stock BR-Z, much detonation during shifts: tune?

[Lonewolf]

Originally Posted by ft_sjo

I really don't understand you people. Someone shares some actual knowledge, rather than repeated garbage they find on the forum/internet, and they come out with sarcastic comments. Bravo, well done, way to improve yourself.

Actual knowledge...seems more like speculation, conjecture, and inferences to me...so not much better than what anyone else is offering.
Now, if you had could explain some logs or scans of what these cars are doing precisely when people like the OP hear these events, that is knowledge...

Or better yet, Subaru or Toyota engineers explain these occurrences with models, graphs, or EMPIRICAL DATA, that is knowledge...

[ft_sjo]

So if I tell you that there is a table in the ECU which controls transient spark during shifts, or when the clutch is depressed, you'd think that was speculation?

[StormTrooper]

Good luck with your "issue" ....

Might try not shifting fast at a point in the rpm range that doesn't benefit you....

[regal]

Originally Posted by arghx7

I don't know the exact formula your Torque app uses, but the only way it could work is by taking some kind of "before and after" comparison or some kind of statistical analysis of spark timing. It can't read the knock sensor over the universal CAN bus. So you're still at the mercy what the knock sensor is responding to. The knock sensor can be responding to driveline noise, or it could in some cases be a little extra sensitive to combustion noise depending on how the engineer set the background learning signal processor and the knock judgment threshold.



I know what you're thinking. "It's either knocking or it's not. If it's knocking, that's bad, and no engine should be knocking on a regular basis because it will cause damage." Wellll...

Ask trained engineers or engine technicians observing the same engine whether the engine is "knocking too much" and you'll get a different answer. There are two different ways of judging knock. There's a cylinder pressure trace method, and there's an audible microphone method. Notice that I didn't include a knock sensor in that list. The knock sensor reading, as processed by the ECU, is a reflection of some judgment call made during development in terms of sensor placement, calibration of the noise learning, and judgment of the "real knock" threshold.

Cylinder pressure, actual microphone, or knock sensor?

First, somebody decided where to put the knock sensor, which was a series of compromises in and of itself. Then during calibration of the knock system, somebody was physically listening to the engine or looking at the cylinder pressure trace. There are two schools of thought on knock judgment. The "microphone guys" swear that it's the best way to judge knock, and that with proper training it can detect real knock before a cylinder pressure trace ever could. The cylinder pressure guys say the same damn thing, claiming it's more representative than a microphone could ever be.

So, you get two guys listening to an engine and they will have their own opinions on how much noise is too much, unless they were trained by the same guy. And their judgments would then be reflected in the knock sensor feedback system on the ECU, which ultimately affects you the driver. But what about the cylinder pressure trace? Combustion pressure couldn't lie, could it?

Let's look at my cartoonish representation of a typical pressure trace at high load and MBT timing (minimum spark advance for best torque). X axis is time/crank angle, Y axis is combustion chamber pressure measured by pressure transducer.



so that's MBT. Usually you have 50% burn by 6-10 degrees ATDC firing, and peak pressure (shown above) maybe 15-20 degrees ATDC. Now here's a retarded combustion phasing under full load. It's retarded because at a given rpm, we retard ignition timing with increased load to mitigate knock. In this example, peak pressure is around say 30 degrees ATDC.











All of these made different levels of power and fuel economy, and often the uglier pressure traces perform better (except for when they don't). So which one is knocking "too much" ? But why not pull timing more so the pressure trace is less noisy? Well if you decide to do that you'd lose output and heat up the exhaust, requiring you to richen the mixture to keep temps down.

Remember, the knock sensor on your car can't read cylinder pressure and it doesn't have a human being sitting there with a microphone. It's just an approximation of that process. Setting an OEM knock control system is very difficult and except for extreme cases, there is no universal consensus on how much knock is too much. It's all somebody's judgment call, magnified by production tolerances and other factors.

Good post, but as an OEM engineer in this industry for 20 years let me fill you in on a couple things:

1. Pre OBDII developed Toyota/Subaru engines were not tuned to the edge of detonation. They were tuned for reliability and durability.
2. Subaru boxer engines have been much less reliable than other Japanese engines since OBDII

Go to any Subaru forum and find the long threads about blown headgaskets and spunt rod bearings. Try to find a post '96 developed Subaru original engine in a 500k mile club.

Also OPer please disregard the false info about a TSB, there is no detonation TSB. It does not exist. This forum needs to be honest and stop posting false information.

These engines are factory tuned to last roughly 60k-100k hard miles that's just how long Subaru engines last on the factory tune before they have to be taken apart. For over 10 years it was their EJ's with blown headgaskets that Subaru did nothing about. Make no mistake a post '96 Subaru engine is not like a Honda or Toyota engine that will last 300-500k miles.

We as a enthusiasts can work on a reliable tune, it will mean less timing and more fuel in spots. It will mean installing a header without cats because the exhaust will be hotter. But the engine will last forever like Subaru engines of old before ODBII.

We can make these engines durable because we aren't bound to different government regulations like the OEMs. But it won't happen by sitting on our hands waiting on the OEMs, they have no incentive to fix this issue and in their defense its because their hands are tied.

The good news is even turbo owners are reporting zero knock with their logs using a good tune, we are in a situation where a modest boosted FA20 with a good tune will last longer than the poor sap who keeps his car stock and the way I see that's a good thing. Probably a big part of the reason Toyota allowed this ECU to be non encpryted.

[regal]

Originally Posted by ft_sjo

The TSB which describes the injector seal-killing det, explains that above 5200rpm and with gear changes faster than 600ms, transient detonation can occur. The cause identified as a lack of effective transient spark angles in the relevant tables. The fix is a revised calibration which enables the transient spark table above 5200rpm and populates the empty parts of the relevant table with useful values.

.

This is a deliberate lie, there is no TSB, you are spreading B.S.

[whitefrs]

Originally Posted by regal

This is a deliberate lie, there is no TSB, you are spreading B.S.

He is correct
There is a TSB but in S. Africa not in the US

[Kodename47]

Originally Posted by regal

This is a deliberate lie, there is no TSB, you are spreading B.S.

Really?




I think that pretty much sums up what @ft_sjo said....

[Suberman]

Originally Posted by arghx7

If you're running US 91 octane, it may really be audible knock. I can pretty much guarantee this engine was designed for Japanese fuel, which is 98 or 100 RON, or US certification fuel which is 97 RON. The lower grade fuel was an after thought.

Try putting 87 octane in and see if it gets worse.

93 PON according to the manual. And BTW the Japanese fuel you refer to as 98 is premium or super fuel in Europe and is 95 PON. There is also higher octane fuel available in Europe but no engine needs to use it.

This little boxer will run happily all day on 91.

Trace detonation, assuming that's actually what's happening, is perfectly harmless. Indeed, the knock sensor doesn't do anything until trace detonation is detected. Frankly, I'm not sure how to tell the difference between pinging and DI noise in an engine like this. The type and frequency of these two noises is going to be tough to tell apart from the cabin.

Harmful detonation is generally inaudible because the engine is pulling very hard when the destruction occurs. Modern street engines certified emissions compliant CANNOT suffer from catastrophic, detonation the ECU will not allow it.

Figure it out gentlemen, diesel piston engines detonate continuously without any damage. So can gasoline powered engines. Destructive detonation is an entirely different phenomenon.

[StormTrooper]

I'd add a few gallons of vp104 race gas and see if it stops....instead of trying to hurt the engine

( there's some helpful info for ya)

[Toma]

All I can say about this thread is.... WTF. Lol

The pressure traces above look NOTHING like detonation.

There is NO TSB anywhere except S Africa.

Stock transient retard table has no retard anywhere in the high load regions at any rpm. Only low load low rpm. And this is normal since high load to high load is not a transient.

So.... if you think transients are ur problem. Just shift wot lol. Ie.... dont lift the gas foot when driving aggressively lol.

[Carwhisperer]

Originally Posted by elefunkd

I will definitely update....
But, what a disappointment in terms of lack of r&d on the manufacturers part.

-T

I agree and so do 4 other of my 86 local friends who have had DI collar issues.

[suaveflooder]

Originally Posted by Kodename47

Really?




I think that pretty much sums up what @ft_sjo said....

This is a toyota document, but not a TSB. It was mentioned in one of the DI threads about what this was. I wish I could remember off the top of my head, and I'll see if I can find it for you a bit later. :happy0180:
@regal, great post! Thank you. Makes me want to tune my car even more

[Toma]

Ps. Diesel engines do not detonate normally. Detonation is 'abnormal' combustion. However.... ever seen how robust a diesel engine is?

Japanese standards state that 96 or higher ron is 'high octane'. This is roughly equivalent to 91 to 92 over here

[suaveflooder]

@Kodename47

Did some digging and this was what I found.

Originally Posted by Calidrifter

That's the South African one that won't be used outside of South Africa as it isn't backed by any other region/corporate.

Originally Posted by Calidrifter

It might not hurt to ask. But I don't see an actual TSB number on either of the two pages.

Not 100% sure on the information. Either way, the "fix" can't be had here anyway. @regal is pretty much spot on with "the fix" as far as I can see in the rest of the DI threads....a good tune. I'll do it eventually, but it's still a ways off for me. :happy0180: