Hi everyone... I see everyone going about NUL, SUL, etc... My WRX SPortWagon is due in 25 days, and i'm wondering if anybody know how that (I'm assuming NUL = Normal Unleaded, SUL = Super Unleaded) translates into portuguese fuel.

Here, we have:

Super with Lead replacement (Supposed to be used in old cars, no Cat.)

Unleaded 98 Octane
Unleaded 95 Octane

Questions:

1.Difference between 98 and 95...

2. Which is supposed to be used in the scooby.

3. What can go wrong if you use the other ?

And finally, I read somewhere that low quality fuel can be very damaging to the engine... How do I detect bad fuel ?

Thanks

Max

One point of note: There is no 98 RON fuel sold in the UK any more and this hasn't been the case for a few years. All garages were meant to change their pumps/signs to read 97 RON but not all have done so. All you can buy from a normal petrol station in the UK is 95RON and 97RON fuel.

Thanks AWD,

but I still don't know the difference between those, which is NUL and SUL, and which the Scooby likes better...

Max

UK Spec cars can be run on 95RON (NUL), but some people use 97RON (SUL) for smoother performance.

Jap spec cars are meant to be run on 100RON! as such it is said that you should run your jap spec car on 97RON, + octane booster, this is even more important if car happens to be an STi.

Now, to add my 2 cents worth. I have a jap import (94 WRX Wagon, 220ps) and have (apart from past 2 months) run it on NUL and have had no problems. This has caused somewhat of a stir and people think I'm mad doing it. But as i've said to them, if my engine blows because of det then it's my own fault. I will be fitting broquet, to see if that helps any, but i'd only use SUL and maybe octane booster on a trackday, or when I could not get NUL, or when I'm in europe where SUL is more easilly available, better RON rating (98 instead of 97) and is cheaper.

Don't use the the Lead replacement fuel, it will trash not only your cats, but the Lamda sensor as well, so thats one off the list. Your left with 95 or 98. Presuming you've got a MY01 Euro spec WRX it will run fine on 95, but will be smoother on 98.

Broadly the higher an Octane number the greater the resistance to "knock" (pinging / pinking) now beiing in Portugal, you will be getting hotter weather than us in the UK. As the point at which knock becomes apparant drops as the temperatures in the engine rise, using higher octane fuel will allow you to produce full power at higher temoperatures without the ECU retarding the ignition to prevent knock. In your position I'd use the 98, but using the 95 will not cause a problem if you can't find 98. If the tax situation is anything like some other countries in Europe, the cost differance is not too much.

AWD, Portugal mate, they still get the nice stuff, its only UK peeps who got stuffed when LRP came out, others in Europe still get 98RON.

Thanks Paul...

So, it I get it right, I should use 98 RON... That will run smoother...

And you're right, here in Portugal, the difference of price between the two is very small (95 - 98) and meaningless if you're driving a Scooby...

Could you develop (Or send me to a thread) the "knock" (pinging / pinking) concept, ignition delays and it's relation to air temperature ? I am no mechanic, but have a general idea how an engine works... And love to understand complex concepts to talk about over lunch with the other car goofs :-)

Markus, I have a 93 WRX which the previous owner ran on NUL for ages with no prob. Early cars have lower commpression pistons and a bigger Turbo, therefore are less prone to pinking than the later (higher compression) cars. I presume this is why the melted piston problem has only been bannded about in the last couple of years. Wouls be interesting to find out how many early cars have suffered from No3 piston letting go. Anyone shed some light on this?

P.s I still run mine on SUL with Octane booster though, as it's still meant to be run on 100 RON stuff http://bbs.scoobynet.co.uk/smile.gif

oooo dear, let myself on for something now.

Don't know the exact figures and in any case they will vary between engine types, but broadly.

knock becomes more likely when...

charge/cylinder temp increases.
ignition is advanced
compression goes up
fuel octane goes down.

Best bet would be to email johnfelstead (sorry John ) and see if he's got a good source, or tey a search on knock.

They're are actually 2 different effects that cause similar problems, one is where ignition of the fuel by the spark plug, occurs too early for conditions, and the flame front hits the piston, before, it has reached Top Dead Centre.

The other is where ignition is provided by a contaminant in the cylinder head (for example a bit of glowing carbon stuck on a valve)

Don't you think it is stupid , producing 97 RON fuel for such a small island ....... Wouldn't it be cheaper for the petrol refiners to get rid of 97 and supply 98 ??????
You've got me confused...........

Nate.

P.S. maybe it would be an idea to get a petition together of some sort , with signatures from sports car drivers , and pass it to a fuel company.........

Whats also wierd, Is that on the continent, LRP is also 98 RON.

Is this a case of the UK being fobbed off with the c**p that the continent doesn't want?


James.