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· Registered
1,229 Posts
I actually read the bottom part... I be reading that stuff somemore... Moto

GP is doing some great things lately IMHO. It's formula's are allowing a variety of configurations to compete on a more or less level playing field. I hope that the technology will filter down to "Street" bikes.

· Registered
3 Posts
Holy Kaw, here be some more of that stuff.

Alan Cathcart quote after testing the Ducati Beare sixstroke

"One thing he certainly doesn't need to worry about is torque, which together with the crisp responsive throttle pick-up and the reduced vibration - even compared to a smooth-action 90 degree V-twin - are three strong points of the six-stroke motor. The Beare engine is unbelievably muscular in terms of torque, and from very low revs, to"

The head height is 150mm the same as the original head so space or location is not a problem.

The upper piston oil scraper rings never enter or traverse the ports , so with extraction system oiling is not a problem.

(1) The 6-stroke engine is fundamentally superior to the 4- stroke because the head is a net contributor to, and an integral part of the power generation within the engine, unlike a cam only absorbing power.

(2) The 6stroke is thermodynamically more efficient because the change in volume of the power stroke is greater than the intake, compression, & exhaust strokes.

(3) The compression ratio can be increased because of the absence of hot spots in the combustion chamber.

(4) The rate of change in volume during the critical combustion period is less than in a 4stroke.

(5) The absence of valves within the combustion chamber allows design freedom.

(6) A one-piece engine from crankshaft to upper shaft becomes feasible. No head gasket.

(7) Fewer components, 15 per cylinder compared to 40 for a 4-stroke. Therefore the cost of manufacture is much less.

(8)Can be fitted to standard engine blocks so the market is much larger than the OEM sector, also includes the retrofit aftermarket sector.

The engine has proven to be robust on the racetrack, & have significant advantages over 4-strokes

(1) The valving is desmodromic

(2) There are no valves to drop or bounce.

(3) The rev limit is only what the bottom end can stand.

(4) Gas flow on intake increase of 20%.

(5) No possibility of engine damage if the timing belt slips or snaps

(6) the reed valves are so close to the intake ports that their tips become the virtual port opening. This achieves variable port area & variable engine demand valve timing. The tips open late & small amounts with low throttle settings & open early & fully at full throttle

(7) air assisted fuel injection has unsurpassed (5 micron with 20% air premix) fuel mixture preparation directly into the cylinder without the inhibiting poppett valve in the way, just a lovely big port. And the injector is protected from combustion

The valving is really piston porting augmented by disks and or reed valves. First the upper piston opens the exhaust ports. No other ports are exposed for 20 to 30 degrees to allow for a blowdown period. When the intake ports are exposed the reed valves prevent backflow and the intake disk is blocking its port. The exhaust stroke continues and towards TDC the exhaust disk begins to close its port and the intake disk begins to open its port. The intake reeds open whenever pressure differentials between intake manifold and cylinder allow. The disks are set in timing for the desired overlap. The exhaust system design plays a large part in evacuating the cylinder and starting the intake, as the ports are fully open at this stage.

The exhaust disk closes and intake continues.

The upper piston closes all the ports at aprox 60ATDC and compression begins. I have found it to be most advantageous to retard the upper piston in its relationship with the main piston by between 10 and 20 degrees to have peak cylinder pressure at the upper pistons TDC or aprox 15degs ATDC ignition timing advance seems to be best at aprox 25 degs advance.

The cycle has some similarities to the Miller and Atkins cycle in that the intake volume is less than the expansion volume.


· Registered
955 Posts

Cool! Great! Clear as mud!

Now, if someone can tell me where I can find a comprehesive diagram, to go with your explanation, my head might stop spinning long-enough for me to comb my hair.

I need visuals, Damn It!

· Registered
771 Posts
Interesting that they lowered the weight on 2 cyl, and uped it everywhere else. They also broke the 4/5cyls apart, and the 2/3 cyl apart (if I remember the 2/3 had the same wt, and the 4/5 ditto)

Bless them for trying for the competion nirvana of multiple motor designs competing on the same track.

Problem is the make no mention of rotary(wankel) type motors (allways liked them). It seems that this directs all the manuf. to the same 4stroke design. Just a different # of cyls.

· The Toad
17,449 Posts
Wait a second. I thought that weight advantages were "unfair". At least that was the chant when the AMA did it. Funny how such things are okay with the same people when it's MotoGP.
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