Octane-boosting petrol additives?

[Sentinel]

I looked through this subforum and there don't seem to be any threads about these.

Several people have told me that Australian petrols don't actually attain the advertised RON - for example, that 98RON is actually around 96, etc.

Having recently had an engine failure in my 118TSI, at least partly due to predetonation, I'm very interested in the subject of octane numbers. I now have new pistons, rings, and injectors - and I want them to last.

I visited a local auto parts store, and saw that there were octane boosting additives from Nulon and Wynn's, which promised an improvement of between 2 and 8 octane units.

My question is - is there any risk or downside to these fuel additives? Could they damage my engine or void my warranty? And - do they actually work?

I would love to get opinions from people who have knowledge about this.

[Transporter]

Both are safe to use. I would go with Wynns.

[leighaus]

they will work, yes.. but nothing will utilize the higher RON like being tuned for it...

[Ryan_R]

5th Gear (UK TV show) tested a bunch of octane boosters a few years ago on a dyno and found no appreciable performance increases, not sure if it's worth the cost.

[Sentinel]

Thanks for all the advice!

In this case, I'm not interested in raising the performance, but in protecting the engine. I've already had to replace all the pistons because of predetonation, and I'm hoping that raising the octane will prevent this happening again.

[Transporter]

5th Gear (UK TV show) tested a bunch of octane boosters a few years ago on a dyno and found no appreciable performance increases, not sure if it's worth the cost.

Yes, even some performance magazine done such tests in the past and you're right as long as the engine is a brand new, they have not measurable effect on the performance. However, using the right additive that works will keep the intake system clean and that will have an effect on performance and longevity of the engine later on when done some +30,000km. Most drivers wouldn’t notice it, because it happened slowly and they’ve adapted to it, unless they drive the same car that used the fuel additive. The deposits in the intake will disturb the swirl pattern in the cylinder and the deposits on the top of the pistons and in the combustion area have potential to cause pre ignition, again not good for the engine. The right fuel additive will reduce the amount of deposits and engine should last longer.

The additive that is added in the refinery is very often used before it reaches your vehicle’s fuel tank (spent on cleaning the storage tanks at the servo). So, adding good quality fuel additive makes sense to me.

[2muchcoffeeman]

Might be some merit in considering the 100 octane United stuff?

You'd likely use more, but $$$$ wise, you'd end up ahead of the additive ripoff roundabout.

[brad]

However, using the right additive that works will keep the intake system clean

How does this work with a direct injection engine.

To the OP: The Octane number on the pump is the guaranteed minimum so if you buy fuel from a high-turnover service station you should be getting what you pay for.

united100 might be an option except VW don't recomend ethanol blend fuels.

Pre-ignition / detonation (two different things) have a number of causes beside the Octane rating of the fuel. Have any of the other causes been looked at?

[Transporter]

How does this work with a direct injection engine.

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.

[wai]

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.

[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.