.... doc, that's way too factual/deep.
Actually Cliché it's not - it's way too myopic as the good Dr. know's full well - he can do much better than that.
When the #1 State of the Art engine - with 54 hp from a 125cc cylinder - had to go through the effort and complexity of sticking the rotary valve on the back on the engine to gain a couple of hp (due to improved intake run into a crank spinning in the same direction as the intake charge) I question how much further they could've gone.
This solution wouldn't fit on a V4....
Power is increased by improving torque or increasing revs.
On the torque side: aforementioned engine made circa 16.5bar BMEP (30odd N.m at 12k)....that's gonna be hard to get a big increase on. A bit more CFD analysis might yield some gains,...wasn't used in that engine's developement
On the revs side: the whole circumference of the cylinder is chock full of ports. There's very little scope to increase time.area. No miracle revs
So where are the increases going to come from?
The main headscratchers before the 2Ts died was part-throttle issues. Deto.
'Power is increased by improving torque or increasing revs'
Why fixate on the limitations of a particular block? That would be akin to thinking in terms of the restrictive function of a cylinder head as opposed to the range of possibilities of optimal scavenging. I don’t understand why you are using such a rigid example of hardware? - a configuration/solution that has nothing whatsoever to do with the future evolution of the V4 500 two stroke. As Stan Stephen’s used to say, ‘think out of the crate for Christ’s sake’. Now instead, BJ.C some genuine insight from the real two stroke gurus that expressed this belief in the continuing potential of the 500s. These true authorities on alternative scavenging methods, in particular their ideas on friction reduction, non-isentropic stimulation, transfer port timings in relation to pulse waves offer fascinating insight. Your man the late Warren Willing was one of them. These guys weren’t simply dab hands with a needle and a jet, Moriwaki was an authority on gas dynamics, fluid mechanics,thermodynamics and combustion and how to harness related developmental strategies so as to provide the required performance characteristics of power or torque or fuel consumption.
As you know ‘No’, the target is not simply raising torque and BHP but with a two stroke how you make and introduce the power across the range – perhaps eliminating those fabled wafer thin power bands. Part throttle issues, indeed – to me heat was another main adversary of two-stroke engines. Stretching the compression ratio to give say a 10% power increase would possibly only yield a 3% return at the most - the rest will be squandered energy and pumping losses. This is why, at lower engine speeds when the cylinder is not be completely filled with fuel/air mixture the power may increase by 5-6% because there is not so much of this heat loss. As I understood it, this is actually the rationale for raising the compression ratio, not to increase maximum power but to pick up mid-range power and therefore possibly widen the power band. Example being, a variable exhaust port that changes height to suit the rpm the motor is operating at, offers increased drive out of corners – think Roberts' TZ500 and the YPVS system that subsequently appeared on the road. Point being, and the point that Bartol was making, historically seemingly insurmountable barriers to development have been surmounted by innovation – and in a prototype series there was huge continuing potential for a racing two stroke 500cc formula. That will to develop disappeared along with the market for two strokes. Interestingly though there is significant impetus throughout global R&D to develop cleaner two stroke technology.
In spite of its shortcomings, the two-stroke never died remember. Instead, improved designs, electronic fuel injection and automatic oil-metering systems kept it practical for chainsaws, outboard motors and snowmobiles. Skidoo pride themselves on their 2-stroke snow mobile specifications and marketing bumf features direct injection, low oil consumption lightweight internals – (I guess having no valves is what they are referring to in the main), 200 Horsepower Per litre, economy, simplicity of less moving parts etc etc. A snow mobile is not a 500cc prototype racing motorcycle – granted, but consumption in particular is significant and I detect, with the technology of conventional four-stroke engines quite mature, there is renewed interest in taming the two-stroke to compete with diesels, hybrids and electrics as part of the solution to meeting future mileage standards. If that then gathers momentum in the marketplace through cleaner more efficient power plants, then the desire to populate a grid full of strokers will return – albeit minus the blue smoke.
I know that GM are working on a opposed-piston, opposed-cylinder project and an electrically assisted turbocharger. Such a concept is admittedly synonymous military, aircraft, marine and industrial engines – all bulky and heavy, but a similar design was employed for the Beetle which was renowned for its compact size and such an engine would have twice the power density. I realise that this is a departure from racing 500cc motorcycles, but I’m attempting to at least encourage you to think laterally and realise that there are so many possibilities in the commercial continuation of two stroke technologies and where these exist race departments of large corporations such as Honda will flex their muscles and start throwing their weight around in the MSMA to institute change.
Interestingly, you mention Computational Fluid Dynamics which in theory resolves the three-dimensional flow behavior inside engine cylinders. Interestingly if we use that unsteady gas-dynamic calculation to control the flow at the entry and exit boundaries of the system then is no logical reason why this same theoretical approach should not be employed for the design of the most complex of tuned 2 stroke exhaust systems – in particular relation to the pressures at the exhaust port in part governing the charging efficiencies over one cycle. Continual development of race exhaust designs can recover a significant percentage of charging inefficiency in addition to raising post transmission bmep levels. In addition to this, and still on the subject of exhaust - I’m sure that you are aware of resonance. The is an exhaust pulse prior to the appearance of the actual blowdown pulse at the release point is the second return of the plugging pulse from the previous cycle which bounces off the rapidly closing exhaust port acting as an increasingly closed end. This precursor to blowdown is a large pulse but it too is echoes off the closed ended exhaust pipe at the port in a superposition manner so it effectively strengthens and broadens the ensuing exhaust pulse through its latency. I remember Hamish Jameison talking about the nascent research into this (albeit in the late 90s) and explaining the effective harnessing of this second-order phenomenon is essential and is yet another vital factor in the design of high specific output engines and the associated power gains to be made. Further, I think you’ll agree, long exhaust port periods – trapping and charging – optimal breathing through exhaust tuning is particularly beneficial to high speed racing two stroke engines.
Discharge coefficiants aside, why dismiss the value of CFD? as a cognate discipline also offers substantial insight into squish velocity and squished kinetic energy values, burning rates and constant volume combustion and how to tailor these effects to the best possible advantage for any particular two-stroke engine. It also greatly assists the designer in comprehending the effect on performance characteristics which are due to alterations of the physical geometry of the engine and its ducting or its scavenging.
