There are several advantages inherent to an aluminum cylinder head including a great deal of weight savings and considerably improved cooling. This improvement in cooling means we can now run higher compression ratios without detonation caused by localized hot spots. Other improvements to this head are less obvious; for example, flow has been considerably improved by reshaping the combustion chamber. This was made possible by relocating the spark plug and upgrading to 12mm plugs. Early tests indicate that this head right out of the box flows comparably to a Longman GT6.
They will be supplied as shown, with bronze valve guides and hardened valve seats, assembled versions have valves, springs and studs installed. As standard the head is ready to fit 1.15" exhaust and 1.31" intake valves and has a 23cc chambers with a thick deck to allow for plenty of skimming.
How does it perform? We've run one on the dyno, and here's what the numbers look like: the test engine was a 1275 with .040 flat top pistons. Test #1 is a stock cylinder head, test #2 is the Aluminum head with standard valves.
RPM HP#1 HP#2 ---------------------------- 3000 47.80 47.60 3500 56.12 56.97 4000 64.22 67.23 4500 70.31 73.30 5000 73.50 76.30 5500 72.93 79.25 6000 ---- 80.27
As you can see, the aluminum head shows a measurable power increase above 3500 RPM, and, whereas the motor would not pull beyond 5500 RPM with the stock head, with the aluminum head it pulled past 6000 RPM! Flow bench tests show the alloy head outperforms the standard at all lifts. Also, early indications are that this head responds well to mild porting above the valves.
Standard Assembly Includes:
C-AHT345=5 Port Alloy (Aluminum) Head
(4) 12G1322=1.15" Exhaust Valves
(4) 12G941=1.3" Intake Valves
(4) ADU4905=Valve Stem Seals
(8) 88G459=Keeper Pair, 1 Groove
C-AEA524=Dual Valve Spring Set, ST
(8) AEA403=Dual Spring Locating Collars
(3) CHS2515=Thermostat Studs
(6) C-53K487=Manifold Studs
903-0000=Retainers, Crane, Set (Alloy Top Caps)
Uses spark plug RA8HC.