YELLA TERRAS LEGENDARY ALLOY 12 PORT HEAD IS BACK!
NOW AVAILABLE AS A "HEAD AND ROCKER" PACKAGE - ACHA 33C56 + ST 2031A
The Yella Terra Legendary alloy 12 port head to suit the Holden Straight 6 has been re introduced into the Australian Market. Revised port designs that flow over 30% better than that of the factory 12 port heads with potential for much higher flow figures when professionally ported. This dramatic improvement is due to the development of the taller, wider ports, improved “short turn radius”, larger valve throats and bowls as well as streamlined valve guides, giving huge increases in port volume and airflow efficiency. Half the weight of as cast iron head, these heads are fitted with 2% nickel iron inlet and hard nickel alloy exhaust valve seats.
The lightweight alloy casting features re-designed water jackets for much improved head cooling. And is available with a choice of 56cc combustion chambers or CNC profiled 72cc low compression chambers for forced induction
This new performance product will transform your vehicle with more free revving power, improved performance and reliability with the following features:
- Excellent Flow figures: 240HP potential out of the box*
- Average of .250” port wall thickness for custom porting
- Over 60% lighter than factor Iron Heads
- Flow over 30% better than the standard Heads
- Holden exterior design with totally revised ports and water jackets for improved cooling, reliability and performance.
- Standard Compression 56cc Chamber
Note for Assembled Heads – Our Assembled 6 Cylinder heads are setup for .470” Max lift. If your engine configuration will exceed .470" lift at the valve, it is recommended you purchase our Alloy 12 Port head as a Bare 74cc or 68cc and source your own Valvetrain to your required specs.
TECHNICAL SPECIFICATIONS BARE HEADS
| MATERIAL | 356 Alloy Heat treated to T6 |
| CHAMBER VOLUME | 56cc - also available in assembled 72cc (Suit Forced Induction) & 48cc (Hi-Comp Road Racer) |
| INNER RUNNER | 82cc |
| EXHAUST RUNNER | 71cc |
| INTAKE VALVE | 1.740” |
| EXHAUST VALVE | 1,480” |
| VALVE GUIDES | K Liners |
| VALVE SEATS | Inlet Cast Iron 1.812”x .250” / Exhaust Nickel Chromalloy 1.625” x .250” |
| SPARK PLUGS | Tapered Seats |
| INSTALLED HEIGHT WITH STD VALVES AND .060” VALVE SPRING INSETS/SHIMS - 1.520” | Spring Seat OD. - 1.250" |
PACKAGE INCLUDES:
- Yella Terra ACHA 33C56 ASSEMBLED ALLOY HEAD
- Yella Terra ST 2031A ADJUSTABLE STREET TERRA ROCKERS SET (1.5 Ratio)
* - With extensive CNC Porting can achieve over 300+ HP potential
