Hi Stephen,
I’ve go bogged down with work and other things.
But in general, what you ask can be done. In fact, I think it should be done in order to get some methodical thinking into all of this. I suspect there are a lot of Chinese whispers involved. Someone told me this, who told me this, who told me …
Trying to think back to what I observed previously …
Alignment of inlets and ports appears to be poor. Significant gains could be made (in the flow simulation anyway) by correctly aligning the ports, gaskets and manifold. This includes eliminating steps and gaskets that are too big. I think this is probably the first priority.
The inlet filter/trumpet appeared very restrictive (in terms of aiming for higher HP). You would want to deal to that. Also the butterfly could be increased. This both reduces the losses through the throttle body and improves the virtual connection between the two Plenum volumes (the inlet manifold and the filter body). I didn’t spend a lot of time modelling the flow through the single butterfly, because my focus was on individual throttle bodies. I did note on the individual throttles that good gains could be made by aerodynamically tapering the butterfly edges (rather than sharp edged) and minimising or eliminating the throttle shaft (and screws!). I designed a shaftless concept, using Yamaha motorbike bearing seals, which I think would work. This approach delivered similar full throttle performance to a slide throttle, but retained the beneficial turbulence at part throttle which is one of the benefits of a butterfly.
The inlet injectors protruded a LONG way into the inlet flow and appeared to significantly restrict flow. (The casting around this area was very crude). I would look to grind those down. There may be a benefit in accelerating the flow around the injector but it just looked poor. Modern injectors would do a better job, and I think are worth considering. I bought an injector flow tester to do some more investigation, but got sidetracked. LOL. Also I would try to check the casting in the plenum where the inlet tracts meet the plenum and make sure there is no flashing and crude creating a turbulent entry. Perhaps worth having it extrude honed?
The whole system showed significant benefit from a continual gradual taper. Again my focus here was on individual throttle bodies. This is probably impossible in a cast manifold, although with 3D printing should be possible in high temp plastic. About time someone came out with a 3D printed version.
Detail modelling of the valve seat had a valuable impact on the flow rates indicated. Although the actual seats that I measured and modelled were well made and well matched to the head.
There is some suggestions that wider lower angle seats increases flow at low lift and is the equivalent to longer duration cams. This did appear to be beneficial. But you would need to consider if your engine wanted more duration and what impact this might have on pressure wave tuning.
The whole system was very sensitive to exhaust pressure wave tuning. You should consider throwing out the stock exhaust manifolds. I had some theoretical numbers for tuned lengths, but this is very dependent upon everything else. It was notable that too large diameter exhausts limited the gains here. In my case, I think I was looking at 1 5/8" primaries on a 6.7L variant. For a 5.3L you might be looking at 1 3/8", as distinct from some of the larger sizes that “look better”.
My work has all been theoretical, and I have yet to prove it in the flesh. So I am totally open to any criticism “show me the proof”. Filter what I suggest through your own common sense.
However, key to my analysis has been to a) try to understand the original thinking of the designers and understanding the limitations of that design, b) try to confirm known published data where it can correlate and confirm my model accuracy, c) build an historic record for future manufacture options.
Cheers
Mark
