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...

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.

Recent Ask MOs:

What’s Up with Snatchy, Abrupt Throttles?

Why are there no Ducatis at the Isle of Man?

Why Won’t My Motorcycle Engine Rev To Redline?


  • Chris

    It’s not gluttonous, it’s just getting what I’m paying for. Shame you have to pay more in money, time, and trouble after paying so much to buy it: “I’m w/the govt., and I’m here to help.”

  • Craig Hoffman

    So how do the Euros manage to meet US regs without drastically limiting top end power?

    • Born to Ride

      Ask VW.

    • ijbrekke

      It was mentioned in another comment section that bikes sold in greater volume are held to different (more strict) noise and emissions standards in the US. Apparently, the Japanese brands sell enough that they have to worry about this, while the Italians do not. It smells fishy to me all around, but I haven’t heard any alternative answers to this problem.

      • Craig Hoffman

        FWIW, I see more newer Euro sport bikes than Japanese here where I live. Harleys outnumber the rest 10:1, easy though.

      • Stuki Moi

        I heard the same thing. From a salesman selling Big4 brands………

        Considering the numbers of S1000RRs BMW has sold in the past years, it sounds a bit, as you say, fishy.

        More likely, the Japanese, true to form, interpret the regs as conservatively as they can. While the Euros go with a looser interpretation.

        The latter being perfectly defensible, as by the time you are in the top 35% of throttle above 10000rpm on a liter bike on public roads, you are violating laws much more immediately obvious than some noise regs. (even whacking it in a low gear at 10,000, won’t give you top 35%, since traction/wheelie control will limit throttle openings….)

        So, the Euros can argue their bikes are sold as dual use street/track machines, with the street applicable portion of the rev/throttle opening space, being compliant, even if the track portion is not… Fat chance someone at Honda or Suzuki will try pulling that off, though….

        • john burns

          I think that’s close to the truth. A Honda rep told me if you stand next to the track at these events like he did, the loudest thing on the CBR is chain slap; many of the other bikes are perceptibly louder. Lots of times the US reps aren’t privy to what kind of emissions/noise strategies are going on in their bikes any more than we are, and if they are aware they’re sworn to secrecy. None of the OEMs want to talk about this stuff in the wake of VW.
          I’m sure the Honda and Suzuki people would like to say “all you have to do is reflash to get the whole horsepower enchilada!”, but of course they can’t say that either, as they’d be encouraging us to make their fully compliant bike non-compliant.
          I’ve never seen anything official that says small-batch manufacturers have to meet less restrictive rules than the big OEMs. Google up Brian Gillen MV Agusta Euro4 to read about how big a job it is to get those bikes compliant; Euro 4 is also very strict about noise.

    • Mahatma

      Not sure I understand the question,but europe is not yet under US legislation 😉

      • Born to Ride

        Was that sarcastic? Obviously the European manufactured motorcycles and cars are subject to American regulation and laws when imported. I’ll just assume you’re aware of that.

        • Mahatma

          I didn’t know that.Why are european cars and motorcycles subjected to american laws and regulations?….

          • denchung

            If they want to be allowed to sell in the American market, they have to comply with local regulations.

          • Mahatma

            ahh.Then it’s me missunderstanding again as haoppens so often 🙁 As you were gentlemen 🙂

          • Born to Ride

            Oh okay, well here’s a good example. The EPA is a federal regulatory body that mandates emissions standards for all motorcycles sold in the US. So if you want your bike to be legal here, you have to meet that standard as a minimum. California however, also has the “Ca. Air and Resources board.” They hold cars and motorcycles to a much stricter standard than the EPA requires. For example, for a bike to be compliant with CARB regulation, it must have an evaporative canister and a purge valve to contain carbon emissions from gasoline in your tank evaporating into the atmosphere. This is a relatively minuscule amount of hydrocarbon emission relative to the exhaust gasses, so some manufacturers omit the equipment of some of their bikes, presumably for cost. Those bikes are not legal for sale in California because they do not meet the stricter standards, but can be sold in all other 49 states in the US provided they meet the EPA standards.

  • Roy Bentz

    there is your missing gixxer bhp