Proper knock readings with hammer
08-05-2018, 08:58 PM
#31
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I'll give you that.
08-06-2018, 07:56 AM
#32
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08-06-2018, 08:16 AM
#33
Three Wheelin'
Thread Starter
could be some level of carbon build up in the head/piston which could add towards knocking, especially if you are pushing the timing envelope
08-07-2018, 03:23 PM
#34
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Fred, the prizes at the bottom of the box of My-engine-knocks-regularly range from reduced life of rod bearings to rods poking through the oil pan.
What’s the prize for the last few percent of horsepower?
The real answer depends upon where on the load cell map the knocking occurs. If the knocking occurs in cells that are only opperative when you are trying to provoke knock then fine. If the knock occurs in cells that you really want to use, then *I* would pull timing until the knocks are few or zero. On the other hand it also depends upon whether the knock occurs under transient or steady state conditions. I will not tolerate any knocking when the second-order of conditions is stable. On the other hand, I will tolerate a few knocks during huge transitions (e.g. cruising on a hot day at 55 in 5th gear flooring it and getting a few knocks during and immediately after the abrupt throttle opening, etc.)
What’s the prize for the last few percent of horsepower?
The real answer depends upon where on the load cell map the knocking occurs. If the knocking occurs in cells that are only opperative when you are trying to provoke knock then fine. If the knock occurs in cells that you really want to use, then *I* would pull timing until the knocks are few or zero. On the other hand it also depends upon whether the knock occurs under transient or steady state conditions. I will not tolerate any knocking when the second-order of conditions is stable. On the other hand, I will tolerate a few knocks during huge transitions (e.g. cruising on a hot day at 55 in 5th gear flooring it and getting a few knocks during and immediately after the abrupt throttle opening, etc.)
Seems we are "like minded souls"! I tend to view knocks as something very undesirable and that there is no such thing as "a good knock and a bad knock". That being said what I have noted is that I have never seen or heard of a S4/GT/GTS motor being destroyed by knock. The only thing I have noted different to your point of view is that over here GTS's seemed to knock chronically at lower rpm's as in you could could hear them knocking. This never happened on my motor when it was stock configuration and as it is now with modest mods.
When I converted to ST2 useage I noted that the stock map my coding plug dialled up was described as being for 98 RON whereas our fuel is 95 RON. A few of the local Porsche owners noted that when we went up to Dubai and filled up with their Super 98 the car did seem to run better. I thus concluded that the knock control system was probably doing its job and sure enough to stop any knocking at full load and mid to high rpms I had to pull a couple of degrees of timing. The cylinders that knocked were invariably No6 and No2 and when timing is pulled it has to be pulled across all cylinders given it is batch fired. Ken actually wrote a patch for me and when I pulled a couple of degrees from those two cylinders I then found I could advance all the cylinders by the same amount. I also figured that the faster exhaust was worth a degree or two so with ST2 I end up with some cells having less rather than more advance. I also did the mapping during the hot season for safety. For cells used during full load acceleration I tried to ensure that there were no knocks at all.
The other thing I found was that despite what some folks seem to think, I noted that when revving high, if the system detected a knock it would apply a correction by the next firing stroke and even though I recorded a few knocks here and there I never heard a thing and would never have known such was going on without ST2 sounding a ping on my laptop. The thing I could never make my mind up on was whether one could safely build in a bit more advance and then rely on the EZ to auto correct. .The EZ system pulls up to 9 degrees so if it is set such that up to 3 degrees of advance are mapped in it still has capability to pull a further 6 were they needed. I really do not know the answer to this but having set my maps such that I get no knocks at full load and then add 3 degrees to the high load cells, the motor is definitely more zippy but then one for sure does get some knocks on the more critical cylinders but by no means every time such cells are visited. Eventually I settled with a safe tune but end up wondering how much I was leaving on the table.
The other thing I found was that running the fuel a bit richer did not make any difference to the knock characteristics as long as the fuelling was at least stoich and the car seems to run best at AFR 13..I also did some lobbying to get some fuel stations kitted out with RON 98. Whether the powers that be listened to me remains to be seen but recently 3 fuel stations now have RON 98 so I may give it a try as I reckon those 3 extra octane points may be worth 2 degrees of advance.
The trouble with something that is infinitely adjustable is that there is one correct setting and an infinite number minus 1 wrong ones - grrrh!
