You might find "The Sports Car Engine: its tuning and modification" by
Colin Campbell an interesting read.
> 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
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