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Marking out inlet man to same dims as head which is at 157.6 cfm at 10” depression on port 3. This dev port has no guides, rough fettled finish to shape, no seat work, so std valve throat angles and diameters.

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Difference after flow correction on one inlet man port. The manifold underflowed development port 3 on the head by 157.6 – 141 cfm prior to mods. Now it outflows the head by 166 – 157.6 which is how it should be bearing in mind the ‘swan-neck’ shape is going to generate a significant loss. The duct shape and entry angle to the head have a a major bearing on how well the manifold will perform when actually offered up to the head.

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When a manifold or port goes from from one section (eg round to semi-rectangular) there are always going to be problems with the airstream around the change of shape. The internal form needs to be carefully developed to prevent extreme turbulence. In other words what ‘looks right’ is not always so. There is one aerofoil shape that ‘works’, and one only, anything else will lead to flow loss. In general the internal shape of this manifold, whilst too small at exit section (to about 1” in) is very good.

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Entry section modified. Finish is 80 grit.

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Non-mod man port left on dev port 3, showing loss generated on head compared with fully developed manifold port at right.

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The loss is an inescapable function of the ‘up and over’ shape of the manifold. A loss is a loss whether the engine is n/a or turbo.

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The GC straight 16v manifold (for throttle bodies) bolted straight up to dev port 3, there is a downstream mismatch which looks huge.

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But in fact the loss is only 1 cfm, which is nothing in real terms. This demonstrates (for one thing) how the penalty of a mismatch is so often overstated. In practice a downstream mismatch has to be about 3mm over 1/3 of the port face area to be functionally significant on a port of this size. An upstream mismatch makes no difference at all, provided that the inlet manifold outflows the head (which is usually doesn’t..)
The other thing this demonstrates is how important it is to get line of sight into the port at the right angle.

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The airstream is quite laminar straight down the middle. The string is picked up by the fastest flowing air.

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The airstream doesn’t follow the port roof, it breaks away and heads for the centre/rear of the valve region. Again not how stable the airstream is.

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Flow across the port flow is quite slow, ie: a low flow region, but stable going over the ramp into the short side radius.

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Down the side the flow is similarly quite stable, note how it does not follow the port wall contour but follows the line of ‘least resistance’.

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Not easy to capture on a static shot, but roughly in the centre of the port at the port face there is a vortex region of turbulent air where mixing of air coming from all directions is taking place. The end of the trace is fluttering violently and rotating in the vortex. If it were possible to get rid of the vortex, the manifold loss would be far less. But it’s not.

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Lots of techno babble there to baffle us with but does it actually work

John

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So what car is this for as in the pictures there is some writing saying `pug 205` & `zetec 1800`

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Head is now ready for guides and seat work, fully flowed.

Flow test final spec on in/ex ports 3 (bare port, no guide only):

inlet 160.3 cfm @ 10", (139 standard), now with full spec in manifold 153 cfm
(loss reduced on final port tidy-up by 3 cfm, was 150 on last test).
To put a perpective on that, 152 cfm is easily enough to give 250 bhp 2 liter 16v normally aspirated - so you can imagine that turbocharged even with very low boost - power will be huge.

ex 125.5 cfm @ 10" (116 std)

E/I ratio with inlet man (ignoring guides as they cancel out anyhow) is 125.5/153 = 82% which is fine. (Sierra Cosworth has incredibly restrictive ex ports and gives only 65% tops in full race trim).

The standard inlet man/port ignoring guides again gives about 139 - 12cfm manifold loss = 127 cfm standard port flow, ex std is 116 cfm so std E/I ratio is about 91% which is way too high.

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Also my cams have just arrived with Guy Croft too, hmmmmm.....

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What sort of power are you expecting to get when you've completed this project begbie? sounds like its gonna slow down the rotation of the earth!!

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Guy croft - the guy gives good head (s)

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Oh dearie me.

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sounds like its gonna slow down the rotation of the earth!!

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hahahah.

brilliant ... but thats Superman's job ...



good stuff begbie , hope to hear more.