490 HORSE POWER 'OUT OF THE BOX!'
EARLY 253-308 PRE-INJECTION HI-PORT ALLOY HEADS
P/No. ABH 308-3 (BARE)
The ultimate basis for power generation on pre-injection Holden V8 engines using “Pre-EFI” style intake manifolds and exhaust systems.
Raised intake port design radically improves “as cast” flow up to 40% over standard heads. Redesigned water jackets allow individual porting shops ample scope for further improvement with intake flow figures around 260 CFM possible with radical porting and 2.02” inlet valves.
Yella Terra cast alloy intake manifold spacers are supplied to reposition manifold face to match revised port location. Exhaust port location matches standard performance exhaust flanges.
“Dash 3” bare heads come with semi finished seat inserts fitted ready for cylinder head specialists to perform further modifications and finish seats to their preferred specifications.
Yella Terra “Dash 3” heads are machined for 7/16" UNC threads to suit screw in studs or Yella Terra 7/16" shaft rocker systems. The alloy castings offer a 50% weight reduction over standard cast iron heads.
NOTE: 'Bare Heads' have been finished machined with brass guides fitted not reamed, valve inserts fitted without valve seats cut and material left on the joint face for final milling.
Technical Specifications
| MATERIAL | AS 601, 356-T6 Heat Treated Alluminium |
| MINIMUM HARDNESS | 88HB |
| WEIGHT | Bare 12.5kg -Assembled 19.7kg |
| COMBUSTION CHAMBER VOL | 56cc* |
| DECK THICKNESS | .575” |
| INLET PORT DIMENSIONS | 1.980” High x 1.200” Wide |
| EXHAUST PORT DIMENSIONS | 1.525” High x 1.170” Wide |
| INLET VALVE SIZE | 1.940” Min |
| INSERT SIZE | 2.100” X .250” |
| EXHAUST VALVE SIZE | 1.600” Min |
| INSERT SIZE | 1.625” X .250” |
| SPRING POCKETS | 1.50” Dia Min |
| MATERIAL THICKNESS | .420” |
| INSTALLED HEIGHT | 1.760” with Standard Length valves and .60” Spring Cup |
| VALVE ANGLE | 5.1 Deg |
| VALVE POSITION INLET VALVE | Standard Position |
| EXHAUST VALVE POSITION | Standard |
- Port Location Inlet Raised .600”, Exhaust Standard
- Spark Plugs Machined to accept tapered set or washer seat spark plugs
- Rocker pads drilled for 7/16” studs
- Use YT 5020 or YT 5010 roller rockers
* Combustion chamber volume may vary slightly depending on types of valves used, and how deep they are seated.
