Real world facts:my understanding is by increasing the pipe size the exhaust gas pulse velocity is reduced, the speed of the gas exiting the engine is paramount to the engines performance.
i will try and explain my understanding a little but its a hugely complex subject and although i understand some of the theory i am by no means an authority in exhausts, so i suggest doing some research yourselves-
the exhaust gas comes down the exhaust in pulses due to the firing order , the pulses of gas need to flow as quickly as possible away from the valves during overlap and, as there can be an area of low pressure just behind the pulse it can help scavenge the gas out of the combustion chamber ready for the next firing cycle, the manifold pipe length is also important here so the pulses dont collide but fit together in sequence . if they are even in length then one pulse has gone past the collector area when the next pulse arrives and so on.
(as i understand this is why many scoobis sound like they do , the manifolds branches are unequal in length so the pulses are unevenly spaced hence the odd noise they make, if you fit equal length manifolds they sound pretty normal. )
if we fit a 3" system then although we have more area inside the pipe the actual speed of the gas can be reduced. people think by fitting a 3" system they will reduce back pressure which is correct however as they lose the gas velocity and then lose power they assume " these engines must have back pressure to work" actual back pressure would mean it was hard for the gas to escape from the combustion chamber, and as we all know an engine is just a big air pump it is critical the spent gas gets out as quickly as possible. so they actually need zero backpressure with the narrowest pipe possible to keep the velocity up.
Same day back to back dyno test, with around 2 degree IAT variance and no air pressure variance.To be fair that graph is so close and so far apart from a time point of view it could easily be the other way around and while it shows gains was the yelling adjusted to suit? IMO its not proof at all.
Ask yourselves what the touring cars used when they were na? Pretty sure they weren't 3" systems
Wont that just restrict the exahaust an make the 3" pointless though?What about noise limits with a bung?
Same day back to back dyno test, with around 2 degree IAT variance and no air pressure variance.
Just because you don't like, it doesnt make it false.
3"ers are loud, you will not pass a 105db sound test for the UK circuits.
I'm genuinely surprised someone with extensive dyno experience doesn’t understand that time is not a metric that alters a reading.10 hrs different, who said i didnt like it? i have been looking at graphs like this for many years, more than some of you have been alive and while it shows a couple of Hp here and there, the graph could easily be the other way around, the curve and pattern is very close i just wouldnt consider a dyno printout like that absolute proof but hey you are all entitled to your own opinions .