Alloy head for the Holden six cylinder blue and black motors.
 
 
Kustom Bitz can supply you a high performance head for your Holden six cylinder engine. These high performance alloy heads are the Yella Terra brand made by Perfectune Engineering in Moorabbin, Melbourne, Victoria. Perfectune Engineering has over 45 years experience in manufacturing high performance engine parts. This 12 port Holden head has a weight saving of approx 33% when compare to the original and you could expect a power gain of about 50hp on a mildly worked over engine.
 
 
Kustom Bitz also has a 4 barrel inlet manifold to suit the Yella Terra head which is made by AussieSpeed. The AussieSpeed manifold is made specifically for the Holden blue and black motors of which is also know as the 12 port engine.
 
 
KustomBitz also stocks the new AussieSpeed tripple weber inlet manifold for the holden 12 port blue and black motor head see below.
 
 
For those of you who are not familiar with the Holden six changes over the years, the earlier Holden 179, 186 and 202 cubic inch Red motors had Siamese inlet ports now referred to as the 9 port engine, where as the head on the later blue and black motors which has 12 individual ports. The 12 port design is a more efficient head for producing better low down torque, broad torque and better economy; this is because the valve events of one inlet valve are not impacting on the air flow of the neighbouring inlet valve only an inch or so away in the same port because the ports are now separated.
 
 
Now YellaTerra have taken this better 12 port design one step further by manufacturing an alloy head with a raised intake port that radically improves the flow over standard heads. As you can see by the photo the intake port is beautifully shaped right up to the valve.
 
 
There are no big lumps protruding down around the valve guide and the area around the valve guide has a gentle taper and good shape to ensure good flow around it. The short turn radius is a smooth and gradual radius up to the valve and into the combustion chamber.
 
 
Here is another photo of the Yella Terra bare head intake ports without the intake valve installed.
 
 
The ports flow good for cams up to about .450 lift, however for head shops that want to play around with the ports to gain better flow figures there is plenty of thickness in the casting for improvements to be gained.
 
 
As you can see the exhaust ports are of a high port design with rounded short turn radius and good volume to allow the exhaust gases to escape.
 
 
This 12 port head design really allows you to take full advantage of exhaust gas scavenging headers because of the free flowing design exhaust ports. The older red motor head had low and bumpy exhaust ports interrupting the air flow out from the exhaust valve, which limited tuning and performance gains.
 
 
The 12 port head has taller ports than the early head hence the inlet manifolds are different too. The photo above shows the difference between the two AussieSpeed aftermarket 4 barrel performance inlet manifolds with the 12 port on the left. The photo below shows the 12 port manifold sitting on top of the Red motor manifold.
 
 
This intake manifold has undergone extensive flow bench testing by Aussie Speed during the design stage to ensure all ports flow within 5 cfm of one another as cast for out of the box bolt on perfromance. The biggest improvement in this manifold’s port design has been the centre divider to ensure cylinders 3 & 4 do not run rich, which has been a problem with all brands of aftermarket manifolds for the Holden six cylinder engine in the past. 
 
 
 
The AussieSpeed design also ensures an even pull of air from under the carb with out the air pulsing sideways every time cylinders 3 and 4 draw from the manifold, this results in improved signal strength under the carb and a more even draw under the carburettor venturis.
 
The inlet valves measure 1.74 inch and the exhaust are 1.55 inch diameter.
 
 
 
The Yella Terra alloy head for the holden six is available in either high compression or low compression model. The High compression head is for your typical street engine with standard or flat top pistons with a combustion chamber size of approx 56cc. The low compression head has a combustion chamber size of approx 72cc. All the photos here show the low compression combustion chamber.
 
 
Essentially the difference is that the high compression head has more shaved off the mating surface to obtain the high compression ratio. These heads are ready to go right out of the box making it pure bolt on performance. The low compression head serves a couple of purposes. First up if you want to turbo charge or supercharge an existing high compression engine you could bolt on the low compression head and even if you have pop up pistons your compression will be lowered enough to run a reasonable amount of boost. Secondly it is almost easier to get forged pop up pistons for the Holden six than it is to get flat tops so if you want a strong piston you can go for a pop up piston then mill the low compression head enough to get your desired compression ratio.
 
If you want to calculate compression ratios then down load our Kustom Bitz Dyno spread sheet on engine calculations here.
 
Another feature of the Yella Terra head is that the rocker cover mounting surface is machined flat in the CNC mill so you can be sure the gasket surface in nice and flat so your gaskets will seal.
 
 
Yella Terra heads for the Holden 6 come complete, assembled with Crow Cams springs with inner dampener, chrome moly retainers and valve locks, suitable for most streetable cams up to .450 lift, or they can be ordered with heavier springs, or are available as a bare head for those who wish to run something more radical and will need to match valve train components. The rocker arm studs are tapped 7/16 UNC.
 
Available now from Kustom Bitz.
 
Article and photos produced by Kustom Bitz 2008.
 

Holden 6 Cylinder Alloy Head Blue & Black motors - Yella Terra
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