Flat Crank's

A flat engine or boxer engine or horizontally opposed engine is a type of engine where the pistons lie horizontally opposed, with pairs of cylinders on the left and the right, as opposed to most modern engines where the alternating pistons are positioned in a "V"-angle. Some experts distinguish between V-at-180° engines and real boxer engines. The real boxer has one crank pin per piston while in the V-at-180° engine two pistons share the same crank pin. Real boxer engines can run perfectly smooth and free of vibrations with a four-stroke cycle, regardless of number of cylinders.

The benefit of using a boxer engine versus a V engine is that it provides perfect balance because each piston's movement is exactly counterbalanced by the corresponding piston movement of the opposite side. Boxer-engined automobiles also generally have a lower center of gravity, giving better stability and control. However, boxer engines are also wider than normal engines and are more expensive to build than traditional engines and, thus, are not widely used by automobile manufacturers.

The flat configuration fits very well with air cooling and aircraft engines. Air-cooled designs such as in the VW Beetle used a flat-4, as did the Porsche 356 and 912. Both the older and newer models of the 911 use a flat-6, while Subaru use the flat-4 and flat-6 design extensively, although referring to it as an "H engine". Ferrari used a flat-12 on the Testarossa. Air-cooled flat-twin engines were used by Citroën in their model 2CV and its derivatives, while the Citroën GS used a flat-4, and a flat-6 was proposed for the Citroën DS but rejected due to impractability. BMW uses a flat-twin in many of their motorbikes.

 

A flat crank in a V engine allows for even spacing between cylinders fireing on each bank of the motor.

Rick

 

A combination of tuned harmonics from various engine parts and sub systems

 

"The V8 is a very common configuration for large automobile engines. V8 engines are rarely less than 3 litres in displacement and in automobile use have gone up to 8.5 litres or so. American cars until the mid 1970s almost universally had V8 engines, and many still insist on them.

The normal V-angle for a V8 is 90°. There are two classic types of V8s which differ by crankshaft.

The cross-plane V8 is the typical V8 configuration used in American road cars. Each crank pin (of four) is at a 90° angle from the previous, so that viewed from the end the crankshaft forms a cross. The cross-plane can achieve very good balance but requires heavy counterweights on the crankshaft. This makes the cross-plane V8 a slow-revving engine that cannot speed up or slow down very quickly compared to other designs, because of the greater rotating mass. While the firing of the cross-plane V8 is regular overall, the firing of each bank is not; this makes designing performance exhaust systems more difficult.

The flat-plane V8 design has crank pins at 180°. They are imperfectly balanced and thus produce severe vibrations. As they don't require counterweights, the crankshaft has less mass and thus inertia, allowing higher RPM and quicker acceleration. They're mainly used as racing engines, the most famous example being the Ford-Cosworth DFV.

The Coventry Climax 1.5 litre V8 evolved from a cross-plane configuration to a flat-plane configuration in its latest versions."

Ferrari V8 is the flat-plane, which does make it sound different than the typical American V8 due to the firing order, etc. Ferrari V8 could be compared to two 4-cylinder engines with a common crankcase, which is why my 348 will run (sort of) when the effing ECU shuts down one bank of cylinders.

Cheers
Kevin

 

Nah, not quite. The good Rev. is confusing the arrangement of the cylinders (boxer engine vs. V engine) - which ain't the same concept as the crankshaft configuration.

Cheers
Kevin

 

Great explanation Kevin! I knew the basics but you explained it very well.

 

I was reading that the new F430 are using a flat crank engine for the first time in the past 20 years. I think I have also read that the Testarossa flat-12s are flat crank engine, were they the last ones to use them until now, ie. the F430s?

 

Not quite. the 430 is the first ALL NEW flat plane crank engine in the last 15 years. All the V8's have been flat plane.

 

Please explain, if all Ferrari V8's are flat plane engines, how can the F430 engine be "NEW"? Is it not just an evolution of the 348 engine as the 355's and the 360's?

 

No, the F430 Engine is an evolution of the Maser V8, which also finds itself into the Enzo with another 1/2 of itself.

I dont think the Maserati V8 uses a flat crank, making the F430 version the first 'new' engine that uses such.

I think I understand this right?

 

It is not an evolution of those engines

And Jordan has it right.

 

TRs have a 120 deg-crank (3 throw directions spaced 120 degrees apart). The characteristic that TRs share with the flat-crank V8s (and I believe all F multi-bank engines) is "alternate bank firing".

 

I knew I could count on good old Mr. Magnusson for any technical answers on the Testarossa. First of all, thank you for answering. Can you also explain why the TRs are at 120 degress crank instead of the 180 degree crank, is it because the engine is a flat-12 (180 degree V12), and is there advantages/disadvantages to the 120 degree vs. 180 degree.

 

The Original Ferrari V8 first appeared in the 308 GT4, then the 308 GTB and GTS, (also the 208 series, then the Mondial, then the 328, then the 288 GTO, then the 348, then the F40, then the 355, then the 360. It changed capacities and cylinder head design over the years but always had a flat plane crank. It also appeared in the Lancia Thema 8.32 with a 90 degree crank and front wheel drive!

All of these engines shared the same basic block structure e.g. distance between bore centres etc. Changes in capacity were achieved by increasing the bore and/or stroke. The F430 engine is based on a new block which has a greater distance between bore centres, so will allow bigger capacities and power outputs. It shares it's block structure with the Maserati 4200, but has a different crank and heads?

 

Due to the dynamics of inline motors with even #of cyls (and Ferrari's are built as two inlines sharing a common crank) pistons operate in pairs, one half of each pair on opposite strokes. Those pairs will be spaced evenly around the 360 degrees of crankshaft rotation. So a six will have 3 pairs at 120 degree intervals and a four will have 2 pairs at 180 degree intervals. Those pairs will also be geographic opposites as well. 1-6, 2-5, 3-4, are paired on a 6 while 1-4, 2-3 are paired on a 4.

 

Anthony -- You can believe me when I say I wish I knew my TR less well

With the flat (180 deg) block you can't get an evenly-spaced alternate bank firing pattern to work out with a flat (180 deg) crank with two rods connected to each throw. Since each cylinder fires every 2 revolutions (720 degrees), you need one piston to reach TDC (firing) after every 60 deg of crankshaft rotation (720 deg/12 = 60 deg) and a 180 deg block - a 120 deg crank = 60 deg so it all works out for alternate bank firing.

For the V8 engines, you need a piston reaching TDC every 90 deg of crankshaft rotation (720 deg/8 = 90 deg) and a 180 deg crank - a 90 deg block = 90 deg so that configuration works out OK too for alternate bank firing.

Can someone please post a picture or drawing of a crankshaft from a 60 deg V-12 F engine? -- TIA.

 

Thanks to all that answered my question on the flat crank, especially Mr. Crall and Mr. Magnusson. It is nice to know that I have a 100% Ferrari engine in my car instead of a re-worked Maserati engine, let the flame begin.....

Also, if I recall correctly, the BMW 850's V12 engine must also be a flat crank engine as well, because I remember reading that it operates as if it was 2 I-6 engine. And I think the V8s in the Porsche 928 series are the same too, right?

 

Don't know the P wagen V8 so I can't say but as far as V or flat 12's go with a very few exceptions the crank configurations are all the same, I will include I6's in that statement as well.

And to correct you just a little when we refer to a flat crank, it is just that, flat. The rod throws are opposite each other forming a "flat". A 12 crank is not flat, if you have a look at the pictures you will see what I mean.

 

Steve I hesitate to say this because it may confuse a lot of people here but on current V12's they really don't exactly alternate banks. The V angle is oddly enough 55 degrees to make the motor narrower. And I believe that Ferrari is not the only V12 builder at this time using an odd angle. Still has a 120 crank just doesn't have exact same periods between power pulses.

 

So it runs like, ......a Harley? Hahahahaha. Just kidding. It took me half my life to understand why they ran so funky. The coolest is a nine cylinder radial with one crank throw!

 

Brian -- Understand your point about F fudging the V-angle slighty for packaging reasons (giving some irregularity in the time interval between power pulses), but are you sure that they've abandoned an alternate bank firing pattern? Can you give the firing order and the cylinder numbering layout?

 

Interesting debate - an additional question: Did the 512BB engine also have a 120 degree crank?

If that's the case it wasn't truly a "boxer" - the description of Boxer coming from Pistons punching towards each other, ie a flat (180) crank as well as a flat engine.

 

If you take the more strict definition from the original "boxer" BMW motorcyle engine (opposite pistons reach TDC and fire simultaneously), I believe there are no true "boxer" automobile engines used today.

But just to get opposite pistons to reach TDC simultaneously requires 1 con rod per throw (very inefficent length-wise) so flat designs with more than 4 cyls typically don't do that (although the manufacturer's still call them "boxers" in their literature).