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Comment by rsj_hn | Hacker News Reader

I wonder how much horsepower you can get out of 50cc if you max it out with all the *chargers. Sounds like a cool opportunity for regulatory arbitrage.

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Unfortunately you can’t turbocharge or supercharge a two-stroke. There’s a material amount of time during the cycle where both intake and exhaust port are open at the same time. If you use any type of forced induction it would blow the fuel/air mixture straight out the cylinder before it could be ignited. You can however use a tuned pipe to cause a pressure wave to reflect back up the pipe and compress the mixture, but that’s usually limited to a pretty narrow powerband

Ahh, so the special regs only apply to 2 strokes? I thought they were based on displacement

They're also valid for 4 strokes but generally speaking 4-strokes have lower torque at high rpm and since it's hard to get much power out of 50ccm anyways, they tend to be 2-stroke.

I remember Honda made waves with low displacement four stroke engines.

https://en.wikipedia.org/wiki/Honda_CB50 https://en.wikipedia.org/wiki/Honda_Super_Cub

I think he’s talking inherent technical limitations, not regulations. I wonder if it still applies if there was a pre-burning occurring in the middle of intake manifolds

You can have forced induction with two-strokes if you use direct injection. It ends up being pretty efficient because you can blow all the exhaust out of the cylinders and have clean air for the next cycle. You also don't need to add oil to the fuel because you don't use the crankcase to pressurize the air/fuel charge. This type of engine is really common in construction equipment and (older) big trucks, semis, buses, etc. Some were even supercharged and turbocharged.

In fact, I believe the supercharger is necessary for them to function.

https://en.wikipedia.org/wiki/Two-stroke_diesel_engine

In the times of 50cc road races you could get 10hp out of it, at maybe 17.000 rpm :) No idea how fast these cars would go with such an engine, they are not made to go 150km/h :) The way you tune a 2-stroke is by polishing the ports of the cylinder to have an almost perfect airflow. In the Netherlands this happened a lot in the sixties and seventies to ride at illegal speeds with your moped, it was considered a craft. In the eighties people just bought a replacement cylinder to go at illegal speeds.

https://en.wikipedia.org/wiki/50_cc_Grand_Prix_motorcycle_ra...

So yes, ofcourse I ended up at youtube, if only for my own curiosity :)

https://www.youtube.com/watch?v=a1KXL1vjTX4

10hp from a 50c two-stroke is easy. Road racers were getting 17+ with 70's technology. Those engines also had about a 100 rpm powerband, though. So you'd see 50cc bikes with as many as 14 gears.

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