Questions and Answers
Four Or Five Cylinders
Q. Vincent, I am a fervent reader of your site. I find that you explain very well, and I always feel more intelligent after reading your articles. Recently, I have been involved in a conversation at work where people were arguing about 5-cylinder engines.
I have 3 questions:
1) Are these engines better balanced than 4-cylinder and 6-cylinder engines? Why?
2) Would they benefit from a balance shaft?
3) Is that true that they inherently produce more torque than a 4-cylinder (for a same displacement)? Why?Thanks in advance,
PhilippeA. For so many years we have come to think that engines have to have an even number of cylinders. Now in a V engine configuration this is true, since a pair of cylinders share the same crankshaft journal. But in a straight line engine, it doesn't matter since one cylinder gets it's own crankshaft journal.
Each cylinder and crankshaft journal is balanced individually, so the number of cylinders doesn't matter. In cars there are 3 and 5 cylinder engines and they run as smooth and even as the 4, 6 or 8 cylinder engines.
The addition of a balance shaft is needed, in my opinion, because the engine it's in was poorly designed. If the engine is so out of balance that you need extra shafts to balance it, you need to make a better engine.
Torque is not so much a question of how many cylinders an engine has as it is crankshaft design. Let's see if I can explain this properly. Let's say you're trying to move a boulder. It's too heavy to lift so you get a smaller rock and a short board to use as a lever. You put the end of the board under the boulder, the rock under the middle of the board and try to move the boulder. You push down on the other end of the board but the boulder doesn't move. So you get a longer board and now you can move the boulder. Read this article on torque at How Stuff Works for a more detailed, and probably more coherent, explanation.
The longer board gives you more torque. Now think of the distance from the crankshaft center line to the connecting rod journal as the board. The greater the distance from the center line of the crankshaft to the center line of the connecting rod journal, called the "Throw", the more torque the engine will produce. This is why diesel engines produce more torque. Diesels have more compression and thus need a longer throw to produce that compression. As a result, there is more torque produced. Gas engines have a shorter throw, and less torque, since they have lower compression.
A 5 cylinder engine will produce slightly more torque than a 4 cylinder simply because it has an extra cylinder. Think of it as using 5 boards to lift that boulder instead of 4.
Additional Information provided courtesy of ALLDATA
