How Oversquare Can An Engine Get And Remain Streetable?

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nicholastanguma
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How Oversquare Can An Engine Get And Remain Streetable?

Post by nicholastanguma »

I'll use a thumper as my example, since this is the engine I like and know best in all of the motorcycling world.

Way back in the day undersquare configurations were standard, torque was the name of the game, and transmissions had only three or maybe four gears. Even racing bikes were like this.

Metallurgy improved, machining tolerances improved, carburetion improved, so pistons started getting bigger in diameter while strokes started getting smaller, and transmissions started using five gears as standard. Horsepower ratings started rising above pounds feet of torque.

Now, since the 80s, ninety nine percent of thumpers are using big bore/short stroke configurations, and transmissions always have a minimum of five gears, but six is entirely common, too. Even dual sport thumpers, which need lumpy torquey bottom and mid ranges, are oversquare. And some of them have positively enormous bores in comparison to their strokes, the kind of bore/stroke numbers that decades ago were only being used by high rpm racing singles.

Just how oversquare can an engine get while still remaining streetable?

I'll use the middle-of-the-road 500cc class for this example: 97mm bore/68mm stroke, with a six speed transmission. Can this thing be tuned for a nice fat idle-to-redline power curve instead of just high rpm horsepower?
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Re: How Oversquare Can An Engine Get And Remain Streetable?

Post by af2 »

Nicholas ride a crf 450 I got one for sale that kicked my 57 year old in the ass. I even put the Rekluse clutch and throttle tamer on it so I could ride.. LOL. I think I am 30 WTF!!
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