Performance Fuel

[smithcity]

Has anyone had a noticeable difference using performance fuel in their GTI? Either in terms of the car feeling quicker or the fuel lasting longer?

[jb182]

Can't comment on the gti but use performance fuel in my blue gt. It certainly seems to last somewhat longer and in my opinion it's smoother in low revs.


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[MIBUCS]

https://youtu.be/WTaBngvsPrc

[Ricmondo]

Same car as JB, same conclusions. Worth the few extra pennies.

[green_comet]

Here's a very recent test by Fifth Gear using a Golf GTI.

https://www.youtube.com/watch?v=d8L-X89duEs

[Penarth Blues]

I tried 98 RON in mine and I think I got some pre-ignition when starting up when warm - manifesting as almost stalling when pulling off changing from reverse to first and putting your foot down a bit. Not nice, and I didn't notice any improvement in performance either. So back to 95 RON and all is well again

Just my ha'pporth

[DKPOLOGT]

Did some accl. test in my BGT, Vpower 99 vs. Statoil 95.

I tested 37-62mph in 3' gear.
It must have been like 10 test with each fuel over some days.
Numbers where very consistent.

The result was same same with each fuel, even with a small win to the 95 Ron.




/ *L*

[RUM4MO]

I think that I read somewhere that the "energy available per unit" was less for 98, 99 etc than for 94,95 due to everywhere now just adding in Ethylene or something else which has a much lower "energy per unit" than the base petroleum spirit. Now what that can mean is, if your car does not need this fuel to run correctly, there will be a small drop in maximum power as the fuel energy available is less, also for cars not needing this fuel to run correctly, I have found that using higher octane rated fuel can give significant gains in drivability - which is what some people are finding. I think that some countries like UK used to produce higher octane fuels by "distilling higher up the stack" and that fuel did retain the original "energy per unit" or more, than 94,95 octane rated fuels, but as Europe does not give a buggar about personal safety, we were left alone in doing this, so it seems that we also went down the "lets just tip some extremely carcinogenic crap in boost octane rating cheaply"! It does make the fumes smell very "nice" though!

Editted:- changed "allow to alone!

[iichel]

Any possible power gain in fuel with higher octane ratings, is due to its resistance to engine knock.
Engine knock is the phenomenon that we actually know very well of a diesel engine. It's the sparkless ignition due to compression.

in the compression stroke in any 4-stroke engine, the fuel/air mixture is compressed. The higher the pressure, the higher temperature as dictated by Boyle's ideal gas law, P*V = n*r*T.
If the volume V goes down (piston goes up), the pressure P and/or temperature T must go up. n and r are constants.
If the temperature reaches a certain number, the fuel/air mixture will not ignite on spark, but will self-ignite. Other names are detonation or auto-ignition.
This usually is bad for performance and engine life, but it is also considered the holy grail in petrol engines (known as HCCI, look it up on Wikipedia, very interesting!)
These little self-iginitions do not occur simultaneously, causing little explosions with their shockwaves at random places in the combustion chamber. This is the pinging sound you'll hear.
In Dutch, it's sometimes simply referred to as 'Ping'

Now an engine usually deals with knock by an earlier ignition timing, after it senses knock with a knock sensor. This way, the ignition by the spark plug is too early, but at least not damaging the engine.

So now we know the process of knock. Why do we want to be knock resistant?
For higher performance, you want to burn more fuel. Fuel = energy and more energy = more power.
To burn more fuel, you'll need more air, about 1 cubic inch of fuel requires 17 cubic inches of air to burn nicely.
So more fuel = more power but for that you'll need more air. Aha! Let's push some more air into the cylinders... higher boost pressure from the turbo.

So now the pressure of the gas in the cylinders goes up (higher turbo boost). Remember P*V = n*r*T? We're upping P already before we started the compression stroke.
So T goes up, increasing the chance of knock. This is where the possible gains of a higher octane level fuel come in. They can deal with more boost.

But most VAG engines are tuned for running RON95, hardly receiving any gain from RON98. They simply don't come in the region where the engine knock drops performance.
If you tune your engine in such a way, that you'll get into the knock region with RON95, that's where you can expect the gains in higher octane level fuels.

Myself, I barely notice the difference of RON91 (they sell this stuff in Germany, dirt cheap) or Shell V-Power Plus which is said to be around 99-101.

You could get an intercooler upgrade to overcome engine knock too, since you're dropping the T of the inlet air. Just saying Long term it might even pay off...

[Parker87]

Blimey iichel, that's a very learned post - I'm going to have to go to lie down for a while after reading it! But thanks very much for providing that info.
My 6R GTI stipulates 98 RON on the label inside the fuel filler cap, so I've stuck to V Power throughout and am currently showing an average mpg of 44 (!) over 3k miles on the car's computer.

[iichel]

VW does recommend RON98 for the 6R GTI, but that's more of a dirty fix for the problems these engines have.
The 6R GTI engines, the twincharged ones, are very sensitive to knock. Due to knock, the timing went completely off. This caused soot on the spark plugs. This caused bad sparks/ignition, causing more soot, causing unburnt fuel in the cylinders. Also the soot would build up on the valves and cylinders, causing misfires and all kinds of nasty stuff.
The ECU software also couldn't handle these timing problems well, again leading to misfires and cycles of too lean and too rich fuel/air mixtures.

[Parker87]

Oh dear
Well, hopefully the VPower is an effective medicine for those issues.

[iichel]

I see you have a '13 GTI, chances are you already have the better CHTE engine. So you should be quite safe from all the GTI horror stories. The CAVE engine was the one with all the problems

[RUM4MO]

I see you have a '13 GTI, chances are you already have the better CHTE engine. So you should be quite safe from all the GTI horror stories. The CAVE engine was the one with all the problems

That is what has confused me on this forum - ie why are there not lots of CAVE engine GTI owners talking/asking about getting their engines sorted/replaced - like there are on the Fabia and Ibiza forums?

Are they just living with it and paying good money to their VW dealers are sorting a VW problem out at customer's cost?

Edited to remove wrong/extra words!!

[green_comet]

I've been using nothing but Vpower in my 6C GTI since purchase, hasn't skipped a beat at all.