Back in the last century, I was an impoverished apprentice at the huge BT-H plant at Rugby and after crashing my Bantam one time too many, my dad sold it and presented me with a 1938 Morris Ten Four. At £2 15 shillings a week from which I had to pay most for the hostel, I decided to run the Morris on 50% cheapest petrol at 4 shillings and twopence per gallon and 50% Paraffin. It went just fine. Now my memory is not perfect, but I seem to recollect that the “POOL” petrol of infamous memory we had just after the conflict with those who were our enemies but are now our friends, was about 75 octane, In 1929, however I am sure that the octane rating of the fuel was no higher than 75 and perhaps lower. A percentage of paraffin should return burning speed to be a bit nearer to the design conditions. As we are using fuel with a different burn speed, I rebuild engines to take this into account.
Anecdote. If you are a bit crazy like me and decide to use a Scott for racing, it is necessary to use all the tricks to get competitive power. About four years back, I finished the season with the engine going fine. Next year, new premium pump fuel as usual, I got detonation and rough running. Pull the engine down and recheck everything, put it together, just the same. The only variant was the fuel to which, I discovered, more ethanol had been added. I went on the internet and compared anti Knock additives that had been tested on a Ricardo Knock test machine. The top performer was an Australian product called NF. I then went to a local garage who specializes in expensive Classic cars. He sells the old leaded four star fuel and told me that he would only run one of his classic cars on the modern muck in an absolute emergency. So with a highly tuned engine and not wishing to use methanol, I take one gallon of four star leaded to which I add 220cc of Castrol R 40 and 15cc of NF anti knock and it all works just fine. Of course I am using petroil which I prefer and have a three way dripper which gives a small drip feed to each main and a small feed to a brush oiler that runs above the bottom run of the primary chain and extends its life considerably.
Kind Regards Roger
