YELLA TERRAS LEGENDARY ALLOY 12 PORT HEAD IS BACK!!!
The Yella Terra Legendary alloy 12 port head to suit the Holden Straight 6 has been reintroduced 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 (Rough Cut).
The lightweight alloy casting features re-designed water jackets for much improved head cooling.
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
- Low Compression (Standard Chamber) 74cc - Can be faced to 56cc chamber size
BARE HEADS ONLY (ACH 33C74) HAVE .080" OF EXTRA MATERIAL ON THE JOINT FACE TO ALLOW GREATER RANGE OF COMBUSTION CHAMBER SIZES.
Punch some life into your Holden 6 with Yella Terra!
Available in 74cc bare or 72cc & 56cc assembled form.
Valve Seats installed - Rough Cut
Technical Specification
| Material | AS 601, 356-T6 heat treated aluminium |
| Assembled Weight |
11.5kg |
|
Assembled CC Volume |
48cc |
|
Bare CC Volume |
68cc |
|
Intake Runner |
82cc |
| Exhaust Runner | 71cc |
| Intake Valve | 1.740" |
| Exhaust Valve | 1.480" |
| Valve Guides | Solid Brass |
| Inlet Valve Seats |
Cast iron 1.812"x0.250" ROUGH CUT |
| Exhaust Valve Seats |
Lo nickel chromalloy 1.625"x0.250" ROUGH CUT |
| Spark Plugs | Tapered seat |
| Deck Thickness | 0.450" |
| Installed Height | 1.520" |
| Rocker Post | Machined for 7/16" screw in stud |
|
Spring Seat OD |
1.250" |
| Assembled Part No. | ACHA 33C72 / ACHA 33C56 |
| Bare Part No. |
ACH 33C72 |
* - With extensive CNC Porting can achieve over 300+ HP potential
