i keep seeing this high octain stuff in petrol stations and was just wondering,

can high octain fuel be used in the 1.4 340 dl?

and is there any point?... will it improve running? .....

basicly whats it for?

i also read that you need to adjust the timing in some cars if you use this type of fuel,..... does this apply to the 340?

Higher octane fuel basically gives you a more potent mixture for combustion. The higher the octane rating, the bigger the explosion = more power. Thats the basic theory. A lot of people will argue for and against the benefits/costs, some saying that all it does is prevent pinking etc etc. Others say you get more mileage, it cleans your engine's internals etc etc.

When my 340 GL was a 1.4, it ran fine on high octane. (seemed to run better, but that might just be me) and didn't need to adjust the timing, as my car was a later model, with the more advanced timing for unleaded fuel (Volvo earthed the renix unit, which advanced timing by a few degrees). Depending on your year of car, the timing should already be in place for unleaded fuel, regardless of octane (say '85+ . . . maybe). The older models were designed to run on leaded petrol.

I use high octane now as my car is now fuel injected (valver conversion) and other octanes are 95, which I think is too low. Even in the volvo handbook, it recomends 96 or higher. Its 8p more a litre, which isn't too bad really. Either way, it doesn't really matter, so long as its nothing lower than 95.

Other peeps on here are far more knowledgeable on the older models in the series and their runnning, but I hope thats given you the basics of high octane!

mines the 1987 340 dl (cvt)....

would you say that the timing is already in place on mine?

I would say so yeah. If its a CVT though, I wouldn't bother with the higher octane fuel. The gains will be much less noticeable in the auto I would assume. Up to you though, it won't do anything detrimental.

I think you can run the valver no 95 with no problems? I never noticed a difference using 98/99 until I got a new fuel map. Also isn't 99 less explosive than 95?

Seems to run fine yeah. I've got 95 in at the mo because of lack of high octane at the station I stopped at, but it seems fine. Dunno why, I just prefer the idea of a higher octane fuel. Not too much more either.

Sods law'll be its just the corporate people BS'ing about higher fuel ratings etc, and its actually just the same fuel as lower stuff, just labelled different

RON (research octane number), the standard octane rating petrol is sold with in the UK is a measure of the fuels resistance to auto-ignite. The higher the octane rating the greater the more retarded the timing can be before knock occurs.

Any engine designed for unleaded fuel will usually be timed for 90 RON or less fuel, in the UK normal pump fuel is 95 RON.

In an open loop system like the B14's Renix unit the timing is fixed and a higher octane rating alone will not make any difference. In a closed loop ignition system with an ECU the ignition timing will automatically be advanced/retarded depending on the fuel, so putting in higher octane fuel may make a difference in a valver, if the ECU is able to recognise the change.

Premium fuels do have different additives to regular unleaded that may well make much more of a difference to both performance and engine cleaning/wear. If there is any advantage to putting super unleaded in an old engine this may would be it.

Alex Laidlaw wrote:In an open loop system like the B14's Renix unit the timing is fixed and a higher octane rating alone will not make any difference. In a closed loop ignition system with an ECU the ignition timing will automatically be advanced/retarded depending on the fuel, so putting in higher octane fuel may make a difference in a valver, if the ECU is able to recognise the change.

Pretty much, mine can notice 95 vs 99 when I change. On the orig Williams map with the differences my engine has it'll pink continually on 95, I just don't run stock map

ive also heard that using high octaine fuel in the 340 1.4 can make the tickover a little smoother.

any truth to this?

or have i been miss informed?

Might be wrong but I only think this is for the very early ones.

It's certainly not going to do any harm, try a tank and see if you can notice a difference.
I did, can't really say I noticed a difference. Maybe slightly smoother but nothing clear cut.

Every single thing I read about Octane (C8H18) is wrong, or at least contradicts the last thing I read.

If I go back to a 1930's engineering book I took the time to read:

Higher octane burns cooler and slower and is less likely to detonate.
Low octane burns hotter and faster and detonates at lean mixtures.

Burning faster does not mean more powerfully.

Burning cooler does not mean less powerfully.



they sell 99RON at tesco petrol stations.