flat plane crank

hinoonaz · #1 (**permalink**) 04-05-2016, 06:22 PM

What exactly is a flat plane crank. What are the advantages etc. Curious

Luce · #2 (**permalink**) 04-05-2016, 06:50 PM

I'll bite. I haven't seen a good explanation and I think I have a good grip on the subject.

A flat crank looks like the crank you would find in a 4 cylinder where the throws are 180 degrees apart. Using it in a V8 makes the engine fire LRLRLRLR instead of the familiar RLRRLRLL pattern all american V8s share. Some start at different parts of the sequence, and some may do it backwards, but they all share the same pattern.

The big advantage is the exhaust pulses are evenly spaced on each bank making standard headers scavenge better. That's why the GT40 had the bundle of snakes, so each collector and muffler gets an equally spaced pulse every 180 degrees of crank revolution

The disadvantage is the block internal stresses. The kinetic energy in the pistons is being transferred from left to right bank and back every 180 degrees, making the 2 banks of cylinders want to flap like butterfly wings.

wkooiman · #3 (**permalink**) 04-05-2016, 07:42 PM

My non-expert comments…

Plus, you can forge in one process, whereas on a "normal" crank, they are forged and twisted.

Plus, you should be able to have a lighter crank - I think anyway.

Plus, you can sell a flat-plane crank engine for more - because it sounds cooler (the real reason).

hinoonaz · #4 (**permalink**) 04-05-2016, 07:43 PM

Interesting So,a stonger block is needed to handle. What is the advantage of rlrlrlrl versus current firing order?

twobjshelbys · #5 (**permalink**) 04-05-2016, 08:15 PM

Quote:

Originally Posted by wkooiman

My non-expert comments…

Plus, you can forge in one process, whereas on a "normal" crank, they are forged and twisted.

Plus, you should be able to have a lighter crank - I think anyway.

Plus, you can sell a flat-plane crank engine for more - because it sounds cooler (the real reason).

Bingo! Basically, Ford's PR department struck a home run with this one. But there are some things unique about Voodoo. While flat plane crank V8s have been around for a long time, the larger the displacement the more difficult the vibration issues become, so Ford's value add on a 5.2L FPC V8 is that it is the largest displacement in its class... That said, some of the voodoo and black magic (pun intended) that they had to come up with is applied EXTERNALLY to the engine. And these magical twists are why there won't be a Ford Performance Parts "crate engine".

DWRAT · #6 (**permalink**) 04-05-2016, 08:29 PM

Gary,
Here is a video that explains it very well.
Dan
[ame]https://www.youtube.com/watch?v=tybQr44WOn0[/ame]

hinoonaz · #7 (**permalink**) 04-05-2016, 09:00 PM

Thanks everyone. Very interesting. 9K rpm, a cobra is not a high rev sound that I want. Still impressive. Is this the setup for the lambo type cars?
Stevies garage sure did help.

DWRAT · #8 (**permalink**) 04-05-2016, 09:12 PM

Quote:

Originally Posted by hinoonaz

Is this the setup for the lambo type cars?
Stevies garage sure did help.

It's the motor in the new Mustang GT350 & 350r

CHANMADD · #9 (**permalink**) 04-06-2016, 05:45 PM

Yea ..thats the Lambo Ferrari sound...

joyridin' · #10 (**permalink**) 04-07-2016, 02:56 PM

Quote:

Originally Posted by wkooiman

My non-expert comments…

Plus, you can forge in one process, whereas on a "normal" crank, they are forged and twisted.

What do you mean forged and twisted? I go to a few places that forge cranks and I have never seen anything like what I think you are stating.

Bernica · #11 (**permalink**) 04-07-2016, 03:21 PM

Quote:

Originally Posted by CHANMADD

Yea ..thats the Lambo Ferrari sound...

A totally different sound than what most of us are used to in these type cars. I am surprised that Ford pulled a crank like that off on such a large displacement engine. But, technology keeps advancing I guess!

twobjshelbys · #12 (**permalink**) 04-07-2016, 03:32 PM

Quote:

Originally Posted by Bernica

A totally different sound than what most of us are used to in these type cars. I am surprised that Ford pulled a crank like that off on such a large displacement engine. But, technology keeps advancing I guess!

It gets more difficult as displacement increases. But the solid modeling systems that Ford uses these days make it easy to "try something" without actually building it. The new Ford GT was all done in CAD before they built one. I would love to see the compute farm it takes to run such models.

cycleguy55 · #13 (**permalink**) 04-08-2016, 11:23 AM

Quote:

Originally Posted by DWRAT

Gary,
Here is a video that explains it very well.
Dan
https://www.youtube.com/watch?v=tybQr44WOn0

Good video - more here, especially relating to the issue of balancing: https://www.wikiwand.com/en/Crossplane

Jac Mac · #14 (**permalink**) 04-08-2016, 11:33 PM

Don't get to excited about the 'new' ford flat plane crank, its a heavy beast and has the pistons on each bank one up one down along each bank. looks like they need a lot of weight to keep the vibes in check. Has effectively two counterweights for each rod journal/crankpin which is as much if not more than a conventional 90° crank.

Jac Mac · #15 (**permalink**) 04-09-2016, 01:24 AM

Added pic of raw forging and finished crank. Note also 'simple' headers that couple cylinder 1 & 3 , 2 & 4 of each bank.

Luce · #16 (**permalink**) 04-09-2016, 11:19 AM

Are you sure that header was intended for the flat plane crank? It fires inner, outer, inner outer( just looking at the one bank), so the proper pairing would be 1&4 an 2&3 or inners together, and outers together.

MAStuart · #17 (**permalink**) 04-09-2016, 11:39 AM

The crank and header is in the picture it would fire 1 and 3 360 degrees apart and 2 and 4 360 apart. The other bank does the same thing but is out of phase 90 bank to bank.

mark

Luce · #18 (**permalink**) 04-09-2016, 12:17 PM

That's odd. Why didn't they do it up down down up like most 4 cylinder cranks? Then you don't need nearly as much counterweight as 1 and 2 balance each other and 3 an 4 balance.

As the rough forging is, there's a bit of a wobbly vibration that can be eliminated by doing it the other way.

I didn't notice the crank at first glance.

Jac Mac · #19 (**permalink**) 04-09-2016, 04:52 PM

Quote:

Originally Posted by Luce

That's odd. Why didn't they do it up down down up like most 4 cylinder cranks? Then you don't need nearly as much counterweight as 1 and 2 balance each other and 3 an 4 balance.

As the rough forging is, there's a bit of a wobbly vibration that can be eliminated by doing it the other way.

I didn't notice the crank at first glance.

That only really works for inline 4's and when you increase the stroke your into really light ( read Expensive ) rods and pistons plus balance shafts, being the V8 and common pin your stuck with the extra rod BE weight on each journal and since they have used the modular bore spacing large capacity increases are more likely to have to be stroke rather than bore size. I guess I really am turning into an old ford is good ford fan after all these years. Don't think the current fans will be able to think the same!

wkooiman · #20 (**permalink**) 04-10-2016, 08:14 AM

Quote:

Originally Posted by joyridin'

What do you mean forged and twisted? I go to a few places that forge cranks and I have never seen anything like what I think you are stating.

Forging consists of dies that force the steel together, much like you mash snow together to make a stronger snowball. A 90-degree crankshaft would consist of a complicated set of dies, just to get the crank out of the dies after forging. It is simpler to have 2 dies that forge in 1 plane, and then after the crank is removed, the crank is twisted into the correct orientation while the steel is still malleable.

There are non-twist forged cranks, but they are surely more expensive, and the cranks from the 60's were surely all twist forged.

You can google this, and find sites that explain it better.