So the backstory – We’d had an Audi S3 on the dyno for a few hours, and were struggling to make proper power. We’ve tuned so many of these cars the results just weren’t as good as they should have been. IAT’s were normal. Coolant temps normal. No fault codes. Just felt a little flat.
Now, before I go further – timing advance is the point at which the sparkplug fires. Fuel doesn’t completely burn the second the sparkplug fires. The engine needs the sparkplug to fire just before the piston hits its highest point, so that the fuel has maximum burn time on the power stroke to make maximum power. Spark too early and the piston is forced to try and go upwards whilst being forced down, causing extreme stress on the rotating assembly…too late and you’ll just end up with pops, bangs and no power.
We decided to take a look at the ignition timing advance. Stock pull is solid green line, Tuned is the dotted green line.
Detonation, or knock is the point at which the fuel explodes rather than burns. The shock from this can cause severe engine damage, cracked pistons etc. The higher octane rating a fuel is, the more pressure it can withstand before detonating.
We bring the timing back a little when tuning to allow headroom for the increases in cylinder pressure caused by turning up the boost pressure. Keeps it nice and safe, and knock free…however look at the graph, at around 5,300RPM the timing drops out. The ECU has detected detonation, and pulled back on the timing for saftey of the engine. We’re now making 1.7 degrees of timing, rather than the 5.7 the stock car makes…and whilst we’re making more power, it’s not at all good for the engine.
A brief chat with the customer revealed the car was running on supermarket 95 octane fuel. For all performance vehicles a quality super unleaded fuel is a must have – they just can’t run properly on cheap 95 fuel. We got the authorisation to try a bottle of octane booster…so added the full bottle of Redex into the tank, and gave the car a good run. The dyno has a vehicle simulation mode, allowing us to simulate the car being taken for a drive on the road, so gave it a couple of miles to really run the booster through the fuel system.
The results? Solid line is no booster, dotted line is with the booster;
The car made an extra 4 degrees of timing…resulting in 7BHP & 15Nm!
Now, with the extra headroom and the right octane fuel to burn we could really push the car. It wasn’t pulling timing, was capable of holding more boost…with a few tweaks, we saw an additional 37BHP & 97Nm. This graph isn’t stock vs tune, this is a 95 octane tune vs a 98 octane tune on the same car!
We can draw a few conclusions from this data;
*Fuel quality is absolutely critical to get best performance from the car.
*Octane boosters DO work in so far as they’ll bring a standard 95 fuel up to the same quality as a premium unleaded.
*A good quality fuel is actually worth more power real world than most induction kits/exhaust mods – 7BHP & 15Nm is huge!