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MOTO GP Engine rules

By Motorcycle.Com Staff, Jan. 30, 2005
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. Its 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 uni SA XL file sixstroke engine touque calculator

Based on Dual Cycle
Total Torque
Fourstroke 62.00

Main Top
66.05 35.15 101.20

Increase in torque 63.23%



Things are a little more complicated than you would expect
During the intake stroke the main piston is increasing the cylinder volume while the upper piston is decreasing the volume (half of its stroke) so the net change in volume is +722cc . During the compression stroke the upper piston is still reducing volume (half its stroke) while the main piston is also reducing volume, net change -1082cc.
During the expansion stroke the upper piston is increasing the volume (half of its stroke) while the main piston is increasing volume, also net change +1082cc.
During the exhaust stroke the upper piston is increasing volume (half of its stroke) while the main piston is decreasing volume, net change -722cc
if you add all the strokes together and average them you get 900cc
The story changes again when you phase the coordination of upper and main pistons but the average remains constant.
The combustion chamber is only aprox 75 mm in diameter maybe 2 plugs will be OK.

Read more about the six-stroke at: jack-brabham-engines.com

--malbeare