95RON vs 98RON

[BMWRX]

The 135i can run on either 95RON or 98RON, with performance obviously affected by the lower octane fuel. What do most people run their 135i's on?

I ask this as due my test drive the traction control light came on a lot and there was only about a quarter tank of fuel. Then on delivery there was a full tank and the light only comes on when I give it a big bootful. I'm thinking that perhaps the dealership filled it up with 95 and that's why it seems to be missing the extra edge. Thoughts/comments?

[MikeVictor]

BP Ultimate98 without exception. Performance fuel for a performance car and it's better for your engine.

[Taymaishu]

If, and only if i can only have 91 (say stuck out in a shithole somewhere), I use a fuel additive - good old Wynn's! I keep two full bottles of Octane booster and two bottles of injector cleaner in the boot.

But with an NA engine, it's not that imperative i use 98RON. Having said that, i usually get 98RON unless it's over $1.50 a litre.

[Guran]

There's no difference in power output using 95RON and 98RON. The benefit of using higher octane fuel is in terms of greater resistance to pre-ignition (important for a boosted engine), and improved fuel economy (98 is slightly denser than 95 so you get slightly lower L/100km). The traction control light has SFA to do with the grade of fuel in the tank. What you observed with the traction control light was probably just a combination of differences in road service and the weight of your right foot. Another possibility is that if the test drive car was a brand newy and still on it's first tank, then the tyres would probably also still have had a layer of mould-release on them -- slippery stuff that reduces traction until it wears away.

[Taymaishu]

Originally Posted by Guran

There's no difference in power output using 95RON and 98RON. The benefit of using higher octane fuel is in terms of greater resistance to pre-ignition (important for a boosted engine), and improved fuel economy (98 is slightly denser than 95 so you get slightly lower L/100km).

I love you Bryan. Nothing better than to have someone confirm your own thoughts on fuels

[takahashi]

Use anything you like. It is your car .

I use BP Ultimate not even Caltax Vortex 98 which I have vouchers for. I have been staying away from V Power since 6 months ago when the V Power racing was gone.

[Zuzu]

Originally Posted by takahashi

I use BP Ultimate... I have been staying away from V Power since 6 months ago when the V Power racing was gone.

Same here...

[aus135i]

but for me it seems vpower pulls harder then BP ultimate...

[takahashi]

It is very difficult to compare as we are in different state. The Shell in Vic comes from a different source as in NSW and SA.

The BP are imported and I suspect they are the same stuff.

To be honest, they must have changed since last BP no ultimate crisis.

[Guran]

Originally Posted by Taymaishu

I love you Bryan.

Jeez, steady on there. People will start to talk!

[Taymaishu]

Originally Posted by Guran

Jeez, steady on there. People will start to talk!

We can't hide this much longer.....

[MikeVictor]

Originally Posted by aus135i

but for me it seems vpower pulls harder then BP ultimate...

I actually found the reverse was true in my previous car, I switched a couple of years ago. Maybe the formula has changed?

[dontask]

I would always use the highest octane fuel for a NA high compression or turbo car, since knocking/predetonation can definitely be an issue - esp during those long hot aussie summers! That said, if you're using lower octane fuel, the engine management should be able to detect it and adjust the timing accordingly.

[TimMc]

I was of the understanding that engines with knock sensors (like the N54), would give a higher output using a fuel with a higher knock rating (like 98)? Something to do with the engine able to run more advanced timing using a higher octane fuel...

[d3syd]

I always use BP Ultimate when I can. Have twice filled up with 95RON though and experienced no discernible difference in performance.

[d3syd]

Originally Posted by Taymaishu

If, and only if i can only have 91 (say stuck out in a shithole somewhere), I use a fuel additive - good old Wynn's! I keep two full bottles of Octane booster and two bottles of injector cleaner in the boot.

But with an NA engine, it's not that imperative i use 98RON. Having said that, i usually get 98RON unless it's over $1.50 a litre.

I saw a test on myth busters (I think) about octane boosters and there was zero difference in performance.

[BMWRX]

Originally Posted by Guran

What you observed with the traction control light was probably just a combination of differences in road service and the weight of your right foot. Another possibility is that if the test drive car was a brand newy and still on it's first tank, then the tyres would probably also still have had a layer of mould-release on them -- slippery stuff that reduces traction until it wears away.

It was the same car that I took delivery of that I test drove, so nothing different there. And the tyres weren't new. Plus, to top it off, the comparison was coming out of my street, so nothing different there.

It may have been in my mind, but the traction control light certainly came on more the first time I drove the car.

And finally, I concur with the sentiments on Ultimate 98. I would rather push my car home than put Shell into it.

[dontask]

Originally Posted by TimMc

I was of the understanding that engines with knock sensors (like the N54), would give a higher output using a fuel with a higher knock rating (like 98)? Something to do with the engine able to run more advanced timing using a higher octane fuel...

Yup. Basically with a turbo car, because you're compressing the air before it goes into each cylinder, the air that goes into the cylinder is hotter than a normal NA engine. The hotter the air is, the more likely you will get predetonation - eg: the fuel in the cylinder exploding before the spark plugs fire. As you can imagine, predetonation is bad. So, if its detected by the engine management system, the ECU can retard the timing (and cause power loss). Higher octane fuels are more resistant to predetonation than normal fuel. The higher the octane, the more resistant it is.

[Guran]

Originally Posted by TimMc

I was of the understanding that engines with knock sensors (like the N54), would give a higher output using a fuel with a higher knock rating (like 98)? Something to do with the engine able to run more advanced timing using a higher octane fuel...

No expert myself either . From a quick look at the technical documents for the N54, it seems to me that it will adjust the timing if knocking is detected, but there is no direct means to measure the RON of the fuel in the system. Hence, if you're using either 95 or 98 RON and not getting any knocking from either, I see no reason why you would get different power outputs. And considering that the N54 uses low boost (0.4bar) in order to minimise the risk of knocking, I'd not expect to see any power difference between 95 and 98 RON.

On the other hand, I could be completely wrong, and I'm happy to be corrected!

[petersracing]

Originally Posted by Guran

No expert myself either . From a quick look at the technical documents for the N54, it seems to me that it will adjust the timing if knocking is detected, but there is no direct means to measure the RON of the fuel in the system. Hence, if you're using either 95 or 98 RON and not getting any knocking from either, I see no reason why you would get different power outputs. And considering that the N54 uses low boost (0.4bar) in order to minimise the risk of knocking, I'd not expect to see any power difference between 95 and 98 RON.

Well it's possible the N54 is different from most other cars but generally these days cars explore greater advance to improve specific efficiency and therefore power. This change happened across the industry from the late 90s. There was a time with a WRX for example that you did an ECU reset occasionally or after a low octane load of fuel so it would relearn but that ceased being relevant post 1998. I'd be surprised if the N54 was any different. I know the supercharged Toyota does exactly that and thats a low boost pressure engine.

[BMWRX]

Originally Posted by petersracing

There was a time with a WRX for example that you did an ECU reset occasionally or after a low octane load of fuel so it would relearn but that ceased being relevant post 1998.

The AM (advanced multiplier) reset is still relevant in WRX's, but I think they "relearn" eventually by themselves. My MY05 had to be reset manually a few times until I finally learned that Optimax (now V-Power) was not the best thing to run in my car.

[BMW86]

i've always used 98RON but i always fill up at shell because it's closest to my house. why do most people think bp ultimate is better than v power? or is there not much in it?