[Healeys] IS Bigger exhaust better

[Oudesluys]

Smaller resistance in the exhaust can be a factor in increasing the 
power output but is not always so, certainly not on small well designed 
engines with tuned exhausts.  Tuning the exhaust instead of only 
increasing the bore is a far better idea. This way you create certain 
resonances in the system at specific rpm bands by playing around 
(calculating) with the exhaust manifold (length, collector, bore etc) 
bore of the various components, capacity of the exhaust  boxes, number 
of exhaust boxes, distance between the various exhaust boxes, number of 
pipes, crossovers or not and a few other things. A well trained 
automotive engine designer should be able to do this.
However by just only doing that, you will not gain much if anything at 
all. It will also mean you have to make changes in the induction (e.g. 
length), jetting and ignition, compression ratio, not to mention 
camshafts if you want to extract the most of these tuned exhausts on 
carboretted engines.

Kees Oudesluijs
NL