Flat Plane Crank

This is a Audodesk Inventor file of a flat plane crank I've been messing aruond with. It's designed to fit a Ford 4.6 Modular engines. Specs aren't pefect yet, but close.

Category:

Science & Technology

Tags:

• Crankshaft
• Crank
• Flat
• Plane
• V8
• Ford
• Modular
• 4.6

[justforever96]

In a flat-plane V8 (or any other engine, for that matter), do two cylinders EVER fire at once? In a 4-stroke, two will reach TDC at the same time, but one is compressing and the other exhausting, right? And that's regardless of whether it's cross-plane or flat? I was arguing about that with a guy who claimed that a V8 can fire 2 cylinders at once, and be more powerful. I'd say that you might as well just make a big 4-banger as have a 8 cylinder divided into 4 power strokes per cycle (2 revs)

[gollumandsmeagol]

@justforever96 No, two cylinders firing at once would cause harsh vibrations that could be engine damaging beyond 6000rpm, like a harley "v-twin" engine. The V-Twin doesn't fire two at once, but fires two back to back and has to come back around a long ways before firing again.

You "could" fire a V8 2 cylinders at the same time, but ONLY with a flat plane crank (not a typical dual plane) but it won't make more power. It's always better to distribute the rotational force, not all at once.

[Silver2004Cobra]

That would be wicked in 8-9000 rpm NA 4.6... have you looked into what it would cost to get it made?

[gollumandsmeagol]

Hard to say really. It looks like it might be doable for around 3k, which would be extremely cheap if you ask me. If you own a machine shop and everything capable of doing it, the material alone is no more than about $300 worth of billet, TOPS! So then spend about 20k of your own time researching on how to do it, and you can do it for next to free! But really, how many people have the tools to do it themselves? Braap who commented here does.... But also remember you need custom cams.

[scrfce123]

If you can machine a crankshaft from scratch, grinding some suitable cams wouldn't be too different.

One question though? What about NVH? Wouldn't this engine need a balance shaft? I imagine that without one, It would run fairly rough.

[gollumandsmeagol]

Yea, cam isn't all that difficult. NVH isn't that big of a deal. The engine is naturally balanced just a strong 2nd order harmonic thats much more annoying than harmful. Keep the stroke low and its not a problem.

[SparkDischarge]

The 2nd order force imbalance is the killer.

Lightweight pistons, lighter connecting rods, and short stroke.

Unless you want to install balance shafts, see VW W8 engine.

[marklandynut]

The flat plane does have one big drawback over the dual plane. Because of its shape there is a tendency for the crank to bend like a banana (also common to a 4 cyl crank), and this can also affect the block. A common problem in early flat plane Formula 1 engines. This can be controlled with balance weights on the crank, but it is harder to get right than a 4 cyl because the forces are more complex. If done wrong the centre bearings can wear rapidly or fail altogether.

[marklandynut]

@mikehermesmeglio Yes, this engine naturally fires L R L R etc. because it is effectively two 4 cyls 90deg apart. In fact, its better than a dual plane crank which fires L R R L R L L R. This means the flat plane has the potential for better power because it can make full use of tuned inlet and exhaust systems. The flat plane V8 is already in production in Europe from BMW, Jaguar, Land Rover and Ferrari and was also used by TVR and Lotus.

[mikehermesmeglio]

@gollumandsmeagol

Is the firing able to alternate between left bank and right banks for one complete cycle?

[mikehermesmeglio]

@gollumandsmeagol

Is the firing able to alternate from left bank to right bank?

[justforever96]

@gollumandsmeagol Thanks...that's about what I figured. I wonder if it's worth going and looking the guy up to tell him he was wrong? Probably not....=)

[seamless4]

thats impressive and would be amazing in the mustang