Packard Forum Index » Pre-War (1899-1942)

Hi all, I have two cylinder heads for my 1930 740. The one that is on the car has the letters "HC" stamped in the top of the head on the driver's side near the firewall. The other has no such markings. I assume HC stands for high compression. According to the Kimes book, Packard often offered engines with a choice of different heads / compression ratios. I don't believe it is stated in the book whether such choices were offered for the Super 8s, 740 and 745, although it mentions such a choice for the 734 speedster. Does anyone know whether different heads were offered for 740/745?

5.03, 6.00 and 6.52 heads were offered for the 726/733/740/745. This info from the 7th Series Part List which is available on this site for your viewing. There is also a 4.80 head listed for the 726/733 and 4.73 for the 740/745; these low compression heads were generally for export vehicles where gasoline quality was considerably less than in the U.S.

Thanks Owen. Examined both heads closely but can't find a piece number stamped on either, so can't tell if the engine is 6.00 or 6.52. The speedster, which had modified block and carburetion, had a choice of two heads, 4.85 and 6.00, the latter requiring anti-knock fuel but boosting horsepower by 20 to 145. Some specs say the standard 385 developed 105 hp and others say 109. I wonder if a high compression head is what made the difference.

You could "cc" the combustion chamber and then just calculate what your current compression ratio is.

Horsepower increase came from a package of changes including carburetor, breathing (angled ports), etc. I forget, was valve size also increased? It's all well documented but I'd have to look it up.