I've often wondered about this "equal length" primaries business with extractors. I know there is a sonic issue with pressure waves moving at the speed of sound and equal lengths are thought to be beneficial with this concern but i wonder if most engines would ever be used at the consistently high rpms to really justify it.
I was thinking that for most engines what you really need rather than equal length or equal volume, as mentioned earlier in this thread, is in fact equal flow.
Looking at a set of extractors with equal flow in mind you would actually not have equal length primaries anyway.
Imagine the pipes from the front cylinders of the engine, they tend to be long and straight with only slight bends, the pipes from the rear cylinders are bent and contorted in every which way like a angry sidewinder just to squeeze in enough tube length so they are as long as the front tubes.
But a bend in a piece of tube creates friction as gas flows through it. So 12 inches of tube with a 90 degree bend in it
may act as if it is 24 inches of straight tube.
This means those rear pipes with a bunch of wild bends in them to get them the same length as the long front pipes in fact could be much shorter and have less radical bends in them. A kind of balance between bend degrees and tube length would need to be found. Ideally rather than check the pipes volume the pipes need putting on a flow bench.
I guess you can theorize for ever over this sort of thing but the bottom line is you've got to have some pipes that will fit into your car. The theoretically perfect pipes are useless if they won't go into your engine bay.
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