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Old 06-18-2010, 05:40 PM
oldbogie oldbogie is offline
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Quote:
Originally Posted by ThirdDegree
Im talking 305 vortecs vs 350 vortecs, not pre vortec vs vortec, fastburn etc. I have been doing Fords, like what it says in my intro post. The 305 is flat tappet.
305 heads while called Vortecs are not in that they do not include any of the features of the L31 Vortec found on the 350. The 305 vortec is simply a rehash of the 305 heads, some are slightly better than others but none offer the advantages of the L31 Vortec. Something GM's advertising department knows nothing about.

Back in the 1970s and 80s it was popular to use the 305 head as an inexpensive and quick way to get the compression up on a 350. For a 350 this took porting to 350 port dimensions and installing 350 size valves, an activity as like to find coolant as result in usable ports. Regardless of the ports achieved, unfortunately the 305 combustion chamber is inefficient at best. It has the spark plug in a distant location from the center of the cylinder bore as with the large smog chamber 350 heads of that era resulting in a long burn time that requires too much advance which causes the engine to be detonation sensitive and fuel hungry . While most rodders are carried away with port and valve sizes as the path to power, the subtle shapes of the combustion chamber are equally as important if not more-so toward power development. This is where the really important changes in the L31 head occur. The combustion chamber of the L31 head returns the lost knowledge of Sir Harry Ricardo to engine design. Over at Ford it's the GT40 head and at Chrysler the Magnum LA or Ram head. All of these heads push the spark-plug as far toward the center of the chamber as the valve location permits, introduce the so called heart or liver shape which provides dual side squish and quench for fine fuel and air mixing (squish) and an area of heat sink (quench) which builds detonation resistance. A beak is projected from the squish/quench deck between the valves to isolate and redirect intake flow from going out the exhaust valve during cam overlap. All this is long known technology from before WW-2. These configurations can be found used on the 1953-55 Lincoln Y block and the 1954-55 Ford Y block, in a somewhat simplified form on the 1955 to 1970 Chevy small block, as well as others. But gradually these features were removed by the finance cost cutters at the factory which had the effect of reduced engine efficiency and detonation resistance. The factory's figured that the cost they saved of a few cents per head which reduced your performance and increased your operating cost due to higher fuel burn rates, and the increased emissions into the environment could just be transfered to the end user. This worked into the mid 1980's when increasing government regulation on emissions and fuel mileage finally forced them back to original and more efficient design principles.

The incorporation of electronic fuel injection and Honda's stratified charge combustion chamber being the final irony as both are American inventions rejected by American manufacturers back in the 1950s. EFI was developed by Bendix using the then new transistor technology and offered as an option by Chrysler in 1956 and 57 but people were more interested in putting their extra money into air conditioning. The hugest irony is that the stratified charge technology used by Honda was developed by Texaco under a government contract with NACA (the predecessor of NASA) to develop a method to increase the range of bomber aircraft so that Germany and Japan could be reached by bombers from the continental United States should England and Hawaii fall into enemy hands.

Anyway 305 heads on 350's is old hat. The work and cost it takes to make them competitive against a comparably equipped L31 Vortec headed engine isn't worth the outcome. The money is better spent on L31 heads even for, and they will fit, a 305, just getting the valves into the cylinder bore, but just is more than good enough in this case.

Bogie
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