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Help Needed - RB26 Detonation (Knocking, Pinging, etc...)

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Good day all,

I had a R32 Skyline in my shop for a while, had a couple problems with it (boost creep from my other thread on here...), then started tuning. Steady state was done with no problems all the way until 4000rpm, then switched to ramp run. I had a random misfire at around 6000rpm and some knocking with low timing (6 to 8 Deg @ 210 KPA), after a couple of pulls, the water pump bearing shattered into pieces at redline (I could see the moment that the water pump/alternator belt flew away on the log of battery voltage). Talked to the customer, said yes to the OEM water pump replacement, I also proposed him a PRP Cam/Crank Trigger at the same time, and he said yes.

Fast forward after the install, did the base timing setup, everything checks out on the ECU Master scope... Good to go. I double checked the steady state, did a couple of correction at the ignition timing, nothing crazy.

Now my problem is : it knocks. A lot. I am using Plex Knock Monitor v2 with a bosch sensor plugged in the front OEM location, and the in back location, there is a OEM sensor plugged in the ECU Master. Both are reading the same knock, and I am obviously hearing it. Note : The misfire @ 6000rpm is now gone.

I tried to enrich it, went all the way to Lambda .72 at WOT, didn't help. I thought it would be some bad gas, added a fresh 20L of 91 Octane to an empty tank, still knocking. Confirmed my A/F ratio with a Innovate LM-2, same reading as my AEM UEGO Type-X from the car. Removed more and more timing, helped a bit but still knocking with 5 deg at WOT. Re-did the base timing with more "gap" in between the cam and the crank signal on the scope, no change. Pulled the plug after a ramp run (immediately shut the engine down at the end of the run, no idling) and they are white, with sign of knocking. You can see for yourself on the pictures. It also doesn't make much power (300 whp @ 220 kpa - 8 Deg timing)

I am a bit lost, I've never came across that situation. Especially with a Cam/Crank trigger kit which usually solves problems like timing drift, etc...

Here's a quick list of mods :

Built RB26 (Forged Pistons and Conrod)

Tomei Poncam 260deg (I heard these cams have big overlap, I need to idle @ 0.95 lambda to have not to bad idle)

Docrace T4 Single Scroll Manifold

Precision 6266 Turbo

Twin Precision 46mm Wastegate (to avoid boost creep)

ID1050x Injectors

Splitfire Coilpacks with BKR7E gapped to .028

Chinese Intake Manifold - Single 90mm throttle body

PRP Cam and Crank Trigger Kit

ECU Master Classic

I have attached the EMU and a .csv log (starts at 14:00min, before that it's me re-setting base timing), the tune, and pictures of the spark plugs.

Any input is appreciated.

Thank you,

Frank

Attached Files

I'm not sure how your 91 octane relates to our local fuel but we have 91, 95 and 98 readily available at the pump and 91 would definitely not be my choice. I'd be expecting the engine to be pretty knock sensitive on that grade of fuel. On 98 (which is what I'd usually run) I'd expect the timing to be around 8-10 degrees higher than what you currently have. The other part that is a little suspicious is your map value at idle. From the log it looks like you're around 65 kpa where as I'd expect closer to 45-50 with those cams. Have they been degreed properly?

Hey Andre,

Thank you for the reply.

As regard for the fuel octane, here in Quebec City, Canada, our fuel octanes for pump gas are 87, 89, and 91 (91 got no ethanol in it, others can have up to 10%), and very few places have 94 oct in Montreal area. So 91 oct is what the customer is going to be using.

For vacuum, the customer is using stock cam gears. I am not really familiar with those cams, but I did degree a set of these cam on a similar setup (same manifold and cams combo) to true TDC according to Tomei Spec and it didn't really help for vacuum. Could these vacuum values be because the intake manifold has a plenum compared to the individual TB of the stock intake manifold?

Again, thank you for taking the time to check at my files.

Have a great day,

Frank

Any chance the water pump failure caused the cam timing to slip?

Hey David,

Negative, the timing belt was still on its mark before the water pump disassembly. And I had to take off and reinstall the timing belt to change the water pump as it is sitting behind.

Thanks,

Frank

There are two 'octane' ratings,

Motor Octane Number which is derived by actually testing the fuel on a specially designed engine

Research Octane Number which is assessed by the chemical composition of the fuel

You can find more information on the here - https://www.sciencedirect.com/topics/engineering/motor-octane-number - and I would bring your attention to fig. 13.1 which has both the MON and RON numbers, note the difference!

That difference is critical when comparing fuels in different countries as Britain and (most?) Commonwealth countries just use RON, but the USoA uses the average - (MON + RON)/2. From the octane numbers cited, it would seem they're using the US' rating and 91 octane in the USoA is ~95 RON.

You say it's a 'Chinese' intake manifold - that could be causing air distribution problems?

You only showed one spark plug - are they all the same? Spark plug heat range 'should' be fine, but the insulator tip and ground electrode look a little lean and/or hot, so maybe try 8's? Do you have a spark plug viewer to look at the base of the insulator and body? If the other plugs look different, it may be a problem with the injector(s) - were they new/tested and was there any chance if their getting rubbish from the fuel system?

Hey Gord,

Thank you very much for your input. I was aware of the differences of RON and MON, still a very good read!

Yes, all the plugs are the same, I forgot to mention it in my first post. This was after the ramp run and wideband showed 0.75 lambda. I thought the same about having air flow issues, but it doesn’t seem like it.

Injectors are brand new, as well as the whole fuel setup that I did myself, using an AEM FPR, 10 microns Aeromotive fuel filter right before the fuel rail, and Vibrant braided hoses and fittings.

To be honest, I am not super familliar with spark plugs heat range. I think it’s their abilities to dissipate heat, right? Maybe if they’re too hot, this could cause pre-ignition?

Yes, spark plugs that are colder/harder (different folks use different terms) have shorter insulators so the combustion heat can make it's way to the main body and cylinder head faster and keep the spark plug tip colder. the reverse applies with hotter/softer spark plugs that are sesigned to hold more heat and so burn off deposits more readily.

Usually, when modifying a vehicle, you will need to use colder spark plugs because of the rise in combustion temperatures and one, or two, grades is common and with extreme examples I believe up to 4 grades have been used. One thing to watch out for is that different manufacturers use different numbering for the heat ranges - with some higher numbers are colder, with others higher numbers are hotter!

With the earth electrodes, there isn't a lot that can be done to pull the heat out of them, although some will use copper cores or other alloys to assist heat transfer and/or use different designs. The ultimate are the spark plugs where there is no earth electrode and the spark gap is between the centre electrode and the body of the sparp plug - this type is also use in some very high compression engines as they can increase the piston dome without needing to have electrode clearance. Many years ago I experimented with shortened earth electrodes, even cutting them off entirely - but that was a N/A engine and it had a LOT of HT voltage.

As you say, if the spark plug is too hot, it can act like a glow plug and add to the normal compression temperature rise to the point where it can ignite the charge early - this is pre-ignition, rather than detonation, but it can also cause the latter.

I'm not saying it's the problem in your case, although it's something to consider I suspect the main problem lies alsewhere, but it is why colder spark plugs are required as the engine produces more cylinder temperature.

Hi Frank

Your coil dwell time look a bit high for this type of coil and maybe the coil pack start overheat/autofire. Try to remove around 0.70ms for all the table.

Thanks Gord for the infos, it's really appreciated!

Jonathan,

I'm back at it today, I'll try that for sure and keep you posted!

Further analysis of the ECU logs showed that most of the knock happens to Cyl 5 and some on Cyl 6, which I will confirm by attaching my trigger input to the Plex today. Could be a flow issue I guess.

Thanks guys,

Frank

I have seen this a few times with other engines, And its often a Emap problem. ( muffler collapsed, or just a really bad design. )

Try removing the exhaust completely and do a pull.

Canada uses the same method of Octane averaging as the USA. AKI. R=M/2.

Petro Canada has 94 AKI Octane available in Quebec. It is probably the best Pump Fuel in Canada for Turbo engines. If you can find Petro Canada ULTRA 94 Plus fuel... that is the one to get. Tuners of Big Turbo Audi's on East Coast of USA have reported it behaves like 100 AKI Race Fuel .

The " normal " Petro Canada 94 Octane is still pretty good from what I have heard. I did an online search and there are lots of Stations in the Montreal area with the Petro Canada 94 Octane fuel. I didn't do a search for the 94 Plus Ultra fuel.

Here in BC, we have Goat Piss for fuel. Shell Nitro 91 is fairly decent. Chevron 94 used to be terrible.... but in the past 2 years has gotten better. Chevron changed their supply chain a couple of years ago and things seem to have improved.

Chevron 92 Octane in Washington State ( Cherry Point Refinery ) was always way better than our " Canadian Chevron 94. But they seem to be closer now. Most local tuners think it is the local Refiner in Burnaby BC that was the issue. We've ( Local Tuners ) complained for years about the quality. Maybe they finally listened. East Coast and Alberta Chevrons didn't seem to have the same issues with Chevron 94 that we used to have.

Not saying that this is the issue... but there should be a good supply of 94 AKI Fuel in your area. Best to eliminate variables first.

Hey Frank,

On thing to keep in mind with the RB26 engine is that it is a straight 6 engine, so the combustion chambers retain more heat, as they are the last in the cooling circuit, and on an RB series engine can really suffer with a completely standard cooling system layout.

Depending on the combination, I found running cylinder 5 2% richer and cylinder 6 a little bit richer again would help a bit with cooling, and make those back 2 cylinders less prone to knock.

Particularly with the water pump bearing failing, I can only imagine cooling system flow wasn't at its peak in the lead up to the pumps failure.