Porting the VW/Audi 8v head with port energy discussion

[Carnut1]

1202171028.jpg[/attachment]Smoke, we are on the same page. I am thinking I can get to all the areas of the runners with one cut and then enlarge the plenum. I will need to do some calculations on plenum size and figure the tapee. Stock runners have a taper and would probably work well if they were straighted and a bit larger. I was also thinking of just building a flange at the cut with 3/8" aluminum plate. Bolt on the plenum for street or bolt on the stacks for racing. Just an idea, customer has the say. Thanks, Charlie

[Carnut1]

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Since the stock intake knocks a full 30 cfm off a modified intake port I wanted to see what could be done without welding and cutting, I was able to slightly enlarge and reduce taper 6.25" into the flange. This was worth 6 cfm. A discussion about anti reversion (a.r.) and subsequent mods lost about 1cfm at high lift and low lift flow took a hit. Now llf will be important on this build due to the engine design restrictions. I will need to consider the advantages of a.r. vs. The llf loss. Thanks, Charlie

[mag2555]

Treat it some what like a short turn Charlie!

Widen out and flatten it little by little for a distance of half way thru that 90 degree bend and then switch off to widening the long side of the bend on the other half of the 90 as it approaches the head.

I guess your next issue even if you only pick up 15 cfm per runner is the restriction the throttle body may become now?

[Carnut1]

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This project has been near dead for a year but is back with my international customer doing lots of prep, design and fabrication work. Check out the 2mm offset plate that is reversable and custom built (and honed to size) bore adapter. We decided the stock block bores are thick enough to offset bore 2mm safely. I will be posting more soon. The custom intake looks really good. Thanks, Charlie

[David Vizard]

I can very well see where too much swirl will go from keeping fuel suspended to slinging it to the edges of the chamber and creating a dead spot in the center. Maybe that's not what too much swirl does but it makes sense by my logic.

cgarb,

Too much swirl and a carb that delivers insufficient atomization will do just as you describe. Saw this on many cup car and similar engines back in the late 90's.

By the time we got to 2005 it did not seem to be a problem as most setups had veered away for high swirl ports and chambers.

It appears from my experience testing swirl that if you are targeting power up in the 9 -10,000 rpm range that swirl is unnecessary as having any motion stagnation would be very unlikely. On the other hand at 1000 - 5000 rpm swirl is an aid. I have a swirl test graph in my cylinder head book I can poach and post if anyone is interested.

DV

[Carnut1]

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2mm bore shift on old test head. This head has a bit too much deshrouding on intake. This mod makes easy 10 cfm on the intake vs. -2mm.. Thanks,Charlie

[Kbails]

what about extrude honing for the intake?

[Carnut1]

what about extrude honing for the intake?

You will like the intake. I will be able to port it now.

[JoePorting]

Have you thought of putting in a larger intake valve? Should respond good with that open chamber.

[Carnut1]

I have Joe, The valves that he bought for testing are 7mm stem which we are going to use. But a much longer stem. The customer was even thinking of changing the cam perches and lifting the cam higher. I feel like that is just an insane amount of work for an unknown amount of performance. He wants to keep the rpm to 7000. The 7mm stem valves that are pictured are from a crossflow VW head. Thanks, Charlie

[Carnut1]

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2mm shift with stock head gasket. This gasket's fire ring is not wide enough to survive. That would mean custom gaskets. A 1mm offset may be wiser.

[Carnut1]

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Modified VW manifold bottom. Flowing each section to see where the restrictions are. Clay radius on unported botton half.

[Carnut1]

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Modified VW intake top runner section.

[Carnut1]

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Trumpet that will need to be epoxied in place.

[Carnut1]

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Throttle body view of custom plenum with trumpet placed for quick flow testing.