Performance fuel

[monkeyhanger]

Do they? Where do they say that? Go with the guidance on the fuel filler flap sticker.

https://www.volkswagen.co.uk/need-help/need-help-faqs/owners/Fuel

 That’s what I was trying to get at - why do they put they recommend 98 ron on their website but on the fuel filler cap at least with the 20 plate models it say 95 ron ? It just seems Contradictory

That is a very general bit of blurb on their website, it's not even model specific. It says all VWs are fine on 95, with recommendation for 98 for GTI and R. Taking that as read, they recommend RON98 on the Up! GTI 1.0TSI 116ps.

If you look in the technical bits of the brochures (not the pricelists), it tells you what the recommended minimum. Fuel is. Can't find a very recent MK7 one, but the 2015 one shows 220ps and 230ps stating RON95, and R stating RON98 - same differentiation as you'd find on your fuel filler cap sticker. It states minimum because if you could only find RON98/99 fuel to fill up your RON95 optimised car, it reassures that you won't damage your car using it. It won't advance the timing to compress it further than it would compress RON95 fuel.

[monkeyhanger]

My TCR on the filler cap says 98 RON, min 95 whereas the GTIPP I had said 95 RON min. So the TCR should be 98 but you can get away with 95 whereas a GTIPP will be fine on 95 but 98 would be better. Does it really need to be made any more confusing than that?

GTI PP won't be better on RON98. The only reason the TCR needs RON98 is that it has been set up with the capability to squirt enough fuel in per compression cycle to achieve 290ps, and the PP hasn't.

As said before, RON98/99 fuel is NO MORE ENERGY DENSE than RON95, but it is less volatile, so you can compress and ignite more of it per compression cycle.

The ECU is set up on each car with a map that manages fuelling - so at full tilt, the TCR/R will be combusting more fuel than the PP at full tilt. Just because you fill your GTI PP with RON98 fuel, the ECU isn't going to decide to suddenly unlock TCR/R levels of fuelling to allow you to get to 290ps. A 230ps PP on RON95 will be 230ps on RON98 because it won't take any more fuel in.

You need to increase your fuelling to increase your bhp. Running your stock PP on RON98 makes no sense for gains, running your remapped PP  on RON98 makes perfect sense to prevent pinking with the amount of fuel that 300ps PP will be chucking in at full tilt.

[wolly440]

maybe I'm missing some thing or some of you guys are more technically minded than me. But the octane rating is the temperature that the fuel ignites under compression. The higher the temp, the bigger and cleaner the bang, given improved power and emissions.

[monkeyhanger]

maybe I'm missing some thing or some of you guys are more technically minded than me. But the octane rating is the temperature that the fuel ignites under compression. The higher the temp, the bigger and cleaner the bang, given improved power and emissions.

You are correct. You can compress an air/fuel mix further, generating more heat, if that fuel has a higher RON number. Not a hell of a lot of difference between a RON95 optimised car and a RON98 optimised car for effective compression ratio (about 10:1 max for RON95, 11.5:1 max for RON99 and 25:1 max for diesel), so efficiency differences are marginal.

The difference between a petrol and diesel engine air:fuel mix pressure/temperature is huge. Diesel is compressed much further, self igniting at a much higher temperature to make a bigger bang and converting more of that bang to kinetic energy. Diesels also run with air at a large excess, which is not the case with petrols.

However, people generally assume that RON98/99 fuel has more chemical energy per litre than RON95. It doesn't, and in many cases the higher RON fuel is less energy dense. Ethanol has a much higher RON number than petrol, so it's often used to increase RON number in higher octane fuels. RON95 is typically E5 rated (5% Ethanol), RON99 is often E10 (10% ethanol). Ethanol only has 2/3 the fuel density of undiluted (no ethanol content) petrol. So E10 petrol has around 98.5% of the energy density of E5 petrol.

For a car optimised for RON99, burning that RON99 E10 fuel, it needs to be burning it marginally more efficiently than a RON95 optimised car burning RON95 E5 fuel to match it in mpg. This lower fuel density burned in a marginally cleaner way under higher pressure cancels out.

As you use more throttle and fuel per ignition cycle, there's a limit to how far you can compress that fuel:air mix, so cars optimised for RON95 have less fuel in at max output than RON98 optimised cars. This is why the likes of the TCR and R need RON98 fuel to attain their max outputs because the amount of fuel required would cause pre-ignition if that fuel were RON95.

Due to this limit on how much fuel a RON95 optimised car is metered to add per ignition cycle, there is no need to advance the timing to compress the fuel further if the car is being fuelled with RON98.

[monkeyhanger]

For starters the figures I stated are not Dyno..they are direct readouts on live road data from the ECU...Torque is a direct ECU readout parameter...BHP is accurately calculated from various other sensors/data ..& more accurate than a rolling road dyno as no tyre slip..

My engine is an EA211 light pressure turbo, and bhp will increase easily compared to torque.

I also know of several other EA211 140/150PS engines which have had dyno results before & after remaps…& those which run on 98/99RON BEFORE the remaps always run more BHP & torque than those which are just run on 95RON before the remap....& that's in different countries & dynos & the trend is the same...& those which run 95RON are always close to book figures, or only a few bhp over...

You miss that the fuel door sticker states "95RON Min"...basically that's the lowest grade fuel the ECU will cope with.

The ECU is programmed to respond to 98/99RON grade fuels...& the exhaust cam shaft is variable by 40deg & the inlet camshaft by 50deg...so that's plenty of range to allow the ECU to fully use the advantage of high octane fuel....

The ECU doesn't throw more fuel in on a RON95 optimised car if RON98 fuel were to be detected. As RON98 fuel is no more calorific than RON95 fuel, the output does not increase in using the same amount of RON98 fuel. If it did, the car would have 2 published outputs - 1 for RON95 usage and 1 for RON98 usage. TCR/CSS/R need more fuel to achieve 290/300/310ps than a GTI performance needs to achieve 245ps output. The amount of fuel a GTI Performance needs to max out can be handled without pinking, using RON95 fuel. Not the case for TCR/CSS/R - hence they need to use RON98 fuel.

How do you get these torque and power figures from the ECU without the need of a dyno. Genuinely interested in finding out what my car does without putting it on a dyno. VCDS? OBD11?

Min values on fuel cap to denote minimum RON value. There's no insinuation in any VW literature that you'll increase your bhp with higher octane fuels, and certainly not 21% over stock. If your car is performing that well, it'll be down to VW understating published output and having been run in well.

[wolly440]

Now I'm confused! Is a standard 7.5 GTI optimized for 98ron with a minimum of 95ron. Or is it optimized for 95ron?

[monkeyhanger]

I wonder if the additional additives in vpower will help gpf cars that are no longer dual port?

Doubtful Chris, you need port injected fuel vapour washing the backs of the intake valves to keep them clean. The American YouTuber was using V-power exclusively and still had gummy valves at 10k miles and slightly crappy injectors.

You should be using higher octane fuel in your TCR though anyway.

[monkeyhanger]

Now I'm confused! Is a standard 7.5 GTI optimized for 98ron with a minimum of 95ron. Or is it optimized for 95ron?

It's optimised for RON95. Output figures are for RON95 fuel and the engine won't give you any more power for burning the same amount of RON98 fuel using the ignition timings it would use for RON95 fuel. it won't advance the timing to RON98 optimised engine settings either. There's no advantage for the engine to do so.

A TCR/CSS/R can use 95RON and have its top end curtailed to about 285ps to prevent pinking at the top end. The opposite is not true. You can't take a stock 220/230/245ps GTI, feed it RON98 fuel and effectively get a free remap because it'll now decide it can be fuelled more at the top end to increase output.

[mcmaddy]

I wonder if the additional additives in vpower will help gpf cars that are no longer dual port?

Doubtful Chris, you need port injected fuel vapour washing the backs of the intake valves to keep them clean. The American YouTuber was using V-power exclusively and still had gummy valves at 10k miles and slightly crappy injectors.

You should be using higher octane fuel in your TCR though anyway.

how do you stop it from getting the carbon build up? It's the only concern I've got when I get my car. Any other tips/methods etc?

[golfdave]

The ECU doesn't throw more fuel in on a RON95 optimised car if RON98 fuel were to be detected. As RON98 fuel is no more calorific than RON95 fuel, the output does not increase in using the same amount of RON98 fuel. If it did, the car would have 2 published outputs - 1 for RON95 usage and 1 for RON98 usage. TCR/CSS/R need more fuel to achieve 290/300/310ps than a GTI performance needs to achieve 245ps output. The amount of fuel a GTI Performance needs to max out can be handled without pinking, using RON95 fuel. Not the case for TCR/CSS/R - hence they need to use RON98 fuel.

How do you get these torque and power figures from the ECU without the need of a dyno. Genuinely interested in finding out what my car does without putting it on a dyno. VCDS? OBD11?

Min values on fuel cap to denote minimum RON value. There's no insinuation in any VW literature that you'll increase your bhp with higher octane fuels, and certainly not 21% over stock. If your car is performing that well, it'll be down to VW understating published output and having been run in well.

I used a stand alone device called Autopolar which connected to the OBD port & read the data...I have full unlimited VIN VCDS which will do the same...there is another device called Vector (I think) which will do the same....the data has always been there...there is a thread on an Audi forum that's years old which went into details of creating Excel spreadsheets for logging in VCDS for bhp & torque & creating graphs...eg dyno sheets...

Back to fuels & ECUs

The ECU is programmed with the various responses to the available fuels in its sales country, this is why it states the "95RON MIN" or "98RON MIN".....& other countries for the same engine will state "91RON MIN".

The ECU is written with a lot of parameters, & most of the fueling is controlled by two main parameters, knock sensors (pre-detonation)..& Lambda levels..(% scub of the exhaust gases registered between the two Lambda sensors).

Basically & simply put it has no idea what fuel you have put in, but it LOOKS at how the fuel has combusted, in the terms of two questions:- "can I advance/retard the timing & how much before I get knock?"...The second question it asks is "is the burn/emissions within the stochiometric parameters?".

The higher the octane rating the HARDER it is for the fuel to ignite.....this means LESS auto-detonation….(knock)...this also means more heat & energy is required to ignite it..this is why better ignition systems are required..with a more powerful & open spark.

Conversely it means that when the engine is hot & under load & at higher rpm, the ECU can better "open up" the timing/fueling until it hits the prewritten parameter end values in the ECU data by using a cleaner & more COMPLETE burn fuel like 98RON...compared to 95RON...

This is why in my car running Vpower (used as an example) it now generates MORE %BHP than torque increase over factory....its working rate has improved more, but the FORCE twisting the crankshaft (torque) has not increased much....thus the car is more responsive when you floor it....