Fuel

[MarkB]

Hi all

I'm new to the forum and don't as yet have an S4 but hope to be out shopping soon. I've noticed that alot of you are using 98 octane fuel. I realise that this gives more performance but is it really nesessary? I currently have a 4.3 TVR that was built to run with 98 but has since been chipped and tuned to run 95. Still goes fast enough for me...

Mark

[NeilMc]

If you're the type of person who admits something is fast enough for them then 95 would be ok... but most people aren't, and the manual recommends 97/98. There is a difference, but it's not like it's sluggish on 95.

[Nige_RS4]

I doubt that the TVR ECU's are half as clever as the latest Bosch units in the S4/RS4 (well, all of the Audi range, in fact). They can adjust themselves based on the quality of the fuel, which does make a noticeable difference. Yes, the TVR may be fast, but I bet you have triple breakdown cover and it must be hairy in the wet

[kies4]

better fuel helps against every turbo cars woe, detonation/pinking

[MarkB]

If you're the type of person who admits something is fast enough for them then 95 would be ok... but most people aren't, and the manual recommends 97/98. There is a difference, but it's not like it's sluggish on 95.

I must admit that the TVR ECU is not as advanced as the Audi. It doesn't control ignition so can't <beep> the ignition when needed. The problem I had using super was finding the stuff and with a fuel tank that only lasts for about 130 miles its a regular search

[tartan_rob]

130miles.... what size is the tank...

[MarkB]

Not very big. Or maybe the fuel guage isn't very accurate...

[Dippy]

The S4 was developed for 98 RON. As you know, the ECU will automatically <beep> timings for 95 RON with consequential loss of engine performance. If you're happy with this then fine, but why buy a performance car if you're going to intentionally <beep> that performance?

There again I see you've done this with your existing car, so go ahead...

[MarkB]

With the TVR the higher octane gave little differnece in performance. They did it to make up for poor mapping from the factory, they often over fueled. A car with a bestoke fuel map and an advance curve for 95 runs better than standard from the factory.

If the car can adapt for the fuel it's using currently then that is good. I don't see the point of burning or worrying about sourcing 98 RON fuel every day driving but is a nice boost for track day fun.

Seat of the pants can you actually feel a big difference between the fuels in use? Can 10 or 20 hp be felt in a 300 BHP car?

[Nige_RS4]

Seat of the pants can you actually feel a big difference between the fuels in use? Can 10 or 20 hp be felt in a 300 BHP car?

Hard to believe, but I can feel the difference. It's not so much top-end power (is it ever in the S4?), but mid-range pull - there is definately more urgency and a crispy throttle to boot.

Oh, and I get better fuel economy with Optimax too.

Nige.

[MarkB]

Its the mid range where the largest amount of ignition <beep> would be needed for lower octane fuel so more torque rings true...

[KayGee]

I definetly got better economy with any of the 'super'. Since turbo swap run optimax almost all the time. Works out to about the same price with the extra mileage per tank.

[ShaneyB]

Had my remapped B5 S4 Avant on the rolling road running BP Ultiomate and it was pushing out 312bhp and 375lb/ft torque. I took it back again a while ago running Optimax and was then at 326bhp & 389lb/ft torque. I know some slate Optimax but locally mine appears to be pretty good.

[Bisonone]

I can definately feel the difference between optimax and unleaded. I recently took my car on a run to Newcastle. I filled up with normal unleaded on the way and optimax on the way back....

The car was more responsive and better (mpg) using the optimax, it just didn't feel the same while it was running on normal unleaded.... imo....

[UKS4APR1]

This subject has been brought up before, maybe worthwhile having another look at the thread..........
http://www.rs246.com/index.php?name=PNp ... light=fuel