Modern Inline Eight Gasoline Engines

Author: July

Nov. 28, 2023


Just a few notes

The Straight 8 developed because of the need for more power. Luxury car lines like Buick, Cadillac, Cord, Packard, Bugatti, Miller, Duesenberg, Alfa Romeo, and Mercedes needed more power for speed, more torque for smoothness relative to that days other power plants. The Inline 6 was popular so the natural progression was the inline cylinder. Back then it did not matter that the engine was way more heavy than the other types of engines in production. I believe the engine case (block) was produced by investment casting where you put a mold into a sand box and iron was poured into the mold and melted the model leaving an iron 8 cylinder block. This was an expensive process adding production cost to the engine. Only rich people could afford to pay the price.

The V8 design was introduced about 10 years before the straight 8 production engines. V8 had very high production costs and a big secondary vibration problem before the advent of the 90 degree crank shaft.

The 1 piece V8 block was a very complex casting, harder to make than a straight six or straight eight. The alternative was to make the engine block in 3 pieces and bolt it together. So luxury car makers ignored the V8, which was inferior in terms of smoothness, and stuck to the big 6 cylinder, which has the minimum number of cylinders giving perfect primary and secondary balance, and overlapping power impulses.

Besides being heavy the engine was long hence the long hood requirement. Unless you slung it way low and did some expensive things to the oil pan the darn thing stuck way up in the air requiring the entire car to be relatively high compared to other cars of the day. You had to see the road over that long hood. That change after WW2. We had an Interstate Highway system and road speeds were up. Speed and power was the name of the game and the automatic transmission meant the car did the shifting unlike the manual transmission prewar that demanded a lot of gear shifting on the V8 compared to the big torque range of the inline 6 and 8 engines. These engines also had long stoke designs not liking high rpm operation. The public wanted speed smoothness. Comfort became a marketing issue. A lot of ladies who worked on the assembly line during the war wanted cars they could enjoy and drive. A clutch pedal on the straight 8 would wear you out on a long trip. It was all mechanical in the early days and you had to be a body builder to wrestle the early transmissions around. Pushing a button and letting the car shift was a required was a selling point. Foundry technology made the mass production of a flathead / OHV V8 practical and competitive.

The compact (size wise) flathead V8 was putting out some good power number and the Automobile engine was undergoing a lot of refinement. Chrysler produced a very nice Hemi V8 and it grew to 392 CID but it was one heavy engine. The Small block V8 from Chevrolet was introduced in 1966. I had one. This engine would go on to win more races than any other engine in the world and still is as a matter of fact. In the 1960s the requirement to get the cost out of production meant going to a thin wall casting design to save front end weight. Power plant designs were as numerous as the brands. Chrysler took their straight 6 cylinder engine and tilted it for lower hood profile and we had the Slant 6. Chevy offered a 4 cylinder, straight 6, air cooler horizontal 6 cylinder, and two or three versions of the V8 design.

Nowhere was the straight 8 in play unless in a Jeep or other applications requiring a lot of torque.

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Modern Inline Eight Gasoline Engines

.....inline 8 = i8? : r/BMW




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