I am currently modifying my boys XT660x for him as its his first bike and I have had many.

He is limited by his A2 license which is 47bhp (it does not stipulate any max torque figures) and 175kg is the minimum weight.again it does not stipulate if this is the dry or wet weight.

I believe the 660x comes in at 177kg, I am unsure if this is the wet or dry weight. Could anyone advise please?

I have ordered a second hand set of dekalvic twin pipes and kevs fuel controller and the o2 mod. Question- Has anyone ever done a dyno test with a set of open pipes and both of kevs little boxes of goodies but with no air box mods?

I don't plan on doing any mods to the air box as that is, I believe, is where the largest power gains are to be had and I can't get it to produce any more than the 47hp limit as that will invalidate his license and his insurance policy.

Any advice would be greatly appreciated

You might be on a sticky wicket here? Pipes alone liberate around 2hp (mainly due to the lack of catalysts) and Kev's Fuel Mod on it's own gives a 1.5hp increase in power with stock filters. This will take you over 50hp at the crank (which is what insurers and the DVLA are interested in). Stock XTs generally make 43.5hp at the rear wheel (47hp with the mods above).

Kev/Freez did some dyno runs with various mods. Have a read of this thread.

Like Pepsi suggests, your best course of action is to talk to the insurers first and see what are acceptable modifications.

BTW - the wet weight of an XT660X is 186Kg.

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I just want turn it into a backfiring, loud antisocial big single but keep it legal.

The fuel mods are not to get the extra power but to sort out the fuelling which will make it easier to ride and give him a bit of confidence.

I am a bit stuck!

Insurers are fine with the exhaust unless it adds another 5% to the output.

I will have chat with them tomorrow