Possibly a rather technical question so here goes:
I'm trying to put together a design for a custom inlet manifold to fit a Z16XE engine in a MK4 Astra. Much consideration goes to the way DBilas have already designed their inlet...
My massive difficulty has been in sourcing some suitable tube/pipe to use for the inlet runners. Anyone who knows this engine may be aware that the inlet manifold is in two parts:
1) The lower section housing the injectors which bolts to the cylinder head
2) The upper section which is rather lengthy and twisty, and has the throttle body mounted on the top
The lower section, as with DBilas, will stay at this stage. Added issue for me is that I have a factory fitted LPG conversion which has the LPG injectors drilled into the lower inlet section.
The upper section is, in essence, reasonably easy to design a DBilas style replacement - aside from the fact that the runners are a flat-oval shape (internal diameter 25mm x 42mm). Typically, this size of tubing is not commercially available and fabricating this custom size is rather costly - extrusion is at least £900+VAT for nothing more than a sample (which would be enough for one manifold), then the minimum orders I've found so far are from £500 upwards. I cannot justify the outlay at this point in time, even if I aim to fabricate more than one manifold to sell.
I am basically after any advice on where/how I could sensibly fabricate or source some suitable tube/pipe without having to spend £1000+.
I have pretty much rang around all the places I can find online who fabricate or supply tubing, both extruded/drawn or electrostatically seam welded.
I further looked at perhaps using a circular tube, compressed at one end into a flat oval, but initial calculations show that the cross sectional area of the circle is so large vs. the end flat-oval that I'd be likely to lose more power than I'd stand to gain due to the massive drop in gas flow speeds through the circular section (unless I'm missing something!).
So, basically, advice welcome