High Performance Engine Pump Fuel Octane Information


Fuel Octane Information

When using pump fuel, SBD recommend the use of a high-octane fuel (98/99RON) for all competition engines. If possible, it should always be purchased from a petrol station with a high turnover.

It is our opinion that care must be taken when buying fuel from petrol stations with a slow turnover of fuel as it will often have been stored for some time, during which time the RON rating reduces through evaporation. Under these circumstances an Octane booster is highly recommended to ensure the RON rating of the fuel is sufficient. If it is necessary to use lower octane fuel (if a high octane is unavailable), it is recommended that an octane booster is used.

SBD have seen good results from Shell V Power 99 & Tesco 99 fuel

It must be remembered that one of the main reasons for using Race Fuel is down to the strict control of the RON rating, it is guaranteed standard and can be relied upon to be consistent throughout the year, something which cannot be said for pump fuel.

Head gasket deterioration & pump fuels

We first noticed towards the end of the 1998 season that our high spec engines (2.0L 16v XE's running 8 injectors, circa 290bhp), were required to have the head gaskets changed due to deterioration of the gaskets themselves. We put this originally down to possibly a batch of head gaskets that had had the material specification changed. But during the 1999 season, these same engines needed the head gaskets changed on a more frequent basis. We still considered the possibility that the gasket material was causing the problem. At this time we were not seeing any problems occurring with engines in lower output & specification. By the time we reached the 2000 season, engines were being returned for routine rebuild, it was noted that the engines of around 270bhp were showing signs of slight deterioration in gasket material, but this was still producing no problems.

We decided to invest in a higher specification gasket with stainless steel firing ring. During the 2000 season, we noticed the newer gaskets did give significant improvement and engines that were inspected mid-season, showed less sign if any, in gasket deterioration. But by the end of the 2000 season, although the new gaskets were helping to extend time between maintenance, they still had not cured the problem. At this point, we decided it was not the gaskets causing the problem & by replacing the gasket with a higher specification was trying to cover the problem up, rather than fixing the cause. By the beginning of the 2001 season we were getting reports from other engine builders, not only people who build Vauxhall engines, but other makes as well, who had been suffering similar problems, particularly on high compression engines. We had also noticed during programming of engines on the Dyno, that specification engines that require for example, 32 degrees of ignition in 1998, were now requiring ignition advance in the 20 degree regions.

We believe the problems are being caused by the components used to produce the current pump fuels. As far as we can gather from various sources, many of the components such as Tolurine (highly carcinogenic), have been banned from use. There are other similar components, which have also been banned. The advantage that was gained with these now banned components was they took a lot longer to deteriorate in the fuels, than their replacements. Again from the information we have received, although the octane levels as far as RON (Research Octane Number) have not changed much since 1998, obviously the fuel is new. So when the tests are carried out, the fuel reaches the desired octane level. Unfortunately, due to the fact that the components being used deteriorate quicker, by the time it has been stored in the petrol pumps or in your fuel tank, its octane level drops much faster than it would have done with the now banned components. The longer it is left in the car, the faster the octane level will deteriorate, particularly when the weather is hot.

So although our results cannot be claimed to be conclusive, we recommend that if you are to use pump fuel, you try and purchase it from a petrol station that has a regular turn round, therefore making sure the fuel is as fresh as possible.

It is also suggested that the engine is programmed on the particular fuel you intend on running the engine on. Due to the fact that pump fuels components are changed by the fuel manufacturers continually throughout the year, it makes it extremely difficult to programme the ignition on an engine & then expect it to run on varying grades of fuel at its optimum. So it is suggested that you either run a control fuel if possible, if not keep a good check on the engines condition. Unfortunately it is quite difficult to determine head gasket deterioration, unless the engine is stripped on a regular basis. If you wait until the head gasket has failed, the resulting damage can be quite considerable due to the fact water & oil are sucked into the combustible fuel, rapidly accelerating detonation. The resulting appearance to even the most professional eye would make you think the engine has been programmed with excessive ignition. Since the cylinder head & pistons will usually be eaten away, giving the appearance that somebody has chipped away with a small chisel on both surfaces. The effect accelerates at an exponential rate. We have seen in some tests the damage described appear in seconds.