V POWER
It would be interesting to find out what the highest MON rating was as I believe it is the difference between RON and MON that dictates how sensitive the fuel is to charge temperatures. Obviously this doesnt matter during winter so much but during the summer months (do we get them?) it will have an impact on the octane requirement of the engine.sdminus wrote:Both tesco and v power are bulked out with mbte for the magic 99 RON number. I bet the true MON value at the pump is quite a bit lower and varies a lot.
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Ian (DaOne)
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slarty bartfast
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ScoobieWRX
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Interesting. The Thorney test also reported some inconsistency for v-power compared to tesco99 and bp102 (http://www.thorneymotorsport.co.uk/tuni ... date.shtml).ESL wrote:I found another 2-3 deg advance over most of the WOT range on V-power cf Tesco 99. Worth about 10ish bhp. I have seen some variability on knock count with different batches of V-power though and it does seem sensitive to rebreathing.
What's rebreathing in this context Andy (...am I being thick here?)
Andy
The Thorney test wasnt using an EJ20 so will lose credence in the case of Subaru. It certainly doesnt reflect my findings, that my knock count over time is less with V-power than it is with Tesco99. Shell has the superior base stock, Tesco, as Spence has mentioned, achieves its RON value by the addition of biomass ethanol.Andy916 wrote:Interesting. The Thorney test also reported some inconsistency for v-power compared to tesco99 and bp102 (http://www.thorneymotorsport.co.uk/tuni ... date.shtml).ESL wrote:I found another 2-3 deg advance over most of the WOT range on V-power cf Tesco 99. Worth about 10ish bhp. I have seen some variability on knock count with different batches of V-power though and it does seem sensitive to rebreathing.
What's rebreathing in this context Andy (...am I being thick here?)
Andy
I might be using the wrong word, but by rebreathing I meant my crankcase breathers are still connected to my induction path. With an instance of positive crankcase pressure, oil vapour is reinjected into the induction line. Some of it will condense on the intercooler piping and manifold walls but some of it will enter the combustion space with the fuel and air and effectively lower the RON of the charge. I suspect that is why I am getting inconsistent knock readings (some full throttle applications will just see green, a few will show reds on a knocklink). The knock count also varies between tanks. Fuel life is a much discussed subject, and some suggest its better to use fuel from a busy garage that is regularly changed. My car always runs an IAM of 16 though, so the ECU is always happy to maximise the advance, and its had 3 hard years since I rebuilt it without letting go.
As a recent experiment, I have been adding small amounts of NF to a tank to see the results. Just 1 ml per litre, completely cleans the knock trace up. I'm going to try less to seee how far I can stretch it, but its effect is significant.
I have the same problem and came to the same conclusion as you , i sometimes have knock spikes especially if lifting off from full boost, i also think its oil vapour and blowby gases causing it.
My knock is displayed on my power fc but with Tesco 99 it will peak over 60, with V power it rarely goes over 40 and with V power and lucas octane booster is rarely goes over 20
My knock is displayed on my power fc but with Tesco 99 it will peak over 60, with V power it rarely goes over 40 and with V power and lucas octane booster is rarely goes over 20
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Sprint Chief
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Just to add to what Andy said about the limitations of the Thorney tests:
Those tests were carried out on standard cars. But, standard cars (even with closed loop knock control) have limited authority to advance the ignition. Manufacturers put in closed loop knock control so that if you get a batch of duff fuel, the car will adjust for it. But manufacturers like a safety margin, and they do not set up their cars to live too close to the edge of knock. Usually they will set the car up to be comfortably away from knock for the specified fuel (95 RON, or 97 RON etc). I say usually because occasionally even manufacturers make mistakes
The advantage of higher RON fuel is the ability to take more timing. If your ECU does not have authority to use that extra timing, which most standard ECUs won't, then you won't get much difference (as Thorney observed). If you remap your ECU to take advantage of the extra fuel, then the gains seen will be completely different to those Thorney found. Also, the potential gains from the fuel are MUCH larger through remapping than using the standard ECU.
As noted by Paul Blamire on scoobynet, the ethanol present in the Tescos 99 changes the effective AFR of the mix, because ethanol brings its own oxygen to the party On a forced induction car, leaning the AFR will almost certainly increase the power output, but at the expense of higher temps on boost. On a standard car, you are probably just eating into the manufacturers (usually big) safety margin. On a remapped car, you are probably eating into a rather smaller safety margin (unless the car is remapped specifically to Tesco 99).
In summary: the Thorney results are only valid for standard cars, not for remapped cars, and certainly not for cars remapped to a specific fuel. Furthermore, they are only really valid for the standard cars under test.
Spence.
Those tests were carried out on standard cars. But, standard cars (even with closed loop knock control) have limited authority to advance the ignition. Manufacturers put in closed loop knock control so that if you get a batch of duff fuel, the car will adjust for it. But manufacturers like a safety margin, and they do not set up their cars to live too close to the edge of knock. Usually they will set the car up to be comfortably away from knock for the specified fuel (95 RON, or 97 RON etc). I say usually because occasionally even manufacturers make mistakes
The advantage of higher RON fuel is the ability to take more timing. If your ECU does not have authority to use that extra timing, which most standard ECUs won't, then you won't get much difference (as Thorney observed). If you remap your ECU to take advantage of the extra fuel, then the gains seen will be completely different to those Thorney found. Also, the potential gains from the fuel are MUCH larger through remapping than using the standard ECU.
As noted by Paul Blamire on scoobynet, the ethanol present in the Tescos 99 changes the effective AFR of the mix, because ethanol brings its own oxygen to the party
On a forced induction car, leaning the AFR will almost certainly increase the power output, but at the expense of higher temps on boost. On a standard car, you are probably just eating into the manufacturers (usually big) safety margin. On a remapped car, you are probably eating into a rather smaller safety margin (unless the car is remapped specifically to Tesco 99).In summary: the Thorney results are only valid for standard cars, not for remapped cars, and certainly not for cars remapped to a specific fuel. Furthermore, they are only really valid for the standard cars under test.
Spence.