How to detect detonation in the 930?

[RarlyL8]

I know what the "death rattle" of detonation sounds like in a water cooled engine. I have never heard it in my 3.0L SC motor and am wondering how I could possibly hear it in the much louder 930 engine under boost. The waste gate is dumped atmospherically, fairly noisy when it lets go.

I have the mixture set on the rich side and run 94.5 octane fuel @ 1.0bar so I don't think there is a problem. I would like to know what to listen for if there BECOMES a problem.

[Superman]

You very well might not hear it. I'm guessing you'll keep a close eye on the spark plug electrodes. Under detonation, they will likely be white, and may also burn/wear.

[Vipergrün]

RarlyL8, are you running a lot of advance?

Here is a note I received from BA himself when I asked a similar question about my 80SC 3.0l motor
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"What you would need to do to come up with a different
timing would be to do a spark search on a dyno and pick the maximum power for each rpm setting without any detonation. You really need an engine dyno with some knock sensing equipment for this. Usually you would do the same for fuel
optimizing the mixture for each rpm.

You need a know sensor to hear the detonation for you to be safe. The air cooled engines make so much noise at higher rpms under a load it is hard to hear detonation."
--------------------------------

I am currently running 30 degrees max advance at 6K RPM and I fear detonation, even after blending in some 100 octane fuel. Don't hear any, though. BA indicates spec is 23-29 degrees max. However, from a previous msg Superman (hope you don't mind ) is running at like 35 degrees max advance (approx 12 degrees at idle) without detonation. So, it sounds like getting the car on a dyno would be the way to definatively know.

Cheers
-Brad
80SC

[Superman]

I'm flattered. Those are exactly the timing specs I am running. JW swears that these engines can generally benefit from 35 degrees of full advance. But then, "these engines" may mean just the normally aspirated ones. And he told me to listen for detonation. There is none, but his instruction suggests there can be...at 35 degrees.

I'd agree that these engines are loud enough that a knock sensor makes sense.

[79targa]

I have used an aftermarket knock sensor that gives me visual display in LED lights on supercharged OTP cars. 2 greens - background, 2 yellows - series noise detected and 1 big red light - get off the throttle. The sensor bolts to the block. I don't know if air cooled motors would require a different type sensor, the control module does have a variable gain but I prefer to run it full sensitive.

CS

[island911]

Detonation in the NA engine is a simpler problem than in a turbo'd engine. Boost is the added variable. . . The MEP (mean effective pressure) peak can happen over a much broader range. So general comparisons between the two about timing should be avoided.

As to hearing it, driving next to jersey barriers (or such) with the windows opened, helps make knocking more obvious.
CS's device above would be even better.

[Emission]

My 930 was knocking earlier this summer when I was running 1 bar and 91 octane. I could hear it, especially with the windows up under hard acceleration!

Since then, I am 'back' to .8 bar and now run TRICK octane boost or Unocal Racing Fuel mix.

No more knocking, thankfully.

[RarlyL8]

The timing is set at 5*ATDC @1000 RPM.
Unfortunately the pulley is the dual A/C type with marks every 120*. Not useful at all for measuring 29-30*BTDC @ 4000 RPM, so I haven't done that. I'm thinking about degreeing the pulley later on.

Emission - do you have a dump pipe on your waste gate? You say you could hear the detonation. I've been listening real close but the wastegate noise just drowns everything out.
I am fortunate enough to have 94.5 octane fuel readily available where I live. I won't use anything less at 1.0 bar.

[diverdan]

Sorry I didnt't reasd this before my last Hoooooooly Shiiiiiiiiiiit posting. You are on to the expensive demon.

diverdan

[Emission]

Originally posted by RarlyL8

Emission - do you have a dump pipe on your waste gate? You say you could hear the detonation. I've been listening real close but the wastegate noise just drowns everything out.
I am fortunate enough to have 94.5 octane fuel readily available where I live. I won't use anything less at 1.0 bar.

I have a dump pipe.

I could hear the pre-detonation when I would push the car hard up a long grade. It was pretty obvious.

I was running 91 octane, with outside temps 80-90. If you are running 94.5, I don't think you are pinging because of the octane. I was able to 'solve' mine with 93 octane!

[emcon5]

Originally posted by RarlyL8
The timing is set at 5*ATDC @1000 RPM.
Unfortunately the pulley is the dual A/C type with marks every 120*. Not useful at all for measuring 29-30*BTDC @ 4000 RPM, so I haven't done that. I'm thinking about degreeing the pulley later on.

Sears sells a timing light with an advance knob on the back, you can dial in advance from 0 to 60 deg. Looks like it is on sale now, $59.99.

Check it out.

Tom

[RarlyL8]

Glad to "hear" that pinging can be detected when the engine is under a load. I don't have a problem right now.

Unfortunately I have another issue - overboost. I'm going to post a separate thread on this one.

Thanks Tom, I'll check out the light.

[Emission]

Originally posted by RarlyL8


Unfortunately I have another issue - overboost. I'm going to post a separate thread on this one.

I just solved my overboost problem!

Turns out I had a tear in the wastegate diaphragm. I ended up re-building the wastegate myself.