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.
• Both Standard Compression and Turbo Versions

Technical Specifications Bare Head

Material 356 Alloy Heat treated to T6
Chamber Volumes Standard Head- 56cc Turbo Head 72cc
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”
Valve Seats Exhaust Nickel Chromalloy 1.625” x .250”
Spark Plugs Tapered Seats
Deck Thickness 0.450”
Installed Height with Std Valves and .060” Valve Spring Insets/Shims 1.520”
Spring Seat OD 1.250

Yella Terra Rocker Rockers to Suit:

• Yella Terra YT 5008 Stud Mount
• Yella Terra YT 5029 Platinum Twin Shaft in various ratios from 1.5:1 to 1.7:1

Product Reviews for YTACH 33C74 - YT