cheers:P

Seriously, it's the optimisation of the compression gap between the piston and the cylinder head.

Rgds, Rob

Try this
http://www.motorcycle.com/mo/mcrob/rt-fuel2.html

its also mentioned in here somewhere http://www.docv.org/articles/bench2.htm

And not forgetting Sigma http://www.sigmaperformance.com/916_senna.html

Paul

Thanks for that info' (yea, a lightened flywheel would be nice).

The reason for my question is that there is obviously a lot of talk about the supposed / presumed benefit of the 620 and I was trying to establish if anyone had 'gone all the way' with the BB so we could make a direct comparrison.

My interpretation of the rules, the thinking behind the rules and the other supporting tech' info' has always led me to believe that a BB would require all the possible mods' in order to be comparable with a 620.

Therefore my take on the technical options has always been; EITHER buy an expensive donor 620, don't fiddle with it much ('cos the rules won't let you) and just race it, OR buy a cheap donor bike (600) and be prepared to do a lot of creative / highly skilled (and ultimately also expensive) technical fiddling to make it competative.

Having said all that, a 'hot' BB would deliver its power / torque in a different way to a 620 so there would probably be some circuits that favoured the 620 and some that favoured the BB - perhaps.

I chose a 620 because I didn't want the hastle of extensive engine work, I do not have the skill to do it myself and I thought it would probably work out more expensive in the long run to pay someone else to do it for me. There was also the little matter of bugger all time between me raising the funding and the 1st meeting.

Judging from the response to my question and the fact that the series is still only two meetings old, it seems to me that there has not yet been enough time / development to prove whether or not a "full monty" BB can be competative.

Just a thought.

I can't see how a Full Monty BB will ever match a Full Monty 620 as the only real difference in the tuning allowed is the Big Bore kit, which you will never get the best out of with standard Cams, Ports and valves.

Even getting individual smoothbores setup on short inlet stubs is going to be costly just to try and match the 620s standard setup with a PC3 attached and tweaked on a Dyno. Even the cost of a 6-speed gearbox for a BB bike is going to set you back a bit.

I like the mention by Ian of "creative / highly skilled (and ultimately also expensive) technical fiddling" I would love to go down that route but the rule restrictions prohibit it.

I see as you may as well put a fair bit of money intop a 620 and add a few mods or keep it cheap (£2k max) and run a 583 with some basic mods

As for the standard downpipes on a 600SS they are tiny but then I doubt if the head flows enough for it to be a real worry.

You have to untie him now and then Hun - A blokes got his limits you know :lol: