OK this is just a general theory working around my head so bear with me.

My engine normally runs ron 95 unleaded as probably 99% of engines do,,from the Shell web site it says that:-

Shell V-Power is a high octane fuel (99 RON) designed to help maximize the performance of many modern engines with adaptive spark timing capacity.

Now if my ignition system can not tell if ron 95 or 99 then it would suggest that I would have no gain from trying the higher octane fuel.

Am I correct in thinking the higher the octane the more advanced the ignition is shifted and lower octane the more the whole ignition map is brought closer to TDC?

OK now to my thinking theory!

The ignition system is Sierra Esc-Hybrid with a normal setting for 95 ron fuel. There are two wires that would adjust for 91 ron fuel if I ground them.

So what if I measured the spark point with a degree wheel and timing strobe on standard settings and found it fired 10 degree BTDC.

Then set the system for 91 ron and found it fired at 6 degree BTDC. Then with a new bracket with adjustment to move the crank sensor, moved the sensor to set the timing back to 10 degree BTDC.

Now if the wires are put back to normal, I would expect to see the ignition move to 14 degrees BTDC. Would this be better for the V power higher Octane fuel.

Does anyone know if the whole of the ignition map moves the same amount across the range the same amount for a given increase in ron?

On an engine that does 100 bhp would there be much improvement worth bothering with?

Adrian

[Edited on 11-6-10 by AdrianH]

Tuesday.

megajolt

don't bother - the only way you'll get any real gain is to up the CR [compression ratio] of the engine (e.g. skim the head)

and if you can up the CR enough to make full use of a 99RON fuel (btw tesco also sell 99) - you won't be able to use 95RON....

[Edited on 11/6/2010 by mcerd1]

Tuesday should have it sorted.

I have megajolt but needed to swap to MAP so never bothered.

Good point on the CR did not consider that. But it depends on what you mean by real gain, I have read people have paid hundreds to get a few percent extra!

Adrian

[Edited on 11-6-10 by AdrianH]

if you run it on 99 you might find you have to change the ignition just to stop you lossing power

your engine has been built to run on a min. grade of fuel and they've picked a CR to let it do that
high CR engines will give you the best power/ torque/ efficency - but need high grade fuel for avoid 'knocking' [aka: detonation, pre-ignition, pinking]

the ignition timing is just the fine tunning - have a read at this: linky (probably more than you ever wanted to know )

[Edited on 11/6/2010 by mcerd1]

[Edited on 11/6/2010 by mcerd1]

I hope my engine never kocks....

^^ edited

I run a fairly pokey Saab Turbo - with active sid computer so I can monitor all of the engine functions, including knock count.


If I ring its neck out I collect more knocks (knk) and more misfires (mifi)


If I use Morrison 95ron council pop, its knocks and misfires no more than Shell Volumexpensive.....during normal daily motoring.

Day to day running is fine, Volumex when I intend ringing its neck out.


Not sure what engine you run, but my 2.0 Saab runs fine on council pop, with Volumex as an expensive option for trackdays and neck ringing sessions.


If you trackday your car use shell, if you dont just use Morrisons council pop its cheaper.....


My knock count only climbs at wot 5000rpm + in fourth, everything below that doesnt count.

Must stop reading and thinking about things at this time of night.

Read the article and it is interesting, especially about all the hype and false claims given by suppliers.

Back to my old CVH engine and this is just for your thoughts, the car has a CR of 9.3:1 was designed for leaded 97 ron but would run unleaded 95 ron, but no adjustment was given or allowed for between the two. It does not have a knock sensor

The Pinto or OHC engine was 9.5:1 and static timing changed by 4 degrees when going to 95 ron. The same change for the 1.6 CVH. It was just the 1.8 CVH that never changed as it had the particular ign module.

That was why I considered it.

Adrian

T66, Seen your post after posting mine, Noted for day to day use I do use the cheap stuff generally Shell/asda cheap.,was just wondering about the benifits from the 99 ron and how I might use it just to keep up with the more modern engines and faster cars a bit better.

When I blow the engine, then I go Zetec!


[Edited on 11-6-10 by AdrianH]

It will give a small increase in power and you can always run plane jane unleaded by using the setting that was before for 91 ron

I ran a MR2 turbo for a while, these have electronic boost control. When on optimax it ran a few more PSI of boost above lesser fuels, it made quite a bit of difference but then this was probally worth 10hp/PSI.

On lesser cars I have never really noticed any difference in power.

There is an optimal ignition moment for a particular engine, taking most aspects of the design into account (like CR and gas flow) Assuming that the original manufacturer has designed the engine properly (i.e. to run without knocking, even under high load, with the recommended fuel), then there is no benefit to be had from higher octane fuel, except maybe in turbo engines where more boost can be applied without detonation occurring.

In Adrian's case, tricking the engine ecu to advance the timing when using higher octane fuel will probably not make much (if any) difference to a standard engine's power. However, if the CR is raised it will allow more advance to take advantage of the higher CR and produce more power.

HTH

Most newer cars adapt to the type of fuel being used, by adjusting the timing when knock is detected, hence running a high grade fuel gives better economy and power, (talking about high power jap engines here with 11.5:1 compression etc from the factory)

But because you don't have a knock sensor I wouldn't play with the timing unless you have a way to detect knock etc, so just keep to your normal fuel.

[Edited on 12/6/10 by nz_climber]

If your engine is knock limited, i.e. the ignition is retarded from the optimal point to prevent knock then higher octane fuel plus ignition timing adjustment is likely to show some improvement.

If the engine is not knock limited, the higher octane fuel could actually show a power decrease, since the ignition timing will need to be advanced to compensate for the slower burning fuel. The more ignition advance you have the greater the pumping losses because more time is spent with the fuel burning whilst the piston is still rising.

Lots of advance certainly isn't something to be desired.