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Discussion Starter #21 (Edited)
Nice post SteveN:)

Pavlo said:
..In the days of the internet, being documented is not the same thing as being proved.
I wasn't referring to the internet. It is unlikely to find such advanced topics on the net for obvious reasons. Even more unlikely to find free computer models for them.
But you can make them yourself.

'The Internal Combustion Engine Volume2' by Charles Fayette Taylor is a good start if you want to delve into this sort of thing.:)
 

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We have / use some of the most advanced CAE combustion modelling available anywhere. These models would not be able to predict spark advance change with changes in combustion camber shape.............guess what, you do it empirically on an engine dyno.....
 

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ExScoobyT said:
We have / use some of the most advanced CAE combustion modelling available anywhere. These models would not be able to predict spark advance change with changes in combustion camber shape.............guess what, you do it empirically on an engine dyno.....
Exactly.

I am not doubting that the process works, but as the linked passage says you are going to increase flow with deshrouded inlet valves, that should increase VE, which should increase peak cylinder pressure and perhaps increase likely hood of det for a give PR or TP (just one example).

I assume that the method of calculation is based around finding the adiabatic flame temperature, followed by flame front speed, and then looking at the change in distance from plug to nearest squish zone. I dare say it's more complicated than that, but when you can change the valve material, or valve seat width, port shape, piston material and get a change in detonation surpression, I find it hard to beleive you can quantify the exact magnitude of the change in ignition timing from removing that lip.

Paul
 

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Discussion Starter #24
Very true.
No computer model can get it spot on first time round, if several other peripheral parameters have also changed.
It will just give you a starting point, and you fine-tune it on the dyno afterwards.
There's nothing like the DetCans.;)
 

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Nice posts on this thread for a change, glad to say I agree with many of them, especially good post from SteveN on head preparation.

I have heard it said that the initiation of the flame is more affected by the AFR than the flame front speed and obviously the quality of the cooling system will have a great effect on detonation.

Water wetting agents in the cooling system might also have their place in keeping combustion temps in check with payoff in detonation reduction and resultant increase in ignition timing.

SteveN said:
You will not hear the detonation, but it's there. A knock meter won't pick it up in a 700 hp engine because mechanical noise is substantial.[/i]
Possibly overstating things on this one, with the correct frequency filters + amplification, the smallest levels of detonation can be heard / datalogged / alerted by LED.

Although I do agree that it can be very hard even with good amplification to hear detonation when your car is on full chat.
 

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Discussion Starter #27
Hugh Keir said:
I have heard it said that the initiation of the flame is more affected by the AFR than the flame front speed ...
Many people mistake misfires for ignition deficiencies, even when they really are AFR-related.

There is a maximum flamefront speed for a given fuel and charge density. Going leaner or richer slows it down. After about 3 AFR points it slows down a lot more steeply.
That's one of the real reasons that people find out experimentally that it's safe to run very rich. Without realising it they are slowing down the flamefront, effectively retarding the ignition.
 

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Hugh Keir said:
the quality of the cooling system will have a great effect on detonation.

Water wetting agents in the cooling system might also have their place in keeping combustion temps in check with payoff in detonation reduction and resultant increase in ignition timing
Funnily enough, the same people who I quoted in my post made a big deal about the "GT" head cooling system like you see on some top GTRs.

They made their own though.
 

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Pavlo said:
Exactly.

which should increase peak cylinder pressure and perhaps increase likely hood of det for a give PR or TP (just one example).
Paul
PCP, although significant, is not the only factor in the propagation of detonation.
 

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Nice picture Steve.

That head is very similar to what we do, but I don't remove quite as much squish as that on the intake side.

Have to agree with Hugh on the det detection tho, with the correct equipment it is quite easy to hear it, even on engines well past 700hp.

Steve, what do you mean by the "GT head cooling"?
 
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