Well, I suppose you have a point.

As exhaust gas temperature has a direct effect on the speed of the gas pressure wave, I suppose you could say that fitting race pipe and changing the jetting does effect the CR and thus the potential for detonation but the base CR will be the same unless you skim or change the ratios.
For every 1 degree of change in exhaust gas temperature the tuned length of a spannie can vary up to 0.5m - 0.7mm. This is vital on a stroker as the scavenge 'charge is directly effected by the gas temperature and the pipe itself.

Quote - Mark Dent (nice bloke too!)
When designing an exhaust lots of factors come into play, Port timing, Peak RPM, Exhaust port diameter, Horn coefficient and unsteady gas flow to name but a few.
Unquote.

If you change the jetting and the motor runs cooler or hotter you strictly speaking need to have the pipes to match and the porting to match.

You know what I reckon, the NSR engine is in such a high state of tune anyway that changing parts of the bike - pipes, jets and cylinder size etc.. in the quest for more performance, leaves you with an engine that demands a lot more thought and care in setting it up to be reliable . Setting up the jetting right by doing plug chops and listening to the engines beat will give you a basic set up. To really get it right you need to know exactly what is going on and that is beyond may of us, not through lack of ability or understanding but because we just don't have the kit.

E.G. if you go from a 250cc engine that ran well and was reliable to a 300cc, rejet and so on but use the same pipes, the chances are that the exhaust temp ould have gone up. Give a 'guesstimate' of say, 20 degrees which is very conservative (my RG exhaust temp went up by over 35deg from stock to Swarbricks) your pipes are now around 12mm too short.
The hotter the exhaust gas, the faster the return pulse and the longer the pipe needs to be.

That's just one tiny factor on pipes, think of what else needs to be considered like port timings, blowdown, mixture, combustion chmber volume and so on before you start to look at ignition / advance curves etc.. I guess this is part and parcle of tuning an already tuned and relatively high-spec motor ?

As quoted in PB over the stroker hey-days of the 80's, 2 strokes are as reliable or docile as you want them to be. From the factory they are usually rock solid, start playing and fiddling and reliability will suffer.
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