V8 Crank Education Please!

[Triggerfish]

Now, I could have brought this up on any number of forums, but hey, you lucky Maserati fans, I thought I'd park it here!
Can anyone explain to me, in layman's terms, why V8 engines sound so different depending on the heritage? American muscle V8's have a sound of their own. Why did my GT sound so different (Better!) than my Ferrari 430 considering they had the same engine, albeit a different crank. Why does my 458 scream and my 289 mustang rumble? Ferrari flat plane, maserati Crossplane? What does this mean, and why does it make such a difference to the sound?

 

[Zep]

A flat plane crankshaft means that the big end journals and the main bearing can be intersected by a single straight line. In practice, this means that pairs of pistons reach the top of the compression stroke at approximately the same time (in fact, it is slightly out, based on the angle of the vee). This means that a flat plane V8 could be described as two 4 cylinder engines firing a few degrees out from each other. The net effect on sound is that they sound like a four cylinder in stereo. Hence the scream.

A cross plane crankshaft mean that the big end journals are at different angles to the main bearings. Hence why they are sometimes called bent 8s. This means that the firing of the cylinders is not equal, with some of the cylinders firing closer to each other and others further apart. The net effect is that you have the offset “throbbing” note that you hear from an American V8. The difference between an American V8 and a Maserati one is exhaust tuning and camshaft timing.

or something.

 

[Mr Spoon]

A cross plane crank is the most common V8 crank. The firing order will dictate the sound.
Number your pistons 1 to 8. Odds on passenger side, evens on driver side.

As an example, a common firing order for a cross plane will be:

odd, even, even, odd, even, odd, odd, even

Having two consecutive cylinders fire on the same bank limits exhaust gas scavenging (the vacuum affect) which gives the traditional V8 sound.

The flat plane, if i remember correctly, is race car technology. They do not need counterweights so are smaller and lighter, they rev faster and higher because they fire left, right, left, right etc


If you imagine a crank shaft. For a cross plane, imagine a cross. The top being 1 and go clockwise, 2, 3, 4 etc.

if you imagine where the con rod connects to the crank, 1 is at the top, 2 is the right side of the cross, 3 the bottom, 4 the left. So when you look side on, its in the shape of a cross.

Flat plane, when you look side on they appear to be in the shape of a capital I.

Balance, exhaust scavenging, firing order, vibration all make up the sound of the engine.

Flat planes are much more difficult to balance than a cross plane.

 

[2b1ask1]

Nicely put Zep, Might want to add the Septics predominant sticking with push rods v overhead cams allowing the latter to rev higher and generally a much better performance for capacity. For example a modern Hardly Ableto motorcyckle at 1700cc boasting a whopping 60HP compared to a Ducati Paniale at 955cc outputting 155hp.... I know which one sounds better to me

 

[Triggerfish]

Thanks all. Thats really interesting. I don't know why I waited so long to ask the question. So the race track heritage is the reason Ferraris are Flat plane?
Funny you mention the Harley. I wanted to bring that one up but thought I'd stick to four wheels. I thought I was the only middle aged man who really doesn't like the sound of a HD

 

[Zep]

On the subject of balance, the flat plane crankshafts actually have smaller counterweights than a cross plane, because there is less mass perpendicular to the lightest point. So they are actually easier to balance form a rotational mass point of view, and give better throttle response (less inertia), which is why it’s sometime known as “race” technology. The first V8s were all flat plane, by simple virtue of them being easier to make.

However they suffer from secondary out of balance forces (where balance force acts vertically against the mounts, also a problem with flat 4/6/8 engines).

This secondary force is not managed by balancing as such, but is dealt with by harmonic balancers like a weighted front pulley or balancer shafts.

Cross plane engines are far more populous, because with a cylinder firing every 90 degrees they are smoother. But with heavier rotational mass and therefore lower rev limits.

 

[Zep]

A lot of early Ferrari road engines were derived from race engines or designed by race engineers. Some moved away from this for refinement, Ferrari didn’t.

Interestingly the Ferrari V8 that was installed in the front of the Lancia Thema 8.32 had a cross plane crank, despite the base engine being flat plane.

 

[Mr Spoon]

Another way to view this is, cross plane, fitted every 90 degrees. Flat plane every 180 degrees

 

[midlifecrisis]

Further to above, altering the crank pin angles within an engine alters the torque characteristics. Maserati cross plane is smoother for cruising.
A prime example of altering firing angles came in motorcycle racing.
The 500cc V4 2stroke engine in a Grand Prix Motorcycle became viciously powerful with an all or nothing powerband in the late 80's and the tyres couldn't translate that power into forward drive. This often resulted in high-side crashes exiting a corner.
Honda changed the crankshaft so that all the cylinders fired within 90degrees, the so called Big-Bang engine. This eased the stresses on the tyres and the racing got safer and ironically faster.
Nowadays, the 1000cc 4-stroke MotoGP engine produces 250-300bhp but electronics and aerodynamics (on a motorcycle!) reduce rear tyre spin and also control wheelies, meaning better forward traction.

 

[davy83]

I was under the impression that US V8's were (at least in the past) long stroke giving them more torque and a deeper rumble, but poor HP for size and not allowing for high revs. Whereas a short stroke engine will rev higher and also Newtons comment about push rods vs overhead cams also adds to this higher output capability. My old TVR S2 had a 3 liter ford V6 with push rods and it didn't rev high, and produced 170HP on a good day, whereas my 3200 has a 3.2 L V8 producing more than 400HP so more than double. I reckon its long stroke, vs short stroke and overhead CAMs and probably compression ratio, and possible the two huge F%^K off turbos

 

[allandwf]

I have seen an excellent animation showing both. The Cerbera was flat plane, and I wanted to see the difference then. I will try and track it down .

 

[allandwf]

This explains how one burbles .

 

[TimR]

Honestly, I think this short, animated naration is far more informative...
Sorry to say you guys are riddled with typos and errors throughout this thread...to the uninitiated like me, it is all but uninteligible...! lol