Some proof that octane makes a difference

Started by le mans, April 09, 2024, 09:43:20 PM

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le mans

On the FB page occasional discussion arises around different fuels and octane ratings. I've been running my vag cars on 98 RON fuel for as long as I can remember. The owners manuals for my A4s state that 95 RON can be used with an expected reduction in power. With the exhorbitant cost of fuel at present I decided to run a tank of 95 in each of my A4s. In the avant I ran a tank of PakNSave 95 RON and in the sedan a tank of BP 95 RON. I drive both of the cars and I thought they felt a bit flat when on the gas. So I decided to run some logs. Well they told a story - lots of timing retardation due to the poorer knock resistance, especially with the PakNSave fuel. I've recently filled up the sedan with BP 98 RON and the avant with NPD 100 RON and taken some more logs. Massive difference and both cars came alive when on boost. Now both these cars are MTM tuned so likely running more aggressive ignition maps than stock (and certainly more boost than stock). Both cars are the exact same make and model with same ECU and same MTM tune.

Now the graphs... just to explain the 'Retardation Sum of Cyl,' this represents the total retardation of all 4 cylinders. So a number for 6 = average 1.5 degrees retard per cylinder and a number of 32 = average 8 degrees retard per cylinder. As you retard ignition from MBT (minimum timing for best torque) you reduce power output. So here are the results, worst to best...

PakNSave 95 RON (A4 avant)
Screenshot 2024-04-09 201701.png
Screenshot 2024-04-09 201508.png

BP 95 RON (A4 sedan)
Screenshot 2024-04-09 205258.png
Screenshot 2024-04-09 205122.png

BP 98 RON (A4 sedan)
Screenshot 2024-04-09 204446.png
Screenshot 2024-04-09 204302.png

NPN 100 RON (A4 avant)
Screenshot 2024-04-09 202551.png
Screenshot 2024-04-09 202428.png


Would be curious to see a comparison between the 98 vendors, BP, Gull & Mobil. With Gull being the anomaly featuring 10% bioethanol.

And no, that's not an offer to provide a tank.

le mans

That would be an interesting comparison. By the way, all the graphs above are wide open throttle in either 3rd or 4th gear, so a decent amount of load.

le mans

So to summarise the above...
PanNSave95: peak retard 32 degrees or 8 degrees per cylinder
BP95:       peak retard 18 degrees or 4.5 degrees per cylinder
BP98:       peak retard 11 degrees or 3 degrees per cylinder
NPD100:     peak retard 7 degrees or 1.5 degrees per cylinder

You can make your own conclusions about the PakNSave95 fuel, I know I have.

So, taking the PakNSave fuel out of the equation, the cars gained 1.5 degrees of timing going from BP95 to BP98 and then another 1.5 degrees going to NPD100. Note, you will generally only see these gains at high load where the engine is knock limited from achieving MBT timing.


Current: 2007 Audi A4 2.0T DTM sprint blue, 2007 VW Golf V 2.0 TDI BKD 4motion manual white.
Past: Audi A4 2.7 TDI silver, 2004 Golf 4 R32 black pearlescent, 2009 Audi S3 8P white / panoramic roof, 2004 Audi A4 B6 1.8T blue, 99 Golf mk4 GTI black, 2005 Audi A4 B7 2.0T black.