GM Performance Parts (GMPP), the corporation's high-performance arm, has just released a new cylinder head that can add as much as 41 horsepower to the 355hp ZZ4 crate motor. These new Fast Burn cylinder heads (PN 12464298) are the result of what GM calls "cast-ported" technology. In effect, GM engineers utilized what they learned from modifying GM's own cylinder heads and built the new heads accordingly. Designed specifically for use with a flat-top piston, the Fast Burn heads can be decked down as much as 0.080 inch for ultimate racing applications. For less radical applications, GM recommends adjustment of the installed height of the piston to increase the static compression ratio, rather than decking the cylinder-head surface.
Crossing a GM Performance Parts (GMPP) ZZ4 crate engine with GM Fast Burn heads will net approximately 40 additional horsepower. Ken Duttweiler's engine dyno proved the gain.
As the name implies, these heads are designed to burn fuel quickly and more efficiently via the increased cylinder pressures that they are capable of creating. Therefore, they derive more power per given quantity of fuel for better mileage and better power production. Using a taller head casting with a 0.400-inch-thick deck, the factory port design removes more material internally than would be possible with Bow Tie and other previous GM heads.
The intake ports incorporate runners with floors that are 0.024-inch higher than those in a conventional 23-degree Chevrolet cylinder head, providing a better "line of sight" from the intake manifold to the back side of the intake valve. Total intake-port volume is 210 cc. On the exhaust side, the D-shaped ports have a volume of 78 cc. As an added benefit, water-jacketing volume has been increased for better cooling, something not possible with Bow Tie heads due to a lack of deck height and port-to-port casting material. According to GM, the 62cc combustion chambers are the most efficient ever incorporated in a GMPP cylinder head because the chamber is shaped for a cleaner flow through the gasket quench area. Though the heads are fitted with 2.00-inch hollow-stem intake valves and 1.56-inch sodium-filled exhaust valves, the seats can be machined to accept the familiar 2.02/1.60 variants.
The initial dyno test included Fast Burn cylinder heads, a modified intake manifold, and high-profile aluminum valve covers (PN 10185064).
To test these new castings for ourselves, we enlisted Ken Duttweiler's ample dyno facility to run the baseline numbers. We used an out-of-the-crate GMPP ZZ4 motor (with 1.5:1 ratio roller rocker arms and 10:1 static compression ratio), which yielded 353 hp at 5,300 rpm and 410 lb-ft of torque at 3,900 rpm. The ignition timing was 35 degrees; the exhaust was comprised of Hooker headers with 1 5/8-inch primaries and Borla XR1 mufflers; the induction system was a 950cfm Holley on an unmodified GMPP dual-plane intake manifold (PN12366573), which utilizes the Vortec bolt pattern.
With the new heads in place and no other changes, the figures increased to 391 hp at 5,700 rpm and 420 lb-ft at 3,900 rpm. The bottom-end grunt was the most impressive as the torque curve remained essentially flat from 3,300 to 5,100 rpm. In the 1970 four-speed Z28, in which this particular engine will ultimately reside, this kind of streetable torque is what gets things off the line in a hurry.
While this cylinder-head swap is a worthy one, it carries a heavy price. Each Fast Burn casting (complete) lists for $625. Is 40 more horsepower worth that much? Some people think so.
Fast Burn
Tech Notes:
• 78cc D-shaped exhaust port and runners provide excellent out-of-the-box flow.
• 62cc Fast Burn combustion chambers create high cylinder pressures by burning more of the available fuel before the piston begins its downward power stroke. In effect, the engine creates more power for a given quantity of fuel.
• Intake mating surfaces are drilled and tapped for GM Vortec and conventional raised-port intake manifolds.
• Features taller-than-normal rocker-arm rails to provide better clearance for the rocker arm and valvetrain supports, as well as raising the valve-cover gasket height to lessen leakage potential.
• Cast porting allows for larger water jacketing and better cooling.
• Front head surfaces are drilled and tapped for typical accessory-drive bracketry. In addition, the heads are drilled and tapped for plug-wire retainers above the exhaust-port faces.
• Uses conventional rocker arms, valvetrain supports, and hardware.
• GM testing netted maximum total engine timing of 34 degrees.
• Equipped with lightweight, 2.00-inch hollow-stem intake and 1.56-inch sodium-filled exhaust valves, as well as lightweight spring retainers to ensure long-term high-rpm durability.
• Accommodates 2.02-inch intake and 1.60-inch exhaust valves.
• Utilizes 3/8-inch screw-in rocker studs and can accept self-aligning-style roller rocker arms.
Fast Burn Head Flow-Bench Test by GM Performance Parts
(using Super Flow 600 flow bench at 28 inches of H2O)
The heads were equipped with 2.02-inch intake and 1.60-inch exhaust valves-the exceptions include the Brodix Track-1 (2.080-inch intake valves) and the L31 Vortec (1.94-inch intake and 1.50-inch exhaust valves). The Fast Burn heads used 2.00-inch intake and 1.56-inch exhaust valves.
Intake Flow Comparison Valve Lift GMPP Edelbrock Dart Brodix Vortec World Fast Burn Performer Rpm Conquest 200 Track-1 L31 Sportsman II 0.100" 62 66 60 60 58 65 0.200" 136 135 124 130 114 121 0.300" 187 186 180 178 173 177 0.400" 232 215 221 223 216 210 0.500" 266 220 254 256 225 212 0.600" 275 222 261 259 222 225 Exhaust Flow Comparison Valve Lift GMPP Edelbrock Dart Brodix Vortec World Fast Burn Performer Rpm Conquest 200 Track-1 L31 Sportsman II 0.100" 55 55 54 50 43 48 0.200" 104 103 98 103 88 95 0.300" 133 135 130 142 125 120 0.400" 158 151 156 166 143 138 0.500" 180 165 168 175 149 143 0.600" 193 169 175 183 152 152
