The wait is over as the new Mummert aluminum heads have now been run on an engine with the following results.  56 horsepower increase over the stock heads!!!!!!  In their first day, a total of 24 pulls were made with the aluminum heads to test a variety of timing, carburetion, carb spacer, jetting, and exhaust changes.  The aluminum heads themselves were tested as delivered and used in the ‘out of the box’ configuration with no porting being performed.

The engine used for the test is a +060 over 312 with the cast flattop pistons 0.025” in the hole and stock G heads that had only a good valve job with hardened seats installed and a 0.025” mill to clean up the deck side of the heads.  No port work.  The compression ratio calculates to be 9.2:1.  The engine is running the factory 1.54:1 rockers, Mummert single four intake manifold with a two inch four hole spacer, and a 750 cfm vacuum secondary carb.  The camshaft is a Crower Monarch grind ground on 110° lobe centers, 280° advertised, 238° @ 0.050”, and 0.430” lift at the valve after the lash is set.  Prior to the head test, a 465 Holley, a modified 600 Holley, and a 750 Holley were all tested and the 750 simply shined above the rest.  The 465 just gives up earlier and the 600 fell in behind the 750.  These same carbs were used with the aluminum heads with the performance order being the same but much more pronounced.

To keep the tests reliable and truly comparitive, both the iron and aluminum heads were ran back to back and on the same day.  The engine was ran first in the morning with the iron heads to get some baseline numbers.  The dyno numbers for the G heads are 286.1 HP @ 5300 rpms and 336.4 lbft torque @ 3400 rpms.  Although there was a 290HP number on one of the pulls, it was disregarded due to the water temperature being on the cool side.  These are still respectable numbers for stock unported G heads.

It took just a bit over two hours to swap out the iron heads to the aluminum versions.  The engine was then started, heated up, stopped, and allowed to heat soak.  At this point the valve lash was rechecked.  As an FYI, the heads grow about 0.004” from ambient to hot so setting the valve lash at 0.015” initially nets 0.019” hot.  After a series of dyno pulls to determine what the engine preferred for new ignition timing and fuel mixture attributes, the numbers for the aluminum heads are as follows:  340.6 HP @ 6100 rpms and 357.5 lbft torque @ 4400 rpms.

The new heads do like leaner fuel mixtures and considerably less total timing.  They are definitely more efficient.  Whereas the iron heads liked 38-40° total timing, the aluminum heads are happiest with 32-33° total on this particular combination.  Intial testing shows an Autolite 3924 spark plug being a good middle of the road spark plug to start out with.  Spark plug gap for the tests was at 0.035”.

With the 2” four hole carb spacer, the aluminum heads outperform the iron heads at all rpm ranges.  With the 2” tapered carb spacer and below 2800 rpms, the iron heads are only marginally better in torque than the aluminum versions, but after 2800 rpms, the aluminum heads simply run away from the iron versions with the best peak horsepower numbers.

With ‘out of the box’ aluminum heads and no port work, 1957 supercharged performance is now available without having to use the supercharger.  There is still some more dyno testing yet to be performed after which point the heads will be pulled off of the engine and disassembled.

Lorena, Texas (South of Waco)