Are octane boosters worth considering?

[Jeags]

Hi all,

As I have exactly 46 days until I can FINALLY drive my 8, I have been considering the best approach regarding preventative maintenance and am planning to replace plugs and leads ASAP as I have noticed a slight misfire at idle (roughly once every 10 seconds but no pattern). I didn't pay much (£750) for mine, but would like to think that it is in surprisingly good condition for the price both cosmetically and mechanically. I was looking into the premixing option and have heard (correct me if i'm wrong) that if you premix, you need to use premium fuel as it lowers the octane in the fuel. I was wondering if it's worth premixing with regular unleaded and adding both an octane booster as well as 2 stroke as I assume this is cheaper than buying premium fuels and not adding an octane booster, but 2 stroke? Again, correct me if i'm wrong, i'm relatively new to this so would appreciate any advice!

Cheers,

Joe

[Bigblueknight3k]

Tesco 99 ron yes i premix and have a sohn kit fitted

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[warpc0il]

At the ratio of premixing (100-150cc per tank) there would be no measurable decrease in octane rating.
Higher octane fuels often include other additives that may, or may not, be advantageous to rotary engines.

FYI F1 racing regulations limit the amount that of oil that engines are allowed to consume, as this was being used by some teams to increase power/range.

[Jeags]

So would you suggest I try a few different fuels i.e. standard unleaded with 2 stroke and then try a premium like bp ultimate with 2 stroke and see if I can tell a difference or should I just stick with using premium with 2 stroke? Basically, all I want is to ensure I am doing as much preventative maintenance as I can as the need for a rebuild would lead me to have to find another car due to my financial situation (student starting apprenticeship this year). I could save, but would rather prevent!

Cheers.

[warpc0il]

On Shell V Power my mpg increased by a higher percentage than the premium of the pump price, plus my car runs more smoothly on it, so it would be a no-brainer for me - if only you could by the stuff here in NI.

Tesco used to sell Momentum in NI but withdrew it 4 years ago, and have been telling all their would-be customers that "there's no demand"

Sainsbury offer a 98 octane, which my 8 prefers over the 95, but it's not the same as V-Power

Maxol Fuels offered a premium grade at some stations, like to the one down the road from Kirkistown Track, but their website doesn't currently show it. Maxol are a Republic of Ireland company, so may withdraw from NI if Brexit goes badly.

[Ollie]

I run tesco momentum (because theres no other high octane alternative near me other than possibly some Gulf stuff maybe?) and premix. I once ran my car on normal unleaded for a week... And I noticed a difference in how it was behaving so went straight back to premium. For the price difference of 5 quid a tank? I'd rather be running premium and getting optimal performance than run unleaded and live with that noticeable performance difference.

[Honkytonk]

I'm a contrarian here, as I don't use the expensive stuff, although I premix. I put in one tank of V-power to see if it made a difference and it didn't (other than making me wince). If anything the idle was a little bit more lumpy, but I don't want to chalk that up to one tank of posh petrol. Other than the one tank I put in, it's been run almost completely on non-premixed cheap unleaded for at least the last 3 years. I don't think I've ever seen a hard reason to go for any premium fuel via any real world test other than wishy washy marketing blurb.

This is not to say anyone is wrong for running theirs on premium, or that I am right for running it on 'cheap' stuff. But it's worth remembering the quality of even cheap supermarket petrol in this country is incredibly high if you compare it to many other places around the world where 8's are sold.

I am quite fond of the concept of mechanical equilibriums that are built up by machines over time. If you use the car regularly, like me and my cars previous owners, then that is possibly more important than if you take it out once or twice a month. And if you're kny taking it out once or twice a month the extra money per fill-up probably won't add up to much!

TLDR; Give it a go if you want, but I don't think they're required.

[Ollie]

I suppose the extra 5 quid a week or so adds up to a whopping 250 quid a year if you drive it all year round!

[Bigblueknight3k]

There is tests done on the fuels most a waste of money top was tesco 99 octane have a look on youtube

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[jondkent]

I tend to run Tesco's Momentum as I have noticed a difference with that compared with 95 RON, plus is pretty cheap. However the most difference I have seen is with V-Power, but not available locally. Always premix btw.

Jon

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[GreySilver Beast]

My car is Mapped for different Fuel Ratings

[RenesisRaceBuggy]

Most piston engines can keep advancing the ignition, until knock is detected, and then back off a bit, in order to get the maximum benefit from higher octane fuels.

Not so for the rotary, as by the time knock is detected, it's all too late...

Also there's very little additional power to be gained from advancing the ignition on a rotary anyway.

[New Duke]

I'm a contrarian here, as I don't use the expensive stuff, although I premix. I put in one tank of V-power to see if it made a difference and it didn't... and loads of other good points I'm just snipping to shorten the quote!

I read that it takes time or a battery disconnection/manual reset for the RX8 fuel trims to reset. So a single tank full, especially if it's blended with some regular unleaded in the tank, may not have been enough to test it.

I'm doubtful whether higher octane makes a difference to MPG or engine/fuel system life. There are way too many variables to test it outside of a lab. Aside from having a smoother idle, the only anecdotal experience I have is that I always run on Tesco 99 Momentum and on occasion when having to fill up a very empty tank (like less than a litre left) on 95 RON due to limited fuel availability, the car has been very lumpy and more than once stalled before exiting the fuel station. Both stalls were when filling up after very long 200 mile drives (another variable!) and the engine sorted itself out a while later. I doubt the fuel trim could even have changed that quickly, but it left an impression.

Anecdotal evidence is all we really have to go on though. And I certainly wouldn't buy any of the shelf octane booster additives.

[PeteH]

Octane rating has nothing to do with fuel trims. The trim should be almost* entirely unaffected by the type of fuel. The octane rating can influence ignition timing, but not on the rex because, as Dave says, the rex doesn't push the ignition timing anyway.

*It depends on the exact details of the fuel blend, the calirific value, and the stoichiometric ratio, all of which are pretty much unrelated to the octane rating.

[acegeezer]

.. also the tickover of a rotary is not smooth, it has slightly variable revs notable in the sound .. what makes you think it's a misfire?
Get an OBD2 reader and look for any fault codes.. and I had my R3 for 6 years.. tried all the fuel from the basic 95ron to Vpower the higher octane stuff did nothing, so 95 all the time for me

[Honkytonk]

To clarify for OP - you don't need to use premium if you premix.

Whether you should use premium is a matter of much debate

[Devon_Fourie]

On Shell V Power my mpg increased by a higher percentage than the premium of the pump price, plus my car runs more smoothly on it, so it would be a no-brainer for me - if only you could by the stuff here in NI.

I also always use shell v power now as I also get a range improvement and smoother running (with pre mix). I tried Tesco momentum as it was the closest petrol station while out and I was quite disappointed at the low range I got, it felt the same as using Morrison’s regular fuel.

[Jeags]

.. also the tickover of a rotary is not smooth, it has slightly variable revs notable in the sound .. what makes you think it's a misfire?
Get an OBD2 reader and look for any fault codes..

Ah, I could be wrong then. I bought an OBD2 reader and nothing came up but it was only a cheap one which I assumed was not much good unless there is an obvious issue. It's probably me being too picky then, it idles smooth appart from a little splutter now and again so it may be nothing to worry about if it's not showing on OBD2. Again, I'm new to all this so it's probably me!

Cheers

[Jeags]

And I certainly wouldn't buy any of the shelf octane booster additives.

What's wrong with off the shelf booster additives? Again, I haven't a clue but am just trying to consider as much as I can.

[GreySilver Beast]

Tesco 99ron isn't the same as Shell 99ron Vpower

The Tesco version reminds me more of top end 97ron you get from BP

My first RX-8 ran on 95ron for the first 3yrs of it's life, but then they changed it slightly and the car just didn't like that grade of fuel, so changed to 97ron and what an improvement on the smoothness of the car

The second RX-8 was an R3 and was always more than happy on 95ron and in fact there wasn't a scrap of difference when using 97ron or above and the only time I put Super in was on Track Days

My current car is a completely different animal to the RX-8

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[warpc0il]

And I certainly wouldn't buy any of the shelf octane booster additives.

What's wrong with off the shelf booster additives? Again, I haven't a clue but am just trying to consider as much as I can.

Many (most?) are "snake oil" and do nothing other than take your money.
Some contain ingredients that are incompatible with rotary side seals and could cause long-term damage.
None are certified by the manufacturer as being tested safe on the Renesis.
The rotary engine doesn't benefit from higher octane anyway and the smoother running associated with V-Power etc is probably related other components in the fuel, not just the octane, which is why supermarket premium fuels make so little difference.

[Honkytonk]

And I certainly wouldn't buy any of the shelf octane booster additives.

What's wrong with off the shelf booster additives? Again, I haven't a clue but am just trying to consider as much as I can.

I didn't say this (yet somehow you've quoted me ), but Warpcoil's comments are accurate. Some of them may make no difference or have arguably marginal benefits in a piston engine. The Renesis is not one of those, so best not to feed it stuff that's not proven to help (unless you feel like doing that for everyone else's benefit, in which case, good on you and I hope you've saved for a rebuild )

Things like Cataclean or (good) 2-stroke oil are proven beneficial through the 15+ years of experience listed on the forum.

Again, would like to state that I don't disagree with people whose cars run better on the posh stuff. It's your car, you know it best.

[Jeags]

I use Optimax in the race car with Lucas Octane Booster.
At Brands a couple of weeks ago I did the first race and had a slight mis just above 9K, on topping up for race two I remembered to put the booster in. Result was the mis went and people reported more flame

OK, seriously now.##

Be very very careful adding octane boosters as many contain oxygen and can change the map leading to issues.
I investigated this with Lucas and found that they do not incorporate oxygen plus they were the only brand I found that actually said "suitable for Rotary engines"

[Jeags]

I didn't say this (yet somehow you've quoted me )

Sorry! On phone squinting at screen so it isn't the easiest to get right! Thanks for the advice though, I'll have a play with fuels when I'm driving it!

[Mazzarx8]

My impression is that the use of higher octane fuel in these rotaries is down to the fact that you get a cleaner burn reducing the amount of possible carbon build up, as well as v-power ect using fuel additives to clean the fuel system and possibly help remove said deposits