Restrictions of the GSXR
(and how to de-restrict them)

This is a question that comes up fairly frequently on the .infoboard, and thanks to Del doing a substantial amount of research we have some definitive answers.

We'll start by getting rid of a myth concerning the restriction of the GSXR750 power outputs, that is that the Japanese Spec CDI is the same as the UK spec CDI (identical part numbers). So we can safely assume that there is no restriction there.

Bikes that were originally destined for the French market are not worth attempting to de-restrict unless you have the necessary time and parts to do the work; they are restricted with a different head, different carbs, different cdi and a restrictive exhaust. Bikes originally destined for the French market will produce no more than 104bhp (this is a law that applies even today with modern 180bhp superbikes being castrated to a mere 104bhp).

During the mid 80's there was a lot of talk, mostly from the politicians of the time, to restrict all bikes to 100bhp. The motorbike manufacturers had a "gentleman's agreement" to cap horsepower to 125bhp. We can thank Triumph for shoving it up 'em and producing the Daytona with 147bhp, this led the way for all the other manufacturers to de-restrict their bikes (fitting proper carb-tops, removing webbing from the carb-rubbers, etc.).

So what does this have to do with the GSXR750?
The Japanese restricted their bikes to a maximum of 77bhp and 110mph. Anyone who's ever ridden a Japanese specification GSXR750 will tell you how strangled it feels compared to a UK spec bike, and that it really does need some more power unleashing to get the best from it. As a lot of Japanese bikes got imported to the UK and mainland Europe during the "grey-bike" and "parallel-bike" boom of the 90's, there are a lot of them that will have never been allowed to run freely.

So take a look at the back of the clocks of your slabside GSXR. The picture below shows a UK spec clock, which has the hole in the casing but no wires leading into it. The next picture shows the back of a set of Japanese spec clocks. On this picture you can see the blue wire and the black plus white-tracer wire leading into the clocks. If you have these wires leading into your clocks simply disconnect them. Ensure you tape off the terminals on each side (not that you're ever going to need them again) to keep things tidy and to prevent the possibility of any shorting from an unfortunate earth problem or something similar.
Back of UK Spec clocks
Back of Japanese Spec clocks

Restrictions on the GSXR1100
The slabside and slingshot GSXR1100's were never officially produced for the Japanese market. Any bikes produced for the Japanese market over 750cc produced before 1993 had to be restricted to 100bhp, which does make you wonder why if 100bhp was the legal maximum, why did they restrict the 750? - Most likely because the 750 would have been the faster/better bike based on the power/weight ratio, although that answer is purely speculative.

The 1100's that were destined for the American and the Canadian marketplace received almost full power and unleashed nearly as they should be. However, Italy aside, Europe got a strangled version, restricted to the "gentleman's agreement" of 125bhp. The lucky Italians got the real full-power models. Fortunately for us, the restriction was fairly basic and most bikes will have been derestricted by now.

The restriction takes place in the outlet of the exhaust-silencer (end-can); the UK and mainland Europe models had a 24.5mm outlet, the American and Canadian market bikes had a 28.5mm outlet, yet those lucky Italians had bikes with a whopping 35mm outlet. So you don't have to be a rocket scientist to work out that any aftermarket end-can will produce more power than the bike originally came with.

So now you know, go out and de-restrict your bikes and gain some extra power. Enjoy!