Why dual distributers?...I figured it out...maybe. ;) | FerrariChat

Why dual distributers?...I figured it out...maybe. ;)

Discussion in '308/328' started by mike996, Apr 17, 2021.

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  1. mike996

    mike996 F1 Veteran

    Jun 14, 2008
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    In doing work on my 328, and actually nothing to do with the ignition, I happened to be looking at the dual distributers and thinking again, "Why did they do that, one distributer/one coil would have been easier AND less expensive, wouldn't it?"

    It suddenly struck me that the Ferrari setup, with two 4-cylinder distributers/coils provides double the distributer dwell time and therefore, much more available spark voltage then a single 8 cyl distributer would! Modern cars have gone to a coil for each cylinder which proved even more dwell time but that wasn't commonly available back then. SO I think that's why they did it! Of course, I could be wrong - not about the dwell time/spark difference - but whether that was the primary reason for the configuration
     
  2. johnk...

    johnk... F1 World Champ
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    I doubt it. Probably because Fiat knew more about 4 cylinder engines and how to apply Bosch 4 cylinder Motronic to a V8. :) And when you look at the 355, even the 5.2 version, they still have dual coils BUT they use a wasted spark ignition so any benefit from longer dwell would be negated by firing 2 spark plugs.
     
  3. mike996

    mike996 F1 Veteran

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    Thanks John! It was just a thought. Your explanation makes better sense than mine.
     
  4. 4rePhill

    4rePhill F1 Veteran

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    I think you're seriously over thinking this.

    Here is Ferrari's "dirty little secret" when it comes to their older cars - They did things by the simplest method possible!

    The mechanical set up on older Ferrari's is just simple, basic car engineering - If you can work on a FIAT, you can work on a Ferrari!

    The wiring on older Ferrari's is just simple, basic car wiring.

    The interior trim is fitted in the most basic way possible. Where the likes of BMW, Mercedes and Audi would use special clips, and screws hidden by covers, Ferrari simply screwed the trim on, and leave the screws visible. They didn't even bother to cover up the wiring underneath the driver's side dashboard, as the Germans would have!


    When it comes to the Ferrari V8's, they use a flat plane crank - Basically, two in-line 4 cylinder' engines, set 90 degrees apart, that share a single crank shaft, and fire a single cylinder from both banks, at the same time.

    To keep things simple, Ferrari treated the engine as two in-line 4 engines, and fitted two distributors to supply the spark to "both engines".

    Ferrari took this concept of treating the V8 as two in-line 4 cylinder engines to another level with the 348 that came after the 328.

    The engine was now longitudinal, rather than transverse, but, a 348 has an ECU for each bank, a fuel pump for each bank, a fuel filter for each bank, a MAF for each bank, a coil for each bank, etc., etc., etc.

    With the 348's V8, with the exception of the crank shaft, the left bank and right bank run completely independently of each other!

    Keep things simple - Ferrari's "dirty little secret"
     
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  5. thorn

    thorn F1 Rookie
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    Truth. And sometimes, that's a great approach. Other times (cough: wiring), not so much.
     
  6. kcabpilot

    kcabpilot Formula 3

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    huh? o_O
     
  7. tomberlin

    tomberlin Formula Junior
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    Didn't Euro cars often have a single dual point distributor? 4 cam lobes, dual level rotor and cap. I ran one for a while but I had to take the distributor out to adjust the points. Also, I didn't notice a performance difference between that set up and 2- 4cyl distributors.
     
  8. miked

    miked Formula Junior

    Feb 7, 2001
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    I am still going with they needed room for the second set of points for the emissions related retard timing set-up. Without twin distributors there would have to be 4 sets of points in one distributor (yikes!). Twin distributors were only in emission laws markets, primarily the US.
     
  9. lm2504me

    lm2504me Formula 3
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    Euro 308s had single distributor with a single mechanical advance curve.
    USA carb had dual distributors due to addition of extra set of points to retard ignition at idle. Also has two different advance curves, unless you can set them to match perfectly at all rpm.
    I am modifying a single distributor with two sets of points to fire front and rear plugs. I have to move one set of points by 135 degrees. I will have one advance curve.
    Image Unavailable, Please Login
     
  10. mike996

    mike996 F1 Veteran

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    Just curious - how does adding another set of points change the timing at idle but not change the timing at other speeds? I am very familiar with conventional dual-point distributers for performance purposes but offhand I can't figure out what "disengages" the idle set of points/shifts the ignition to the other set. Is there some sort of vacuum or centrifugal system that moves the idle set out of the circuit at some speed, shifting to the other point set?
     
  11. lm2504me

    lm2504me Formula 3
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    There is a microswitch operated by the rear passenger side carb. When at idle, the switch is made up which connects to the additional set of points in both carbs to retard the timing. When you press on the gas pedal, the switch is not made up and you return to the more advanced timing.
     
  12. lm2504me

    lm2504me Formula 3
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  13. Kidasters

    Kidasters Formula Junior

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    OK - here's my confession - I converted my distributors to electronic ignition. Removed the points.
     
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  14. mike996

    mike996 F1 Veteran

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    Interesting! Thanks!
     
  15. lm2504me

    lm2504me Formula 3
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    #15 lm2504me, Apr 17, 2021
    Last edited: Apr 17, 2021
    Oops, meant “in both distributors”, not carbs
    I need to proofread prior to posting.
     
  16. AZDoug

    AZDoug Formula 3

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    None of that stuff was on my '79 US car. The dual dizzies had only a single breaker point each (and to my recollection, there was no place to attach second set of points on either dizzy), no microswitch at the carb, the heat riser valve on the air box inlet was professionally wired always open, KPH only speedo.. Calif sold car at Newport imports Feb 1979, built Oct 1978, had air pump and cats, i am the second owner since 1984.

    My original hypothesis way back when was the dual dizzies were for increased dwell at higher RPM, so as to not have to use a heavy springs on the points, which causes dwell to go out of spec quickly, but i was told i was wrong as per above. Maybe, maybe not.

    Thats all in the past, the single dizzy BSM electronic unit replaced the old dual setup several years ago..

    Doug
     
  17. lm2504me

    lm2504me Formula 3
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    Good to wire airbox flapper open. If it shuts at speed and charcoal canister is connected, the carbs will suck the charcoal out the canister and into the carbs. It happened to my 78 308 after purchase by original owner. I have dealer invoice for work done.
     
  18. ProvaMo

    ProvaMo Formula Junior

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    Interesting thoughts regarding dual dizzies on 308's, long understood for USA is to house the dual points for the extra set of retarded points for idle emissions.
    Still amazes me that my old BBi had so many dual "things", but only one distributor and one coil. The Boxer had dual CIS injection systems, dual alternators, dual oil filters, dual shocks for each rear corner, and a dual plate clutch...
     
  19. 4rePhill

    4rePhill F1 Veteran

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    Quite simple really - As already stated, the flat-plane crank engine acts as two in-line 4 cylinder engines sitting side by side (but sharing the same crank shaft)

    The ignition system fires the cylinders in pairs - One from the front or left bank, at the same time as one from the rear/right bank.

    A cross-plane crank V8 on the other hand, fires it's 8 cylinders one at a time - one after the other.

    It's why Ferrari V8's sound/run smoother than (most) American V8's, don't have the traditional American V8 rumble, don't develop low end torque like a traditional American V8, rev higher than a traditional American V8, and develop their power at the top end, rather than at the bottom end/mid range (like a traditional American V8)

    As I've posted previously: With the 348, the engine runs both banks completely independently of each other - With the exception of the crank shaft and cambelt (which is also shared between banks), the left bank has nothing to do whatsoever with the right bank.
     
  20. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    #20 Steve Magnusson, Apr 21, 2021
    Last edited: Apr 21, 2021
    No, they are "interleaved" -- a cylinder fires every 1/2 crank revolution in each bank, and the two banks are offset by 1/4 crank revolution:

    1 - 3 - 4 - 2
    - 5 - 7 - 8 - 6

    so the complete order is 1-5-3-7-4-8-2-6

    No, both flat-plane crank V8 and cross-plane crank V8 fire the cylinders one at a time and one after the other. The difference is that the flat-plane crank in a 90 deg V8 never fires two cylinders in the same bank one after the other = the time between the exhaust pulses entering the exhaust manifold of each bank are all the same = sounds really sweet and every cylinder has the same behavior (this is called alternate-bank-firing and every 2-bank Ferrari engine has this characteristic -- even those without flat cranks). With the cross-plane crank in a 90 deg V8 = the time between the exhaust pulses entering the exhaust manifold of each bank are not all the same = sounds "rougher" and every cylinder does not have the same behavior = this flattens and broadens the torque curve so is not necessarily a bad thing, and is why "ordinary" cars have cross-plane V8s (but slightly reduces the max power for the same displacement).
     
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  21. kcabpilot

    kcabpilot Formula 3

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    #21 kcabpilot, Apr 21, 2021
    Last edited: Apr 21, 2021
    Okay, you got that part right but the "two in-line 4 cylinder engines sitting side by side" are 90 degrees apart. So if you know how an in-line 4 works it fires 180 degrees apart. When #1 and #4 are at TDC then #2 and #3 are at BDC. So in a flat plane 90 degree V8 when any cylinder on bank 1 is at TDC all of the cylinders on bank two are halfway between TDC and BDC (90 degrees from 0 or 180) two of them are at 90 and the other two are at 270. So obviously it's not possible for any of them to fire at the same time as the opposing bank.

    It can seem confusing but Steve explained it pretty well with the diagram. If you've ever had one of these apart so you could turn the crank and see what's going on it gets easier to understand. Then you have to get used to the cams turning the opposite direction of the crank but hey, it's a Ferrari YaY!! :)

    EDIT: I should clarify this because the whole cycle is 720 degrees for a four stroke engine so each of the cylinders would be at either 90, 270, 450 or 630 degrees. See? All clear now (ha,ha)
     
  22. J-P

    J-P Formula Junior
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    I'm guessing this does not apply to the GT4? I have a '74 Euro, but it has dual distributors.
     

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