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A rather common question coming to our Technical Department and to retailers in general is about these two parameters. Misleading advertisement has pushed, over the years, the less knowledgeable racer to compare engines, and the two-stroke one in particular, right on these two parameters only. Often we see in the ABC micro-motors figures like 6hp at 24000 RPM. While the figure is impressive in itself, it does not mean much without the much more important and basic data pertaining to the specific use and application in which the engine is going to operate. Interesting is the fact that before reaching the figure stated by the manufacturer, in the best case scenario, the engine will produce only 10-15% of that power at a level where the model is used 50-70% of the time.
Result: often the model maker is left wondering if that engine has any power at all or if the claim of the manufacturer is just a wishful dream.
The fact: in the cases where the claim is legitimate the effort required in balancing the various components in the racing models to achieve such values is beyond the scope of the average model racer.
When such values are achieved, the engine will perform within very critical limits (read: narrow power band). Before and after such limits the performance will drop significantly to often unacceptable levels for the average application. The engines in our line, in their various configurations, span widely in power output within the same displacement. Commonly we want to have the most power (please read hp) at the highest rpm but we soon find out that this is not necessary so to achieve the best result in some specific applications. We have often used this example to explain these concept in brief none-too-technical terms. Let us consider the best engineered 125 cc engine for a grand prix motorbike and the best one for a world class off-road bike. The grand prix bike will employee an engine producing some 50 hp at 13500+ rpm. This engine inserted in the frame of the dirt bike will do very little for the need of off-road racing. To the extreme example a similar displacement engine designed for "trial" will develop a meager 15-18+ hp but now such power is distributed over an rpm range that allows the biker to move from 2 Mph and yet in a second open the throttle for an acceleration up to 50 Mph. What is the difference? Is the "trial" bike engine less powerful? The answer lies clearly in the specific application and use. The grand prix engine requires the ability to reach a certain high rpm range that will be maintained with little variations during the race, fast turns and straight a ways will require a lot of gear changing and the consequent rpm range but not nearly as many as in a off-road competition where acceleration and deceleration phases are allmoast a constant. The trial bike need to be able to have the engine revving at almost idle speed and yet have enough horse power to propel bike and biker in the short straight away.
This very broad concept explained in somewhat simplistic terms introduces other important data: power band.
The power band indicates the range of rpm at which the engine produces a certain horse power. Ideally, we would like to have an engine that produces the maximum hp from 0.1 to 20000 rpm. Does that remind you of something? How about an electric engine!. The problem for us is that we are dealing with internal combustion engines and 2 stroke in particular.
We realize that this theoretical discussion could go on for much longer involving even more factors and so let us address some specific applications using some of our best known engine designs. Marine engine prospective owners seem to be the ones with the most questions on the issue, so, here we will use the marine engines for our example. Some of the basic elements to take in consideration when choosing an engine for a marine hull are: 1- type of hull 2- size of hull 3- weight of the hull 4- number of drives 5- type of drives 6- type of propeller 7- size of propeller 8- pitch of propeller It would appear that we should consider first the type of race/application we intend to participate in with our boat but, intentionally, we have left this consideration out for the time being as it will be discussed later in relation to engine design and quality, not to mention "pocket-book". Type of hull and size will influence the power band required as monohull will tend to be used in more twisting circuits as the "M" ones and tunnel hull instead will be used more in oval racing. A circuit full of turns will prefer an engine with a power band that allows for power at mid to low speeds and for fast accelerations out of the turn. Cat/tunnels hulls will not be used likely in "M" courses and they will enjoy more the fast turns of the oval racing with the longer straight away at full speed and on plane. The typical "M" course used in the 30+ minutes enduro in Europe is the best ground for a "Competizione" or a "Casa" since such engines have a power band that allows the engine to accelerate from a relatively slow rpm to full throttle. The torque produced by this type of engines is best suited for propellers designed to work fully submerged of semi-subsurface. These types of races usually require fully muffled tuned-pipes that also prefer a broader power band. Hydroplanes, tunnel hulls, are primarily used in oval racing riggers, this are boats that find their best balance riding on a cushion of air. This type of ride is very critical to maintain and as a matter of fact in real life scale this type of hull implements an array of additional airplane type controls to aid in keeping the best asset of the hull. There are not large variations in throttle settings in this type of racing with fast and faster being the main "gears". SP and VHP versions of our engines are the choice for such hulls. The HP in these engines comes into a power band that "sits" very high in the usable RPM range. Elevating the power band makes it also narrower and therefore if we gain in ultimate speed we do lose in "elasticity" or amplitude of usable power band. Given that in this type of racing the variation in speed is not too evident here, we can choose the engine that will produce the highest RPM. These types of hulls prefer fully ventilated propellers (supercavitating props) that allow also the engine to reach the highest rpm range without the push required to keep the hull out of the water. These propellers can reach considerable pitch sizes otherwise difficult to implement in a fully submerged prop configuration.
Can we use a Competizione in a cat and a VHP in a Monohull?
We can improve the RPM range or the RPM limit in either type of engine by selecting a different design of pipe. How much can we "modify" the power curve of such engines? 50% is not an exaggerated value. Yes!, just a tuned pipe can modify the ultimate power produced by any of these engine. It has long been a tradition for major Motorcycle manufacturers like Honda or Yamaha to show at the testing sites with a couple of official motorbikes and dozens of pipes in various designs to modify the engine response in accordance to the condition and type of race course. It will do us little good to have in our out-rigger hull a "Casa" engine revving at some 14000+ rpm and some 200 gr. of extra weight when we can use a much lighter VHP speeding at over 16000 rpm. Likewise it will take much tweaking and refinement in the set-up to achieve good results using a high revving VHP mounted into a mono hull that will sink into the turn at some 20 Mph to be than brought up back into plane and back to 60+ Mph till the next turn arrives. We assume that this indicates that to rely on just an arid HP-RPM value can be grossly misleading and eventually turn an expensive "combination" into a disappointing and costly racing set-up.
Did we say yet how many HP and at which RPM?
Clearly, you have now an idea that the issue is not as "clear-cut" as one would expect. So, why not say that a Mathe SP will develop 8 HP at 15000 RPM? The type of pipe used, the octane of the fuel, the hull design, the propeller design and size, the type and design of the tuned-pipe, will directly affect such results. We have seen in the past engines like the SP 35 being literally "killed" simply because the wrong exhaust pipe was used or a VHP idling in the lake because of a propeller to small in diameter or pitch in relation to the hull displacement. Do other manufacturers show such figures? Yes! Some of them are very impressive too. Who is at the top of the gas racing classes (35cc UIM/NAMBA/FIM etc.) in world championships around the world in the last few Years? MATHE! Who has the current gas world speed record with a stock engine (35cc)? MATHE! ... and still, we will state that all claims of specific HP and RPM data on our engines are the sole and non-authorized claim of some retailers of our engines. Did you ever ask Honda, Kawasaki, Ducati, or Ford or Ferrari what is the HP and RPM of their Indy or F1 racing engines? Data is purely indicative even for the engines they sell to private parties after the official racing season is over. For all the above reasons and with the last ones as our own pride in producing a true racing engine we feel that it would be more a commercially motivated "come-along" statement right because of the many variables involved in achieving such values.
Do you still want to know? A 35 MATHE Marine in the broadest power band and least critical set-up will produce more than 6hp (and up from there) at 11000 RPM (and up from there). Are we out-powered? Please refer to the results stated above. Will you ever know exactly how many HP and RPM? We will tell you what your specific engine can do, and some more but we will wait to see you at the race with your MATHE "in The Winning Style".
Luigi G. Girotto - Tech.Serv.Dept.
Eli-Ka Technologies/MATHE U.S.A.
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