Timing/ Octane rating

As a VS (VS 1915 with Kadrons) owner in Germany I run the car exclusively on 95 ron petrol and could run on 100 ron if there is likely to be any benefit. Question is where should the timing be for 95 octane, the threads i have looked at using a lower octane fuel?

Thanks

Tim,

Our (European) 95 RON petrol is broadly equivilent to 91 octane US gasoline. They use a different scale (MON+RON/2 where MON is typically 8-10 octane lower than RON)

Determining the Compression Ratio of your 1915; the 95 Octaine would be fine if the Compression Ration is not up there. If your engine is operating properly (Not Detonating or Other Fuel Related Problems)run the 95. If you have a higher Compression Ratio, Lean Carb Adjustment and have allot of Ignition Timing I'd use the Higher Octaine.

In Germany, You can do a Spark Plug Check to actually see what's going on at high speed in you engine. If you aren't aware of what a Spark Plug Check is this is how you do it.

Warm the engine up.

Take the car in high gear maximum throttle, hold it for a short period of time and the "Stick the Clutch In" and turn the Ignition Off.

Stop and pull a Spark Plug. Inspect the Spark Plug. The appearance of the Spark Plug will indicate what's going on inside the combustion chamber and if your fuel mixture is lean or rich etc. Learn to read spark plugs so you can get your "Tune Up" properly adjusted.

Jack Blake

I've heard that a 1776, with stock heads and no shims will have a compression ratio around 8.5 to 1. A 1915 having larger cylinders will have a higher ratio than that. According to Gene Berg, for a compression ratio of 9.5 to 1 you should use at least 99.75 RON. For 7.0 to 1 91.0 RON is recommended. For longevity in air cooled VW engines Gene Berg recommends a compression ratio of around 6.9 to 1 to enable you to use modern gasolines with lower octanes without knocking. I have a 1776 in my VS, I use 93 RON and don't experience any knocking. The name of the game here is preventing knocking.

Tim:

I think with your Kadrons you are also running a Vacuum advance distributor, yes?

If so and if you continue with 93 gas, then set your timing at 6 degrees BTDC at idle to start. If it does not knock or "ping" [but on aircolled VW's, the "pinging" sounds more like a rattle ;>) ] then you can try more spark advance at 7 degrees at idle. I wouldn't go more than 8 degrees advance at idle, or 32 degrees full advance at 3,500 rpm. If you advance it and the engine starts to knock, then back it off a degree or so until it stops knocking again.

You may also check the total advance by running the engine at 3000 - 3500 rpm and see where the advance goes. If it is between 28 and 30 degrees and you hear no knocking with 93 gas, then that's fine (the best range should be between 26 and 32 degrees full advance). With a 1915 you could even try 1/4 tank of the next lower grade of gas and see if it knocks. If it does, either back off the advance a degree or two at idle, or just go back to the 93 grade gas.

If it is not knocking on 93 grade gas, you probably will not notice any difference running the more expensive 100 grade fuel.

Gordon