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Predictable Engineering

September 8 2013 at 10:27 PM

George Pence  (Login gpence)
A1
from IP address 108.218.153.39


Response to Re: the stories about the cylinder walls are great , very entertaining

Thin wall casting technology was not about saving weight, it was about saving money. The idea was to avoid using any more iron in a casting than what was necessary for the application. If a manufacturer uses $1 less iron in a casting, and they cast a million of them, the manufacturer has saved a million dollars! Stuff like that is important to the stock holders of a corporation, and its important to the President and CEOs who have to make quarterly and annual reports to the stock holders. If you can accept that truth, and if you accept the fact that automotive engineers are not idiots, then the design of engine blocks should become predictable for you.

The necessary thickness of cylinder walls is dependent upon two things. (1) The compression ratio of a motor, which is in turn dependent upon the octane of the available gasoline. (2) The accuracy of a manufacturers casting process.

In the late 1960s four barrel carburetor equipped motors had fairly high compression ratios, but 1970 or 1971 was the last year of high compression engines among the various manufacturers in Detroit or Dearborn. So 1970 or 1971 is the last years you'll find the cylinder walls cast thick enough for 10.5:1 or 11:1 compression. The 1970 351C 4V was intended to have 11:1 compression. Of course Ford changed their mind at the last minute and by the time the 351C went into production the compression had been reduced to 10:1. So its safe to expect the earliest D0AE blocks will have slightly thicker cylinder walls, because they had been cast for 11:1 compression.

These years were a transitional period. The big deal was gasoline octane, the oil manufacturers were taking the lead out in order to prepare for catalytic converters; lead coats the catalyst in catalytic converters and renders them inoperative, that's referred to as poisoning. In the late 1960s the high octane pump gasoline sold in the US and Canada had octane ratings in the range of 95 to 98. But when they took the lead out the highest octane gasoline sold here in California was 91 octane low lead, or 92 octane unleaded. That's why the Cleveland never had 11:1 compression even though Ford advertised it.

As the compression of engines was reduced the engineers designed the cylinders a little less thick in order to save the corporations a little bit of money in each casting. The manufacturers didn't necessarily reduce compression from 11:1 to 8:1 in one fell swoop, for instance Ford reduced compression of the 351C in steps, from 11:1 advertised in 1969 to 10:1 for 1970 to 8.5:1 for 1972 then finally to 8:1 for 1973. The reduction happened over a relatively short period of time however. In 1969 Detroit and Dearborn were producing motors with 11:1 compression, but by 1973 8:1 was the dismal compression of motors.

The engine blocks cast for low compression have thinner cylinder walls. A block can be cast thick in areas other than the cylinder walls however. When Ford cast heavy duty blocks for trucks, tow vehicles, boats, and post 1970 police interceptors those blocks didn't necessarily require thick cylinder walls, because those motors weren't necessarily high compression, but they needed more material in other areas, like the bulk heads, to sustain heavy loading for sustained periods of time.

I'll guarantee you, it doesn't matter who manufactured it, a 1969 Police Interceptor block had thick cylinder walls AND reinforced bulkheads too, because it was designed for high compression AND sustained high speeds.


-G
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This message has been edited by gpence from IP address 108.218.153.39 on Sep 8, 2013 10:31 PM


 
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