Kenno was hitting on a plenum chamber subject a little while ago but i can`t find it anywhere so i`ll throw these pics up here & everyone can have a gork
we used to make round (cylindrical) plenums but now we make square (rectangular) ones--> i know that may not make much sense but still, the pics will tell the story better
This is about all these particular hi-los are good for

& even then they`re not that good at that either

but still , it`s what i use to make my ram tubes
i cut short tubes of alloy & put them in the press ontop of the hi-lo & press away , down to a pre-described point, bang the hi-lo out & hey presto,,, one nice neat cheap ram-tube pipe ready to weld into my plenum/box thing
then we cut out a piece of alloy RHS , mark it then cut & shape it up to suit
they come out a treat when welded & the flange plate for the throttle body is fitted
we taper the bottom of the plenum to help direct & ram/squeeze to share the air more evenly between the inlets,,, but also to help clear the alternator underneath the end of it
i`m trying to find more pics of this stuff but they`re in this computer somewhere
some of our old stuff here,,, inlet plenums & exhaust manifolds & extractors & their respective Jigs-->
nice shiny bling-bling ceramic coated ones now too
more to come