Ah, back to Shell again :)

No idea how you guys can say you can feel the extra power.

I mean cmon - what extra bhp are you getting? 1%? 2%? 20%?
 
BP 97 is **** , never going to touch it again. Last week i filled up on it as i was too far from my optimax / v-power station and the car ran like a dog. It was as if my ecu was cutting the fuel on full boost and the flat spots!! must have been 30bhp down on power... was VERY noticable, we thought maybe a boost hose was loose or something of such nature. Anyway couldnt work it out and it was time to re-fuel.... this time i had filled up on v-power and the car was back to normal: BANG power back! as simple as that. Never going to touch BP again.
 
I was under the impression that as long as the engine had a knock (detonation) sensor then the ECU would constantly change the timing untill it was just on the limit of detonation thus always maximising the power available.
So no matter what the ECU was originally mapped for if you add a higher octane rated fuel, the ECU, via the Knock sensor, will automatically advance the engine timing to account for the fact that higher octane rated fuel will not detonate as readily at advanced timings, thus you will get better perfomance and more power.
Conversely if you have a low octane fuel the ECU will back off the timing so you will loose power and performance.
 
Entai said:
I was under the impression that as long as the engine had a knock (detonation) sensor then the ECU would constantly change the timing untill it was just on the limit of detonation thus always maximising the power available.
So no matter what the ECU was originally mapped for if you add a higher octane rated fuel, the ECU, via the Knock sensor, will automatically advance the engine timing to account for the fact that higher octane rated fuel will not detonate as readily at advanced timings, thus you will get better perfomance and more power.
Conversely if you have a low octane fuel the ECU will back off the timing so you will loose power and performance.
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There comes a point where the ECU will stop advancing. This is why if you stuff race fuel in a car wanting 97 ron - it wont make any more power.

Also there comes a point where the fuel is so resistant to burning that it burns too slowly when ignited. This leaves a lot of residual heat in the chamber, and things can start melting.
 
Entai said:
I was under the impression that as long as the engine had a knock (detonation) sensor then the ECU would constantly change the timing untill it was just on the limit of detonation thus always maximising the power available.
So no matter what the ECU was originally mapped for if you add a higher octane rated fuel, the ECU, via the Knock sensor, will automatically advance the engine timing to account for the fact that higher octane rated fuel will not detonate as readily at advanced timings, thus you will get better perfomance and more power.
Conversely if you have a low octane fuel the ECU will back off the timing so you will loose power and performance.
Click to expand...

lol no way, that would be very dangerous, driving the engine into detonation all the time would probably give it a life of about 1000 miles :p

Besides which, running the ignition timing advanced to the point just before knock occurs will not give you maximum power anyway. There is a band between optimal power and knock where you can add advance but with no power gain and simply reduce the margin for safety. This band happens to be smaller on a turbo engine than an NA though.

Either way, knock sensors are there purely as a safety device, most will retard the base ignition timing if they detect knock, and thats it.
 
Agreed, if you have a more advanced system that detects knock through the spark plugs you should have an ECU that can correctly advance or retard the ignition as appropiate. I don't think many cars have this though

Saab's have for the last 13 years, but the only others I know of are the very latest BMW's as they specifically advertised it on the M5, I'm sure there would be a few others too.
 
Clarkey said:
lol no way, that would be very dangerous, driving the engine into detonation all the time would probably give it a life of about 1000 miles :p

Besides which, running the ignition timing advanced to the point just before knock occurs will not give you maximum power anyway. There is a band between optimal power and knock where you can add advance but with no power gain and simply reduce the margin for safety. This band happens to be smaller on a turbo engine than an NA though.

Either way, knock sensors are there purely as a safety device, most will retard the base ignition timing if they detect knock, and thats it.
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I have been reading up on this and chatting to some collegues here at Millbrook in the Powertrain and Emissions departments.

They pointed me to this web page which explains it all pretty well.
Click Here

The web page deals particularly with Scoobies, but apparently pretty much every modern car has a knock sensor as it is a major part of the emission control system.
 
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I'll need to give the V-Power stuff a go as my car has been responding a little lumpy through the revs recently. The car has been super chipped and the ECU remapped so hopefulled the V-Power fuel will makes a difference.

Nearest Shell garage from me is 8 miles away.
 
Entai said:
I was wondering that as well no-one here has ever heard of spark plugs detecting knock???
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It requires a direct injection system. The Saab's use a direct injection cartridge instead of leads from a coilpack and the DI cartridge has built in microprocessors to do fancy stuff.

A brief technical overview was provided to me by a fellow Saab member

Knock control

A high compression ratio is favourable for engine efficiency and thereby fuel consumption. The tendency of the engine to knock increases with the compression ratio, however, so a compression ratio is selected that is as high as possible with regard to the knock resistance of the engine's recommended fuel. Knock control in modern engines is not a safety function but a normal one. Therefore, there is nothing wrong with knock control being active during normal operation.

Trionic T7 does not have a conventional knock sensor. Instead, the ignition discharge module analyses the ionization current across the spark plug gap on all cylinders and sends a knock signal from each cylinder to control module pin 38.

From the combustion signals, the control module will be aware of which cylinder has fired and if a knock signal above a certain level is registered at the same time by the control module, it will gradually retard the ignition for the cylinder in question until the knocking ceases. Timing correction then returns slowly to zero.

Note
To ensure optimal engine performance, the correct spark plug should be used for each respective engine type. See Technical data, Spark plugs (157).


If the mean value of the ignition retardation on all cylinder exceeds a certain level, fuel enrichment will take place. If the mean value of the ignition retardation on all cylinders increases further despite fuel enrichment, the maximum permissible air mass/combustion will be limited.

The control module expects the knock signal to be at a certain level as the spark is produced, so it will therefore start the actual knock detection in the respective cylinder only after the spark has been produced.
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Presumably nicked from a technical manual somewhere. It also works the other way and will increase the timing and boost when better fuel is detected. Saab have one of the only cars which is designed to run on Bioethonal and that uses *exactly* the same T7 ECU as on the current 95's. The system is that good it simply set's itself up to run the 105ron or so which bioethonal is. No adjustments required.

Not many OE ECU's can do that, but I think Saab might have the DI cassette design patented.
 
merlin said:
No idea how you guys can say you can feel the extra power.

I mean cmon - what extra bhp are you getting? 1%? 2%? 20%?
Click to expand...

Aye no difference from Optimax that I can see. Obviously I get a load more power than 95RON with V Power
 
Cheers for that description of the Saab system Stonedofmoo, I'd not heard it could be done like that. :cool:

I think the Subaru method I linked to above is patented as well, I guess soon there will be other ways of doing it as it does seem to be becoming necessary to have active ignition timing to help balance emisions and power delivery across the rev range.
 
merlin said:
No idea how you guys can say you can feel the extra power.

I mean cmon - what extra bhp are you getting? 1%? 2%? 20%?
Click to expand...

Like I said, in my case it's probably because I hadn't driven the car for a couple of weeks. I literally took it straight to the garage to fill up (was virtually empty, so very little mixing wth the Optimax I already had in there).

The thing is though it continues to feel really lively and responsive, more so than on Optimax :/

It's probably due to the cooler weather TBH.
 
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