Is "ultimate" petrol a waste of money?

[craigowl 0]

Got the following on the Canadian C forum, re VR6, any comments, guys?

 

"...Well low octane fuel is not a constraint, it just makes knock more likely. And when knock occurs, the spark must be retarded away from MBT, which produces less torque. In the presence of high-octane fuel there is no compromise. That said, it's important to realize, high octane fuel only helps when the engine would otherwise knock, i.e. when it is at the knock limit. But if you look at a load vs. rpm vs. knock map, there are only very small areas where knock occurs, meaning these are the only possible times you would get more torque with high octane fuel. I think it's only at a small region of low rpm / high load, and at very high rpm full load. At every other operating point of your engine, low octane fuel will perform exactly the same as high octane."

[davidwort 0]

put the cheapest stuff in that doesn't cause knock, or the knock sensors to reduce advance.

 

High compression or forced induction engines will be more susceptible to knock though, and that sort of means all Corrado engines.

[G60Jet 1]

From what i understand you can get knock from the ignition being not advanced enough. normally this is due to timing issues, however it can become apparent with high octane fuels (higher than mapped for)

 

My TDI runs a lot better on the ultimate diesel, you do get a few more MPG, however you pay for it at the pump. Engine is more responsive, but no increased value for money imho.

 

BTW Supermarket Diesel contain 5% bio diesel! hence the "low sulpher" its awefull stuff.

 

not that you guys buy much diesel :lol:

[steve_16v 0]

One of the mags did a rolling road test with quite a few different brands and octane rated fuels, can't remember the exact details but the likes of Optimax and Ultimate were consistently giving a few extra bhp over 95RON. Obviously that test was performed under full load so didn't show if there were any benefits in normal conditions, but I can tell the difference when overtaking so will keep using v-power in mine.

 

The branded fuels also have higher quality detergents in them than supermarket stuff so are better for your engine.

 

You also get quite a few extra mpg when using higher octane fuels, the last time I went up to Lancashire I was getting over 40mpg on the MFA, on lower octane it averages about 35. That makes quite a difference on a 600 mile round trip.

[Henny 0]

I do now, and I'd bet Supercharged has put a fair few gallons in his Corrado! :lol:

[craigowl 0]

steve_16v wrote

One of the mags did a rolling road test with quite a few different brands and octane rated fuels, can't remember the exact details but the likes of Optimax and Ultimate were consistently giving a few extra bhp over 95RON

 

I saw similar article where either the BP or Shell "superpetrol" gave less power than the 95ron. This was put down, by the manufacturer, I think, to the fact that the additives were "off" or not up to scratch!

 

So, I'm not convinced either way yet. I do not get any knocking whatsoever from Jet 95 ron.

[dr_mat 0]

Depends on your car. As hinted at above, if your engine is tuned from the factory for 98/99 octane it will get the benefit of it, and if you put crap fuel in it will get knock and it will retard the ignition and you WILL lose power.

If, however, your engine is tuned for 95 Octane, adding 98 is pointless.

The VR says 98 on the flappy thing where you put the petrol in. Believe it!

[Kevin Bacon 5]

The ECU must first 'hear' the knock in order to correct it, so if it doesn't hear it to begin with, then a higher advance will be maintained. So rather than the ECU clawing back timing with 95 regularly, it won't see knock at all with 99 (in theory), so can add more advance. Which is where the extra power/torque comes from - on part throttle at least. For optimum WOT performance, you need to map it specifically for the fuel and the knock-knock-knocking on heaven's door sensors will poop the party if things get out of hand, but again, if the fuel is of a sufficient octane, they won't do anything.

 

A certain amount of power is also freed off with these fuels because they contain upper cylinder lubricants. They bamboozle you with clap trap, but that's essentially all they do.....squirt a bit of oil into the petrol! That's basically all redex is useful for actually, it does shat all to injectors tho :-)

 

VW only put 98 on the flappy thing because they don't want the car underpeforming at the press conference :lol:

 

Interestingly, BP found about 50hp on Carrera GT2 using 102 octane - after a remap! Impressive stuff. But fair enough, such exotica represents a very small minority of cars and they make loads more power with minimal extra work anyway.

[chubbybrown 0]

Our valver doesnt knock with 95

but as a treat to it and us,every so often we fire in some optimax.

its more perky...Honest!

 

The only special petrol that doesnt come through our local terminal is the Ultimate super unleaded,that is brought in specially due to not much being sold and to keep it fresh!

Depending where you live,is where the petrol comes from;

what Im trying to say is SHell pull out of BP and the opposite too.

Bio diesel is big in the south,thankfully due to transport constraints its not really present in the Scotlandshire area.

[Trig 0]

the knock-knock-knocking on heaven's door sensors will poop the party if things get out of hand

 

:lol:

 

Now where are those tests EVO did on a MK5...

 

Found them

[Yandards 0]

Chuck my oar in with the 'you get what you pay for crowd' here. The engine will only benefit from higher octane fuel if, as mentioned above, it was designed for it and the timing is set up for it.

 

As for supermarket fuels being crap I used to work with a guy that bought a 3 year old Turbo diesel Volvo estate (He had dogs) to run around in. Despite looking after it the turbo expired after about 6 months. The reason the mechanic offered after asking which petrol he used was that 'Tesco fuel blows turbos because of less lubricants in it' It wasn't the first turbo explosion due to supermarket fuels he had seen either.

[dr_mat 0]

Since when did fuel go anywhere near the turbo?

You would HOPE that the fuel gets all burnt before it comes out the exhaust pipe and hits the turbo vanes.

I'm sceptical, me.. :)

[G60SC_Stoney 0]

ive been running tesco 99 in my G60 for a about 3 months now, and find that not only is it cheaper than Shell/BP it also seems to increase performance more. (however car wasnt really mapped properly until a few weeks ago)

[Andy665 0]

My Aqua G60 has run mainly Tesco normal unleaded with no problems whatsoever for most of the last 30k miles. My Nugget G60 hates normal unleaded and seems to need Optimax / Ultimate / V-Power etc, guess its a case of it being more modified

[TomB 0]

chubbybrown, if you're willing to buy 1000l at a time, then you can buy biodiesel and have it delivered... http://www.bulldogbiofuels.com/biodiesel

G60Jet, I use a blend of 80% recycled vegetable oil in my Golf, and it prefers it to the stuff from the pump.

I found that in the 1.8 valver, there was very little difference between running on 95 and 97RON tbh, even though it was specified to run on '98. I never put Optimax in as it was too pricey!

Cheers,

Tom

[ReekieVR 0]

Wierdly, i always 'feel' more power during the 1st tank of 95 after several Optimaxes.