Which Valves Produce More Horsepower/Torque

Hello, OK the short answer is Yes and No. When comparing the same size two stroke VS four stroke the the two stroke has more horse power. That's only part of the whole truth. The rest of the story is torque. A four stroke has more torque and is able to turn a larger prop. As far as I know the glow plug makes little difference on the exhaust performance.

What should be considered is application. If I were going to build a very fast pylon plane that had to accelerate quickly I would choose a two stroke If I were to build a aerobatic plane I would choose a four stroke for raw pulling power.

Acceleration and power (torque) are the main differences.

One thing to remember if your old enough, Old muscle cars (heavy) used big block engines (torque) and newer light weight cars rely on Horse Power.

Horse power = time to do the job

Torque = power to do the job

Hope this helps, personally I prefer four strokes in all my planes.

Hmmm. It's a long time since I flew model aeroplanes and I won't take exception to your choice of engines for different applications, nor the claim that 2 strokes generally have more power than 4 strokes - but I get real anxious when terms like power and torque are misused.

Power is how quickly you can get a job done, and Torque is about the level of "force" that is used to do the job. In simple terms - a high torque-low revs engine gives the same output as a low torque-high revs engine when an appropriate gearbox is fitted. At optimum revs the highest power engine will always win.

Of course in practice an engine is not always operated at max power and a gear box is probably not fitted. The relative advantage of one engine over the other then derives from two causes.

First is that slow speed propellers are probably more efficient than fast ones - and certainly this is the case when the tip starts to get supersonic,

Second is that low torque high speed motors are often highly tuned and peaky so that the performance at less than max power revs drops off quite quickly. An equivalent statement is to say that the torque curve for these is not flat.

Just a thought: If the cam operates at crankshaft speed, ie. cam is part of the crankshaft, the engine is a two-stroke.

My 0.60 ci was a ported design.

QL

Twaddle.....

Tuning the intake and exhaust might be able to bring the peak power to a speed that more closely matches the prop requirements.

If you want to try an experiment, try making a small dynomometer to load the engines. A small wheel driven generator that was used on bicycles could be driven by the RC engine, and voltage monitored. I believe that you would have to load the generator by having it power a high powered light, like a vehicle headlight.

If you are a tinkerer, you could replace the glow plug with an ignition system. MSD has some systems for converting Briggs and Stratton engines to electronic ignition. Look at the components on line, and then use automotive components instead. An older Chrysler distributer pick up ( 1972-80 ) can be triggered by a passing screw head. Then wire in the same year control module. If you need to you can bend the curved section of the pick up to clear a larger flywheel if needed. Using slots on the pick up mounting bracket will allow timing changes. There are 10MM threaded spark plugs available so rethreading the cylinder head is not that big a problem. I have heard that an ignition system improves these RC motors by a good amount. What else are you going to do with those engines?

A constant source of ignition is a great idea. I know when I remove my glow starter the RPM's drop quite a bit. One consideration would be to look into a gas powered engine. I know some use electronic ignition.

I never really checked to see if running WOT and leaving the glow starter makes any difference. Maybe I will check it out next week.

Also a tuned pipe is a good idea on two strokes. I know they can make a huge difference. I am not sure one can be had for a four stroke. It would be interesting to find out though.

Great post Bob!

Please don't make my head swell any more than it is.

Tuning intake and exhaust dimensions are useful on four strokes as well. Think of the mid sixties Chrysler products with 2x4 intake manifolds that were wider than the valve covers on the 413s and 426 wedges. And there are headers for everything.

If its a modern engine, in otherwise good condition I would be surprised if you could improve its power output.

Now someone who "Knows" how to do it (does not need to ask on CR4!!), would just "do it!"

If the engine is old, it may have some higher value to a collector.....unmodified of course......

Tuning of engines, especially tiny ones, is an art that comes with many years of painstaking knowledge and research.....