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!).
Most certainly, however you then end up with very short runners which so far as I can tell will result in useless low down power and everything so far up the rpm range that it would be horrible to drive. The DBilas kicks in a lovely flat torque curve from well under 3000rpm, and is still showing a rising bhp curve at 6500rpm - I suspect mounting a plenum a-la the Mantzel powerbox onto the lower inlet section would be a bad idea for useable performance. The X16XE engine has a lower inlet section with much longer runners, which basically come up to a flat/level surface to mount the plenum onto - the Z16XE has a much shorter lower runner length meaning the plenum would be sitting at an angle and much lower down in the engine bay.
How long is the lower one? I can't remember the figures off hand but the length doesn't have to be that much to catch the resonant frequency I don't think. Unless it's mega short (like 3 inch) then you shouldn't suffer too much. The plenum size will probably make more difference.
Lower one is around 3" in length - adding another 3" to this via the runners to the plenum pretty much matches the DBilas length. Whilst you still hit some resonance frequencies even with shorter runners, the shorter they are, the less times you hit the resonance hence you lose even more low down torque. I'd rather stick to the somewhat 'proven' lengths if at all possible.
I had initially thought the upper section runners were about 6" which was difficult for having some custom ones drilled out of aluminium block - at 3" length they may well be much easier to do, in fact CNC'ing the entire lower flange and runners in one peice could even be possible, got a meeting lined up with a local fabricators to discuss options
Because it is fun and I've learnt a good amount from the project!
I've pretty much sussed it all now at this stage without a purchase at this stage:
* Plenum volume and material is sourced
* Runner tubing is sourced
* Final vernier measurements of the mounting flange and plenum base etc. are done and just need entered into CAD
Next step is to decide if the outlay is worth it - all in, I have to spend about £450 on parts and labour, however the parts are sufficient to produce up to 8 inlets...if it comes off, I could have a commercial product at a significantly lower price than a DBilas. All this is backed up by a significant amount of maths, spreadsheets and info taken from an existing DBilas inlet.
Have a scan through my thread on another Astra related forum you frequent
Raise from the dead, but we're on the second prototype now, final one due very very soon:
Not my car/engine:
Some serious work to get to this stage but we are pretty much there, should have a final 'production' model with luck this month. Fabrication has been done by a friend so for the most part, cost so far has been a small amount of metal and lots of time! Big hassle was getting the inlet runners shaped and also curved, otherwise it doesn't fit and hits the brake piping behind the engine block.
That's the next step - we'll get the air/fuel checked on the standard ECU map, then some RR figures (if it's safe on standard map). We have the facilities and expertise to remap the ECU so we should have a before/after on standard map and before/after a remap as well.