I was reading a 60 year old motoring magazine the other day which had an article on the octane rating when there were different grades of fuel available at the tanks and it stated that the reason back then for the different grades was connected with engine knocking and how the engine was timed. You basically bought the grade that the engine was designed to use and had nothing to do with performance.
These days engines are far more efficient and flexible so both grades can be used in cars sometimes with very little difference. However, performance cars will recommend you use the higher grade to extract the most performance but will still happily run on the lower grade.
Personally, I only use Shell V Power in the MX5 but both in my Mazda2. In the 2 I find it is smoother and has better acceleration with the V Power but is perfectly happy on the vanilla.
Ish… most new engines will sense the detonation (as opposed to the burning) of the fuel and will self adjust to optimse the engine to the capability of that fuel. That is not quite the same as engines a little bit older, such as the NC (correct me if I am wrong) that will happily burn anything above a minimum rating but offer no performance benefit if higher octane fuel is used.
I would have to check the book but doesn’t it tell you to use the higher one in the NC? Can’t remember. But it’s all I will use in mine anyway just to look after it and for the miles I do the extra cost is not a problem. I certainly wouldn’t use unbranded.
It’s written by the fuel filler: 95 RON.
The CR of the DI Skyactive in the ND is far higher than that of the port injected NC, I can see how this would want to take advantage of a better fuel.
As the NC is a relatively modern engine which has full electronic control, a knock sensor and lambda sensor and can adjust fuel trim in the short and long term it would be surprising if it didn’t optimise timing according to engine speed, load and knock feedback.
Just done a bit of reading where it states the dhe 2000 duratec is designed to be run on 95 ron octane. I assume this spec extends to the Mazda flavour.
So assuming the car runs well on 95, there would be no improvement on running 98. Likewise, it can run lower octane but doing so is sub optimal and puts extra stain on the engine so should be avoided.
What the knock sensor detects is a shock wave caused by self igniting fuel and air caused by too much heat. (The self igniting fuel has a burn front which hits other burn fronts from other areas of self ignition or from the flame ignition of the spark, thus the shock or knock). This shock wave causes further excessive heat and thus if ignored will start melting things. So the engine management advances the ignition to ignite the mixture before it can detonate.
That is right, it advances the ignition.
This causes the mixture to burn before optimal and will reduce power output.
So, if you have a carbon build up (causing increased compression ratio), or an incorrect mixture that causes more heat to be generated than designed, then your knock sensors may be advancing the ignition, lowering power output and increasing fuel consumption. In this case, moving to a higher octane rating may reduce the knock tendancy and therefore make the car perform better.
But if the engine and fueling are as designed, 95 is the correct fuel to use and no benefit will come from using the higher grade. But equally no harm is caused except to your wallet.
All of the above is purely about octane rating (which relates to the heat required to self ignite the fuel, hence higher octane allows higher compression ratios). It says nothing to the ‘better fuels have better detergents’ argument, which do not affect short term performance, but may help long term.
As I stated earlier in this thread I popped in £25 worth yesterday for the first time…
Today when out shopping she was running at 1100rpm on idle ?
Then on the way home my engine management light appeared.
Seem to run ok but will have it plugged in to check out issue.
Maybe a coincidence ?
Shell make no specific claims about economy or power AFAIK, but they do adduce evidence of the detergent effect. I don’t doubt the piston tops will be cleaner with the super-fuel, my thinking though is about the inlet tract and valves, which on a port injected engine will get the benefit of the detergent, but not on a DI engine which the Skyactiv-G is. Perhaps I should have made clear I have an ND. From memory the Duratec in the NC is also a DI but I am happy to be corrected.
The point of mentioning Momentum 99 is that it is also claimed to have a special detergent package. It’s not Shell presumably but it still might have similar benefits. Shell certainly has the best marketing but we only have their word that V-Power is the best fuel.
What a can of worms this is. I just pay up and hope for the best.
Definitely felt a slight increase in power on the standard ND2 engine and it ran much smoother at higher revs. However if you don’t use this increase in power and drive at the same speed you may get improved fuel consumption. I reckon I get 2 mpg more using Shell V power, which offsets the increase in cost. BBR only publish their figures using 99 Ron as they find (as does Rodders) that 99 Ron gives the potential to achieve more power.
I have had my ND 2.0 for 1 1/2 weeks now and am (just) on my second tank. I have only filled it so far with Shell V Power and the car goes well and the economy on a run yesterday for 25 miles, taking it fairly easy (with the occasional burst) on country lanes was 47 mpg, so I have no complaints. I have no idea what it would have been like on regular 95RON, as these things are very subjective. I will continue to use the V power though and I am lucky that we have a Shell station in our village.
Depends on the tech. Some retard to reduce temps, but if the engine is knocking and the throttle stays on, then the retardation does nothing as the fuel is already burnt and there is no cooling effect. Advancing the ignition burns it before detonation point.
Evening guys
We have done the same test on both ND1 & ND2 cars and seen the same results.
The direct injection engines will suffer from carbon once they get a few miles on their back and a car that has only run on better fuels (shell in my case) when stripped had a noticeable reduction of carbon.
Once we are allowed gatherings I’ll happily have an open evening and strip a mk4 engine in front of everyone
Maybe we’ll never know but using high end fuel vs chucking 1/3 of a bottle of seafoam in every tank/fill up to reduce carbon build up. Maybe it’s a product you have not used or do not rate but seems very popular.
Basically wondering if its cheaper to just buy some sea foam than use higher octane fuel for the same results, even though I would buy the higher fuel, it’s just for science.
Blimey Paul. You’ve made me a liar. I sold NDs for 5 years in Australia and NCs for 5 years before that. All the sales training always said both were tuned for 95 and that anything higher octane was a waste as the ECUs could not recognise it.
