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Hi

Rereading a January 2011 Hemmings Classic Car article detailing the 1933-54 Pontiac Straight Eights engines, as well as recalling anedotes of an old-time mechanic familiar with those cars, set this line of thought in motion. The article details multiple engineering features designed into those Pontiac eights that contributed to their longevity. Although Pontiac and Packard were in different price segments for the most part, their long histories with straight eights makes for interesting comparisons.

First was a relatively low bore-to-stroke ratio in an era of long-stroke L-heads. For comparison, here's some numbers:

Year/Make......Cu.In......Bore & Stroke...........S/B Ratio.........Torque @ RPM
'33 Pontiac Eight....223.4........3.187 X 3.500.........1.09:1...153@1,600
'35 Packard 120.....257.2........3.250 X 3.875.........1.19:1...203@ 2,000
'35 Packard Eight...320.0........3.187 X 5.000.........1.57:1...260@ 1,600
'35 Super Eight......384.4.......3.500 X 5.000............1.43:1...300@ 1,600

One point was the Pontiac shorter stroke allowed main and con-rod bearing journals a degree of overlap which contributed to rigidity, in five main bearings. Intially that was the case for the 120, also a five main unit. For the Senior engines, nine main bearing providing the support and stiffness. By 1940, we find:

Year/Make............Cu.In.......Bore & Stroke...........S/B Ratio.........Torque @ RPM
'40 Pontiac Eight.....248.9.........3.25 X 3.750......1.15:1......175@1,600
'40 Packard 120......282.0.........3.25 X 4.25.........1.31:1.........225@ 1,700
'40 Super Eight 160..356.0.........3.50 X 4.625......1.32:1...292@ 1,800
'40 110 Six.............245.3.........3.50 X 4.25......1.21:1............192@ 2,000

While the 120 ratio increased with displacement, the 356 c.i. was significantly reduced from the old Senior engines. The Six is added to comparison.

The 1948 comparison:

Year/Make...........Cu.In......Bore & Stroke...........S/B Ratio.........Torque @ RPM
'48 Pontiac Eight....248.9........3.25 X 3.75......1.15:1.........190@2,200
'48 Packard Eight...288.0........3.50 X 3.75......1.07:1............226@ 2,000
'48 Super Eight ......327.0........3.50 X 4.25......1.21:1......266@ 2,000
'47 Packard Six......245.3........3.50 X 4.25......1.21:1......192@ 2,000

The new 1948 generation engines reduced ratios further, the 288 c.i. lower than the smaller displacement '35 120 unit. This also highlights the missed opportunity a decade prior when the Six went to 245 ci to utilitize the tooling to create a 288 ci to replace the 282 ci and further the 327 ci. Just on the greater tooling untilization and reduced manufacturing costs, one would think this would have been obvious at the time.

The final Straight Eights, 1954:

Year/Make...........Cu.In......Bore & Stroke...........S/B Ratio.........Torque @ RPM
'54 Pontiac Eight....268.4........3.375 X 3.75......1.11:1......226@2,200
'54 Clipper Eight....288.0........3.50 X 3.75.........1.07:1......260@ 2,000
'54 Cavalier... .......327.0........3.50 X 4.25............1.21:1.........310@ 2,200

Most striking is the low bore/stroke ratio of the 288 ci, that by '54 it had torque nearly equal to the '48 327 cu.in.. The affect of increased compression ratios for both makes.

My understanding is the pre-war years with mid-60's fuel octane and compression ratios in the 5.5 to 6.5 range, the higher B/S ratios produced more torque at lower rpm's. That was their strength, conversely higher sustained rpms reduced engine longevity. As postwar fuel quality and octane improved, higher compression was possible, above the 8.1 range limit for L-heads. One wonders what the 1948 288 and 327 could have been as higher compression OHV designs

Of the anedotes related by an old-time Pontiac mechanic, he maintained those straight eights really were good for the 100,000 miles they advertised. He claimed they rarely did complete overhauls on those engines until after that mileage if maintained with regular oil changes. I didn't dispute him, though I think the last point is the reason.

So, would anyone care to enlarge on the relative merits and deficits of various bore/stroke ratios?

Steve

your "B/S ratios" are actually "S/B ratios" - these are undersquare designs with B/S < 1. Seems to me there is nothing too surprising - the bigger displacement, longer stroke Packard engines make more torque. Would a shorter stroke engine have tend to less cylinder wear - well yes, but provided rpm was equal, and metalurgy was equal, and lubrication was equal, etc.

The columns labeled "B/S ratio" should be "S/B ratio" since these are all under-square engines (stroke larger than bore), but otherwise an interesting data listing.

Most modern V-8s are over-square design with a few notable exceptions (Pontiac 455 for example). This has to do with superior breathing due to the overhead valve arrangement where a larger bore unshrouds the edges of the valves. In a flat head (L-head, F-head etc, the smaller bore is more appropriate and compatible.

Longer stroke means more low RPM torque because of the greater lever arm of the crankshaft. An obviously important factor in moving a heavy vehicle from start, but clearly not as a good a "feature" today with the common high freeway speeds.

Craig

Steve, if I read your data correctly, the best Packard engine would be the 1953 9-main bearing, 327 cu. in., 180 h.p., 8:1 c.r. because of the s:b ratio and the number of main bearings. It would be the most powerful, have the lowest s:b ratio, and have the rigidity benefit of all those main bearings.

(o{}o)

Hi

Thanks for correcting me on the bore/stroke vs stroke/bore ratio, I should have realized since these are undersquare engines that would be the case.

JW, that was my conclusion too, that a '53 Patrician 327 has all the most desirable qualities to make it the most durable, smooth and powerful of the '48-'53 straight eights.

The '54 359 S/B ratio at 1.26:1, 8.7:1 cr still makes it the most desirable, though no one should turn their nose up at a '53 Patrician with that fine engine. Or any of the others, for that matter.

Steve