Cobra Make, Engine: Lone Star with IRS, 427W with megasquirt, T56 magnum
Posts: 309
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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.
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".
Cobra Make, Engine: Contemporary Classics, red white stripes
Posts: 139
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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.
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.
Ok...I have never seen a twist forging. I visit a couple places that manufacture cranks and none of them use this method. Thanks!
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.
Cobra Make, Engine: CSX #4xxx with CSX 482; David Kee Toploader
Posts: 3,574
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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!
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All that's stopping you now Son, is blind-raging fear.......
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.
Cobra Make, Engine: Lone Star with IRS, 427W with megasquirt, T56 magnum
Posts: 309
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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.
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.
Cobra Make, Engine: Lone Star with IRS, 427W with megasquirt, T56 magnum
Posts: 309
Not Ranked
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.
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