Knock Retard On Throttle Close

[swingtan]

Hi all,

I've been logging for a while now and have noticed on a number of occasions I get an amount of KR once the throttle has closed. Can anyone explain why this occurs?

At first I thought it might have been the spark ramping in too fast, causing knock, but it's normally still falling when the KR occurs.

Here's a a segment of a log file showing the KR as the throttle is closed.

Thanks in advance,

Simon

[hymey]

Turn off burst knock, And adjust your KR sensitivity values.

[swingtan]

JezzaB and I have talked about this a bit and we did discuss Burst knock. My understanding ( which may be wrong ) was that burst knock would not effect the octane scalar level, as it was actually a "predictive" knock not a "measured" knock. If this is the case then this can't be burst knock as the octane scalar value rises when the knock occurs.

Note that for the E38, the octane scalar is a factor, not a percentage. The octane scalar for the E38 should always be "0" ti indicate there has been little or no knock retard.

I'm happy to be proved wrong on this, I'd just like to understand the why it's occurring. Have you seen this or is this just a suggestion?

Simon.

[hymey]

I think you are right there swingtan. I have found that IAT get high and that pulls timing. And knock further reduces timing.

Infact I temporarily switched of the knock sensors and found the motor would ping on the high octane table from factory on 98ron fuel. When ECT was lower(around 80) it would not knock due to IAT being lower. Once it rows to the usual 95 deg C the motor would knock easily. I guess due to the combustion chamber temps being so high that it would initiate knock much more easily.

I had to lower my timing a little everywhere until pinging stopped then turned the knock sensors and no more knock now.

[mr.prick]

i saw a whopping 1.6 degrees of knock in one spot and no WBO2 data.
your 1.6 degrees may have been from hitting a lean spot in the MAP area.
was this log saved after it was filtered?
because it was quite short.

[swingtan]

Hymey: yes the E38 in the Holdens knocks pretty easy, especially around 30% throttle and 1600rpm. that's my usual bad spot. I've dropped the timing in that area and now rarely get knock in that region. I've built a set of knock phones so I should be right to try turning off KR and doing some real testing. Oh, and IAT's should be addresses soon to, with the installation of an OTR.

mr.prick: A "whopping 1.6"..... yes I know. I wasn't so much concerned about the amount, I just wanted to know why it occurred at that spot. Knock under load I can understand but knock with minimal load seemed a bit confusing. The log is short because I cut it out from a longer log.

I fixed the lack of WB data by getting a WB bung installed last weekend. I did a couple of dyno pulls and there was no indication of a lean out, but also no knock on throttle close. However, given that the timing was low and load was low, it has to be a lean out or it was simply false knock from something mechanical.

[hquick]

Just for a bit of a reference....is it possible that we get too hung up about knock? (I know I am Lol!)
I was speaking to a buddy of mine who writes the Cal's for GM. He was saying if you check a factory tuned vehicle you'll see alot of knock.
I think it was the new Camaro's he was saying they were basically told/directed..."don't worry too much about the amount of knock....just make it NOT blow up". He was also saying they have had cars/engine's on the dyno's (new VE commodore) and tried to have them knocking to destruction and he's only known of one to let go. That's with registering HUGE amounts of knock running flat out for days...non-stop.
Also, apparently there is alot more 'slack' allowed in the tuning of the US vehicles than the Aussie vehicles (ie...the US vehicles are 'allowed' to knock ALOT more).
Of course...none of us want to see ANY knock...but how much is too much?

[hymey]

The motor may not crack pistons etc, But when an engine detonates the shock on the internals is 3 times higher than normal so you will basically get less life from your engine.

Most new jap cars knock, Just listen to them driving past in traffic.

The LS series engines no doubt will handle it, But it is no good and kills hp. The Knock sensors are over sensitive. But if you change there settings they fail to pick up "real knock". So a safer high spark table with no knock, with a bottom table 2 degrees retarded over standard is the way to go. You could find a better map than factory on a corn flakes box.

There are cheaper and easier ways of reducing IAT. For $695 you can by an OTR. Or for a lot less you can holesaw a 4" hole in the air box, And run ducting to the front bar with the addition of a K and N filter. This will cost $100.

The ECT are 95 deg C, Go for a 160 thermostat and change your fan settings and it will sit on 80 deg C all day which will reduce 15 deg C from your inlet pipes minimum.

[swingtan]

OK, I already have a 2 Hole mod and cold air box. I do still run the std paper filter though. An OTR is certainly on the cards at this point.

I'm a little undecided about changing thermostats. While the lower temp achievable with a 160F thermostat is beneficial for power, there are many other things to consider. I've read a fair bit on the operating temps of motors and the thing that stuck with me most was that most engine oils are designed to run at the std. thermostat heat range. Running a colder thermostat means that the oil may take longer to reach optimal temp, or may not reach it at all.

I know lots of people use the 160F thermostats and that's fine. I just want to see how low i can get my IAT without changing the normal operating temp of the motor.

The funny thing about the knock in the log though, is that I haven't been able to reproduce it since.......

[hymey]

Good point swing, but a 5W-30 or 10W-30 oil is already very thin oil, and 95 deg C operating temps means that standard the oil is most probably exceeding an adequate temperature. And if you were to circuit race this vehicle it would need a decent oil cooler.

And I would think running safer oil temps would mean less oil consumption and less oil mist exiting the breathers.

The first VT LS1 had big troubles with seizures in the bore and bent rods. The cast liners were very thin and high ECTs combined with an efficient radiator meant that once the thermostat opened, cold coolant come in contact with a 100 deg C block and the liners quickly contract locking the bore in the cylinder.

The high ECT is there for emission only.

It would be good to see what you can get down too with a OTR. I read 8 degrees over ambient on a VE. Less chance of heat soak, etc. It is the prime choice I know it all adds up but I want 100rwk gains not 5 so I am spending my money on a cam upgrade.

Lifting the hood on my car at operating temp near burns my face. So I am fitting a 160 thermostat.