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japanese restriction / whats that got to do with us

Discussion in 'General Motorcycling Discussion' started by Tomcatalex, Jun 25, 2008.

  1. Japanese laws on power and speed restriction:

    Prior to 1993 the maximum horsepower were the following:
    250cc class: 45hp
    400cc class: 59 hp
    750cc class: 77 hp
    over 750cc: not allowed

    The new limits for the models built in 1993 and after, were:
    250cc class: 40hp
    400cc class: 53 hp
    750cc class: 77 hp
    over 750cc: allowed, but restricted to 100 hp.

    All motorcycles for the Japanese home market is restricted to 112mph. Bikes with more powerful engines and unrestricted topspeeds are made for export only. However, a Japanese person is allowed to import an unrestricted bike from another country for private use.

    What about us importing japanese bikes, are they restricted? and my bike is a 1992 built 1993 model (end of 1992) would it be full power. And a funny thing my bike has 45hp at 14500rpm but redlines at 16500, so what happens after its reached its peak hp, why does it have to rev beyond that mark?
  2. Actually all vehicles are restricted to a 180kph maximum, even cars. Though I believe 80kph is the maximum speed limit in Japan anyway.

    Your bike most likely would have been 45hp when new. Like any 250 though I highly doubt it'd be producing anywhere near that figure now simply because of age so whether a bike was restricted or not is really of little importance compared with how the bike's been treated over the past 15 years.

    As for peak power occurring before redline that's common. Power is basically just torque X rpm so although the torque peak is earlier power keeps increasing due to the increased revs. Eventually though a point is reached where the torque drops too far for revs to be able to compensate and power continues to drop. The redline is simply a figure set by the manufacturers which is considered the maximum the engine can safely rev to.

    If you're really so worried about how much power your bike has - take it to a dyno and find out for sure.
  3. If you privately import a 2nd-hand Japanese bike then you get a second-hand Japanese bike.

    As jd said in the other thread, a lot of the "restricted power" bikes like the CBR250RR complied with the rules by total re-tuning of the engine, not just a screw in the throttle-stop.

    Time and space collapse in on themselves and a singularity forms inside the engine crankshaft.

    ... OR, the power that the engine makes begins to decrease (often rapidly).

    The 'overrun' is good to have because:
    * Sometimes a lower gear will still be pulling harder than the next gear, even though the engine's power is rapidly decreasing beyond peak-power RPM. (Only way to check is to plot the power and torque curves in Excel, gear for gear)

    * Having a bit of "overshoot" is good, because in a racing environment it would be better to rev past peak power for a moment, make one second of less-than-peak-power, then brake into a turn and accelerate out of a turn... than reach peak power, change gears (half a second of no power), accelerate for an instant, then change down gears again (another half second of no power)....
  4. And often with a significant improvement in the amount/availability of torque - so can actually be a good thing in the real world (other than the paper world of peak figures).
    Same thing happened with a lot of their cars. Something like a GTR Skyline isn't fast because you can modify it to produce stupid amounts of hp (in fact that can actually make it slower). It's fast because the Japanese had hp limits on cars too so they designed it to produce plenty of torque at almost any rpm.
  5. My missus has a 1999 Suzuki Across that would appear to be even more restricted than yours. It builds power until about 12-13krpm, and the rest, all the way up to the 18k redline, is flat overrev with no additional power.

    My understanding is that it's a restricted japanese import - it certainly doesn't have the top end of some other acrosses, although it's still a fun and smooth ride. If you find anything out about how to derestrict them I'd be interested to know, as she's decided she has no desire to upgrade from this bike.
  6. The GSX250F has either a black top engine (up to 91 built) or a silver top engine. Silver has a few less ponies.

    And you can keep revving when you go past peak power as 1) you're still making decent power and 2) when you change gear you'll remain in the vicinity of your peak power.

  7. JD and Spots...

    You 2 sure know what you are talking about! I am pretty mechanically minded and I dont think I could have put it in any better words.

    Tomcatalex take their explnations and advise seriously. :)
  8. What colour is it? Any particular graphic pattern? You can normally pick the bikes year & origin by the colours.

    I rekon theres not much they'd do to restrict it other than a tweak in the carbs to restrict air/fuel or having a retard on the timing which is usually vacuum controlled.

    Maybe have a poke around and see if you can get replacement carb or any vacuum ancilliaries from a wrecked Aus model (which you can pick by the colour as mentioned above).


    Disclaimer: I might be talking out my arse. Results may vary.
  9. May have simply been restricted by changing the CDI - I've seen aftermarket CDIs on fleabay claiming to de-restrict the whole series of GJ7 Suzuki engines. Of course there may be more to it than just altered ignition timing.
  10. mine is metalic wine red, with sticker on the side that looks as if its been scraped on the gravel
  11. Cheng's is the standard teal green.
  12. whats the max power of the new kawasaki ninja250 is it 40hp?
  13. Simple answer to redline being beyond peak power is that if the power delivery keeps going up in the same manner and hits the limiter you don't get a feel for when to change gear.

    Having it drop off or plateu is a good shifting cue.
  14. 31.5hp in the US and Canada.
    29.6hp in Europe.

    So I guess it's 31.5hp
    Although other reviews state 33hp.
    Who really cares.

  15. Yeh i hear 36 ps but its a 250.. so.. yeah... you could walk if you wanted to go faster?
  16. you gotta be able to get one first.
  17. 40hp? Far short of that. The old one had about 35hp and the new one has 31.5hp, with 25hp at the wheel. The new Ninja 250r looks real fast, but is engineered for economy and ease of use.

    If you want more, you'd need a 4 cylinder.
  18. It wasnt that long ago we just whacked Holley carbs on things to get more ponies :LOL:
  19. When you say upgrade Loz, upgrade from an Across or upgrade from *that* Across? My reason for asking is that the 2nd gen (around '95) were lighter and had more power than the 3rd gen ('97 on) I have read (various web resources). We're not talking about big changes, 7kg less with 5hp more from memory, so it's probaby not worth going through the bike change over process.

    I still look back fondly on my '95 Across, the motor and gearbox was a gem. It really surpassed my expectations of a I4 250. If they had used that engine in a slightly more sporty frame I think they would have had a brilliant 250.