What makes a V8 sound like a V8?

[Agent WD-40]

I'm assuming it has to do with when the cylinders fire in relation to the rotation of the crank. I'm also assuming the degrees of crank rotation aren't evenly spaced between the firing of every cylinder (eg one will fire at 30, the next 60 the next 75...). Is this correct? Can somebody break down when each cylinder will fire in a given number of crank roations?

Anybody have an animation of when each cylinder will fire in a V8? Thanks!

[dezert_rida]

Originally Posted by Agent WD-40

I'm assuming it has to do with when the cylinders fire in relation to the rotation of the crank. I'm also assuming the degrees of crank rotation aren't evenly spaced between the firing of every cylinder (eg one will fire at 30, the next 60 the next 75...). Is this correct? Can somebody break down when each cylinder will fire in a given number of crank roations?

Anybody have an animation of when each cylinder will fire in a V8? Thanks!

The degrees of crank rotation must be evenly spaced or there would be a horrible imballance.

You have 360 degrees of crank rotation, so a cylinder fires every 45 degrees on a V8.

4 cyl motors fire every 90 degrees of crank rotation, thats one reason they dont sound smooth. V8s sound deeper because there is more rotating mass.

[Agent WD-40]

Originally Posted by dezert_rida

The degrees of crank rotation must be evenly spaced or there would be a horrible imballance.

You have 360 degrees of crank rotation, so a cylinder fires every 45 degrees on a V8.

4 cyl motors fire every 90 degrees of crank rotation, thats one reason they dont sound smooth. V8s sound deeper because there is more rotating mass.

Yeah, it seems they would need to be evenly spaced. Good point.

In a 4 stroke engine any given cylinder will fire every other revloution of the crankshaft (once in 720) so in a V8 you would fire once every 90 degrees and a I4 would be every 180 degrees.

How often the power comes will have a lot to do with how smooth the power delivery is. Longer spacing between cylinders firing will make it seem less smooth.

The other part of balance of an engine has to do with the movement of the mass inside the engine. Some engines are naturally harmonically balanced (I6, V12, V16, any flat engine). Some aren't. Some engines, like a V8, can be fairly easily balance by adding a few counter balance shafts.

[moosehead9]

Originally Posted by Agent WD-40

I'm assuming it has to do with when the cylinders fire in relation to the rotation of the crank. I'm also assuming the degrees of crank rotation aren't evenly spaced between the firing of every cylinder (eg one will fire at 30, the next 60 the next 75...). Is this correct? Can somebody break down when each cylinder will fire in a given number of crank roations?

Anybody have an animation of when each cylinder will fire in a V8? Thanks!

You may find an animation on the How Stuff Works website or try a Google search on the subject.

A 4 cycle V8 engine will fire every 90 degrees and will be evenly spaced. A 4 cycle engine takes 2 complete crank revolutions to fire all cylinders. There are engines that have uneven firing pulses...those that are V type with an odd number of cylinders per bank like a V10 or V6. This was overcome on modern engines of this type by using offset crank journals. They still aren't totally in balance though and some use balance shafts to correct this farther. Flat engines don't suffer this problem as was pointed out by others already.
An inline 6 or a V12 does have the best balance naturally by design. There are many different firing orders possible for a V8 engine so the animation would be somewhat different for each firing order.