Full Monty Big Bore?

[the old man]

More of a question really; is anyone running a big bore that fully exploits the regs', ie., shorter inlets, bigger carbs, squish clearances optimised, cams degreed in etc?

[AK]

std carbs etc on ours:)

oh, and we have shortened inlets & the squish has been done (please can someone tell me what that is?:puzzled: )

AK wants to do mucho more, but hands are mostly tied by the reasoning that none of the parts from the engines in the series are interchangeable

C:)

[Edited on 9-6-2005 by CK and AK]

[ali]

Originally posted by the old man
More of a question really; is anyone running a big bore that fully exploits the regs', ie., shorter inlets, bigger carbs, squish clearances optimised, cams degreed in etc?

I think Paul Payne is running the best setup BB at the mo. He's running FCR39s and Malossi short manifolds, but I can't remember if the exhaust manifold is standard or not, and I've no idea if the cams have been set, ignition modified or squish set.

Ali

[skidlids]

I think you will find Paul Payne (Paynep) is running near enough the spec you mention, his bike certainlt seemed quicker at Castle Combe with the individual smoothbores now in place on short Mallossi manifolds. It has been set up by Moto Rapido so it should be one of the best BB bikes out there. But is still seriously compromised by the 400SS cylinder heads that are fitted to the 600s and are very restrictive on flow with there undersized valves etc.
Tony Brancatto says there is a lot he can do with my 583 engine and get a lot more power from it, sadly most of the mods are outside the rules,
I know Paul would like to try his 750SS heads on his 674. It would be interesting to see the results.

[skidlids]

Should point out that I do believe that a 674 BB bike with the smoothbores and some head work, but standard cams would be a match for a 5-speed 620 with a pipe filter and some fuel mapping..
6 speed versions have yet another advantage

[Rattler]

Originally posted by skidlids
I know Paul would like to try his 750SS heads on his 674. It would be interesting to see the results.

It would be very interesting - as the 750 belongs to his wife!!!!! ;)

[paynep]

Originally posted by Rattler
Originally posted by skidlids
I know Paul would like to try his 750SS heads on his 674. It would be interesting to see the results.

It would be very interesting - as the 750 belongs to his wife!!!!! ;)

Without wanting to give everything away, I will say that my bike is totally within the rules (including std flywheel !!!!) - with BB, Keihin FCRs, squish set by using a thinner base gasket, cam timing has been done but may be experimented with, and I'm running a std 2-1 manifold and what looks to be a very old DP exhaust can.

However there are a few things that haven't been fine tuned yet, so I expect to get a little bit more out of it yet.

Cheers, Paul

[AK]

can you tell me what squish is please ?

C:)

[Rob B]

Charlotte,

It's what happens when you put 15 people in a 10 person lift.:lol:

[TP]

Originally posted by paynep
Originally posted by Rattler
Originally posted by skidlids
I know Paul would like to try his 750SS heads on his 674. It would be interesting to see the results.

It would be very interesting - as the 750 belongs to his wife!!!!! ;)

Without wanting to give everything away, I will say that my bike is totally within the rules (including std flywheel !!!!) - with BB, Keihin FCRs, squish set by using a thinner base gasket, cam timing has been done but may be experimented with, and I'm running a std 2-1 manifold and what looks to be a very old DP exhaust can.

However there are a few things that haven't been fine tuned yet, so I expect to get a little bit more out of it yet.

Cheers, Paul

Ok, cool. Give us a number ;)

[AK]

Originally posted by rob41b
Charlotte,

It's what happens when you put 15 people in a 10 person lift.:lol:

cheers:P

[Rob B]

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

Rgds, Rob

[skidlids]

Originally posted by CK and AK
can you tell me what squish is please ?

C:)

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

[skidlids]

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

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

[the old man]

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.

[skidlids]

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.

[phoenix n max]

Originally posted by CK and AK


AK wants to do mucho more, but hands are mostly tied

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