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From: Torchy the Fiery Fast RC Turtl, USA
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ORIGINAL: BigGrump
I believe all standard principles of hot rodding apply here. First the carb. Anytime you want more HP at high rpm's, carb area is raised. In case of Harley, a bigger bore on carb. On cars, 4bbl carbs and multiple carbs.
Timing and flow, I would not know how to change it in a 2 stroke, but on both your harley and cars, you change valve size, air flow around the valves and valve timing and duration with cam change.
Never does a hot rodder change stroke by 2mm in order to shift torque and hp to higher rpm's.
Last, longer rods do not change piston speed, which is the average speed in feet/second. What the longer rod does do is change the accelleration rate of the piston at the top and bottom of the stroke where the piston is changing from static to moving. Longer while making it easier on the piston to make the change in direction, average ft/second does not change.
Dennis
No disagreement here on most of your points. Power increase is the sum of all the engine's parts working in unison and all of them matched to maximize that power increase. Change one thing, and to maximize the potential of that one change, you really need to change everything else to match it. For example, if you slap on the biggest baddest carb possible on an engine, you might get some power increase, but unless you upgrade the rest of the engine, that carb will never see its full potential. So, if you put a 1050cfm mega-4bbl carb on a 3cylinder, that is utterly useless because that carb is meant to feed a massive V8. The same principle applies to our tiny 20-35cc 2stroke gassers.
So, lets say you have the biggest baddest gasser, for example, lets say there is a 35cc professionally modded QUALITY engine for ground RCs with the best porting possible, maybe a TS bottom end. Run that engine with a box exhaust and you are only putting a ball and chain onto its feet. Put a good pipe matched to its timing profile and that monster comes to life. Or lets say you put a tiny nitro engine carb on it (extreme example, but I hope you get the point). That will starve the engine of air!
Now, to tie this all back to what we are talking about, modded larger displacement engines, let's look at two identical engines: they have the same pipe chosen, they have the same timing profiles, carbs, etc, etc. To also control out displacement as a factor, lets say both engines displace the very same amount of CC. The only difference is one has a larger bore with shorter stroke and the other has a smaller bore with longer stroke but both still displace the same amount of CC. Due to the frictional forces involved, the shorter stroke engine will out-rev the longer stroke engine. Sure, a larger bore will present more area for frictional forces to exert itself on, but when you calculate the work-energy done to overcome frictional forces, the longer stroke engine has to do significantly more at higher RPMs.
Longer stroke does increase linear piston acceleration for a given RPM. But since acceleration is a mathematical derivative of velocity (speaking calculus-wise here), linear piston velocity also increased for that same RPM. And when put into work-energy calculation, and also considering acceleration is a squared function (which force has and force is a factor of work calculation as well as kinetic energy calculation), you will see that higher linear piston speeds will result in more friction, as a matter of fact, exponentially more friction.
I hope this is not too complicated; understanding of high school physics should be enough to understand what I am trying to say in my last paragraph.
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All Forums >> RC Cars, Buggies, Trucks, Tanks and more >> RC Giant Scale Cars >> RE: GP29 race ported versus none ported 36mm kit 
RE: GP29 race ported versus none ported 36mm kit - 
I'm lazy I guess.)
