FUEL TYPES
Fuel choices at the pumps might be limited to just a couple of variants of petrol and one or two different blends of diesel, but venture a bit further away from the local filling station and you’ll find there is a much wider variety available, with everything from specialist road mixes to hardcore race fuels. Take a look…
PETROL
By far the most common fuel for a fast Ford is petrol.
In the UK, forecourt petrol is either 95RON for regular unleaded, or 97-to-99RON for the various brands of super unleaded. All performance and tuned cars should ideally run on super unleaded rather than regular, and compared to many countries we are lucky to have such high-octane fuels available. While it’s no comparison to a true race fuel, impressive results can still be seen using the higheroctane super unleaded fuels. But if you want to reliably run high compression and high boost pressures, you’ll need something more exotic.
DIESEL
Gone are the days of the old, clonking Ford 1.8-litre diesels pushing out a measly 60bhp; diesel technology has improved so much in recent years that the current range of turbo diesels are impressive performers. Due to the fact a diesel engine is a compression-ignition engine, diesel fuel is deliberately of a low octane rating so it will self-ignite with relative ease. Thankfully, due to the nature of a diesel engine, detonation or pre-ignition isn’t really an issue, so a low-octane fuel doesn’t cause the same problems it would in a petrol engine. Although not very common, and with their effectiveness still open to debate, there are actually performance diesel fuels available too. These have a higher cetane level, which is a general measure of diesel quality and how rapidly it will combust. In theory, at least, diesel fuel with a higher cetane level should improve performance at higher rpm, but without a thorough independent test to back it up it’s not something we would want to comment on.
LPG
LPG stands for liquefied petroleum gas, and was very popular as a cheaper alternative to petrol a few years ago. But since the price of LPG has increased, and the complexity of direct-injection fuel systems on modern engines has become more involved, the benefits of using it over traditional petrol lessened, and it’s almost completely died away today.
LPG was used almost solely for economy reasons; at first it was about a third of the price of petrol. What you may not realise, though, is LPG actually has a very high octane rating and is very cold; that means it’s very resistant to detonation and should have a lot of performance potential.
Unfortunately, you can’t just fill your tank with LPG like you can with race fuel. Instead, you actually need a completely different injection system, which most LPG equipped cars have fitted alongside the usual petrol injection. Another disadvantage of LPG is that despite its high octane and very cold temperatures, LPG has a lower energy content than petrol, which means unless your car has been specifically tuned for LPG, you generally end up with a small performance decrease over petrol when running on it.
E85 ETHANOL
E85 is a mix of 85 per cent ethanol and 15 per cent conventional petrol, and it’s become a popular cheap alternative to race fuel. It’s got similar properties to LPG as it has a high octane rating and runs very cold, which drastically reduces the chances of detonation. This means forcedinduction engines can run higher boost pressures without the fear of damaging things. In fact, some cars running on E85 have been known to remove intercoolers and chargecoolers, because the fuel alone will cool the inlet charge sufficiently.
Thankfully, unlike LPG, E85 can be used in conventional fuel systems – although you will need much larger injectors due to the lower energy levels in the fuel, meaning more of it is needed for any given power level. Also, in theory E85 can corrode rubber hoses too.
The main downside with E85 is availability. Until recently, E85 was available from the pumps at certain petrol stations in the UK, but it’s no longer available. This has made it far harder and more expensive to source, and therefore less viable for use here in comparison to pump or conventional race fuels.
AVGAS
AvGas is aviation fuel and comes in various grades, including AvGas 100, which is has an octane rating of 100MON. It is therefore highly resistant to detonation and could be considered an alternative to conventional race fuel; and at under £2.50 a litre it’s much cheaper too. There are two main issues with AvGas: first, sourcing the fuel may not be easy as not all airfields will sell to non-aircraft fuellers, and secondly it’s intended for low rpm use, and in a high rpm engine it’s said to not work well at all.
RACE FUELS
The term ‘race fuel’ is a very broad subject, but for the purpose of this feature we mean highoctane petrol-based fuels that have been specially blended with various chemicals for maximum performance. There are a wide variety available, all with various different octane levels; C23 has one of the highest octane ratings at over 130RON, making it hugely detonation-resistant.
Some race fuels are also oxygenated, which means (as you may have guessed) the fuel has additional oxygen molecules suspended within it. This means more power can be achieved compared to a similar octane-level nonoxygenated fuel – ideal for a naturally-aspirated engine looking for every last bit of power.
METHANOL
Methanol is usually reserved for drag cars, although some hardcore circuit cars such as Indy Car racers also use it. While it’s rarely used as a main fuel, it’s often additionally injected as an antidetonation aid on tuned turbo and supercharged engines, either to supplement or replace water injection. Methanol fuel is very consistent, runs very cool, has a high octane rating, and is cheap compared to most race fuels too.
Unfortunately it’s rarely suitable outside drag racing as it’s highly corrosive to aluminium, a huge amount needs to be injected in comparison to conventional fuels, and very frequent oil changes are required to prevent the methanol from seriously degrading the lubrication of the engine.
NITROMETHANE
Rarely used outside of the world’s fastest drag cars, nitromethane is among the most powerlucrative fuels money can buy. It’s very rich in oxygen, is very cool, and due to the huge volumes required to flow, it drastically reduces the temperature of the inlet manifold and the intake charge within it – all of which adds up to a recipe for massive power.
Unfortunately, nitromethane is incredibly expensive, and is very hard to accurately control due to its power potential and the massive fuel flow required. Not to mention, in the wrong circumstances it’s actually more explosive than TNT. We don’t think we need to tell you, it’s not really viable for anything other than the most extreme drag engines…
E5/E10 ‘ECO’ FUELS
Unlike E85, which has an 85 per cent ethanol content and is really rather very good for performance engines, the latest range of E5 and E10 fuels seen at filling stations across the UK are being introduced for the economic benefits, not their performance advantages.
The E5 and, from 2021 onwards E10, refers to ethanol content, which makes up five or ten per cent of the volume. But this is bioethanol, produced from renewable sources such as crops of sugar beet; the main aim here to reduce fossilfuel usage. As with E85, ethanol is less energydense than petrol, so for the same amounts injected into an engine, power will actually decrease, and as ethanol is both hydroscopic and a solvent, there are some concerns about prolonged use causing corrosion and degrading rubber hoses – especially when using E10 with older classic cars in particular.
The good news for us performance fans is that while regular petrol will be switching from E5 to E10 this year, super-unleaded fuels will remain at E5 for the next five years – and in reality the bioethanol content of these is typically around two-to-three per cent anyway. Just another reason to put your hand in your pocket and pay the extra £5-to-10 per tank at fill-up time.
FUEL ADDITIVE
There are various fuel additives on the market all claiming to do various miraculous things, but mostly they revolve around cleaning your fuel system components and even the inside of your engine, increasing the octane of your fuel, or indeed both.
While all well-respected brands will certainly have some effect, don’t expect magical instant results every time. And with the octane boosters especially, don’t expect to have instantly turned your fuel in to race gas, as the results are often quite small.
We can’t recommend specific additives without personally testing them, but with some internet searching you will certainly find lots of independent testing, especially of the octane boosters, which will help you decide what, if any, additives will suit you.
FUEL LONGEVITY
You might not realise it but fuel goes off, and some fuels go off far faster than others. Many of you will have heard of, or even experienced yourself, cars that have been standing for a very long time that refuse to start due to the fuel going stale, but octane levels can drop in fuel far faster than you may think.
Overall, due the evaporation of the chemicals used in them, higher-octane fuels lose their potency faster than others, and even super-unleaded pump fuel is meant to be well past its best if it’s been sat in the tank for over two weeks; on an engine operating near the detonation threshold, that can prove to be a potentially serious problem. To help prevent fuel going off too quickly, leaving a car with a full tank minimises the amount of air in the tank and therefore lessens the chance of evaporation, but you’ll never be able to stop the fuel going off, so it’s something that needs consideration.