I've been rescaling my injectors and got to log a nice (not!) case of knock today. I've attached the Evoscan log file. Looks like the ECU starts to gravitate towards the low octane timing map at ~10 knock counts. It pulled a LOT of timing in a very short amount of time in this run.

As reference for the spreadsheet:
- at 3375 RPM timing is getting well below the high octane map and approaching the low octane map
- at ~3600 RPM the timing is spot on the low octane map
- between 3750 and 5000 RPM the timing actually stays below the low octane map

Effects of the pulled timing can be seen in the slowly decreasing knock counts. It's an odd case of knock, since none of the other runs exhibited this behaviour. This was coming out of a toll booth ... maybe the road surface had something to do with it :shrug:

interesting stuff, IMO.

l8r)

 

Thanks. I was looking for the octane value in there, I bet it would have gone right down then. It sure pulled a lot of timing, sounds like a bit of phantom knock especially given that you were on part throttle when it kicked off and that you can usually run through these areas fine?

 

What makes you think that the long term updated octane value isn't what makes the gravitation towards the low maps and the knock sum is the short term "save your *** now" way to pull timing?

 

Better to get false knock counts with no knock than holes in pistons with no knock counts !

The stock ecu sometimes pull timing with modified cars when there is no knock due to increased harmoics

It can occur on random pulls which is why I try to do a few pulls at the end of a tune

 

You can get real part throttle knock on sub 8:1 compression 4g63's let alone the higher compression evo motors. At those cylinder pressures it causes no damage however. Octane value is typically updated when your knocking (no real associated value unless you can find it in the code) and for how long your knocking. Its updated in a similliar way that the low/mid/high fuel trims are updated. If you stay rich (or knocking) for a predefined period of time then the trim (or octane value) will be accordingly updated.

Typically you get quite a bit of knock transitioning into boost and at peak torque. At low rpm's the fuel spends more time in the cylinder to absorb heat and the greater the chances of detonation occuring. At higher rpm's the grams/rev (ie: load) is usually lower and the fuel spends nearly half as much time in the combustion chamber absorbing heat so detonation threshold is much higher. You'll usually see knock low when you go into boost and die out up top.

Going onto a stutterbox hard from idle will cause knock. Hitting rev limiters will cause knock. Shifting hard will cause knock. Any rapid RPM movement (free revving) will cause knock. NLTS will cause knock.

 

I'd like to think about this a little bit.

Why would harmonics cause knock one one pull and not the next? The harmonics of the engine should remain the same.

This is true of vibrations 95% of the time too. Why would it cause knock one pull and not the next?

I know you've been around DSM's and EVO's. Are the EVO's knock that much different? When I first got my car 6 years ago and it was stock I would get 20 counts of knock on every pull. The car ran well but was in a bad shape of tune. I changed the lash adjusters, plugs, wires, knock sensor, tightened up the exhaust, and added stiffer motor mounts to keep the motor put. Not my knock sensor is the most useful tool for tuning, and I'm making 3 times the power I did back then.

 

Yeah I've noticed that on my car, the downpipe on my car occasionally rattles against the crossbar and I am actually picking it up as knock in the knock counts.. That is the worst incident I have encountered on my car though.

 

my car seems to be very sensitive and pulls timing and boost in a big way on warm days with the ac on

 

Yeah, I have a nasty buzz coming from my exhaust somewhere - usually around 2200-2800 rpm. I haven't tracked it down yet. Just heat wrapped my DP last weekend to hopefully eliminate the buzz, but it's still there...

l8r)

 

Here's another log - same exact spot after the tollbooth ... similar results. This time I also logged the Octane number. Note how quickly it recovers back to 255.

Merry x-mas jcs.

I think I need to add some fuel in the part throttle load cells. Seems like I occassionally see knock activity in these cells.

l8r)

 

Here's another example of part throttle knock..probably phantom.


RPM TPS Knock Timing
3406.2 36.0784 01 29
3406.2 38.4314 00 30
3406.2 40.7843 00 25
3406.2 41.9608 02 20
3406.2 42.3529 02 16
3406.2 42.3529 06 14
3406.2 41.1765 13 13
3437.5 42.3529 12 12
3437.5 41.9608 12 12
3437.5 41.1765 11 14
3468.7 40.7843 12 16
3468.7 40.3922 11 17
3500.0 39.6078 09 18
3531.2 39.2157 08 20
3562.5 33.7255 08 27
3531.2 13.3333 01 37

No good reason for the above....at 40% throttle I'm just barely into boost.

For some reason evoscan cuts off any TPS lower than 13.3 as 13.3. My other loggers don't have this problem. Anyone else encounter this in evoscan?

-Peter

 

It seems to pick up exhaust rattle or small debris hitting the exhaust as the knock. I have seen 23 knocks for no reason with 105 octane race gas in the car( my car gets 2 knocks at most with my conservative 91 octane tune usually). It seems that knocks ensor gives you the good protection of the engine but at the same time, it is very problematic when it encounters false positive. when It encountered 23 knocks it pulled timing like -7 and my EGT temperature shot up and ended up in back fire.

 

yeah thats how everybodys is

 

Merry x-mas indeed Ludikraut. "Nice" to see it working.

Thanks for the info dan l.

 

Don't wrap your dp. Here is why:

Hi,

Wrapping the downpipe is NEVER advisable. You want to have as little heat and back-pressure behind the turbo. Otherwise you lower its efficiency. Meaning it's harder on the turbo and the engine and you make less power, but create more knock probability.

Regards,
Klaus

and:

Hi,

When you wrap the downpipe (behind turbo) you keep heat in the exhaust gas. Heat equals pressure because the exhaust behind the turbo has to flow a higher volume. This increases exhaust speed, that's true, but the flow resistance (and therefore back pressure) goes up with the square of the gas speed.
A turbo (turbine side) runs best and most efficient with as little back-pressure as possible. Remember, the turbine in a turbo runs off the mass-flow of gases, which is dependent on the pressure difference between in and out of a turbine. You want to maximize that pressure difference.
Therefore it is advisable to wrap the headers BEFORE the turbo. This keeps the energy in the gas that the turbo uses to function. I'm too busy to calculate the % right now, but wrapping the downpipe is equivalent to reducing it's diameter.

Heat in the engine compartment would much more likely come from the turbo housing itself and the primaries (which can be wrapped). The downpipe will not contribute as much as it is quite a lot cooler. The high pressure exhaust gas expands in the turbo and thereby cools down.

Regards,
Klaus

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