Re: Did Chevy consider Packard V8 BB Design?

Posted by Rusty O\'Toole On 2009/3/8 10:24:51

The Chev was also known as the porcupine head and semi hemi.

Chrysler did not invent the hemi head engine. The oldest version I know of was on a 1903 National race car. The french Peugeot firm built a rather sensational race car in 1912 that had a hemi head and that was the one that made them popular in race cars.

But Chrysler was the first company in the world to put one in a mass produced car sold at a price. Before that they were all in race cars, sports cars and expensive imports.

They used a very clever layout for the valve mechanism. The pushrods are quite short and stiff. Given the RPM range the engine was capable of, there was no incentive to use OHC. The pushrods were simpler cheaper quiter and easier to service and repair.

It was 20 years later that the toothed rubber drive belt came along and made OHC practical for mass produced cars.

Better breathing was only one benefit. The hemi also has a better combustion chamber shape and better cooling of the valves. This led to what Chrysler called "mechanical octane" meaning, the Chrysler hemi made full power and performance on regular low octane gas. It did not need high test or high compression. This is one of the long lasting myths, that Chryslers need special high octane gas, quite the opposite, they will run happily on lower octane gas than any comparable engine.

In fact, when high octane gas and engines of over 9:1 compression became available the hemi started to lose its advantage. So they dropped the hemi for a conventional engine.

The T head was also a misunderstood design. Ferguson, the designer of the Pierce Arrow T head engine, said his goal was simply to match the horsepower per cu in of the latest V8 engines from Cadillac and others. He considered making a V8 but at that time (1915) they had problems getting even breathing and smooth running, and they had a 4 cylinder type vibration period that made them unsuitable for a luxury car. These problems were not cracked until the introduction of the 90 degree crankshaft in 1923.

In the meantime, Ferguson took another look at the Pierce 6 cylinder. Close analysis revealed that the V8s had a much larger valve area and this was the secret of their performance. To get the same valve area in the Pierce he would need to use 3 inch valves. This was impractical due to problems of weight, valve wear, noise and valve burning.

So he tried using double valves, 1 1/2" diameter. These gave the better breathing and higher horsepower. Plus the valves and valve springs were so light, the valve action became practically noiseless and valve life was much improved as well.

The T head design was the best way to get a 4 valve cylinder. Overhead valves were not necessary or desirable. The gas available at the time did not permit a compression ratio over 4 or 4.5:1 anyway. So the large wide open combustion chamber was no problem.

The end result was the Pierce Arrow Dual Valve Six. An extremely powerful, long lived luxury car engine. It was smooth, silent, and it would pull a 3 or 4 ton limousine in high gear from a walking pace all the way up to 80 MPH without a tremor.

The new 48HP engine produced more power than the former 66HP and was as economical as the 38HP. So they dropped the 38 and 66 and produced the 48 for the next 10 years.

These are taxable horsepower ratings. The Pierce 48 actually developed over 100HP.

These engines were also popular in boats used by rum runners in the 20s. They prized them for their power, silence, and unfailing reliability.