Holden red6 siamese-port head

[johno]

The ported race head from above actually started life as a "closed chamber" head but Yella Terra realised that the "open chamber" heads flowed more so they laid back the chamber walls to nearly the same shape!! Thanks for that web site Steven , any idea what one of Joes heads are worth?:;):

[stevenford]

Your original race head has the right chamber but it not opened up enough in the chamber. You need the ACL race series head gasket with the larger chamber opening and bridged fire ring between the exh and you need to open up the chamber to suit.

The problem with using an open chamber is you have to mill so much that sometimes the deck gets thin and you get head gasket failures. The closed doesn't get milled much so you have more piston to valve clearance, the pistons may not even need reliefs. You might not even have to notch the block bore when running 1.74 valves if your cam is small. Ours had to be notched because we didn't move the head sideways.

I have never seen a open out flow a closed when done right. The casting has more to say about flow than the chamber. Actually I find the closed flow better.

Ignore all the old wives tales, Yella Terra said this or that, trust the flow bench. I did about 50 tests just on the inlet developing the red head.

You will have to ask Joe.
It's a lot of money but you get a lot and it's 1K less than Duggan sold them for.

[johno]

I see what your saying about the difference in mating face thickness between 'closed' and 'open' chamber but the point i was trying to make was that the 'closed' chambers arent actually 'closed' chambers any more due to the amount of deshrouding required for bulk flow, the 'opens' don't need the same amount of chamber work.Iv always used a stage 6 solid heatseeker cam and also 'fly-cut' the bore tops for valve clearance and flow, sealed with 'Larry Perkins' race series gaskets (p.s. did you hear ACL is going BROKE!!).Were the JZ heads the ones that Duggan designed? Do you know what they flow? :;):

[200cfm]

Anyone have any theory ideas why the head works so well on the track using a shared port.

I am still trying to understand what the air and fuel are doing once they hit that shared port. As I see it the two valves have a shared collector or plenum to draw air/fuel from. Since two manifold runners are feeding the common port the CSA of the runners is now double. And the available air is double with less resistance. So would that mean the air speed in each runner drops down when compared to a divider in the port? Then what happens to the air speed in the collector? I would think it would slow down again, but maybe not. But if it did, then the common collector port would have a high pressure zone common to the back side of both valves. I would think it would be higher than if a divider plate was between the two valves.

What happens during overlap periods on the common collector port? Why does it work?

[johno]

The guy who did all my flow-testing back then said that it was a combination of the 'branch-manifold' (triple-webber), as he called it, with two runners joining, and the heavy taper to the back of the valves (the floor rises sharply) causing a ram effect in action. The boost from 105.7cfm to 115.7cfm on the flow bench, was also obvious on the road, it goes like a scalded cat! (i tested the 4 barrel set-up also, just cause i had to know!).

[stevenford]

[johno]

Steven, what did you mean by the 'close fitting cones' on the closed chamber heads to aid in pressure recovery? I contacted Joe at J.ZED and he said the heads can be hand finished to flow from up to 480hp!! They arent cheap though and parts are only available through him because they are all custom made, two rather larger draw-backs, which is a pity as the design is as close to perfect as you'll get!

[stevenford]

[johno]