For all intents and purposes, this bike started its life as a run of the mill Honda CB550. A stock CB550, while beautiful in its original form, is capable of a stock 50 bhp at 8,500 rpm. In a day-to-day application these numbers, when combined with stock carburetion and exhaust, amount to a modest performer of a bike suitable for daily commuting and short highway jaunts. Now, take a look at the cam profile in these photos of Robb’s motor. If you’re new to the inner workings of reciprocating engines, look hard. See that cam profile with its long duration, tall lift, and steep flank? This beefy cam isn’t stock, it’s part of a Stage 2 kit from Action Fours, an old school performance mods company out of California. When all is said and done, this Stage 2 kit transforms a stock CB550 into a 590cc machine capable of 80bhp, suitable for prolonged fun on the road and occasional track time.
Before the days of electronic rev limiting, companies like Action Fours used thoughtfully designed racing valve springs that effectively float to protect your engine from over-revving, in this case, at 13.5k RPM versus the stock 8.5k RPM. Heavy duty Japanese-made piston heads and rings were also included in their kits, bulked up to match the stresses associated with Stage 2 type performance mods. That said, it’s never enough to aimlessly “go big” with everything when modifying your engine. For example, there’s no sense in running a hot cam without high compression to match. Every modification that you make to your engine presents a new set of variables that need to be thoughtfully balanced, or “tuned”, to make for a fast and reliable motorcycle.
For those of you that know Robb, one of our lead mechanics, you’re probably not surprised to miss a glamour shot of a period-correct cafe racer in this blog post. For Robb, it’s just not like that – mechanical perfection is priority one, and then there’s everything else. Form follows function, or in his words “a bike that runs well looks good.” For the sake of discussion, this no-frills CB590 will likely be a well running and ridiculously fast drag bike with a short wheelbase…but don’t expect to see a polished tank anytime soon.