Definitive octane answer

[5MUG]

My Sunday Times tells me in the '10 mad myths of motoring' that it is nonsense that some cars have to run on 98 exclusively.
I know I am covering old ground, but we have always tried to use 98 in our TVRS because it seemed to be the safest option given all the conflicting advice. Are we wrong? Who is qualified to put this subject to rest finally?

Sarah and Andrew
(Confused)

[joust]

I saw that as well - it's crap. Unless your car has a knock sensor to retard the ignition (most modern cars do - so I suppose that is where the article came from) then your ECU will be hard wired to a certain octane rating.

Too low an octane and the engine will be in danger of seriously overheating.

See
www.lancerregister.com/faq/M01/m01.html

an article by the chief bod at VW
www.automotivetechnology.net/articles/article5.html

the FTC's advise (that clearly states prolonged knocking will cause engine damage)
www.ftc.gov/bcp/conline/pubs/autos/octane.htm

www.xrefer.com/entry/489539
etc. etc.

J

[5MUG]

Thanks for that. Reassured and better informed.
Sarah and Andrew.

[dannylt]

Not that simple. All the early 4.2 Cerberas were originally tuned for 98. The early piston design & ECU required it. Later 4.2's were tuned for 95 with a different piston. Certainly a not so late 4.2 on a rolling road was pinking quite a bit on normal unleaded.

All 4.5's are 95 (except the Red Rose version, which have a switch for 95 or 97). All later 4.2's are 95. If in doubt, call the factory, but they have the correct label on the filler cap.

As for the Rover engines - some of them definitely pink on 95. But some even pink on 97/98 too

danny


>> Edited by dannylt on Tuesday 14th January 19:35

[dannylt]

PS All Speed 6 engines are 95 too.

[t8rus]

i know this may sound a bit of a dumb question but has anybody thought about converting to "LPG" while everyone is on the subject of fuel ratings.

[mudstud]

DannyIT, if 4.5's are tuned for 95 octane why is there a sticker next to my filler cap stating 98 octane only? And if I can't hear pinking does that mean it's OK? Not too many Shell's around me so keen to go to 95!

[gazzab]

LPG - what !!!??
If you cant afford the petrol then get a diesel.
Maybe I am being too traditional but I say sod the petrol costs.

[dannylt]

mudstud said: DannyIT, if 4.5's are tuned for 95 octane why is there a sticker next to my filler cap stating 98 octane only? And if I can't hear pinking does that mean it's OK? Not too many Shell's around me so keen to go to 95!

They didn't have a 95 sticker to hand? . Was yours a very early 4.5 - maybe they hadn't got round to changing the stickers. You can always call the factory and quote your engine number to find out.

danny

[jurdy]

Have had a 99 4.5 for a year now and have either fed it on 97 RON or Optimax. Are you guys saying that I have been over cosseting my car? I thought that if I continually used 95 the engine would pink like crazy like it did in my first S3. Totally confused......

[anonymous-user]

mudstud said: DannyIT, if 4.5's are tuned for 95 octane why is there a sticker next to my filler cap stating 98 octane only? And if I can't hear pinking does that mean it's OK? Not too many Shell's around me so keen to go to 95!

My Speed Six has the same sticker.

[cammy]

I specifically asked my dealer whether I could use super-unleaded. The answer was yes. Have been running my S6 for over 15 months on super-unleaded and latterly Optimax. The 'handbook' says to use super for track days.

[johnmckenzie]

My 4.5 is very early (Feb 1998 build)and has the 98RON super unleaded sticker and the handbook says it must be used too. Whilst in the wilds of Scotland (well North of Inverness anyway) super unleaded was rarer than hens teeth. Ran the car down to fumes and made an emergency fill with 5 galls of regular 95RON. It immediately pinked like a B*****D. Spent 60 miles treating the throttle like eggshells till the real thing was available again.
So, anyone out there with definitive facts on what should be used, including engine numbers to back it up.
BTW - I use only Optimax now

Regards

John

[waddler]

My 99 speed six also has 98 octane sticker. It has done the past 3K on optimax and runs very well.

[jamesk]

If in doubt use highest rating you can find? It cant do any harm and besides, I couldn't look my TVR in the eye if I'd fed her normal unleaded

[tims]

OK, a couple more pretty dumb questions so please bear with me - not particularly engineering minded!!

What is pinking?

Could the engine have been retuned for 95? When I bought my late 97 4.2 in November the chap I was buying it from said he used 95 unleaded normally, and using 98 didn't seem to make much difference. The car also seems to run cooler than many people's - at a reasonable pace (ie not hammering it) the engine temp reads around the 80 mark. If I push things it nudges up to 90. This doesn't seem to suggest it's overheating, but now v concerned that I've been doing damage to my engine... any help gratefully received!!

[joust]

tims said: OK, a couple more pretty dumb questions so please bear with me - not particularly engineering minded!!

What is pinking?

Could the engine have been retuned for 95? When I bought my late 97 4.2 in November the chap I was buying it from said he used 95 unleaded normally, and using 98 didn't seem to make much difference. The car also seems to run cooler than many people's - at a reasonable pace (ie not hammering it) the engine temp reads around the 80 mark. If I push things it nudges up to 90. This doesn't seem to suggest it's overheating, but now v concerned that I've been doing damage to my engine... any help gratefully received!!

Pinking is a noise that is hard to explain - but you'll know it if you have it.

To "tune" an engine to 95, all you have to do is retard the ignition enough - you'll loose power and use more fuel, but apart from that there isn't much else to do.

So - I'm not an expert on TVR engines, but in principle you could have it "tuned" to 95.

If you can't hear it pinking (it sounds like a funny tapping sound when you put a large load on the car - i.e. open full throttle going up a steep hill in a highish gear) then I wouldn't worry about it - but probably best to give the factory a ring or get your dealer to check the timing next time it's in.

Before you can do serious damage you'll notice the noise - so don't panic!

J