Premium vs standard fuel

[warpc0il]

Yes, I know this topic has been discussed before, nearly to death, but I wanted to share my observations from today and recall some ancient history...

My '04 231 loves premium fuels, though they're very difficult to find over here and the only one within reasonable distance is Sainsburys Super Unleaded. There are no Shell stations and Tesco withdrew Momentum over here five years ago, and refuse to bring it back - despite "having to keep telling people that there's no demand"

The difference is immediately noticeable and, while it runs okay on standard fuels, the tickover is smoother and the acceleration cleaner on Super. All my fastest track lap times and most economical long-distance runs have been on Super (of some kind).

I took two spare cans with me to Kirkistown a couple of weeks ago and didn't get in as many laps as I'd hoped, so still had a full can in the boot.

Today the lawns needed a massive crop, having burst into life after the drought & rain.

Having used-up the open can in the shed, I filled the mower with the Super I'd just removed from the boot; just because it was there.

Within 10 minutes of running the mower engine (500cc OHC single Briggs & Stratton) sounded as if it was about to sh!t itself. I seriously thought it was about to throw a rod and even stopped to check the oil level. Whenever I switched-off it was sounding a massive back-fire from the exhaust as it stopped.

Half an hour later it was still running, noisily, but needed yet more fuel, so a grabbed another can from the shed - this one (almost certainly) being Tesco standard unleaded.

Five minutes later and normal service was resumed. This old mower could never be accused of being "smooth" or "quiet" but it was waaaay better than it had been before.

Today's episode reminded me of riding around France with the (motor)bike club back in the '70s. In those days French petrol stations sold "Essence" and "Super". IIRC "Super" was about the same as our old 3-Star and "Essence" was so poor that it wouldn't have even registered on the UK Star scale.

We had a wide variety of bikes in the group and soon discovered that the 2-strokes (Yamaha 350 & Suzuki 500) really liked the Essence, which was great as it was cheap. A couple of the 4-strokes (Triumph Tiger & BSA something) didn't seem to care, while the Honda 750/4 and 500/4 didn't really like the Essence at all. The Norton Commando with a "Combat-spec" engine refused to run on Essence and wasn't that happy on the Super either - having been tuned to run on 4-star.

I seem to recall that those old 2-stroke engines had fixed ignition, e.g. there was no auto-advance as the revs increased, whereas the 4-stroke bikes had automatic advance. Whether this, or the compressions ratios, or some other factors were in play, the results were consistent over many trips, filling stations and brands.

My old mower is a 4-stroke but obviously at a very low state of tune (power/weight) and I've not investigated if it's got some form of advance in its ignition system.

My conclusions from all this is that the "best" fuel isn't necessarily the highest octane or the most expensive; it all depends what your engine is best suited to.

BTW I used to run my highly-tuned '64 Honda 350 on 110 octane AVGAS and also used to top-up my '68 1750 Alfa Romeo with AVGAS on the few occasions that I got the chance - and they both loved the stuff

Most modern performance piston engines will detect higher octane fuels and deliberately take advantage of them, basically they're always trying to push the ignition advance for more power and only back off when "knock" aka "Pre-ignition" is detected. The higher octane fuels are more resistant to pre-ignition, so this is where they get the benefit.

Back to the RX8, the Renesis doesn't use this strategy because;
- 1 there is very little power to be gained from advancing the ignition on a rotary engine.
- 2 by the time you detect knock on a rotary there's a good chance that major damage has already be done.

The Renesis has a knock sensor (the R3 actually has two) but these are just there for safety, not for performance.

However - if you haven't tried at least a couple of tankfuls of Super Unleaded in your car then you should. Some report that it doesn't make any noticeable difference at all while others would never go back to using standard, given the choice.

[Humane-Hobgoblin]

Having read through the history to waste a bit of time at work, I can (personally, of course) say that my RX8 much prefers Super Unleaded (99 octane) from Tesco. I have tried it in normal unleaded from there, super Unleaded from the local Esso station (97 octane) and I think a Shell station.

My 8 doesn’t run very well I think on ‘normal’ octane unleaded, lumpy idle, doesn’t rev as freely and most importantly, doesn’t backfire half as much.

Of course sometimes I have no choice but to fill up with normal unleaded, but 99% of the time I swear by Super Unleaded. But this is all my opinion.


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[warpc0il]

I meant to add that some have suggested that the additives within the premiums fuels may help to clean injectors and engine internals and that may be why (some) 8's seem to perform so much better using them.

While this makes some sense, it doesn't explain the behaviour that I and others have observed, where the difference (good or bad) is noticeable within a few miles of leaving the petrol station, depending on what just went in to the tank.

The placebo effect can also be discounted as, on more than one occasion, the difference has been commented on by my passenger, who didn't know what I'd filled with.

[Humane-Hobgoblin]

Ahh additives could explain a lot too. And I know what you mean but the placebo affect. The first time I filled up with some normal fuel after using higher octane I thought that exactly, but after a while I forgot that I had filled up with normal fuel and felt a difference (does that make sense?)


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[PeteH]

That's a nice little write up. Having been around for a few years, I have a few fuel stories I can contribute.

My first car was a Spitfire. It was standard, and could hardly be described as a "tuned" engine. But it was designed at a time when 4 star was the main fuel. On a long motorway journey I made the mistake of putting 2 star in it instead of 4 star. It caused huge pinking (expected), and then stopped the engine entirely (unexpected!). Even at that tender age I knew that fiddling with the distributor could change the timing enough to get it running again, but it refused to start. I had to ring my dad, who was 100 miles away to come and get me. He promptly got lost because his map didn't have the new M42 / A42 link road on it. I kept trying to start it, without success. He arrived after about 4 hours, and suggested giving the engine one final crank. The bl##dy thing started! (No, really dad, it was broken!!!). Clearly it had cooled down enough to not pre-ignite anymore, so I proceeded to drive the 100 miles home at about 30mph to avoid putting any heat into the engine. A fresh tank of 4 star, and it was as good as gold. That tiny difference in octane totally disabled that car.

A couple of years later I had a 1978 Suzuki GSX750. It was the time unleaded had just been introduced. I wish I had a quid for every petrol station attendant who warned me that I was putting the wrong type of fuel in my "smelly old bike". What they didn't know was that most Jap bikes from the mid-seventies onwards had been designed for regular unleaded fuel. For a brief period I had unfettered access to the green pump, until every other car eventually caught up.

My race RX-8 always runs on Shell v-Power. I don't think it increases the power. And I can't honestly tell you if it makes a difference at all (I never did a back-to-back). But I do want to keep the engine as far away from detonation as I possibly can, so that extra few RONS keeps me happy.

Same as you Dave, I keep can of v-Power in the garage for my race car. So my lawn mower also gets to run on v-power (some Briggs & Stratton 2.5hp four stroke thingy). It runs like a dog, hates to start, stalls regularly, and refuses to hot start unless I clean the always-sooty spark plug. I have no idea if it will run better on normal unleaded, but I quite enjoy winning my weekend battles with that cursed machine. What I can say is that v-Power certainly doesn't keep a Briggs & Stratton spark plug clean!! I can also say that the ignition timing is fixed. It's rather clever actually. The flywheel has a magnetic 'window' on its perimeter, and when the ignition pick up (just a magnet) passes that part of the flywheel it induces a current, which directly generates the voltage for the spark. There's no other parts. It's no wonder the spark is weak. I know this because the pick up does wear, and the gap opens up, which stopped my engine once. The way to get it going is to put the engine into its firing position (rotate it to get the pick up next to the magnetised bit), then put a piece of paper between the pickup and the flywheel, and loosen off the pickup. The magnet will pull the pickup and the flywheel together, separated by only the paper. Now tighten the pickup, and slide the paper out, because this is the perfect gap for a strong(ish) spark.

[Bullet5]

A few years ago I was running a couple of 50cc 2 stroke motorbikes. All of them ran far happier on the premium fuels, one of which to the extent that it would increase the top speed from roughly 40 to 55 on the flat, idle was smoother and it pulled off the line with a very noticeable amount more go. Not only that but it wasn't unusual to hit 105MPG on a trip with premium fuels in comparison to roughly 80 on this particular bike with standard fuels.

This may be an extreme example, but as it made such a big difference to them, I've always tried where possible to fill up with V-Power. As for the 8, I did once try the car with a tank of Tesco and while the performance didn't suffer massively, it certainly didn't idle anywhere near as smoothly, and seemed less willing in the higher RPMs. The same in that respect as my '99 Bandit 600. It doesn't make as big of a difference when pootling around town, but at idle once warm the RPM wavers and it doesn't have the same "go" higher in the rev range.

On the flip side a Virago 535 I had a few years ago seemed the fairly neutral and didn't care what it was running, although that poor bike had been through hell with it's previous owners. When I first got it it seemed very down on power (especially when compared to the 50's and the Bandit). I had it dyno'd to check the air fuel mix and prove to myself I wasn't going insane and it was producing 12HP when it should have been making circa 40. Soon fixed with some carb work, but it never really ran any better on any particular fuel.

It's certainly not for everyone (especially given the additional initial outlay at the pump), but I'd highly recommend trying out a tankful or two with any new vehicle to see how it behaves on both.

[kopite72]

First time I took the 8 to RR I was using shell V Power and the difference was night and day compared to the stuff we have over here ( 95 ) Engine was creamy smooth and it ran like a dream,needless to say I brimmed it before boarding the ferry.

I emailed shell shortly after wondering why they pulled out of Ireland and got a response,the contents of which I can't remember exactly but we all know it was because they were making damn all money over here pretty much.Pity because that shell V Power is very good juice IMO anyways.

I would have thought you could have had shell V power in NI Dave?

For anyone who's interested......which will be no one

https://www.google.com/url?sa=t&rct=j&q ... Fjc-AcxKph

[delta0]

I use Premium as it will keep the internals cleaner and as a bonus there is less chance of knock. Whilst the engine won’t take full advantage of 99 it definitely won’t retard at all.

[AutoGibbon]

By my accounts, I own two cars (both are the only cars I've ever owned). The 2007 Mazda 6 definitely enjoys a dose of vpower, and shows this by being slightly nippier from a stand still, picking up its torque slightly earlier also.

The rex has so far had Shell Vpower and Tesco 99. So far I've been pleased with both, and haven't noticed any appreciable difference between the two other than a £12 difference per tank. No points for guessing which fuel I'll be using more often.

[Phil Bate]

What I can say is that v-Power certainly doesn't keep a Briggs & Stratton spark plug clean!!

I wonder if this is down to the lubricants they add?


Weirdly, my mowers love a bit of V-Power (again, the 2.5hp Briggs & Stratton engines) - I gave it to one of them for a laugh one day and it made such a difference that's all I've bought for them ever since.


Now where's my timing light?

[Ainmhidh]

Hmm... We have a briggs and stratton and I have 2 cans in the garage, one v-power and one normal... Time for so expiremelontation

[SeriousSam]

Our BS mower runs like a bag of spanners no matter what fuel you give it. It's better than it was, when it was left at this house we were told it was broken - soon fixed that with a good service. But it runs equally badly no matter what fuels or additives get run through it.

[AndyBrad]

I find that the car performs better on vpower but ive just moved to standrd recently and have noticed an increase in mpg (although im adding premix as well but only 1 tank)

my previous bikes and cars have all run better on vpower. I do not use supermarket fuel.

It does turn the spark plugs a little red ive noticed.

[Nerdstrike]

Weirdly, my mowers love a bit of V-Power (again, the 2.5hp Briggs & Stratton engines) - I gave it to one of them for a laugh one day and it made such a difference that's all I've bought for them ever since.

Now where's my timing light?

Please tell me that you're not going to fettle your lawnmower for extra speed? And then create a tuned resonator to quieten the exhaust...

[wiggles]

[Phil Bate]

Please tell me that you're not going to fettle your lawnmower for extra speed? And then create a tuned resonator to quieten the exhaust...

I've already modified the governor to increase the operational RPM on the self propelled one, so it's now quite the challenge to run after it as it merrily chomps its way through whatever shrubbery lays before it


Just to note for those with poor-running (2.5HP) B&S engines - if it's consistently smoking and fouling the plug this can sometimes be down to a worn gasket between the carburettor and fuel tank. A circle area of the gasket forms part of the very simple fuel pump, and when it stretches with age it can cause the engine to run very rich. It's worth checking if your mower is a few years old, as the rebuild kit is nice and cheap

[MARKTHOMASBRAND]

Regards,Mark.

[untakenname]

Anecdotal but my previous car (Saab 9000) had a realtime knock count and it would increment massively for the next few miles if I filled up on the motorway as I'd use the cheapest fuel when normally I'd use the best, the Sab was quite advanced with it's ignition advancement as it would take it right to the limit under load before backing it down a touch.
My rx8 will go down to 5mph without stuttering on Tesco Momentum but if I use the cheaper one then it will only go down to 7mph before stuttering, as it's only an extra 3p per litre I'll go for the best fuel, had a shock when I visited a shell garage as it was 20p a litre more than the standard!

[SeriousSam]

That does vary depending on where your garage is. My local Shell station has a delta of about 8p between Fuelsave and V-Power, whereas the garage down the road from Brands Hatch has a difference of more like 25p per litre. Supply and demand seems to be the driver.

[HwAoRrDk]

The fuel I've found my RX-8 likes the best is Tesco Momentum 99. Not necessarily in terms of power, but the smoothest and most consistent. Never repeatedly found positive effects with any other brand of premium fuel (e.g. BP, Esso, Sainsburys). My experience with Shell V-Power has been the exact opposite to seemingly everybody here; the couple of occasions I filled up with a tank of it, the car ran poorly.

So long as I'm not planning on thrashing it (e.g. trackday), I will happily fill up with whatever bog-standard 95 RON fuel is available, and the car rarely ever has any complaints.

I think there's a lot to said for where and when you fill up. It would be interesting to see a scientific comparison between two extremes: a tank of regular from a modern, highly-frequented supermarket station where the fuel was delivered only 24h earlier, and a tank of premium from some crusty old backwoods brand-name station where the underground tanks are dirty, leaky, decades-old things and the fuel has been sitting around for several weeks because hardly anyone buys it. Or indeed the exact same brand and grade of fuel from two different areas of the country, supplied by tankers from two different regional fuel terminals.

[warpc0il]

My father worked for Gilbarco for a while and he was told to avoid filling-up at a station while the tanker was in.

The theory being that the action of filling the storage tanks stirs up any muck, which takes a while to settle back to the bottom.

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[SeeJay]

My local station - my supply of Esso Ultimate - blocks access to the forecourt whilst a tanker is refiling the tanks..no doubt due more to the 'elf 'n' safety aspect,rather than concern for what Dave has just mentioned above

[warpc0il]

Please tell me that you're not going to fettle your lawnmower for extra speed? And then create a tuned resonator to quieten the exhaust...

I've already modified the governor to increase the operational RPM on the self propelled one, so it's now quite the challenge to run after it as it merrily chomps its way through whatever shrubbery lays before it


Just to note for those with poor-running (2.5HP) B&S engines - if it's consistently smoking and fouling the plug this can sometimes be down to a worn gasket between the carburettor and fuel tank. A circle area of the gasket forms part of the very simple fuel pump, and when it stretches with age it can cause the engine to run very rich. It's worth checking if your mower is a few years old, as the rebuild kit is nice and cheap

My B&S engined mower is rated at 14.5hp, which is just as well as, when it's not doing grass cutting duties, the grass box gets replaced with a "pick-up" box (the empty chassis of a old washing machine) full of logs and tools, or fitted with a tow hook and chain to drag the trunks and branches of 40ft trees that I've been felling.

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[722Adam]

I'm too young to have any first hand experience of leaded petrol, but over the years I've run 3 engines on Super (Always V-Power unless I'm stuck) and while I've never noticed any power benefits (not that I expect them), all of them definitely ran smoother and 2 returned better fuel consumption as well.

I have to run my 8 on 99 now due to its custom map. Shell have recently increased V-Power from 98 to 99RON so I can keep using it. What it doesn't say in my warranty anywhere is whether I can run anything higher... Barrel of Sunoco anyone?

On a side note, I recently bought my first diesel car, I've resisted the urge to try the Super DERV so far, but I know that won't last long

[Pensive]

I can’t comment on power but I did multiple brim to brim tests on long journeys (I used to go to Manchester and back in a day from basingstoke) with a remapped 225 Audi TT - going between Tesco 95RON and Momentum 99 I determined conclusively that

1) the official Tesco Momentum “independent” report glossy was lies and more damn lies. They’ve since removed it from the public eye.

2) I got just enough extra MPG to offset the additional cost. I didn’t save a penny but I basically got to run momentum 99 free

3) the engine ran significantly smoother and of course my remap made it a bit more fun at the redline, again - a much happier feeling engine.

So I just ran momentum 99 forever.

I’ve yet to try the same with Rexy.