSMA is also looking at perhaps reducing the 2005 rule for a 22-liter fuel tank capacity (down 2 liters from current rules) for the 2007 season.

The introduction of 4-stroke machines to MotoGP has resulted in a huge amount of newfound interest in the class. Now, with revised regulations again on the table, the series might get even more interesting.

The Testastretta engine fitted to the Ducati 998R 2002 version, the bore is 104 mm.
Unfortunately, such a large bore currently causes combustion problems with dramatically decreased efficiency.
This stems fundamentally from the need to augment the injection advance and from the worsening of the "shape factor" of the combustion chamber which, with the reduction of the bore/stroke ratio, becomes ever broader and flatter. The "shape factor" is a critical synthetic value to check a combustion chamber's good operation, and a good indicator of its compactness and "thermal efficiency".
It should be borne in mind that aspirated racing engines require rather extreme valve lift and overlap angles, therefore, cavities are made in the piston crowns to prevent contact with the half-open valves. The combustion chamber is therefore practically contained in the piston cavities, such cavities becoming bigger as the stroke/bore ratio decreases, which makes it hard to obtain the high compression ratios required by high specific power engines.

The Beare sixstroke does not have these limitations because the main lower piston does not have valve cutouts and the combustion chamber is a compact design with squish contribution from both upper and lower pistons. The shape is much more like a fist than a flat hand hence thermal efficiency is high .
Combustion chamber diameter oprox 75mm
The main piston is lighter and stronger than the 4-stroke, because the lack of cutouts allow a thinner slightly domed top
Malcolm does believe that the sixstroke 15kg weight advantage will be a major benefit for the Beare Sixstroke, much more so than the 30kg handicap enjoyed by Twins in 500cc twostroke racing. "Working on the assumption that all these four-strokes are going to make enough horsepower, 15 kilos is a lot," he says. It’s straightforward enough, the Twins will have a 10 percent weight advantage and force equals mass times acceleration, so it is a big difference.

Sixstroke Beare 900cc Vtwin MOTO GP

Bore 116.25 mm stroke 42.5 upper bore 82mm upper stroke 34mm
compression ratio 12.25 to 1
power 337HP @ 15000 RPM
torque 74.6Ft/Lbs x80% x2 = 118Ft /Lbs
piston speed at 18000 is 5019 Ft/min or 25.4965 Mtre / sec
XL engine file
Torque 101.2 NM or 74.6 Ft /Lbs discount by 20% and multiply by 2 for twin cylinder is 118 FT/ Lbs
6 port design with 3 exhaust ports leading to a rotary disk, 3 intake ports,One intake rotary disk and 2 reed valves with air assisted injectors. 2 or 4 10mm plugs per cylinder.
The port area is oprox 20% to 30% more than a 4 valve head
Results of XL file sixstroke touque calculator

        Based on Dual Cycle                
                Total Torque        
Fourstroke        62.00        
Main        Top                
66.05        35.15        101.20        
Increase in torque                63.23%        



A tidy mind not intelligent as it ignors the random opportunities of total chaos. Thats my excuse anyway


If I am correct the it gonna be reduced from 990 to 800 cc...


One of the bikes at the Laguna Seca GP race sounded awful, I belive it was the Kawasaki.  Were they running a three cylinder engine?  It reminded me of the V6 Busch cars of a few years ago, people would leave the stands to avoid the noise.


Kawasaki running an inline four, I haven't hear them so I can't comment, weird firing order perhaps.  A couple of years ago they were triple running, Aprilia and Proton I think.  As far as I know, there are no more triples out there.


Kawasaki's are fours running a closed up firing order as is yamaha



Kawasaki's are fours running a closed up firing order as is yamaha

Do you mean that the crank is still the usual 180-180-180-180 shape, but cylinders fire in pairs?  Or is it more interesting than that?


zhelyo (Automotive) 9 Aug 05 8:50  
If I am correct the it gonna be reduced from 990 to 800 cc...

This is a useful tool http://www.ducatitech.com/info/bore.html

So we change the bore to 110mm and stroke to 42mm upper piston bore about 77mm  stroke about 30mm
The reduction in cc's only makes the V twin with 4 pistons more viable

A tidy mind not intelligent as it ignors the random opportunities of total chaos. Thats my excuse anyway


Not really sure of the exact firing order, I dont think that it as been publicly released for either yamaha or kawasaki. Thinking is that the crank is still approximatly a 360 deg crank +/- a couple of deg for the firing pairs. This is offsetby a counterbalance shaft to reduce vibration. The firing pairs may be up to 15 deg apart to give an extended big bang every 345-360 deg also to reduce crank case forces. The other way is what virgin yamaha in the uk have done to their R1's. Used a standard crank & rephased the camshafts to fire like a lopsied triple. Cyl #1 - 180 deg - #2 & #3 together - 360 deg - #4 fires(hope I got that right. Apparently works well. Subsequently then banned in WSB.


Kawasaki and Yamaha are running Big-Bang engines.They are not the conventional type of a 4 cylinder engine.
The first ever Big-Bang engine has its roots in the 1992 season-part of the golden era of the 500 cc two strokes machines with Mick Doohan,Wayne Rayney etc.Thing was that they changed the firing order and the crankshaft of the Rothmans Honda in a try to make the bike way friendlier with the rear tire.
Now lets look at some little science.The key thing about the big bang engines is that every time when there's an expansion stroke(ignition)-the forces that actually "push" and power the bike occur.So at every expansion stroke the rear tire is being pushed and every time that happens-it looses grip.In a 4 cylinder machine with a normal firing order there's an expansion stroke at every 180 degrees of the crankshaft rotation.And as it follows-at every 180 the rear tire is being pushed-therefore it looses tracion and of course-makes a small step of being worn out.
If you take a look at a V-twin machine there's an expansion stroke at every 360 degrees of the crankshaft rotation-therefore the bike is way friendlier with the rear tire and of course it has tremendous amount of grip-especially exiting curves.
So the Rothmans Honda boyz tried to make..something like a 4 cylinder V-twin by changing the specification of the crankshaft and of course the firing order.
In modern days the Big bang engine for the Yamaha squad was choosen by Rossi in the first test at Sepang(he also chose the direction of which the Deltabox chassis would be developed).He had a total of 4 engine configurations to test..and he chose the big bang.
What they did with its engine is do a completely new engine mapping,completely new firing order,crankshaft...
Word is that in Rossi's M1 there's a 310 degree "peace" full of grip before the tire is being "pushed".In other words-there's an expansion stroke at every 310 degress of the crankshaft rotation.The advantages of course are being friendly with the rear tire-it preserves it fantasticly towards the end of the race-and way more usable powerband.
So far as Kawasaki...I have no idea at how many degrees there's an expansion stroke..but I'm pretty sure that the 4 cylinders are working like..almost in pairs.
Interesting is that in World Superbike-all of that is totaly banned-the firing order must remain "stock".
In British Superbike however things are a bit more interesting-they are allowed to change the firing order..but not the crank!
Anyways I just hope that the Big Bang project keeps on developing so that one day we could ride a big bang motorcycle on the road!


I was aware of the 2 stroke big bang bikes.  But it's easier to do if you have the luxury of 2 cranks - anything's possible then.  It's interesting that the big boys are doing it with 4 strokes now.


I remembered reading an article on this in "Race Engine Technology" Magazine. I've dug out my old collection and its in the April 2005 issue.

The title of the article is "MotoGP engines - a Big-Bang creation" and in it the authors (Blair & McCartan) discuss the merits of big-bang in the MotoGP arena, using worked examples - very interesting!

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