Supermarket Petrol - Good Or Not So Good?

[Silver Arrow]

Hmmm The graphs are hard to read as neither have a consistent period at the same revs/load - other than in the middle (between 1944 and 2023,on both graphs as seen). The ignition seems more consistent on the Superstuff, but as you say how much of a difference that makes is very negligible.

I still think it's all very clever marketing. At best you're gonna see a 4-5% improvement, but in what (i.e. 95-99RON = 4 extra RONs)???? Power? MPG? Top Speed? No one drives to within 0-4% consistently anyway - you can take the same journey to work everyday, and even if you try, there will be things in road conditions, a slow codger in front, traffic lights, etc etc that will make it hard to tell if you can translate that extra cash into something tangible.

Like I say there have been some tests in the past, none have been conclusive enough, and unless you're on a racetrack maxing it all of the time, it probably isn't worth the effort (or expense).

[flotsam]

Super unleaded is WELL WORTH the extra expense. As I've posted many times before on these fora (but which have been subsequently deleted), the octane rating is how much you can compress the fuel before "pinking" or "knocking" occurs. High compression engines are supposed to be more efficient like a diesel engine which typically has compression ratios of about 16:1.

An engine with compression ratio of up to 10:1 doesn't need super unleaded. But higher than that and you do.

Modern engines have anti-knock sensors which retard the timing to compensate for too low an octane fuel. A high compression engine can run on ordinary unleaded but the timing is moved away from maximum brake torque.Severe knocking will eventuallly shake an engine to bits.

The Audi R8, for example has a massive compression ratio of 12.5:1 and probably needs about 110 RON fuel to run properly, though it's probably offset by a richer fuel-air mixture!!!. Even on 98 RON super unleaded, it only gets 371bhp and 292.8 lbft of torque according to rototest.com. However, it should get 420bhp and 317lbft of torque.

Here's Tesco Momentum's specifications:

http://www.tescopfs.com/momentum99/specifications

Note the high sensitivity (RON-MON). If, as they say, the sensitivity is normally between 8 and 10, then Tesco Momentum will make your engine run smooth at idle (RON) but will leave your engine feeling no better than 97RON super unleaded when you put your foot down (MON). This agrees with my experience of it.

Tesco claim 2.85% better economy over a range of vehicles and test routes.

Here's Shell V-Power which has an even higher sensitivity but note NO ETHANOL ADDED:

http://www.acetech.com.my/Download/Shell_V_Power_info.pdf

Here's BP Ultimate (95RON):

http://www.bpdrakensberg.co.za/wp-content/themes/kzn/docs/products/TDS_BP_Ultimate_ULP95.pdf

Here's BP ordinary/premium unleaded (93 & 95RON):

http://www.reddyfuels.co.za/products/petrol.php

The only BP ultimate spec I could find was in german showing a better MON thatn Shell/Tesco and 1% ethanol max:

http://www.bp.com/liveassets/bp_internet/bp_ultimate/bp_ultimate_austria/STAGING/local_assets/downloads_pdfs/0_999/produktdatenblatt_ultimate_super_v1_0.pdf

Harvest Energy claim 97RON and maximum 5% ethanol for their super unleaded.

I'm running on Harvest at the moment. Noticed a surge in ooomph straight away and feels like I have to keep my foot OFF the accelerator in 30mph zone otherwise the car will run away from me, as it were. Engine is completely silent (!) but MPG is low or perhaps I'm just putting my foot down. I always thought it was Tesco's ethanol which made my car feel sluggish but Harvest has a maximum of 5% too. Is the difference of 1 MON THAT noticeable (assuming it has a similar spec. to BP who no longer supplies Harvest)?