Petrol again!

[Robin Fairservice]

From Wikipedia:
'There are different conventions for expressing octane ratings, so a fuel may have several different octane ratings based on the measure used. Research octane number (RON) for commercially-available gasoline varies by country. In Finland, Sweden, and Norway, 95 RON is the standard for regular unleaded gasoline and 98 RON is also available as a more expensive option. In the UK, ordinary regular unleaded gasoline is 91 RON (not commonly available), premium unleaded gasoline is always 95 RON, and super unleaded is usually 97-98 RON. However, both Shell and BP produce fuel at 102 RON for cars with high-performance engines, and the supermarket chain Tesco began in 2006 to sell super unleaded gasoline rated at 99 RON. In the US, octane ratings in unleaded fuels can vary between 86 and 87 AKI (91-92 RON) for regular, through 89-90 AKI (94-95 RON) for mid-grade (European premium), up to 90-94 AKI (95-99 RON) for premium (European super)."

I have experienced conversion from Imperial to S.SI. units in three countries and they all now spell it "litre"!!!

[paul wilks]

Thanks for all this information, Robin. It is interesting and detailed.

So what do UK Javelin owners tend to use? I am with Drummond re Shell- I use it in my Ford (NOT Jowett!) Focus and swear it is cleaner and makes the engine 'livelier' but that might be just a perception/prejudice!
But what about the Javelin? What experience have UK owners had in using 'branded'/supermarket petrols?
And what about octane- premium or super?

Bear in mind my heads have NOT been modified- no hardened valve seats.

Thanks

Paul

[Keith Clements]

Having travelled in many countries in Jowetts my experience is that petrol is like beer, it depends how it is kept and made. The main issue these days is the amount of ethanol in the mix. Petrol is a complex mix of chemicals which is difficult to keep constant both in manufacture and storage. So do some manufacturers, distributors and retail outlets do better than others?

[Drummond Black]

Yesterday ( Tuesday ) on our return trip from the club AGM ( and a Rover 75 technical meeting in the Wolverhampton area on Sunday ) we met Paul Wilks at Lymm to do a little bit of spares swap we did, once again slightly discuss fuel. With the volatile position in Scotland regarding the massive Grangemouth petrochemical complex still not settled ( It MAY get worse ) I decided to fill up the Rover on the way north in case I encountered shortages later. The tank was quarter full when we pulled into Gretna Shell Station only to discover that V-Power diesel was sold out and that 95 Octane diesel was in low supply. I filled up with the ordinary Shell diesel ( I normally run on V-power ) and before leaving the fuel station I reset the car computer. 110 miles later at Kirkliston after similar driving conditions we registered a drop of 7 MPG.

Now when I was at the Rover event I had the car on the T4 computer which has the ability to check all functions and running conditions. It was amazing the little faults that showed up and were easily reset. (Must get one , but at £ 3,500.00 !!!!!! ). It did report that the engine management system was functioning correctly..

So, is it Octane figure, We were on Motorway for all the journey. You can draw your own conclusions.

Drummond

[Chris Spencer]

With the amount of diesel that I go through in the works truck I just stick to whatever is available at a reasonble price - although work picks the tab for this - just as well I can fill 3 to 4 times in a week at a cost of £90 per tank - as you can guess I cover some pretty significant mileages in a year (45,000 this year on business alone) - with the classics I again just use whatever is reasonable at the time I fill up and dont bother with the fancy / more expensive brands. However I always add a shot of Castrol Valvemaster lead replacement this is now avilable with a added octaine booster and makes a significant difference to how the cars perform - works as well in the Javelin as what it does my V8 3.5 Rover

[Nick Webster]

V-Power diesel was sold out and that 95 Octane diesel was in low supply. I filled up with the ordinary Shell diesel ( I normally run on V-power ) and before leaving the fuel station I reset the car computer. 110 miles later at Kirkliston after similar driving conditions we registered a drop of 7 MPG......So, is it Octane figure, We were on Motorway for all the journey. You can draw your own conclusions.

Drummond

Diesel is not sold by Octane rating. Discussion of the merits of diesel grades are best not confused with those of petrol.

Nick

[Drummond Black]

Well Spotted Nick, My idea of a bit of BAMBUZALING ????

Seriously, the point was the basis of the quality of the various fuels we are expected to use.

Drummond

[Keith Andrews]

Ideally higher the compression.. and thats the Dynamic compression ratio... or in basic terms, the max cylinder pressure at a given loan and rpm....the higher the octane of the fuel require for efficient burn.
So if u have an old veteran/ vintage car that was designed to run on British Pool fuels between 1936 and 1954 (from memory) that in reality had a octane rating of mid 60s .. they have very low compressions....measure up a stock bradford, CC the heads and u will find a CR around 5.7... excellent for that fuel.
Now run any engine outside its compression/ octane match and it will not run as efficiently , be it mpg or power.

The other factor besides cylinder pressure is the speed of the flame in the chamber from ign thru to max cylinder pressure.
the idea is the get the max explosion at the same time as max cylinder pressure....
This is timing, the advance curves.
higher the octane the slower (yes slower) the burn .. therefore u need more advance.
Also when comparing pre war fuels, and post war leaded fuels compositions with modern fuels, this also results in slower burns.
So increase compression, reduce advance curve, and visa versa... and increase octane , increase advance curve.

Every engine is different, even a rebuild / re bore changes the combustion dynamics and compression ratios....
The area in the cylinder where max cylinder pressure is is between about 12 and 18 deg ATDC....less than this the 'balance' between engine resistance to push the crank over (like pushing a piston in a short block down at TDC) is to great for efficient power/ economy... greater and the piston is too low in the the cylinder to have good compression at the point of max explosion.
And withing this 12 to 18 deg is a very small window of only 1 to 1.5 degs that the particular engine is actually efficient in.

Now there is another factor, the specific gravity (SG) of the fuels higher the octane, low the SG thats weight per volume...and then modern OH fuels takes that even lower...
What does this mean at the pump, putting aside the timing issue for now.
lower the SG then the LESS Potential energy per weight.... ands keep in mind we buy our fuel by volume, not weight.
So when buying more expensive high octane fuel u are buying less potential energy per gallon...
Add that to putting in a car not requiring that octane and u get power loss and big drop in economy.
And visa versa, try to 'save' money by putting low octane in a hi octane engine, and it runs the fuels so inefficient again cost u more money (and gums up modern (post mid 1970s) EGRs causing bigger issues down the line.

On the other hand one can get around and LIMIT this extra cost, false saving, by altering your timing curves.....
Some modern ECU monitored engines will do this automatically, but u are still running a fuel outside the basic design of the engine and even that will not full make up the efficiency discrepancy.

[Forumadmin]

I really need Scott to finish his post mortem examination of Buckwheat after its epic journey. But we had some baffling experiences with fuel economy. The car suffered from numerous fuel and timing issues and enormous variance in terrain, temperature, humidity and altitude.
Frequent examination of plugs was also baffling as once we cured the flooding carbs the plugs went to white from being black yet fuel consumption remained the same or even went up.
Was it that the main jets were too small for the tuned engine and larger capacity? Was it the lack of vacuum advance? Was it a too retarded ignition? Perhaps Scott will enlighten me on further examination .

[Keith Andrews]

Forget reading plugs to set mixture with modern fuels.....only reliable way now is invest in O2 sensors and a data logger (like a Innovate LM 1 or LM2 or DIGITAL AFR meter
There is really nothing one can do when traveling between say snow line and sea level.. if tuned for sea level and getting up close to snow line, one goes lean and runs hotter... and visa versa
lean mixtures burn slower so need more advance...
basically one aims for AFRs in the ball park of
idle bit lean low to mix 15s max
power circuit mid 11s to mid 12s
Cruise 15 to around 15.7 max without injection and ECU THEN once in the ball park start to play with timing at diff loads and speeds to dial/establish in tuning specs..

The most common issue is ppl get their engines dialed in.. then keep on tweaking what is about as close as possible without a 10 million dollar investment in a laboratory... and since they have hit the tune before , they generally refuse to accept that the previous correct tune is right, and spend the next 10 yrs with tuning issues... instead of simply changing oil and se4vicing for that time.
Sort of fixing something thats no broke

[Forumadmin]

On my travels picked up this from Classic Driver NZ, May 2013.

Oh and Scott did examine his Jav and found the dissie drive shaft had become diconnected from the rotor and weights. Amazing the car went at all, let alone had variable fuel economy.

Petrol in NZ was about NZ$2.13 (£1.11) per litre for 91 Octane.