What Petrol & Additives do you use

[TronSpec 0]

Since my swap I've being using premium 95 - 96 octane petrol with the odd tank of 98 when I go through aucks.

But the other day my mrs put a tank of 91 in and my car still just seems to run the same. No pinging, missing or hesitation.......If I'd done this with my old m20 motor it wouldn't like it.

So is it okay to run my m50 motor on 91 as it's cheaper and just put in octane booster every now and then???

Edited January 5, 2007 by MrHamWallet

[kerrynzl 3]

Hey Gary, the cheapest octane booster you can buy is the 98octane fuel [it's already premixed]

Most octane boosters cost $10 a bottle , whereas 98 is usually 4 to 5 cents more than 91 You have to buy 200 litres of 98 to justify the costs of the booster [most boosters don't make anywhere near that amount]

You can make your own booster: 82% gasoline,14% ethanol/methanol,2%Methylethylketone[MEK],& 1% acetone [these percentages are by Weight not Volume]

You can also add up to 20% Toluene to your fuel [but it disolves all the rubber lines etc in you fuel system]

Disclaimer: This is Dangerous sh*t, F**king with petrochemistry-do so at your own risk

[rxsumo 33]

Pinking is generally caused by the MON count not the RON count.

RON is what is usually displayed at the pump.

The MON value is generally a maximum of 10 point below the RON figure, however it can be quite a bit closer than that.

So depending on who's gas you put in the car, and where that gas was sourced from, you might find that the car will run without pinking, however the horsepower may be down as the Engine Management knocks back the timing.

An example of this was a couple of years back, we were running the Si down south. We had been running on Wellington and Christchurch fuel which I suspect is supplied by BP's Perth plant (or Challenge's Imported fuel), we gassed up Shell in Twizel, and the car started pinking like crazy. We put a couple of bottles of octane booster at Invercargill....no difference. We put up with the pinking until we got back home.

I rung up Shell to advise them of potentially crap gas at Twizel, and ended up speaking to one of the tech's that had done a clubnight for the car club. He checked the sample spec sheets for the gas that was delivered to Twizel, and reckoned that he would have been surprised by the results we had. In his opinion the high compression engine in the Si, would probably want a MON count of 88-90 (Car was designed to run on 100 Octane European Fuel), and the MON count of the gas at Twizel was right on the MON count of 85. He said that this probably explained why the octane booster didnt do squat, as it probably pulled the RN count up but didnt do enough for the MON count.

The other point to consider is that 91 isnt really setup for FI cars, its of a weight that is more suited to carbies, the premium fuel is weighted for best flow through injectors.

My attitude is, to run the best fuel you can in the car. The XR8 and the BMWs, get BP Ultimate as a first preference, and then anybodies 95/96 after that.I wouldnt bother octane booster or any other additives.

Edited January 5, 2007 by rxsumo

[Grant 4]

Since my swap I've being using premium 95 - 96 octane petrol with the odd tank of 98 when I go through aucks.

But the other day my mrs put a tank of 91 in and my car still just seems to run the same. No pinging, missing or hesitation.......If I'd done this with my old m20 motor it wouldn't like it.

So is it okay to run my m50 motor on 91 as it's cheaper and just put in octane booster every now and then???

Gary

The M52 ECU will adjust to the grade of fuel, and run ok on 91, however your power output will be down. I am assuming that the M50 does the same.

The M20 ECU doesn't adjust as well (or maybe at all).

Cheers

Grant

[Docile 64]

ive had a little experiment onmy m50..

after i bought it i filled it up with premium for about a month... then after that i decided to see what's the difference with 91 on my engine after making sure that i was almost on empty before i put in 20 bucks from mobile, then from shell oh man what a waste of 40 bucks!!!

right from my exit from the gas stations i felt my car a bit slugish and had to accelerate more often and resulted in a decrease in milage / litre. after my experiment i went back on premium and the engine became more responsive and can notice the power difference

oh and da only additives i use are injector cleaners

Edited January 6, 2007 by Docile

[kerrynzl 3]

Pinking is generally caused by the MON count not the RON count.

RON is what is usually displayed at the pump.

I think you are confusing yourself here! Pinking is caused by the OCTANE being too LOW for the cylinder pressure regardless of whether you use a MON or RON measurement [scale]

MON or Motor Octane is a mechanical calculation, whereas RON or Research Octane is a chemical calculation [measured as a percentage against Iso-octane being 100%]

Pump Octane [uSA rating] is a mean average of both MON & RON. New Zealand uses a RON scale

Grant seems to have answered the question. It sounds like a M52/M50 has a knock sensor to retard the engine on low octane fuel. M50's & M52's have 11:1 compression [race-engine compression ratios from yesteryear] on 91 octane the engine would be too far retarded for power.

Additives that are oxygenates sometimes cause the O2 sensor readings too lean out the engine also lowering the power

[kiwi535 538]

the m20 and M30 have no adjustment for octane ,but i think the m50 does have knock sensors and so alters the timing until the knocking stops.I run 91 in my M30(Its what BMW recommend)and even up Ngaio gorge in a slow line of traffic I havent heard any pinking.The car feels smoother and nicer on 95 and gets fractionally better economy.98 doesnt feel any different than 95..If i go on a gymkhana or similar i use 95 because i will use more throttle (at lower revs) than usual.

[rxsumo 33]

Pinking is generally caused by the MON count not the RON count.

RON is what is usually displayed at the pump.

I think you are confusing yourself here! Pinking is caused by the OCTANE being too LOW for the cylinder pressure regardless of whether you use a MON or RON measurement [scale]

MON or Motor Octane is a mechanical calculation, whereas RON or Research Octane is a chemical calculation [measured as a percentage against Iso-octane being 100%]

Pump Octane [uSA rating] is a mean average of both MON & RON. New Zealand uses a RON scale

Grant seems to have answered the question. It sounds like a M52/M50 has a knock sensor to retard the engine on low octane fuel. M50's & M52's have 11:1 compression [race-engine compression ratios from yesteryear] on 91 octane the engine would be too far retarded for power.

Additives that are oxygenates sometimes cause the O2 sensor readings too lean out the engine also lowering the power

What I was trying to relay, was the information given to me by the Fuel Company Engineers.

As you have said MON is the mechanical calculation, which is as I understand, is really what is important to the engine. The RON count and the MON count dont necesarily have a linear relationship. So you may have a fuel that meets the minimum RON count of 95, but the MON value may not be high enough to satisfy the needs of some high compression engines.

[Docile 64]

so which fuel company should we fill up on in respect to best MON? or does it depend where abouts they import their fuel? i usually fill up at either shell or gull

[cainchapman 0]

95 without a doubt would be the lowest I would run any 3 series E36, 5 Series E34 or newer.

I'll post them again.

The first is the 540 on 95. 165kW

The second is the 540 on BP Ultimate (98). 172kW

I'd only run it on 91 as the last resort (as I had to run my supercharged Commodore in the Outback of Oz).

[kerrynzl 3]

so which fuel company should we fill up on in respect to best MON? or does it depend where abouts they import their fuel? i usually fill up at either shell or gull

[/quote

Silly question mate! All fuel in NZ is rated as Research Octane [RON], go for the highest number when in doubt [Too low can damage an engine]

The best place to go! Without a doubt Challenge on Manakau Rd Pukekohe,or BP at Broadlands Rd in Taupo

They both sell race gas from the pump [you need a race license though]

[tintop 10]

Octane booster is a total waste of money. When they say "boosts octane by 5 points!" it means your 95 octane fuel now becomes 95.5

The tiny amount of toluene in these octane boosters does sweet f all, you need a whole lot more than they provide in the tiny bottles.

[kerrynzl 3]

When they refer to 5 points they claim 95 to 100 which is bullshit [not out of a 500ml bottle]

Toluene is the main Aromatic used to boost octane in unleaded fuels , but they use up to 30% in unleaded race gas [CAMS V8 supercars], the sh*t dissolves rubber [Hence why all the Mk3 cortinas caught fire when 95 unleaded was introduced in NZ,Those clever Pommy designers put a rubber fuel line above the sparkplugs]

I've used a Toluene brew to soften tyres, it also disolved my mobile phone when I got it on my hands

The only thing Octane Boosters improve is the retailers turnover!

[hotwire 352]

Octane booster is a total waste of money. When they say "boosts octane by 5 points!" it means your 95 octane fuel now becomes 95.5

The tiny amount of toluene in these octane boosters does sweet f all, you need a whole lot more than they provide in the tiny bottles.

From my experience a few years ago while owning an Audi Quattro coupe (which I did for a number of years)- 5 cyl 10 valve engine.

On a hot day that car was almost undriveable with ANY of the main 4 fuels,- engine temp would go high & it would rattle like hell if not driven very carefully. Ran on avgas for a test - different car.

Used to run it on Challenge -that was a local station thankfully, & it ran ok on that. Still wasn't what it should have been but was acceptable. This was before any of the main stations had 98.

This was a bog standard car too so was not an engine/ timing issue. 10.5 -1 compression ratio

At that time Challenge was aparently importing their own fuel with an obviously higher octane rating albeit still rated as 95 on the pump. Don't know what their source is now though?

My old E12 520 (M20 engine) dosen't particually like it either but being auto dosen't protest too much - just becomes even more gutless. This car too runs like a gem on avgas!

98 obviously still the best option - thats what they are designed for but as said already- the later cars engine management will cope with the lower but at the cost of performance/ economy.