Are you serious?

I'm done with this.

fundamentals > you

 

This thread really needs less analogies, more data.

aka, less musical instrument references and more (Edit: ANY) data to reference the claims.

- Bryan

 

I was hauling tuba's in my Evo the other day and my knock light was constantly going off. Maybe he has something..........

 

I might buy off on motor mounts and exhausts changing the mechanical noise environment and possibly cause false knock readings. Under no circumstances will it change the frequency that real knock generates.

 

Looks guys I would actually love to discuss this in depth, if it weren't for the complexity and depth of the subject. Anyone could easily talk about this for a few days straight. Heck the basics alone is a semester's worth of information; if not more. Like I stated earlier I will consider doing a write-up at a far future date.

I also stated this should NOT be a concern for most. So go on and still have fun everyone!

 

Why even post about it in the first place if you aren't going to talk about it in more depth? I'm still waiting for any amount of data to get posted to support your claim.

It's like saying the stock boost control solenoid can be tweaked to perform better using a oscilscope but never posting data to support the claim.... oh wait...

- Bryan

 

This is an interesting conversation. I am a professional musician so hopefully I can speak to this subject. The reason why a violin sounds different than a cello or a flute is primarily due to the relative strength of the overtone series. An "A" 440hz (the note that orchestras tune to) is the same on any instrument that can play that fundemental frequency. What makes it sound different is the strength of the overtone series (octave above, fifth, octave, third, etc.) and the shape of the sound wave (sine, square, sawtooth, etc.). A violin has a smaller mass and more vibration resistence (stiffness) and smaller air cavity inside the body. A cello has more mass and a larger air cavity.

The fundemental pitch of the knock will not be changed by something like a roll cage as the influence of that mass is too far away from the engine block. A different exhaust WILL effect the knock frequency when the sound wave travels out of the cylinder and out the exhaust because the cavity of the system will be larger yielding a lower frequency that will influence the overtones and shape of the sound wave . There will also be a slight variation in frequency from when the cylinder is closed and the valves are open because of the larger cavity. Ever blow into a bottle (preferably beer but we will not get into that) drink some blow in again and the pitch (frequency) goes lower? The lips, air speed and resonance of your air flow over the bottle opening creating the vibration does not change that much (good wind players do make an adjustment in air speed and the cavity of their mouth but this is too involved for this discussion) but the volume of the bottle cavity does thereby changing the fundemental frequency.

In the end the cylinder volume (when the preignition occurs in the piston travel) and the composition of the engine block (material stiffness, mass that creates more or less dampening) will have the largest effect on the knock frequency. Hope this makes sense. LOL

 

uhhhhhhhhhhhh....?? Did Mr. Holland buy an evo?

 

I was running 0-1 timing at peak torque on track. When it knocked a bit (as it will even on a perfect tune) it would go down to zero. However, even zero is dagerous on a long haul with modified cam timing. I don't have any pictures but I assure you I melted a turbo. I have it sitting in a tupperware at home, melted inconel turbine and all. I've since raised my peak timing, lowered boost a bit and enriched a bit at peak torque and now I don't have that problem. The pistons are fine as you move the heat into the exhaust stream when you retard timing so the exhaust took more damage than the cylinders. Remember, if you use ignition retard to remove the possibility of detonation, that ignited energy is still going to happen. If you have aggresive cam timing and lots of fire, it's going somewhere... and that's out.

 

Yeah reducing timing moves heat out of the combustion chamber. This is why it reduces detonation so well. Its kinda hard on exhaust valves and turbos if you stay in it for a long time like when road racing like that though.

 

Actually let me be a little more precise. A quick burn combustion chamber can run less timing and not hurt exhaust valves and/or exhaust parts. Such is the case with the evo 9 cylinder head, it burns quicker than the evo 8 heads. When tuning timing, if detonation isn't an issue, one tunes for max cylinder pressure to be at 14-16 crank deg ATDC. If your engine is so awesome that it only needs 1 deg of spark advance to light off the mixture such that max cylinder pressure is at 15deg ATDC then so be it. The air/fuel charge will be sufficiently burned such that the exhaust parts will be fine.

However personally I've never hurt an exhaust valve or turbo or seen it done. Makes sense that it would and I believe I remember older racing porsches having turbo failure issues but I may be wrong.

 

Knock frequency only changes relative to a few variables, one being bore size. Mitsu and Subaru have both published papers that isolate knock frequency to formulaic computation based off bore radius. This has been brought up before and thoroughly discussed.

I can see a header affecting it a little, but the not the 1000hz that is being asserted. A roll cage, really? Burned valves seem to have less to do with EGT and more with random chance than people tend to think. Its an easy explanation to say EGT, but why do completely stock DSMs burn valves? Not becuase they are high boost or have extremely low timing I can guarantee.

I understand what Honk is saying as the cars we tune for track usage always are running less boost than street cars and more timing, a little racegas or on E85 (which is an entire discussion by itself as it drops EGT inherently) and then hammer the car for 20 minutes or more. I dont think you put a number on whats safe though, its a matter of seeing how each combo is going to react over the course of 20 minutes or whatever.

CrCain is really talking about Mark Shead and alot of the way that British tuners (I suppose a fair amount of european tuners as well) have been tuning cosworths, evos, subarus, etc. I remember there was a thread about 2 years ago discussing high boost on pumpgas. It became a heated discussion involving a few vendors and tuners and ended up being pared down and put in the advanced tuning thread.

It then lead to Bryan and myself experimenting with high boost on 91 and 92 respectively. I ended up at 30psi on reasonable timing and Bryan was high 29s as I recall.

 

I think we have an unusual case of someone actually having a turbo failure from a low timing / no knock situation which is sort of hard to believe.

And also a situation where Works is claiming the stock ECU was not reporting false positives (like we often see), but false negatives!

Neither of the above things I don't think has EVER been reported on this board. So maybe they are true but we must gather they are both extremely unlikely to happen.

Finally, my buddy has a stroker, Red, Revolvers, etc... and he has his knock settings, the multiplier I think, set to be about 20-30% less sensitive. And everytime while we tuned that I heard det via headphones and raised my hand, he saw the CEL do a quick flash for a knock sum > 3. So the knock sensor on his car was reliable as you'd expect. And to me, regardless of the car setup, the knock sounds the same as Mark originally described to me, an isoltated tick sort of behind the valve train noise.

I know jid2 wanted to record some knock via det cans.. I've wanted to do it too just as a fun experiment. Would be interesting to see what it looks like on my 2.4l, and my other friends 2l and 2.3l motors. I was thinking of just sticking a mic in the earpiece of my headphones. Might try to do this.

 

Don't let the complexity of the topic stop you from discussing or reporting your findings. I'm sure there are people reading this who have sufficient education and/or experience to understand what you can potentially contribute.

I have a few questions that I'm hoping you can answer:

1) What engine mounts did your roll cage car have?

2) In your experience in measuring knock frequency, does the frequency tend to shift consistently higher or lower than the stock frequency as modifications are made?

3) Do you have frequency response curves for the Evo 8/9 and Evo 10 knock sensors?

 

How did you guess? The evo helps my street cred.

By the way I bet most of you would be surprised with how high pitched 13Khz that EM@works refered to is. Most people cannot hear anything above 16Khz. Go to this link and click on the 12Khz band and you will hear how high this frequency range is!!!

http://www.phys.unsw.edu.au/jw/hearing.html