Talk:Inline-four engine/Archive 1

-Hmm... I was thinking about the article down here of the straight four engine. It is mentioned, that the biggest non-diesel of this kind of engine is the Pontiac's motor. But I have read about much larger machines existing, which used petrol/gasoline or similar fuel and worked in the way of Otto- fourstroke cycle and were used in cars. These cars were built in the very beginning of the 20th century, and they were mainly sports- or racecars. On the other hand these vehicles were also sold to the public and some of them were available in the form of familycar.

To name a few which were driven in a Gordon Bennett Cup in 1900-1905 in Europe, a formula one/rally racing of its time;

Napier, Panhard, Mercedes, Richard-Brasier, Fiat, Renault, De Dietrich, Wolseley, Pope-Toledo...

These considerably large cars had the size of engines that would amaze even those who drive around with their big-block musclecars: Generally the displacement varied from 10 to 16 liters. And these giant engines were INLINE FOURS!!!! One of the biggest singular machines was the De Diethrich's 17-liter straight four which is over twice in size compared to the Cadillac 500cid 8.2-liter v8!!!

But the power they produced was not that amazing. Leadless, low-octane fuel; sidevalve configuration; longstroke or undersquare strokeratio and the low technical experience of the beginning of the internal combustion engines era limited the power available considerably. Spesific output was around 10 horsepower per liter and in practice ranged from 60 to 130 horsepowers in these mammoth machines.

I was wondering that could someone find out if I'm right, or wrong and could it be mentioned, that somewhere in the darkness of history there were mammoth engines with displacemend hard to imagine today.

Please forgive me my poor english, I tried to write as well as I could.

-A Machine-enthusiast from Finland... 28 July 2005

Ok. I took the liberty to alter these pages. Hopefully it is correctly done as this was my first time trying this for real.

-A Machine-enthusiast from Finland... 28 July 2005


 * Most straight-4 engines, however, have been over 1 L in displacement.

Maybe in the USA, but not in Europe. I changed to 0.7 L. Please take a look at Simca 1000, Renault 4, Renault 8, Fiat 600. Fiat 850... Randroide 12:41, 16 November 2006 (UTC)

Displacement Limitation
The current "practical" limit to the displacement of straight-4 engines in a car is around 2.7 litres.

I'm not sure how this conclusion was reached other than the fact that 2.7 seems to be the CURRENT limit before an automaker will employ it a I5, I6 or V6. Porsche had a mass production 3L 4 banger in the 944 and there wasn't anything particularly "impractical" about it other than it was a Porsche. Kensuke Aida 13:24, 19 April 2007 (UTC)

Crank angle and piston speed
This is in ref to 180 versus 90 degrees: "While an even-firing straight-4 engine is in primary balance because one pair of pistons is always moving up at the same time as the other pair is moving down, piston speed—as with all internal combustion engines—is higher through the top 180° of the crankshaft rotation than the bottom 180°."

If you have a straight-4 with two pistons at TDC and one at BDC, and you turn the crank 180 degrees, the ones at the bottom will now be at the top, and vice-versa. This means that the same total distance was traveled by all four pistons during 180 deg of crank rotation. Now, if you turn it only 90 deg instead, all four pistons will be below halfway between TDC and BDC. This means that the ones going up were going slower. For the remaining 90 deg, the opposite is true until the pistons reach their respective TDC/BDC locations. This is why the phrase above should say 90, not 180, because the velocity difference is within each 90 degree rotation of the crank.

I will leave it at 180 for now. Prove me wrong while I go to work, and if proving me wrong can't be done, 90 degrees it shall be. 99.241.100.231 (talk) 11:48, 30 March 2009 (UTC)


 * In the top half of the rotation the acceleration is higher than in the bottom half because the connecting rods are not infinitely long. The difference is not in speed but in acceleration, so I think I'll modify the text to say that. It's rather subtle, some kind of asymmetric sine wave, but the key point is that there are unbalanced forces causing an up/down vibration at twice engine speed. And the bit about "all internal combustion engines" is wrong - there are some unusual and complicated connecting rod designs in that eliminate the problem, so I think I'll delete that bit. RockyMtnGuy (talk) 17:18, 30 March 2009 (UTC)


 * The revisions to the article make sense. 99.241.100.231 (talk) 22:18, 30 March 2009 (UTC)