Avoiding "Super Knock" / Why do I have rod knock?

[joelkillspeople]

Hey all. I'm new to direct injection and the Mazdaspeed platform. I just bought a used Mazdaspeed 6 with ~135,000 miles on it. The clutch is stock, the engine and exhaust are stock, and not much has been done to it. I would normally estimate how hard a car has been driven by how the clutch feels after this much time, and it seems like it hasn't been roasted. Not to say that it hasn't been, but the car seems to be in okay shape.

My car developed a rod knock which I first noticed merging onto the freeway in third gear. I was accelerating from ~50MPH and noticed the noise early at WOT. I don't think I even got to 70MPH.

No warning lights, no sputtering or perceived fuel issues or ignition sputtering. The engine just started knocking, which is incredible.

So looking further into this, I am seeing an issue which is described as "super knock", and appears to be something specific to direct injection turbocharged engines. I have just finished reading a scientific study entitled "Investigation on Pre-ignition and Super-Knock in Highly Boosted Gasoline Direct Injection Engines" which seems to indicate that using a double injection during intake stroke will eliminate super knock, decrease fuel consumption, and decrease exhaust temps.

I have done some cursory searching of the mazdaspeed forums, and have not really seen any tuning techniques which refer to dual injection, and am wondering if anyone's tried to tune this in.

I don't really want to go very far past stock power output, but I also don't want to have my car ruin itself again due to a random pre-ignition, and this paper I'm reading shows some definitive benefits to having two injection cycles per intake.

Has anyone tried this? If so, any results?

Thanks in advance!

[MSMS3]

Has it actually blown up or are you trying to resolve the knock issue? If the former, my sympathies. If the latter and it can be safely started, may I offer a modest suggestion? You need to get a logging device and then datalog the engine, especially looking for timing pull or retard when you have the engine under load. We call it KR or knock retard. What you hear may or may not be true knock.

Good datalogging will provide the information to help you diagnose what is going on and what is causing it.

Do you know if the engine is running on stock ECU tune or whether the prior owner may have flashed an aftermarket tune? Data logging might reveal if the existing tune is safe for the engine.

Often these cars had aftermarket "bolt-ons" to increase power and associated tunes over the time of ownership. Then when the car was sold they "stock out" by re-installing the OEM parts but may have not flashed the tune back to stock. That could result in possible unsafe operating conditions.

Sounds like you got a good one, but you need to explore the source of the "knock" before automatically assuming that is what it is or why it is occurring. The ECU should pull timing at impending knock to protect then engine and that would show up on the logs.

[Fstrnyou]

I don't believe there is a current method to control injection timing with the stock ECU.

A similar phenomenon worth reading about is LSPI (Low Speed Pre Ignition).

I've read the article you mentioned but I can't remember if LSPI was discussed in it.

My personal choice to limit the low rpm knock (back when I had that problem) was to slow down the spooling of the stock turbo by lowering the requested loads below 3500rpm. Worked like a charm. Your results may vary.

Nevermind, I see now the thread title says you blew up. Sorry for your loss.