Hi Luke,
Hope I'm not too late to answer your exhaust question, and spur you on to keep the build going at a good rate!
Siamesed exhausts etc,
A hard one to answer just like that but will try.
Generally you are trying to harness the exhaust pulse waves and tune the exhaust diameters and joins etc to coincide with these waves at certain rev ranges (as the frequency of the waves change with revs and pipe diameter etc. and are very heavily influenced by primary to secondary joins, you can never have it perfect all the time) so a well designed Siamesed system will (hopefully) harness the reversal low pressure pulses from two pipes and make them work on both cylinders, thus engine may work over a wider range than single pipes. However the max power may be slightly down at full revs etc.
Just like megaphones help power at the top but narrow the power band,
Fitting a reverse cone of the right shape will help to widen the power spread but nock the top very slightly.
Siamesed pipes will give a better spread of power but not the absolute ultimate "number"
On the road you will probably feel little difference although a boost in the low to mid range will certainly be present with a good set of Siamesed pipes.
Sometimes they also help to "fill in" a noticeable dead spot in the low / mid range and for this they are invaluable!
We see on the rolling road quite often that a certain adjustment or setup gives a few more bhp at the top but can rob 5 or 10 bhp in the mid range.
This is why you never just look at the big numbers without studying the complete graph. Give me 5 in the mid range any day over 2 at the top!
Twin pipes sound better though
And can look amazing.
Any one see the lovely A65 café from Japan in the recent Classic Bike Guide? Awesome styling!!!
Regards,
Julian
PS.
The above is incredibly simplified but hopefully gives the general idea.
