Hello Guys
I've thought about this for quite some time back in my uni days when invloved with Formula Student. There we have the situation that all the air must pass through a single throttle and then a 20mm restrictor before the plenum.
Now, without any forced induction, and ignoring potential pressure waves due to organ pipe/helmholtz theory, then the most air a cylinde can draw in, is the capacity of a that single cylinder. However, you don't get that due to frictional losses in the intake system, i.e. the volumetric efficiency, and the reason we spend lots of money on porting heads etc. A typical engine will only draw in about 75-80% of its actual capacity, a tuned engine might have a VE upto 85%
So if there is only a certain amount of air you can draw in, once you reach this limit fitting bigger carbs will have no affect on the top end power, BUT where it will have an affect is on the throttle response. With the 20mm restrictor example, I've used 50,40 and 30mm throttles and the difference was amazing. The 50mm was like an on/off switch, the 30 on the other hand was a dream of driveability.
So my thoughts on this is that you may be better going for the smallest throttles possible for the equivalent airflow. We can quite easily work out the volume of air required for a 2l pinto at the red line, we can then also do the same for various bikes - the ultimate air being to try and match the redline air flow requirements of the bike carbs to the redline air flow requirements of the pinto. I must say that this is only a theory adn I haven't proved it (yet
)
If I get a quiet 5 min at work tomorrow I will try and knock out a spread sheet to work this out.
Does the theory make sense?
Cheers
Dave