Comments by "EarthSurferUSA" (@EarthSurferUSA) on "The Only Video You'll Ever Need to Watch to Know how 4 Stroke and 2 Stroke Engines Work and Differ" video.

Here is another way the 2-stroke and 4-stroke differ, at least with Motocross bikes: When people with some free enterprise in their hands created the 2-stroke engine for Motocross bikes, say starting in the early 60's I believe, the cost of a dirt bike went down, (and I bought 3 of them as a kid making $1.00/hr at my Dad's store at the age of 10-16, in 1974-1980). But when a dictatorship like the EPA forces the 4-stroke engine on the MX industry, the price almost triples again, (the first time is a similar story of intervention of free enterprise.), and not many people are affording them anymore. The bike I bought for $800.00 as a kid, can not be afforded as a kid today at 10 grand. There is another difference between the 4-stroke and the 2-stroke for MX, and it is the same difference between communism and liberty.
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Ohhh, I love correcting YT vids about things I know a lot about. Let's see what cha got! Ohhh, I have a list. But I must say, you did a pretty good job overall, and I even learned something, that will be in the list. 1) I am not sure, and this is picking hairs, but I bet the 4-stroke intake valve says open a bit longer than BDC to take advantage of a bit more cylinder filling with the intake velocity. 2) Only the red environmentalist have an issue with some of the charge of a 2-stroke going out of the exhaust, and they have their own irrational motives for pushing it as a problem. I can not take their arguments as a issue in reality. They want us poor. They are communists, anti free market communists, but they love to steel our free enterprise to fund themselves. They don't deserve any recognition. 3) There are actually 5 phases, mostly overlapping, in the cycle of a 2-stroke: compression, combustion, blow down, scavenging/transfer and intake,---I think. :) 4) I think Motocross is throwing out the "2-stroke makes twice the power of a 4-stroke per displacement. The modern 450cc MX 4-stroke is making about 65hp and the old monster CR500 2-stroke made about 60hp. Now that is for MX, and the engine power delivery has to be controllable. The EPA got lucky, (forced the expensive 4-stroke on the MX industry, called a dictatorship), because the pulse of a 4-stroke does hook up better to the ground, as proven now. But even for a high rpm application like drag racing, I have a hard time believing a 450cc 2-stroke can make 130hp naturally aspirated, (of course for a 2-stroke) on gas. 5) Reed valves do still flow a bit after BDC do to intake velocity, which is why I assume the intake valve of a 4-stroke may stay open a tinge longer. 6) I have seen HP 2-stroke engines run a gas/oil mix as rich as 10:1. RC boat racers with 30cc 20,000rpm engines run that thick quite often. If the jetting is good, the combustion is hot enough and the oil burns. I think it is overkill, but they run it. A company named Quick Draw, making their own engines for TC boat racing insists on a mix that thick. But I think it is because the steel honed cylinder liner eats up the ring quick until the hone smooths out a bit. Other guys are running 10:1 with plated cylinders. Some even run Colman fuel mixed with oil still, which I really don't get at all, but they run, and lubricity is fantastic from a tear down I did for a customer. 7) Oil injection is no more modern than me mixing for a new MX bike,---and sorry, but nothing can be more reliable. Race bikes in MX still do not use oil injections, sans KTM now with transfer port fuel injection with a new oil system---that can break down. I replace a piston/ring once a year, about $150.00, for about 5 years for the plating to wear through. 5 years on a MX 4-stroke will cost a lot more. 8) 17:34 Man, that is some fast oil consumption. Still,---it ran the whole time huh. Must be jetted well. :) 9) You bring up emissions again,---and I will rationally ignore it. I will not agree with communism, ever. We need to tell them to get bent. 10) 21:37 graphic. That compression ratio/drawing is actually wrong. The 125cc is the swept volume of the piston only, not the head volume, (which you have at 12.5cc). So the proper math is (125 + 12.5)/12.5 = 11:1 I have seen professional engine tuners get that wrong, but I scratched it off as old age. 11) 2-stroke compression is also effected by the exhaust pipe effects. The returning sound wave actually bounces off the diversion cone (a point just past half it's length.), and not the earlier infuser cone, (that one is for a vacuum, to actually suck a negative pressure into the cylinder to aid scavenging, measure up to -7psi in some old writes. This happens as soon as the blow down phase actually ended, and kept sucking for a bit. The cylinder must blow down the pressure after the ex port opens to zero before the transfers open, or the pressure will force a burning charge down the transfers, (you will see black deposit on the transfer walls, and could indicate a pipe problem,--but my 88 CR250 still ran great.). 12) I am a 2-stroke guy, (for a living), and I learned about variable valve timing for some 4-stroke engines. Interesting, but I bet the cost can be blamed on the EPA force, (which communism in china does not have to deal with. The planet stops there i guess.). 13 That is the first Yamaha ex power valve design, the rotary design, (and it was a smooth transition). The guillotine style is a more modern design, and has linear movement. 14) The ex power valve is not related to the return sound wave as you suggested. The sound wave is pretty much a fixed speed, (goes a bit faster in a hot pipe), and that means it is related to piston speed. The reverse wave is also only pretty effective, (super charging effect) for a range of a few thousand rpm's, (or the fresh fuel would not leak out the exhaust.) The valve does not seal very well, if at all for added compression or down stroke sealing for power, but I would bet there is some overlapping factor there. The higher port lets exhaust gasses out faster for the higher rpm piston speed, (as with higher piston speeds, the ports are open for less time), and some people don't agree, but I think compression should be adjusted accordingly with a mod like raising the ex port, within limits of the application. To ne quite frank, I am not totally sure about the effects of a lower or higher ex port, but a lower port is used for lower rpm applications for more low end and mid range power, and a higher port leads to more top end power. But the pipe effects of the returning sound wave,---can not cover both. 15) I don't know if direct fuel injection will become the EPA forced norm. I know it has been done, but for example, KTM choose to inject it in the transfer port walls. I know it does not have pressure or heat to deal with there, and I am sure those were factors in their decision. That looks like a lot of stuff that I corrected for you and your viewers, but you covered a lot of stuff, and I think you do a pretty good vid. You are good at teaching, but we must know the details or we might as well figure it out for ourselves. The next one should be better. :) Doug in Michigan
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