Octane-boosting petrol additives?

[brad]

It still cleans deposits on the top of the pistons, doesn't it.

...and since the combustion would be more complete the EGR gases would have less pollutants in them, which leads to a cleaner intake.

your experience might be different but since we went to ULP I haven't found combustion chamber deposits a big issue. Every little bit helps i guess - that's why I like ethanol blends.

[brad]

The knock sensor on most current petrol engines should detect detonation and adjust the timing and/or mixture. This is as long as the engine is at the standard tune. If the engine has been modified or the tune not standard, you are going to have to be a lot more careful where you get your fuel.

On additives, I would not put too much faith in them. It does not matter who makes them. You may just have to de-tune the engine because of low grade fuels sold.

The trouble is that a knock sensor is reactive, so the engine has already had a few uncontrolled burns before the ECU changes parameters.

I do wonder if a good custom tune might actually benefit the engine (but with reduced power/torque) if mixture/timing & boost maps were given a real good lookover. Also look at intake temps (bigger intercooler), water/ethanol injection, etc

To the OP: Have you thought of buying high Octane unleaded racing fuel & blending that with your normal fuel? might be a better bet than additives

[wai]

The trouble is that a knock sensor is reactive, so the engine has already had a few uncontrolled burns before the ECU changes parameters.

It is, but far more sensitive that trying to listen for it. The other thing is that it is not a single of short series of detonations that will damage an engine, but sustained detonation.

The issue with additives is getting the mix right, and as I said, it is generally detonation that you cannot hear that will damage an engine when it occurs over a period of time. You may think you have the concentration right, but it could be way out. There is also the issue of it mixing thoroughly and not settling back out.

If you have a customised engine, then the whole ignition system must suit it.