Ignition timing, Motronic and flywheel mounting | FerrariChat

Ignition timing, Motronic and flywheel mounting

Discussion in '456/550/575' started by Barbapapa, Sep 2, 2013.

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  1. Barbapapa

    Barbapapa Rookie

    Jun 23, 2006
    9
    Atlanta
    Full Name:
    Michael S.
    I have a 95 456 engine I'm enjoying working with and am curious about spark timing.

    I'm making a flywheel and have taken things apart and measured them.
    I expected to see a dowel in the flywheel to accurately position since the Motronic depends on the flywheel reluctor 'teeth' being exactly where they should be.

    What I found are 8 threaded holes with one on a different bolt circle. The crankshaft has nothing but threaded holes. The offset hole orients the flywheel but this method isn't ideal for precision and depends on threaded holes and clearance.

    Has anyone ever noticed spark timing being off?
     
  2. Cribbj

    Cribbj Formula 3

    #2 Cribbj, Sep 2, 2013
    Last edited by a moderator: Sep 7, 2017
    Michael, first I own a 550, not a 456, however I believe we share the same flywheel.

    You should see a series of 60 square teeth on the back of the flywheel, with a gap where two are missing. That's what tells the ECU's when the reference cylinder is at TDC. Then there are cam sensors (on the 550) which tell the ECU's whether that TDC is TDC compression, or TDC exhaust.

    Here's a pic of my flywheel, and you can make out the square teeth and the "gap" at about 11 o'clock.
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  3. Ferris Bueller

    Ferris Bueller Formula 3

    Mar 23, 2004
    1,850
    New Jersey
    Full Name:
    Dominic
    John,
    What clutch brand are you using?
     
  4. Barbapapa

    Barbapapa Rookie

    Jun 23, 2006
    9
    Atlanta
    Full Name:
    Michael S.
    It's great to have you chime in, I'm a fan of your knowledge here!

    Yes, I understand the 60-2 teeth and how the gap is "seen". My question was about the reliability spark timing since it's based on where that gap is which is controlled by the bolt circle. Threaded holes generally aren't reliable for positioning and I'm surprised they do that here.

    I just contemplated this in CAD and see that the variation caused by bolt hole clearance may possibly be one degree or so at most so maybe it's not an issue after all.

    What kind of flywheel and clutch is that?
     
  5. Cribbj

    Cribbj Formula 3

    #5 Cribbj, Sep 2, 2013
    Last edited by a moderator: Sep 7, 2017
    It's an OS Giken clutch and flywheel. About 30% lighter than stock, IIRC.

    Josh Hill (ECS of Virginia) installed it for me right after I bought the car, and these are actually Josh's pics.

    It's a triple disc type with metallic linings, so the engagement can be a bit more abrupt than the stock organic, but it sure does rev quickly! You can soften the engagement by tuning the hydraulic ratio. I wound up changing my master cylinder to a 5/8" bore from the stock 3/4".
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  6. Cribbj

    Cribbj Formula 3

    Those holes in the flywheel, and their bolts are an extremely precise fit, and typically shoulder bolts are used. One area a sloppy fit cannot be tolerated is at the flywheel, as if there's any rotational slop at all, it could shear the fasteners and launch the flywheel. That's why when people propose to "egg out" or redrill flywheels to use them for a new application, I shudder. So I would hope there's little or no slop in your 456 flywheel fitment.

    An engine builder buddy has a hole in his engine dyno room where a flywheel went through it. It proceeded to go through three more metal walls in his shop and finally demolished a cinder block wall in an adjacent building about 50 feet away before its energy was spent. The owner of the engine on test admitted afterward that he had redrilled his flywheel. Incredibly, no one was killed or even injured.

    The engine builder has since refused to fix the hole in his dyno room wall as it's a good reminder for him to verify the fitment of all flywheels on all engines that he tests.
     
  7. tazandjan

    tazandjan Three Time F1 World Champ
    Lifetime Rossa Owner

    Jul 19, 2008
    37,986
    Clarksville, Tennessee
    Full Name:
    Terry H Phillips
    John- Seems like David E Davis told a story about a Ferrari with a Chevy engine where the flywheel came apart and took out both of the driver's legs.

    We use flywheels to store energy for space systems and for attitude control. Lots of energy that is maintained for a long time once spinning.
     
  8. Barbapapa

    Barbapapa Rookie

    Jun 23, 2006
    9
    Atlanta
    Full Name:
    Michael S.
    I would guess that the exploding flywheel didn't have a register to hold it concentric to the crankshaft.
    The Ferrari flywheel has a close fit to the bearing that's inserted in the crank. Other crankshafts have a turned diameter on the crank to locate the flywheel. Using a bearing is convenient and positions accurately.

    In the world of engine swaps by DIYers mating different engine/transmission combos and needing some kind of flywheel/clutch, that kind of crap (no concentric register) is probably common.

    Back to the 456 flywheel, here are it's dimensions: Flywheel holes=.410", Bolts=.390".
    Therefore, a maximum variation of flywheel angular positioning based on the clearance is .9°.
     
  9. Cribbj

    Cribbj Formula 3

    Michael, I'm surprised the tolerance is that great between those bolts and holes.

    Toyota flywheel holes are typically 10.15mm for a 10mm bolt, and of course they're special shoulder bolts with a true 10mm, unthreaded shoulder.
     
  10. tazandjan

    tazandjan Three Time F1 World Champ
    Lifetime Rossa Owner

    Jul 19, 2008
    37,986
    Clarksville, Tennessee
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    Terry H Phillips
    John, Michael- That is the tolerance for one bolt hole. If all are accurately drilled on center, the cumulative effect would be much less.
     
  11. Barbapapa

    Barbapapa Rookie

    Jun 23, 2006
    9
    Atlanta
    Full Name:
    Michael S.
    #11 Barbapapa, Sep 9, 2013
    Last edited by a moderator: Sep 7, 2017
    Here's the finished flywheel. It's mating to a different transaxle so I used a smaller reluctor ring.
    It uses a PTT duel disc clutch with their special organic compound. I really like PTT.

    The whole assembly weighs 18.4 lbs compared to the stock 48.5 lbs.

    This engine is getting an aftermarket ecu that can adjust timing but if I were to make one for a Ferrari with Motronic, it would be nice to measure spark timing, disassemble the old clutch, measure the stock flywheel and mount the reluctor wheel on the new flywheel with any needed variation.
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  12. Cribbj

    Cribbj Formula 3

    Dual disc organic? That sounds nice!

    I've only ever driven dual disc metallic and triple disc metallic.

    I'd asked one of the major clutch manufacturers several years ago if they'd do a dual disc organic and got the deer in the headlights stare type response. It was like "why would you want that". To me, it's obvious - to retain the slippability of an organic with the torque holding power of the additional disc.

    Really interested in hearing how this works out for you.

    More photos, especially of the discs would be appreciated.
     
  13. Barbapapa

    Barbapapa Rookie

    Jun 23, 2006
    9
    Atlanta
    Full Name:
    Michael S.
    #13 Barbapapa, Sep 10, 2013
    Last edited by a moderator: Sep 7, 2017
    The idea of multiple discs being able to offer increased friction surface while keeping the mass on a smaller radius isn't affected by material.
    "why would you want that" means they don't sell it, I would scratch them off the supplier list.

    Porsche 928s used a dual disc clutch and it was a fairly lightweight one that you could feel in the quick free revving. Not many OEMs use them because a lightweight mass and multiple discs have concerns for average owners.
    Most average non-enthusiast drivers would not be able to match revs with a lighter mass and would complain about stalling. A heavy flywheel makes the OEM and dealer's lives easier.
    Multiple discs need a method of restraining the floater plate(s) or it may audibly rattle. That's no problem but would bring complaining customers back to the dealer.

    Porsche's 928 used metal strips that restrained the floater plate. That kept it quite but created problems as the discs wore if the strip's self adjusting mechanism didn't work well.
    By 1990 they had followed the trend of heavy flywheels and went to a large, heavy single disc which prevented any trips back to the dealer.

    Driving 928s with either clutch is very noticeable. The earlier twin disc feels athletic because of the lighter mass.

    Here's a closeup pic of the PTT material. They say it's "organic" and I admire them for that, any other company would call that some buzzword packed super sales name. It's not the old organic that looks like shredded twigs pressed together.

    The limit of that material is a stock 12 cyl Ferrari. Anything with more torque and they recommend metallic. They claim to have a handle on keeping driveability by way of less grabby friction material combined with higher clamping pressure. Also the secret of recommending a smaller master cylinder be installed.
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  14. tazandjan

    tazandjan Three Time F1 World Champ
    Lifetime Rossa Owner

    Jul 19, 2008
    37,986
    Clarksville, Tennessee
    Full Name:
    Terry H Phillips
    The 599 and 612 OTO and Sessanta both came with dual plate clutches. Has anybody looked at those to see how they differ? They have proven to be very reliable and long lasting.
     
  15. Cribbj

    Cribbj Formula 3

    Lightweight flywheel/clutch combo's and heavy cars aren't a very good combination, unless they happen to have a diesel or a big V12 with balls of torque.

    My lightweight triple disc setup is quite a handful for most - my son-in-law is an experienced Porsche driver and still has difficulties getting my 550 launched. He stalls it more than 50% of the time. I stall it too occasionally when I have a passenger and am not 100% focused on driving.

    Really interested to hear your impressions how this clutch drives and feels.
     

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