Greetings!

 

I hang out in new gen, so that's why I'm posting this here. I'm having a debate in another forum about the inherent balance of various engine configurations. My understanding is that the inline six, flat six and V-12 are the best balanced engine configurations and that the flat four is superior to an inline four. Is it so or not?

 

You never see an inline four of 2.5 liters without a balance shaft, but Subarus seem to manage just fine without- which I think supports my case for the inherent balance of flat four being better than inline fours.

 

Engineers? (That always makes Nipper perk up his ears!)

 

Nathan

Boxers are the best balanced engines. All opposing forces cancel each other out because everything is 180 degrees apart. This is a well established enginering fact. As they get larger, they start taking up more space then a v engine. In line engines make can make a lot of torque, but are not high reving (longer throw crank shafts mean lower redline).

 

http://www.autozine.org/technical_school/engine/smooth1.htm

 

 

happy reading.

 

 

nipper

Boxers are the best balanced engines. All opposing forces cancel each other out because everything is 180 degrees apart. This is a well established enginering fact. As they get larger, they start taking up more space then a v engine. In line engines make can make a lot of torque, but are not high reving (longer throw crank shafts mean lower redline).

 

http://www.autozine.org/technical_school/engine/smooth1.htm

 

 

happy reading.

 

 

nipper

 

 

Thanks for the article. Interesting and proves my point!

 

Nathan

http://www.autozine.org/technical_school/engine/smooth1.htm

 

happy reading.

 

nipper

 

WOW Nipper that is a reall nice piece of reading, and very simple stated. No big science.

I have a picture somewhere which shows the vibrations of the '91 2.2 legacy boxer (image made by SAE i think)

[...]You never see an inline four of 2.5 liters without a balance shaft, but Subarus seem to manage just fine without- which I think supports my case for the inherent balance of flat four being better than inline fours.[...]

Some weight is needed at the crank ends to smooth out power pulses (more so when an engine has fewer cylinders), but it isn't due to inherent imbalance in the horizontally-opposed designs; that's why the "thing" at the end of the crankshaft is a "pulley" and not a "harmonic balancer".

The two smoothest running engines i have ever seen were an h-4 that was in a '97 impreza brighton that i test drove (had bad torque bind so i didn't get it) and the inline 5's that volvo makes.

The "smooth" thing is a little misleading. The issue with inline-4 engines is not a lack of smoothness you feel, it's a harmonic issue. Anyone here ever heard of 4-cylinder "boom?" It's a sound kind of like a constant booooooooom that you hear when an inline 4 is running, and it's more evident at higher rpm. ALL inline 4s have it, but displacements over ~2 liters (more like 1.8 IMO) are worse if they're not balance shafted. That boom is what the balance shafts are there to eliminate, not some sort of vibration that you actually feel.

As the article Nipper posted also mentioned... second order vibrations are viturally non-existant in a boxer 4 compared to an inline 4.

As far as weight balance goes, the only engines that are inherently balanced are boxer engines and inline-6's.

 

That's why Subaru and Porsche use the boxer engines, and that's why BMW has been using inline-6's for so long (smoothness), and that's why the RB26 in the Skyline is such a great-performing engine.

 

Oh, and rotaries are balanced too, but that doesn't mean they're good engines