What could cause this knock?

Hi there!

A friend of mine is working on his build for some time now. This build consist of a nissan 370z(88.000 km engine) and a twin turbo kit. Now that everything is but together again and starting driving the car(after tune) a bit, we saw a lot of ignition correction in the logs. So we pulled out the link knock block and started listening for knock(audio file included in this post). We think we detected a lot of knock, maybe you guy's have other insights? We pulled the spark plugs and looked at the pistons. Also there we think we see the sand blasted effect(pics also included in this post). So in our opinion: if it sounds like and if it looks like it probably is knock(maybe for you to confirm?).

We have done a lot of work eliminating probable causes:

- upgraded fuel to RON 102

- AFR is(at max boost: 150 kpa) around 11.2

- fuel pressure is steady

- used different spark plugs

- used different coils

- exhaust restrictions, driven without downpipes

- checked ground on the engine

- compression in the cylinders

All these are ok.

Do you guy's have an idea what could be the cause of this? We have a other car with the same build. exact same setup. This takes around 12o of timing around the same load(3000 rpm/150kpa). this car now has 7 and the ignition correction even pull's 5 off until around 2(Log file included in this post).

Hope you have some idea's! love to hear them :)

Kind regards,

Vincent

That is 100% knock that you're hearing! I'd proceed with caution as you risk damaging the motor quickly if you continue running it.

I'm not sure what I can suggest to be honest. While the engine you have is a relatively high compression N/A engine, I'd be surprised if it couldn't be safely tuned with the boost level you're reaching (6-7 psi) and I'd expect it to take more than 2 degrees timing. I'm not overly familiar with this platform though so I don't know what I can suggest. Is there any chance the fuel you're using is contaminated or old? What size are the turbos?

Hi Andre!

Thanks for your response and confirming the knock. We will look into the fuel and replace it with new just to be sure. The turbo's on the engine are 2 x BorgWarner EFR 6758 Turbochargers which were included in the AAM kit. If any pointers come to mind im surely interested. We will update here as our search continues.

Kind regards,

Vincent

I agree, I can hear the knock on the audio. Was there any head work done? maybe something that can cause hot spots and isn't necessarily the fuel or anything else that's causing it? Is your base timing set properly? if it's not, when you're only showing 7 degrees in the table and getting knock, that 7 degrees could actually be 30 degrees if your timing isn't set properly.

also you want to look at the MON of the fuel, MON test is the torture test (high temperatures). RON is the light load test (lower temperatures). RON is the research octane number and MON is the motor octane number. So even though you have 102 RON it could only be 96 MON which is what it'll be in the higher load (and temp) region.

Thanks all for the reply! i wanted to give you an update on this.

We switched to de default injectors and put back the stock tune, opened the wastegates and disconnected the charge piping. Just to eliminate any mechanical aspects. We drove with this still listening for knock. All was fine. even disconneted the POS sensor to eliminate timing issues. All values the way we expected.

As we can not edit or see the tune its hard to debug all the possibility's.

Next we are going to put the bigger injectors back and load to tune, still with open wastegates and disconnected chargepipes so we can not build boost and then again listen for knock. With this we eliminate errors in the tune without boost. If you guys have insights on this i would love to hear those :)

Kind regards,

Vincent

I would absolutely check the ignition timing with timing light at cranking speeds, idle speeds and 3000-4000 RPM just to be sure that there are no issues with EPS sensor wiring and settings.