Query approved.

Interesting.
I think its an evolution.. though the Jap4s are known to share vital R&D know how with each other, especially in times of crisis.
It wouldnt be surprising to know that the same foundry perhaps make the block sets for all these 4 manufacturers.

Though I can't Argue with Argee on any of his question, This one's has just left me unanswerable.

And I also am thinking on the same platform as Satyen, It may be just due to a Evolution, process at the initial stages, that it was designed to be at that spec, or probably, the kind of output they want as a result is best suited at this frame of specs only

Rest, NO IDEA, Sir Ji.


P.S: Calling Old Fox Sir, Calling Old Fox Sir. We have a Man Down with a question

Just like they agreed for 300km/hr top speed for litre bikes, they have now agreed for this boreXstroke size for 600's...


On a serious note. I dont think it is coincidence. This might be the perfect oversquare configuration for a 600 cc inline 4cyl engine. Hence has been adapted by all jap manufacturers.

Pls...can you define what is perfect oversquare engine? Because Wiki says perfect oversquare engine is when bore matches stroke - Stroke ratio - Wikipedia, the free encyclopedia (1:1) and these work to something 1.57:1

@RG Let him explain what he meant. You got yours wrong

Source: Stroke ratio (Square Engines) - Wikipedia, the free encyclopedia

examples of square engines would be Honda Unicorn, Yamaha FZ and Bugatti Veyron

P.S.: I googled 'Perfect Oversquare Engine'. No relevant articles found.

Perhaps they bought over the competitor's bikes to study and reverse engineer them. So to be on par with others, why not have the same dimensions?

Sure.
When the bore size (piston dia) is more than the stroke length the engine is said to have an oversquare configuration,
As mentioned above, all 600's have 67x42.5mm config where Bore=67mm and stroke=42.5mm.
Bore>Stroke.

Perfect oversquare might mean 1:1 bore/stroke ration but that does not mean than it will produce max power.
I mean perfect with respect to cylinder height, weight, block width, torque and power production and many other factors that might be considered for choosing a piston size.

My two cents: if you read the reviews of these bikes old and new, you will find ; at most of the time the CBR is liked for street credibility, the R6 for track, the GSX for torque,Kawasaki for Raw power.Although they might have the same cylinder dimensions but their valve sizes, valve angles, manifold lengths,injectors, and everything else differs, and that makes the most of the difference to the bike's character coupled with different frames and suspensions.

This reply is a complete OT, if it were not you, I would've never answered
How do you say that? Check the same Wiki article you quoted...

Remember, we're talking about "perfect" & oversquare engine, not just oversquare engine; as usual, Harmeet's reply is confusing, since that's OT, I'm looking forward answers on why the 600's have the same setup.

Check the same Wiki article

Satya - Well, my line of thought goes that, no manufacturer repeats the same product that's available in the market; they might bring in similar product with a little variance like, change in config or add few more features or lower the price etc. On that front, I expected one of these guys with a different stroke length or different cylinder set etc. But, here only the CR changes, engine config is precise ctrl+c ctrl+v work.

@aargee:

So that makes the block dimensions to be the only similarity between the bikes. Maybe its the manufacturers' internal challenge to see whose got the best machines built around the same block?

Thinking along these lines, it almost looks liek these 600s are treated as platfroms to test out developments that can be later intorduced on the liter bikes or trickled down to the lower capacity bikes. If thats the case, it would be preferable to keep something major as a constant, as a reference point....and seeing how the block is the heart of things, it would make sense(atleast from my non engineering perspective) to hav the same block dimensions for more control on the test environment and make it easier for comparisons between each other's developments.

BTW all the manufacturers have have the capacity of 599cc if they hav more than that then they won't qualify for SBK and WBS championships as these use road going production models as base on these championships, they (the championships formulae) state a bike having 600cc or less to qualify for 600 category so the 599cc capacity, earlier the ninja 600 had a 634/635cc engine along side a 599cc ninja, both were sold simultaneously,the 599 was produced to that Kawasaki qualifies for WSB , and the higher capacity model which was ideal for road as it had more torque and better real life riding characteristics.

My humble 2 cents:

The reason for the almost similar bore stroke specs is 2 fold. To put it concisely; (1) limitations derived from use of production based materials and (2) Homologation rules by FIM.

Reason 1:
It so happens that all these engines are in-line fours with stratospheric rev limits of 15,000 to 16,000 rpm. Currently, with the traditional valve trains, this is the limit to which engines can rev to reliably. To go beyond these limits is possible by shortening the stroke of the engine but the engine designers still need to address the issue of valve train design and the materials to be used.

Current materials at such increased revs will have such a decreased life duration that it would just not be acceptable in a production bike. Exotic materials and gear driven or pneumatic valve actuation are currently used in prototype racing, but the cost of the same is prohibitively expensive (currently) to bring to production bikes. Remember that the difference of rev ceiling between current production 600 and a prototype 800 is incredibly only 3,000 to 4,000 rpm!!! But to achieve that difference and still be reliable the prototype 800 has to use some fancy engineering indeed!!!

If the stroke is increased then complications such as con rod and crank shaft flexing come into play. While increasing the stroke will give a better midrange attaining the 15 - 16,000 rpm reliably becomes a different story all together.

It seems that the engineers at the big 4 have all reached a common conclusion that 67.0 x 42.5 mm is the ideal bore stroke to achieve the stratospheric rev limits of 15,000 to 16,000 rpm with current material and drive train technology.

That brings us to Reason 2:

For super stock racing FIM prohibits any changes to bore stroke of the engine and to the head and valve trains from the approved homologating specifications. So imaging that manufacture A creates a production bike with 67.0 x 42.5 mm configuration with a rev limit of 16,000 rpm. Another manufacture B creates a production bike with 65.0 x 44.5 configuration with a rev limit of 14,000 rpm. Now, due to the homologating and super stock racing rules, manufacture B is at a serious disadvantage as anyone owning one of their bikes has a 2,000 rpm deficit and has very limited scope of things that can be done to address the deficit.



Kawasaki and Suzuki have agreed to jointly develop engines, but nothing substantial has come out of it till date. Honda and Yamaha hate each other's guts and Soichiro Honda would roll in his grave if there was any corporation between Honda and Yamaha.

Honda's pride in its in-house know how is legendary and it will not accept any know how for any of its competitors. Just as an example, Yamaha uses Magneti Marelli for engine management system for its M1. Honda decided to create its own engine management system for its MotoGp bikes. Its officials went on record to say that they would rather build their own system from scratch then buy something from a supplier who supplies such systems to other Moto Gp competitors.

There is also the story of Mike Hailwood, his six cylinder Honda RC 174 and the dressing down that he received from Soichiro Honda, but that is for another day.

^Ah! Interesting, I thought the intruder was one such platform shared product between Suzuki and Kawasaki.

That probably answers all the questions (and adds a few new questions in the mind)