Modern Inline Eight Gasoline Engines

[Delta Force]

Could a modern inline eight gasoline engine be competitive with other designs, especially for high performance applications such as a limousine or supercar?

 

[Nidum]

There is no answer to that question . The bare fact of an engine being of inline 8 configuration does not tell us much about how it will perform in comparison to engines with other configurations .

All the common engine configurations have advantages and disadvantages as regards performance .

Doing a comparison between one and another engine for a specific application requires a very extensive technical investigation .

Quite commonly though engines are selected on basis of cost of manufacture rather than on pure technical merit .

 

[Ranger Mike]

Just a few notesThe 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.

 

[xxChrisxx]

If it'd be competitive or not is largely irrelevant.

A straight 8 is very long. Long engines are bad for crash performance.

 

[Ranger Mike]

Duesenberg DOHC Supercharged Straight 8 had long stroke, small bore

1948 Buick 320 (144 hp) Inline 8 Engine Bore and Stroke: 3-7/16 x 4-5/16

Just about all the straight 8 engines I looked up had small bores and longer strokes which can not compete with V8 horsepower.

 

[cosmik debris]

Duesenberg DOHC Supercharged Straight 8 had long stroke, small bore

1948 Buick 320 (144 hp) Inline 8 Engine Bore and Stroke: 3-7/16 x 4-5/16

Just about all the straight 8 engines I looked up had small bores and longer strokes which can not compete with V8 horsepower.

Didn't the long stroke/small bore have something to do with tax? I think that tax was linked to bore size which promoted longer strokes for the same displacement.

Cheers

 

[Nik_2213]

Would another factor be the in-line's longer crank-shaft compared to the V's ?

 

[Delta Force]

Would another factor be the in-line's longer crank-shaft compared to the V's ?

That's kind of what I was wondering about. Wikipedia hints at the crankshaft being a weak point of the design, especially at "high speeds." Presumably that explains why there are still inline eight diesel engines, but wouldn't the crankshaft issues still emerge in a V16 gasoline engine?

A straight-eight can be timed for inherent primary and secondary balance, with no unbalanced primary or secondary forces or moments. However, crankshaft torsional vibration, present to some degree in all engines, is sufficient to require the use of a harmonic damper at the accessory end of the crankshaft. Without such damping, fatigue cracking near the rear main bearing journal may occur, leading to engine failure.

Although an inline six-cylinder engine can also be timed for inherent primary and secondary balance, a straight-eight develops more power strokes per revolution and, as a result, will run more smoothly under load than an inline six. Also, due to the even number of power strokes per revolution, a straight-eight does not produce unpleasant odd-order harmonic vibration in the vehicle's driveline at low engine speeds.

The smooth running characteristics of the straight-eight made it popular in luxury and racing cars of the past. However, the engine's length demanded the use of a long engine compartment, making the basic design unacceptable in modern vehicles. Also, due to the length of the engine, torsional vibration in both crankshaft and camshaft can adversely affect reliability and performance at high speeds. In particular, a phenomenon referred to as "crankshaft whip," caused by the effects of centrifugal force on the crank throws at high engine rpm, can cause physical contact between the connecting rods and crankcase walls, leading to the engine's destruction. As a result, the design has been displaced almost completely by the shorter V8 engine configuration.

 

[jack action]

Presumably that explains why there are still inline eight diesel engines, but wouldn't the crankshaft issues still emerge in a V16 gasoline engine?

There are 2 pistons per crank throw in a V-engine. The second piston acceleration probably helps counteract the effect created by the first piston acceleration.

 

[HowlerMonkey]

xxChrisxx is correct about the engine length issue and safety.

 

[Ranger Mike]

cosmik ..this is why i love this forum!
tax the bore stroke ratio...dont say this too loud in the blue states over here
here is great link to why British sports cars were long stroke while the European models were high revving
http://www.mossmotoring.com/stroke-origin-species-evolution-british-sports-car/...the long stoke small bore Usually means lot of torque but low rpm
and that long skinny crankshaft ..to do anything over 5000 rpm would scare me!

 

[cosmik debris]

cosmik ..this is why i love this forum!
tax the bore stroke ratio...dont say this too loud in the blue states over here
here is great link to why British sports cars were long stroke while the European models were high revving
http://www.mossmotoring.com/stroke-origin-species-evolution-british-sports-car/...the long stoke small bore Usually means lot of torque but low rpm
and that long skinny crankshaft ..to do anything over 5000 rpm would scare me!

Yes, the way evolution is controlled by rules is interesting.

Cheers

 

[Fireball Five]

I see these posts are fairly old but my hands on experience may be of interest yet. I ran a 320 inline Buick eight in a dirt track car on 3/8 mi. ovals for 10 years. There are some myths about the BBBIL [Big Block Buick Inline], For one thing I have read many posts saying they are very prone to break crankshafts because of "whip" at high rpm. Another is that they won"t stay together. This is true in stock form. I"m quite sure the broken cranks happen after the main caps break. We fabricated #2&4 from 4130 1 inch steel. Bored a hole then sawed in half and drilled cap bolts, fitted to block then had it line bored. The first engine ran 5 years then broke a rod and junked the block. We built a new one with the same crank and it ran another 5 years and I sold it. This was run from 5200 to 6200 rpm, 2 nights a week each summer for 10 years. that"s 9000 plus laps mostly wide open. I built it without the extremely heavy front vibration damper and with an aluminum flywheel. Of course you could not balance a nickle on the rocker cover at idle like salesmen liked to do in the day, smooth idle was about 2500 rpm with 10.5 comp. ratio and the most radical cam grind Crane had in those days. All moving parts were balanced, the block was modified for full flow oil filter and cooler, oil pump shimed up to 70 lb. press. and pan baffled an deepened with 15 qt. Kendall GT1 racing oil and 3 cans STP. The one major failure was the # 2 rod failed at the wrist pin. I had modified then from a clamper style wrist pin by welding up the slot and boring them for bushing an full floating pins. The 2nd set I took to an aircraft shop and had them zyglowed, shot peened, and heat treated. I think that was the answer. Dozens + of hours were spent boring the ports and valve pockets and grinding pockets for huge Pontiac valves. The 8 would run well over 7000 by accident [spinning.]
It won 3 track season point championships and beat a lot of Chevy V8s. From V8s I chased and those chasing me I would estimate HP about 325 to335. With modern ignition, more compression, racing fuel and improvement in camshaft I think 350 would be attainable. We had 2 Holly 500 carbs and tube intake manifolds
and 8 tuned megaphone exhausts. Nobody ever heard anything like it before or since. It wasn"t a practical thing to build but beating 16000 dollar engines with one designed 60 or 70 years before made it worth while.

Fireball Five

 

[Always Thinking]

Just stumbled on this old post. I love the idea of a modern, aluminum block, relatively high revving inline 8. I have been kicking around the idea of making my own for a number of years. I’ve half heartedly researched the 8’s but never pulled the trigger on creating it. My thoughts were to improve on the Alpha Romeo 159. Any thoughts?

 

[jack action]

I love the idea of a modern, aluminum block, relatively high revving inline 8.

My thoughts were to improve on the Alpha Romeo 159.

Tell us why you love this idea and what are your thoughts for improvements.