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I recently wrote a blog post going into the differences between two-stroke and four-stroke engines, and realized after the fact that there was one area of the discussion I wished to dive into deeper.
If you get a bunch of motorheads around a table debating two-strokes vs. four-strokes, someone advocating for two-stroke motorcycles will eventually say something like, “well, two-stroke motorcycles produce twice the power of four-strokes.”
Even in my own blog post from just a couple weeks ago, I was guilty of being mathematically inaccurate when I said that two-stroke motorcycles “can essentially produce twice as much power as four-strokes of the same size.”
It is true that it all comes down to the power/firing sequence, and that two-strokes are producing more, harder hitting power on every revolution.
However, to say a two-stroke motorcycle is producing “twice” as much power (with power being defined as horsepower) as its four-stroke brethren is just wrong. More power? Yes. Twice as much power? No.
How do I know this? Well I did two comparisons. First, I compared, early 70s two-strokes to four-strokes of approximately twice the size. The result? Yes, the two-strokes produced a surprising amount of power for their relatively small displacement, but they didn’t equal the four-strokes of greater size.
Next, I compared the modern KTM two-strokes and four-strokes of identical size. This was more of an apples-to-apples comparison, with literally the only difference between the two bikes being the engine power sequence. What did I find? Same deal. The two-strokes definitely out produced the four-strokes power wise, but it never hit “twice” the amount of horsepower anywhere in the powerband.
Look, if raw power is your only consideration, you will get more out of a two-stroke motorcycle. I would just advise against going around telling people your bike is twice as powerful as theirs. Dyno tests and specification guides all over the web will state otherwise and numbers just don’t lie. I know, I play with spreadsheets all day for a living.
Didn’t find what you needed in this particular post? Check out the HappyWrench Motorcycle Repair Link Database. It is a one-stop shop for all your DIY motorcycle repair information needs.
Also, forgive any typos or grammatical errors a I wrote this blog post from my phone.