Correct Grade of Petrol

[Chris KC]

Like others above, I have conducted long trips on the continent of Europe and used whatever came out of the pump, and noticed no difference. Any theoretical advantage of one fuel over another is too slight to notice on the road.

[andrew34ruby]

Looking for a bit more hill-climbing ability I have tried most things in my early Ruby with original carb and low-compression head, including running with a 10% diesel mix. The diesel might have helped a little bit when uphill on a cold engine. I now run it just on petrol, any petrol.

[Colin Morgan]

I can't see the small theoretical difference in normal and premium petrol showing up in the performance when running a Seven.

A few years ago, a fuel trial was done using a friends 1920s side-valve Vauxhall where kerosine - heating oil - was added to the normal petrol and a satnav used to see if this improved top speed and therefore performance.  The top speed was measured on repeated averaged runs up and down a quiet stretch of dual carriageway.  The results suggested that the addition of 10% kerosine gave a bit more power.  I seem to remember a couple or so extra mph translated to about 10% more power from the engine, given the cube power law for increased speed (drag being squared, and resistance linear) versus power output.  So, even this significant change to the fuel composition had little effect and wasn't worth the bother.

[Tony Griffiths]

This is purely a personal view, but over the last 40 years I have run my RP (with SU carb and 37 head) on every type of commercial fuel and not noticed ANY difference. It currently runs on the cheapest available at the pumps, 95 E10 and I cannot understand why anyone would want to spend more money on petrol that makes no appreciable difference to performance or economy. During the post war years it wasn't unheard of to add paraffin to eke out the fuel ration, and you could probably get away with adding some diesel as well.

I wouldn't worry unduly. If your car is in good order it will run on whatever you give it.

Spot on. They'll run on almost anything; in any case, it's challenging to notice anything less than a 5% increase in power. Of course, if you monitor fuel consumption very carefully, you might be able to spot a change - but even then it's difficult to divorce differences that might be due to variables such as journey length, roads used, wet and dry conditions, wind direction and load carried, etc. Only really long-term measuring gives a true result and, as we no longer do 20,000 miles a year in our Austin 7s, it's unlikely to be worth worrying about.

[Old Dave]

SO - the petrol doesn't make much difference. Does that include differing Ethanol content as well??????

[John Mason]

I agree with Reckers on the use of cheap supermarket 20/50 oil. The plus side because it is so cheap you can afford to change it more frequently. This must cut down on engine wear in an engine with no oil filter.

John Mason.

[Old Dave]

Crickey!!!!! Is this thread going to save me masses of the folding stuff??

Summary - Just use old cooking petrol and supermarket 20/50 engine oil (I may have some old Duckhams lying around)

I thought we were supposed to look for the lowest E content petrol and a non-detergent engine oil????

HELP

[Reckless Rat]

The only caveat, Dave is the use of detergent oil in an engine that hasn't been properly cleaned out. That's not advisable.
Apart from that, it's a question of how deep your pockets are. Avoid ethanol if you enjoy paying more, same as for straight grade oil. Assuming that you have a " cooking" engine there's nothing to be gained. My car runs on E10 and cheap 20w50 which I change regularly.

[bob46320]

I have found that SP98 "seems to be better" when running in elevated temperatures of +35 degrees C in the summer. The SP95 gives more problems of vaporisation in the carburettor. This is based upon experience and not any theoretical analysis of fuels.

[Ruairidh Dunford]

I thought we were supposed to look for the lowest E content petrol

Who told you that?