Packard Forum Index » V-8 (1955-56)

My 56 Patrician came with a motor rated at 290 horsepower. as I understand it, hp figures back in the day were quite optimistic by today's standards.

What would the V-8s have scored using today's test procedures?

I'm guessing 235, or in that area. Who really knows?

there were 2 differences in hp figures -gross hp then vs net hp now,and the "optimism" applied by the marketing folks

Rule of thumb when converting gross to SAE net HP: subract 15pct, i.e., multiply by 0.85. So, 290HP gross is 246HP SAE net. YMMV.

Craig

"Gross" HP figures were obtained on the test stand or dynamometer. The engines were run with no fan, no generator, no air filter, no mufflers and no transmission. Carburetor and timing adjustments were set to whatever gave the most horsepower even if it meant the engine blew up after 5 minutes.

Some cars also got a substantial boost in power by way of the advertising department.

"Net" HP is as installed in the car with all accessories, adjusted to factory specs.

There is no hard and fast rule but I would say the Net figure is 25% lower. One reason it is hard to compare is that the net figures came into use just at the time all American car makers were killing their engines' power in the name of emissions and unleaded fuel.

The percentage loss from gross to net also depends upon whether the engine is higher performance or not. Since the parasitic losses Rusty listed above are basically fixed, the basis (gross HP) determines the percentage. I.e., a higher performance engine will see less percentage gross-to-net reduction than a low performance engine.

The change from gross to net HP rating occurred from 1971 to 1972. For a specific example, the 1971 Pontiac 455HO (High Output) was rated at 335HP. Essentially the same engine in 1972 was rated at 300HP. The percentage difference is about 10.5%.

The lowest performance engine for Pontiac those years were the 350CID 2bbl. 1971 was 250HP, 1972 was 175HP, which is a 30% reduction. Of course the 1971 numbers were adjusted by the advertising department (the 250HP number was no doubt too high), but you get the idea.

I would consider the 290HP 1956 Packard 374 V-8 to be a "high performance" engine, so 15% reduction is a good value for it.

Craig

I found an article in the March 1955 Hot Rod Magazine on the "then new" Pontiac V-8. It describes the engine testing procedure following the test code adopted recently by GM.

Fuel, oil and water pumps connected and operating.

Generator be rotated by the fan belt, but not charging.

No fan or air cleaner is used.

Carburetor heat is blocked off.

Stock exhaust manifolds used to carry exhaust into large capacity collectors.

Spark advance manually adjusted to produce maximum torque.

93 octane Research gasoline for Pontiac's 8.0:1 CR engine.

Dyno results mathematically corrected to 60F and 29.92in-HG [sea level atmospheric pressure].

For example, Pontiac's 287CID V-8 8.0:1CR engine produced 180HP at 4600rpm, 264 lb-ft at 2400 rpm.

As you might recall, Packard's then new 352CID V-8 8.5:1CR V-8 produced 260HP at 4600 rpm and 355 lb-ft at 2400 rpm. According to an article in HRM on August 1955, the same "GM test code" was followed.

To get the rear wheel horsepower, one can use the 1/4-mile drag test results from car magazines at the same time. A 1955 Packard Patrician which weighed 4800lb with driver and passenger ran the 1/4-mile drag at a trap speed of 78mph. This correlates to 178HP rear wheel. 178/260 is 0.685 or a reduction of 31.5% between gross and rear wheel net HP.

Driveline losses (converter, transmission, gears and tires) are usually considered to be about 15% of the difference between SAE net and RW HP. So, a reduction of about 16% would be a good number for gross to 1972 SAE net HP on a 1955 Packard Patrician.

Craig

Horsepower in the fifties were just as likely to be documented by the Sales Dept. as by Engineering. In an earlier thread we finally concluded that the 1955 Patrician engine and the 1955 Clipper Custom engine were exactly the same. Yet Packard claimed 260hp for the Patrician/400 and only 245hp for the Clipper Custom. Even Packard fudged when the Sales Dept. demanded it.

Quote:

While the engines, per se, were the same, the fitment was not. The Clipper had a SINGLE exhaust, whereas the Patrician had a dual exhaust. +15HP at maximum rpm seems reasonable for a freer flowing exhaust.

However, I will concede that the marketing department had final say on the advertised HP numbers.

Be that as it may, the point I was addressing was the power DIFFERENCE between measurement methods (gross vs SAE NET) regardless of brand.

Craig