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Timing belt conundrum

Discussion in '308/328' started by Irishman, Aug 9, 2019.

  1. mwr4440

    mwr4440 Three Time F1 World Champ
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    Jun 8, 2007
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    Mark W.R.
    John, the EURO's Exhaust closes EARLIER by Crank 4°, 10° ATDC vice 14° ATDC on the US car.
     
  2. johnk...

    johnk... F1 Veteran
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    Jun 11, 2004
    7,584
    New England/FL
    A couple of things to correct. First, I got it backward. Just read it wrong. Thanks for catching that. Second, I was thinking only of the closing and forgot that if the exhaust closes earlier, it also opens earlier since it's the same cam. So there is a compound effect. Opening earlier generally results in increased high end torque, less low end torque. Closing earlier, less scavenging of the exhaust and thus, less intake of a fresh charge at high RPM resulting in reduce torque at high RPM and lower emissions. The net effect on power is ???? But having the exhaust open and close earlier should result in reduced emission. So, in conclusion, I have no conclusion. :(

    One thing has me wondering about the stated difference between Euro and US timing. I checked the Ricambi site and I do not see different part number for US and Euro cars and for the QV the cams for Euro and US cars have the same part number. which to me says both cams have the same timing marks. Likewise, the cam cap is the same for both Euros and US, again indicating the same timing mark. So if the timing marks were (?) perfect, So if you time by the marks, which spec do you have, Euro or US? :confused:
     
  3. kcabpilot

    kcabpilot Formula Junior

    Apr 17, 2014
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    Paul
    If you were to purchase a new cam journal cap would it come with a timing index mark. It would seem that would be done on an assembled engine to coincide with the mark on the cam. I would think that even the position number stamp would be absent but that's just my guess.
     
  4. johnk...

    johnk... F1 Veteran
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    Jun 11, 2004
    7,584
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    You are probably correct. Good point. BUT, I will say that if the difference between Euro and US exhaust cam timing is 4 degrees, WTF is the big deal about timing to better than +/- 1 degree. This is a point I have argued at length in the 355 section where those that are completely anal and, apparently, don't understand the effects of cam timing variations, are obsessed with timing the cams at every belt change to with in better that +/- 0.5 degrees, even though you probably can't find TDC using the "Ferrari" to within 0.5 degrees consistently. Being off from the factory specs doesn't mean the car won't run correctly. It may have less low end torque, but pick up some in the midrange or top end, and vise versa. It may idle a little differently and fuel mileage and emissions may change somewhat. But other than that it will run just fine. I don't have a problem with those who insist that such timing be done at every belt change with the exception of their pontificating that not doing so is somehow neglectful and adversely effects the performance of the car. Unless the car is put on a dyno and different cam timings are compared, there is simply nothing to discuss.
     
  5. fatbillybob

    fatbillybob F1 World Champ
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    Aug 10, 2002
    17,130
    socal
    What you post is true if in your world a "B" is good enough. We are a Ferrari group. Anyone here who is a "B" at xyz is an "A" somewhere else and has capitalized on that to become Ferrari owners. We are an anal bunch if we are in the hobby for any length of time. Being an engineer you well known that a small error at the beginning magnifys its way to the end. You do know the most important step in any process is the one you are currently on. You do know that a relatively repeatable reference point is always a good thing to keep in focus. Degree wheel cam timing adds a hour to the job that takes over 24 hours to complete. Does any DIY'er lack the time to spend another hour on their baby? The only justification I can see for skipping the cam timing step is not having the knowledge to do it and "hope" that assembly marks are good enough. And thus we have the term coined by the infamous Ferrari mechanic DaveHelms..."consumer acceptable."
     
  6. johnk...

    johnk... F1 Veteran
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    Jun 11, 2004
    7,584
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    #106 johnk..., Sep 26, 2019
    Last edited: Sep 26, 2019

    You making my point FBB. Anal twit. You have no idea what +/- 2 degrees of cam time does to performance unless you put the car on a dyno and test it. In fact, if it was known it might be desirable for someone like me to set the car up to perform better at low RPM since I use my cars for touring and spend most of the time below 4k RPM. Someone that tracks there cars may want to set the timing differently. That the 308 with the same cams is set up differently by Ferrari for the Euro and US market is evidence that different cam timing simple means difference performance, not that one is right and one is wrong. Like I said, if you just want to say you prefer to do it, I'm fine with it. But if you want to preach the, "It's only right if you do it the Ferrari ways", well you know where the sun doesn't shine. And for all the arguments we have had in the 355 section not once have you even conceded that it the timing was right to start, a belt swap would insure that the timing remained as it was at the last belt change to within tolerances of around +/- 0.5 degrees.

    Things like variations in fuel pressure, injector spray pattern, O2 senor accuracy, etc probably have a bigger effect on performance than +/-2 degrees of cam timing.

    You bring up my engineering back ground. Yep, difference between engineering and a mechanic that just does what the manual say to do. The point I have made repeatedly, and everyone with a brain know is correct, is that once the car is timed as desired, changing belts can not and will not alter that timing to more that that associated with belt length tolerances. I have done and presented the math several time showing the this amounts to about 0+/- 0.5 degrees at most. So if the car is initially timed to +/- 0.5 degree compared to spec, changing belts can at worse change the timing to +/- 1 degree relative to spec. If you retime the car you introduce the uncertainty of the accuracy of finding TDC, particularly if you uses the "Ferrari" method, which guarantees you stand only a random chance of actually being at exactly TDC, another issue you simply do not except because you don't understand the statistics of mechanical measurement. And if you understood the statistics of tolerances you would also recognize that tolerances are the max allowable variation. Statically, typical QC would mean that better that 68% of all belts would vary buy less that 1/3 the stated tolerance, 95% less that 2/3 the tolerance. That is likely to be true of Ferrari timing belts as it is common in manufacturing. Thus the error in belt swapping would amount to less than +/- 0.17 degrees for 68% of the belts swapped, less than the accuracy you can deterring TDC to. Even at the worst case, multiple belt changes without retiming the engine would amount to nothing more that a random walk between the limits of +/- 0.5 degrees from where ever the timing was when the engine was timed. It is not a cumulative effect. It is always referenced back to the original timing. It like having two walls 10' apart. If you measure the distance between them using various tape measures with an accuracy of 0.01"/ft, no matter how many time you measure it, or how many tape measures you use, the result will always be 10' +/- 1". I have nothing to add because those are ill refutable facts.

    Now you might want to argue about cam wear, another issue, but if there is cam wear you can't ever have the correct timing.
     
    moysiuan likes this.
  7. derekw

    derekw Formula 3

    Sep 7, 2010
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    Derek W
    Count me in as one of the anal twits because reading this made my sphincter twitch for several reasons.
     
  8. johnk...

    johnk... F1 Veteran
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    Jun 11, 2004
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    Make that 10' +/- 0.1".
     
  9. johnk...

    johnk... F1 Veteran
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    Jun 11, 2004
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    I must confess, so am I which is why this subject makes by butt hurt.
     
  10. waymar

    waymar Formula Junior

    Sep 2, 2008
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    Wayne
    #110 waymar, Sep 27, 2019
    Last edited: Sep 27, 2019
    Hi all. I fall into the category of DIY. I degreed my exhaust cams to Euro spec. Had my digiplexs rebuilt by David Feinberg to the Euro spec. No cats. EGR, airpump or cold start air valve. I run 87 octane. My 82GTSi runs better then ever and actually runs better on 87 than 93. I just recorded 14 tankful at 18.91 mpg mostly with AC running. Speedo was rebuilt by paloalto and matched to my sensor. Just saying......
     
  11. mwr4440

    mwr4440 Three Time F1 World Champ
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    Jun 8, 2007
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    Mark W.R.
    WoW !!!!

    Now THAT is data I might can use. :)

    Your now stock 'Euro' motor should be getting 9 MORE Horses over the stock USA Version according to the WSM.

    CAN YOU actually FEEL That, or is it 'more in your mind?'

    Honest question.
     
  12. waymar

    waymar Formula Junior

    Sep 2, 2008
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    Wayne
    I think it more that the car is finally correctly and at the power and response it was originally designed for. That is something you can actually feel vs the condition I bought the car. The ignition was way off and timing way out, etc. Gas mileage is now up from before.
     
  13. Dr Tommy Cosgrove

    Dr Tommy Cosgrove Two Time F1 World Champ
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    #113 Dr Tommy Cosgrove, Sep 27, 2019
    Last edited: Sep 27, 2019
    So what are you saying?






    ....just kidding
     
  14. Dr Tommy Cosgrove

    Dr Tommy Cosgrove Two Time F1 World Champ
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    May 4, 2001
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    Tommy
    Got a link to him?
     
  15. johnk...

    johnk... F1 Veteran
    Owner

    Jun 11, 2004
    7,584
    New England/FL
    And the timing gears go round and round
    And the valves they go up and down
    They're captive on the carousel of time
    They can't return they can only look behind
    From where they came
    And go round and round and round
    In the circle game
     
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