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Flat (180deg) V8 crankshaft questions

Discussion in 'Technical Q&A' started by 4re gt4, Apr 6, 2004.

  1. 4re gt4

    4re gt4 Formula 3

    Apr 23, 2002
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    Roseburg, OR
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    Hans E. Hansen
    I know that this horse has been beat extensively, but I still have a few lingering questions. Other than a comment about the V12, this applies to V8s with 90deg bank spacing.

    The press has shown bits and pieces of a new "430 Modena". It's using the Maserati V8, but modified for nearly 100 more hp. One of the mods is a flat crank.

    Also, when the Maranello came out, they switched to a crank with a different firing order from the 456. (On a V12, I'm not sure it's a 180deg crank.) Supposedly the 456 crank was smoother. (Not positive, but they may have switched to a Maranello-style crank on the 456M.)

    Facts:
    1. The flat crank used on the 308 series allowed Ferrari to build the motor as two separate 4 cyl units. (Altho there are single distr models.) This continued with the early electr inj models, as there is two separate control modules. So there may have been some financial advantage.
    2. A flat crank can allow better exhaust scavenging (sp?), as the pulses in each header are evenly spaced. However, it doesn't look like early F-V8s have any sort of tuned or even length headers, so they are only partially, if at all, taking advantage of this.
    3. If I understood a previous post from Mitch Alsup, a 90deg crank in a V8 vibrates less than a 180deg crank. The 180deg unit has similar problems as a 4 cyl, vibration-wise. This probably explains the 90deg unit in the Maserati, as well as most other cars.

    Possible myths:
    1. "A flat crank gives better torque." Huh? With either crank, there is a power pulse every 90 degrees of crankshaft rotation. Does the end of the crank actually know whether a power pulse came from the left or right bank?
    2. "A flat crank revs better." What about the extra vibration? And, again, the power pulses are spaced the same with either crank.

    I don't understand the advantage in using a flat crank. It seems that there is no real advantage, but using it carries a vibration penalty.

    Anyone?
     
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  3. seschroeder

    seschroeder Formula Junior

    Apr 25, 2002
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    Steve Schroeder
    Makes the engine have that lovely exhaust tone!!!!
     
  4. snj5

    snj5 F1 World Champ

    Feb 22, 2003
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    Russ Turner
    Just to dovetail onto your observations:
    I've always wondered if an exhaust H or X exhaust crosspipe on a flat crank V-8 makes as much of a positive difference as it does on a conventional V-8.

    All of us that have lost ignition on one bank of a Ferrari V-8 can verify that it runs extremely smoothly on just one side's 4 cylinders... :p
     
  5. bert308

    bert308 Formula 3
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    Nov 30, 2002
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    Bert Kanters
    True...and that is the reason for the flat crank: with a 90 degree crank, you have 2 firing cilinders after another at one side, then 2 at the other side. Not front-rear-front-rear bank etc, but front-front-rear-front-rear-rear-front-rear etc, this leaves less air-fuel mixture for the cilinder in one bank that fires right after the other cilinder in that bank. (hope you understand, it sounds even confusing in my own language)
     
  6. BJS

    BJS Formula Junior

    Jan 18, 2004
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    Brad Stephenson
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  8. Mike Florio

    Mike Florio Formula Junior

    Jun 19, 2003
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    Mike Florio
    From Ludvigsen - Ferrari, The Factory pp 98:

    Crankshafts for the 308 Dino V8 were forged rather than machined from the solid. Fully counterweighted, they were of the "flat" or 180-degree pattern usually used in racing engines to create a lighter, stronger crankshaft with better exhaust tuning than was allowed by the 90-degree crankshafts customarily used in production engines.

    So there were probably a couple of factors:

    Forging vs. billet - forging probably a bit cheaper
    Exhaust tuning
    Lighter and stronger
     
  9. 4re gt4

    4re gt4 Formula 3

    Apr 23, 2002
    2,279
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    Hans E. Hansen
    I couldn't open the first link BJS supplied, but here is a brief summary of the second:

    To properly balance a 90deg crank in a V8, crankshaft counterweights have to be added. This makes the crank very heavy. Because of this, it may be required to make the engine block bigger to make room for the weights.

    The 180deg crank DOES have big vibration issues, but is used in high-perf applications because it is lighter and more compact.
     
  10. ricrain

    ricrain Karting

    Nov 1, 2003
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    Ric
    This information is wrong. All Ferrari cranks that I've ever seen (72 forward) are machined from a forged billet. It has been Ferrari's "thumbprint" for a long time. _Inside Ferrari_ has pictures of the process. It starts with a forged cylinder billet that is machined into a crankshaft. The billet is forged, so therefore the end crankshaft is forged... just not die forged to shape. I've never personally handled a 246 crank, so I can't speak to those. AKAIK all 3x8, 355 and 360 cranks are (were) made with this process.
     
  11. Mitch Alsup

    Mitch Alsup F1 Veteran

    Nov 4, 2003
    7,387
    Depends upon what you call big: a flat-plane crank does have about 4X the vibrational energy of a cross-plane crank; but does 4X smooth == rough ? And the energy has different spectral signature. I find the off-cadence burble of the cross plane cranks at least as anoying to my ear as I find the vibrational pattern of the F355 engine to my butt.
     
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  13. mk e

    mk e F1 World Champ

    Oct 31, 2003
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    This is USUALLY true. The reason is that the exhaust scavenges better allowing better cylinder fill. There are a lot of tricks used on 90 degree moters to try and make them as good like "H" or "X" pipes. The same is somewhat true for the intake manifold, they tend to flow better in a 180 degree engine, also increasing torque.

    This is USUALLY true again. Since a flat crank engine flows and fills the cylinder better, it can make power at a higher rpm the a 90 degree engine.
     
  14. snj5

    snj5 F1 World Champ

    Feb 22, 2003
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    So, an X or H pipe is not really neccesary on a flat crank engine as the exhaust pulses are already evenly timed on both sides, right?
     
  15. mk e

    mk e F1 World Champ

    Oct 31, 2003
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    I think that's right, it should not help.
     
  16. PSk

    PSk F1 World Champ

    Nov 20, 2002
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    Pete
    This is not the only reason. The other reason a flat plane crank revs better is because it is lighter!, refer:


    If you have to add balance weights to a crank it gets heavier and thus does not permit revving as well.

    Pete
     
  17. PSk

    PSk F1 World Champ

    Nov 20, 2002
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    Pete
    I would be very surprised if Ferrari still machine from a forged billet and do not move forward and forge their cranks correctly. A proper die forged crank will be stronger than a machined from billet crank I would have thought ... unless you have to add impurities to enabling the forging process (?).

    Pete
     

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