Mycroft

It is only the advance that allows you to gain power, there is also a thread on the GTR that explains that for you... I'll find it and post a link.

http://www.gtr.co.uk/forum/upload/showthread.php?s=&threadid=6346&highlight=octane+j apan

[Edited by Mycroft - 3/3/2003 9:02:45 AM]

john banks

Yes I've read the 22 page thread in detail and the other one you linked.... I cannot advance it this much without the NF without it detting its knackers off. The more advance I can run so far has always netted more power since I am not yet at MBT. So as far as I can tell, the NF is allowing me to tune it for more power.

I'll pull the plugs and have a look, and also post some pictures of the piston crowns when the engine comes out. Hoping they will look nice

[Edited by john banks - 3/3/2003 9:57:33 AM]

milkytadpole

Knocking won't necessarily lower engine torque, depends just how advanced it is, in fact the higher rate of heat release can increase the thermal efficiency (truer to an idealistic constant volume combustion cycle).

Knock, incidentally, is a shock wave whose frequency is a function of the combustion chamber dimensions and density of working the fluid (combustion gases) and typically in the range of 6-8kHz. J

john banks

OK, but it is NOT making knocking noises. I am familiar with the sound of detonation and quite tuned into it. I am convinced that with this much ignition if there was anything to hear I would have done... it sounds really sweet with a really good exhaust bark and impressive performance.

The knocklink has quite a shallow bandpass filter and is also extremely quiet.

milkytadpole

JB, sorry, wasn't aimed at you. Looks as though I've just stepped into an argument over the validity of OB claims. I'm of the opinion that octane boosters do work BTW.

Mild knock can be quite difficult to hear, it normally has to be quite extreme to pick it up over engine noise (the only way to really detect it is with a pressure transducer in cylinder, but that's a tad extreme). Having said that, most tuners are happy to just listen for knock occurance. J

What fuel do you normally run JB?

john banks

Optimax.

Mycroft

You say you have read the OB thread... therefore you are aware that Knock is a post-ignition phenomena, pre-ignition cannot be detected by the Knock sensor. The knock you hear (and the sensors detect) happens AFTER the initial spark and is a result of end-gas detonation.

john banks

And that is the knock I am interested in and am controlling with "octane" , intercooling, appropriate turbo at sensible(ish) boost, fuelling, breathing and ignition timing.

What is your point? Speak plainly what you are thinking rather than talking around the houses... I don't mind and want to know your opinion. Nail your colours to the mast m8 - do you think my car is detting and I am going to have horrendous plugs and piston crowns??

Mycroft

Just making sure.

As to what is or isn't wrong with your motor how on earth would I know?

I do suspect that you will see some brown deposits that look like rust, but that depends on how good you are at mixing the OP with Optimax.

[Edited by Mycroft - 3/3/2003 1:02:08 PM]

milkytadpole

Mycroft, that's not entirely true, under such severe conditions charge can readily auto-ignite, this in-turn is quite likely to lead to knock. So it's not actually the pre-ignition that you detect, but the knock as a result of it.

JB, have you tried any other SUL's? J

Mycroft

Mr. Tadpole, you should know better, there is no 'end gas' until after normal ignition, the 'end gas' will explode at a greater rate and that is the knock, pre-ignition explodes the ordinary mixture that does not EVER cause knock, even my first year Engineering Graduates know that.



[Edited by Mycroft - 3/3/2003 1:21:14 PM]

john banks

Over the last 6 months running around or above 175 BHP/litre on cast pistons I have mapped for Optimax and covered 10000 miles. On a few occasions I tried Esso SUL and found that there was no det until you had been thrashing the car for about a minute and then it was the slippery slope, flashes on the knocklink and very soon after that audible detonation. I normally map to get rid of the det and pull 1-2 degrees out for safety, more if I am mapping on a particularly cold day, or will be taking it on track. The FMIC makes the timing far more consistent, with the TMIC you could thrash the car once and it not det, and then cruise along for a while and thrash it again, having got rid of a lot of the heatsoak and it would det its panties off. Not just my car, loads of them do this. You just have to repeatedly provoke it to get rid of all the det and then add your safety margin.

What is notable is that my ECU still pulls out timing with Optimax and NF if I overcook the midrange timing. In addition, it will still light up a knocklink with Optimax and NF, and you can hear it detting - sounds just the same as ever to me. Put more NF in or retard the timing, or pull the boost, or add fuel (within reason) and it goes away.

Can't find much in my albeit limited experience that squares with Optimax and NF changing the knock signature I have to be honest! But I am approaching this from the practical point of view rather than any particular chemistry understanding.

milkytadpole

I apologise Mycroft, but I severely doubt you're knowledge of fundamental combustion. What exactly do you mean by "my first Engineering Graduates know that"? You surely can't mean that you're affiliated with any teaching institution. Just a few minor points for you.

Charge does not explode, it is a controlled propagating flame (auto-ignition processes are somewhat different)

"End Gas" merely relates to any unburnt charge in-front of propagating flame.

Pre-ignition, as the name suggests refers to an auto-ignition process occuring prior to the spark discharge (often caused by a "hot-spot" in cylinder). Typically followed by a brief period of flame propagation, then occionally knock (condition dependant)

Knock is just very rapid heat-release, nothing more magical than that.

Mycroft

Signature is a good word, a flute if it plays a single note say 'A' (440hz) it has little colour, it is almost a sine wave... now play 'A' on the Piano and it will sound entirely different, the main component is still will hold the note to 'A' but the wave form or 'signature' is very different, for a given volume say 95db then flute would have the greater part of that 95db as pure 440hz, the piano may have only 75/80% of that 95db as pure 440hz.

Do you understand what I'm getting at?

john banks

Yes. I am asserting though that the sound of knock sounds the same on NUL, SUL, Optimax with or without NF. At least on my engine to the naked ear it does. It is knock because it sounds like it and it responds to adjustments in variables such as boost, fuelling and timing as you would expect. Don't see the issue?

Pin dropped in a tin, metallic tick noise whatever, it sounds the same to me and is easily heard in the right circumstances.

From what I see, knock is indeed self propogating - little bit soon leads to lots, and you can easily hear it them. So with this sort of crescendo behaviour I doubt I am missing it? As I said you could put Optimax and NF in my tank or another fuel and as far as I am concerned I would hear significant knock and it would sound the same.

Mycroft

#Charge does not explode, it is a controlled propagating flame (auto-ignition processes are somewhat different)#

Or as I even more correctly called it in the OB thread:- deflagration.
-------------
#"End Gas" merely relates to any unburnt charge in-front of propagating flame.#

Incorrect, #end gas# is weak in mixture, it burns (deflagrates) in an entirely different manner.
-------------
#Pre-ignition, as the name suggests refers to an auto-ignition process occuring prior to the spark discharge (often caused by a "hot-spot" in cylinder). Typically followed by a brief period of flame propagation, then occionally knock (condition dependant)#

As I said it is not and never will be 'knock' and sounds very different.
----------------
#Knock is just very rapid heat-release, nothing more magical than that.#

Oh dear, very simplified to almost breaking point... expand please, perhaps 'surface boundary layer' will help you in Google..

[Edited by Mycroft - 3/3/2003 1:47:46 PM]

Mycroft

Knock sensors don't just look for a frequncy they look for a signature... they may be said to be looking for a 'Grand Piano' and due to an OB in the mix it sounds like a New Orleans Honky-Tonk. Still recogniseably a Piano but not to computer reading an oscilloscope.

[Edited by Mycroft - 3/3/2003 1:46:45 PM]

john banks

What about ears connected through the eighth cranial nerve to an incredibly complex neural network ? Sounds the same to me, and it still does it if you overstep the mark with NF/Optimax - if I'm wrong I'm well overdue an engine rebuild As we know, Subaru engines don't tolerate detonation well at this level!

[Edited by john banks - 3/3/2003 1:51:25 PM]

milkytadpole

Or as I even more correctly called it in the OB thread:- deflagration.

Call it what you will, it is in effect a flame. Incidentally, the word "deflagration" appears in no SAE papers from 1995-2001, unlike "propagation" how odd.
-------------
Incorrect, #end gas# is weak in mixture, it burns (deflagrates) in an entirely different manner.

Absolute rubbish, doesn't have to be weak at all, have numerous instanteous LIF (laser induced fluorescence) images to prove otherwise. Burning rate depends entirely on the local conditions so you can't generalise.
-------------
As I said it is not and never will be 'knock' and sounds very different.

Didn't say it was knock, said it could lead to knock.
----------------
Oh dear, very simplified to almost breaking point... expand please, perhaps 'surface boundary layer' will help you in Google..

Knock is a simple phenomenon, the precursors are more complex.

Unfortunately, my lunch break is over, so no more time to get involved in such banter.

I noticed, however, that you didn't mention what institution you claim to be affiliated with.

Apologies to all other readers.

J

Mycroft

End gases are not the same as those burnt by the engines spark... thank you for that at least.

Knock is an incredibly complex phenomena... the noise is a tiny part of it...

I explained this further on yet another GTr thread... I will return with a link to that... so that Mr tadpole doesn't have to spend all day boning up on the web

http://www.gtr.co.uk/forum/upload/showthread.php?s=&threadid=7895&highlight=boundary +layer

6th/7th post down.

[Edited by Mycroft - 3/3/2003 2:10:43 PM]

john banks

Maybe I'm simple but I base it on whether the engine goes quickly for a long time without damage and if I hear anything funny (with appropriate aids to cross check - eg microphone and amplifier, knocklink etc). We'll see what my spark plugs look like when I pull them later in the week.

Mycroft

I will be genuinely interested... for clarity have you used the same OB and Optimax through-out this mileage and could you re-iterate exactly how many miles you have done since last 'seeing' your plugs?

Cheers...

I'll come back everyday (I like Mr Tadpole) but I will ensure we are all here on a certain day.

[Edited by Mycroft - 3/3/2003 2:19:40 PM]

john banks

It is a bit of mix and match. Prob about 5000 since I saw the plugs, but the engine is running really well despite the specific power output. Used to use SUL with OB before Optimax was available here. Had some orange deposits in the exhaust, but also had this on SUL alone. Certainly there is more now.

I can confirm that I have been using whatever is in Optimax which either stops knock or makes us think knock has stopped to advance my ignition and make more performance for 10000 miles. So it will be interesting to be part of Shell's experiment

Pavlo

I was under the impression that the frequency of the knock was dependant on the cylinder bore, something to do with the speed of sounds in the combustion gas and the distance it has to travel.

Of course that might be some sort of myth.

Mycroft

When you first saw the 'orangey' stuff... what did you think it was?

john banks

Something in the fuel?

It is more a golden coating, certainly not sticky or seeming to noticeably reduce diameter. It was more noticeable after more use of OB and Optimax. The engine to me seems happier than ever, but I am putting a lot of torque through it so it could break because of that. I hope not since I believe I have controlled det. I am almost religious about it, certainly paranoid Although I only use simple low budget methods to assess it I try hard. I map out every single occurrence of what I think is det.

Mycroft

Hi Pavlo.....

To some extent but those things effect the 'signature' not the fundemental frequency.

Mycroft

John, so far then you have not had 'lumps of this stuff form?

john banks

No the downpipe was off 2 days ago, looked OK, the turbine wheel similar.

jason77

wow!

really good interesting reading and banter about 'knock' keep it up :P

j