How much can the stock pipes flow?

Thinking of it as a pump, if your output hose is a certain size and you don't change it, then change the intake hose you won't see any gains in flow if the stock output hose was already the restriction. That's the case on stock rocket's.

Not really true, it will limit your gains, but you can certainly see gains. Turn your garden hose on half way, then open it all the way, big difference.
 
I have to disagree with the net loss theory. I just did this on my 2013 roadster, bone stock. Simply added Ramair and there was no change in power either way up or down, just more noise from the intake, but the instant I opened the secondaries and copied the I3 values to I2 and I1 it was a significant jump in torque literally. If I time it right in first gear it will come up off the ground and occasionally, in second gear too.
Also, if your analogy was true the carpenter 240 kit bike could not make 195hp, it could only make 126hp because of the stock exhaust?
 
When you all have done before and after dynos with stock exhaust the SHOW the power loss come back. I do and lost torque across the lower and mid RPM range while maintaining the same Peak horsepower indicating that yes it flows at least as much as this stock intake at high RPM. But it also shows that the stock intake assists filling the cylinder at Mid and low RPM. This is why the stock intake is as long as it is rather than ending under the tank with an air filter fitted.

A carpenter bike using the stock exhaust will make more power than stock because it's an entirely different head and cam package and does not rely on the Scavenging of the exhaust to increase power which is what you're doing when switching to aftermarket headers to increase power on a stock internal bike.

All that said, the stock exhaust CAN make 500hp, just takes a 700hp supercharger setup strapped to the bike, doesn't mean it's at all efficient, when working with NA, you start with the biggest restriction, then the next biggest, then the next biggest. The stock Rocket restrictions, in order, are secondaries, exhaust, intake, cam, head.
 
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