Re: How come Packard didn't make an OHV straight 8?

Posted by Rusty O\'Toole On 2008/6/20 21:44:25

It is a serious mistake to assume that OHV engines are better than flatheads. For almost 30 years, the flathead was better in every way.

In the early days of making engines, they tried every possible arrangement of valves. By 1920 or so, most could be classified as either OHV (overhead valve) or L head(flathead).

Then, English inventor Harry Ricardo invented the Ricardo head. This immediately made all other designs obsolete, at least for regular road going vehicles.

The secret of the Ricardo head, an improved flathead design, was to bring the head down tight to the top of the piston. This did 2 things: reduced the effective size of the combustion chamber, and caused the piston to squish or squirt the mixture into the valve chamber. This swirling turbulence made the mixture burn very fast and evenly, when the spark plug fired.

Flathead engines already had advantages of simplicity, low cost, silence, and reliability. The Ricardo head made them as powerful and economical as an OHV.

After 1921 nobody made a new OHV engine for almost 30 years. The only exceptions were companies that had pinned their faith the OHV engine years earlier and stuck with them out of tradition. This included Chevrolet, Buick, and Nash in the US. All had made OHV engines for years and all stuck with them, even though they had no advantage over the new flatheads in power economy or anything else.

Every other new car engine from 1921 on was a flathead.

The only exceptions to this rule, were racing engines and semi racing engines. By semi racing I mean expensive cars like Stutz, Mercedes Duesenberg and Bentley. For racing it made sense to spend a lot of money to get a small increase in power. These were not ordinary OHV pushrod engines. They were overhead cam, and in some cases hemi head engines. If they had any advantage in performance, it was small and it was bought at a high price.

In most cases they were no faster or better than comparable luxury cars with flathead engines.

So why don't we buy new flatheads today? The answer is in gas quality or octane.

It was only when heavily leaded, high octane gas became available in the early 50s that the flathead became obsolete.

The typical flathead engine is limited to a compression ratio of 7 to 1 or 7 1/2 to one.

It's hard to believe today how little advantage the OHV engines had at these compression ratios.

For example, in 1949 both Cadillac and Lincoln introduced new V8s. Both were similar in size, 331 cubic inches and 337 cubic inches respectively, and both were designed to power luxury cars.

The new modern OHV Cadillac made 160HP. The obsolete, old fashioned Lincoln made 154HP. Both had compression ratios of 7:1.


More sophisticated designs like the Hudson and Packard had higher compression and a power output nearly equal to their OHV competitors. The highest compression flathead ever made was the 1954 Packard at 8.7:1. It was a 359 cu in 212 HP straight eight,standard equipment in the Packard Patrician.

The most powerful engine made that year was the 235HP 331 cu in Chrysler Hemi V8, optional in New Yorkers. Their standard engine was the same engine with 195HP. Cadillac's standard engine was also 195HP.

So you see, up to that point the power advantage of the OHV design was small or non existent.

Hudson and Packard both made excellent flatheads but they overlooked one thing. The public wouldn't buy them.

When they finally switch to OHV V8s it was too late.

In the meantime oil companies increased their octane to the point where 9:1 and 10:1 compression ratios became feasible. By this time, the flathead was relegated to utility duty and all performance engines were high compression OHV designs.