Categories: Features
31 | Updated 03

Where’s the Missing Horsepower?

Ask MO Anything: Why don’t the U.S.-spec literbikes make as much as the Euro ones?

By John Burns

Dear MOby,

After reading your Superbike Shootout (Parts One, Two and Three) over the last couple of weeks, I’ve decided the GSX-R1000 is for me, mostly because I really like the blue paint but also because my dealer made me a deal. 162 horsepower will probably be enough, but what if I want more later? On your dyno chart, the hp curve stops climbing at 11,000. What do I have to do to make it keep climbing to 14k like it’s supposed to do? I don’t like loud pipes.

Fast and Curious


Dear Curious,

The GSX-R1000 and the other Japanese literbikes are all afflicted by tuning strategies that limit top-end power so that they meet the EPA’s noise-emissions regulations. Both Don Guhl of Guhl Performance and the guys at Attack Performance agree that on the GSX-R, it’s just ECU tuning of the intake system that causes the bike to suffer premature emasculation.

“Power makes noise,” says Don Guhl. “The answer is bigger mufflers or less power, and the mufflers are about as big as they can get. All of the new 1000cc supersport bikes are throttle-by-wire, which has lots of very good capabilities, but they are also used by the motorcycle companies to control noise (power). As the revs/power/noise go up, they start to close the throttles to reduce noise and the power goes along with it. That’s why all of the new bikes’ power drop off in the higher revs. Thank goodness for  aftermarket ECU flashing!”

Telling the Suzuki’s and Honda’s throttles to stop strangling them at around 11,000 rpm, or the Kawi’s and Yamaha’s around 12,000, should let them make just as much power as the Aprilia and BMW up top. Not that you need it very often, but…

Jozef Tomasovich at Attack Performance agrees: “The RbW throttle closes as much as 35% at high rpm. When you flash those ECUs (about $600 for a flash and dyno tune), they pick up incredible hp. For instance your GSX-R made 160 hp. After it’s flashed and the RbW throttle restrictions are removed, it makes about 180 hp.”

And that’s with the GSX-R’s stock exhaust pipe and catalyzer in place, meaning you’re still green and only louder on rare occasions. Similar results apply to ZX-10Rs and Yamaha R1s. Those results seem in line with what our friends at Motorcycle News in England found when they strapped the same stock bikes to their dyno: The Suzuki spun up to 184 hp at 13,000 rpm, and the Honda CBR1000RR made 179 at 12,500 rpm.  

Doing this in California, anyway, means your bike is for closed-course operation only from now on. At this point, some might see the logic of throwing on an exhaust and high-flow air filter. Now you’re bumping up against 190 hp or more.

We didn’t really notice any power limitations when riding the superbikes on the street, where there’s very little need to rev these bikes past 10,000 rpm or so, but it became apparent on the dyno and on Auto Club Speedway’s banking. We hate to be gluttons, but more is more.

Send your moto-related questions to If we can’t answer them, we’ll at least make you feel temporarily better by thinking you’re talking to somebody who knows what they’re talking about, even if we don’t. It’s the thought that counts.

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