Observations on Octane Vs Performance
04-17-2010, 10:03 PM
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Observations on Octane Vs Performance
I thought I'd share some simple observations regarding the performance of my engine with different octane rated fuels. The data comes from the Porsche Mt. Panorama track event (see earlier post). The graphs below show speed Vs distance comparisons at two locations on the track:
1. Mountain Straight (sustained up hill climb - no skill required other than a firm planted right foot and some resolve to pursist when the car gets light with lateral movement cresting the hill in the end stage of the climb - accounting for the unsettled long G data at this point) and
2. Conrod Straight (sustained down hill run)
I've chosen the best runs from two different sessions:
a. Blue run - 98 RON (my usual fuel) - midday - session 3
b. Pink run - 102 RON - 0800 - session 4
For the record 98 RON cost us about $1.40 per litre ($5.60 per US Gallon), whilst the 102 RON which I had never used before cost $3.30 per litre!
The unknowns here, unfortunately, are the respective ambient temps (although this was stacked against the 98 RON as its data came from an afternoon session where the temps were probably 5-10 degrees celcius hotter), the IATs as I don't have an easy way to measure these, and the air pressure although this might have worked a little against the 102 RON as a cold front came in over night with an approaching low pressure cell that in fact brought rain and ruined Grant's last session. Nevertheless, if anything overall, these factors are likely to have favoured the higher octane fuel. The 102 run was lap 8 on this fuel, so I'm not sure how long it takes for the ECU to recognise a change and modify its respective behaviour in respect of timing and boost.
So what I see, is very little difference in performance between the two. You might observe that the top speed on Conrod for the 102 was higher, but this was only because I had backed off on the 98 run because of traffic - so the 70 - 230 portion of the run is what is relevant.
So I guess its was interesting, and in some ways disappointing, but given the fuel cost differential, it becomes a "no brainer" as to which fuel to use - at least for simple club sprint events.
I'd be interested in other members comments and experiences....
1. Mountain Straight (sustained up hill climb - no skill required other than a firm planted right foot and some resolve to pursist when the car gets light with lateral movement cresting the hill in the end stage of the climb - accounting for the unsettled long G data at this point) and
2. Conrod Straight (sustained down hill run)
I've chosen the best runs from two different sessions:
a. Blue run - 98 RON (my usual fuel) - midday - session 3
b. Pink run - 102 RON - 0800 - session 4
For the record 98 RON cost us about $1.40 per litre ($5.60 per US Gallon), whilst the 102 RON which I had never used before cost $3.30 per litre!
The unknowns here, unfortunately, are the respective ambient temps (although this was stacked against the 98 RON as its data came from an afternoon session where the temps were probably 5-10 degrees celcius hotter), the IATs as I don't have an easy way to measure these, and the air pressure although this might have worked a little against the 102 RON as a cold front came in over night with an approaching low pressure cell that in fact brought rain and ruined Grant's last session. Nevertheless, if anything overall, these factors are likely to have favoured the higher octane fuel. The 102 run was lap 8 on this fuel, so I'm not sure how long it takes for the ECU to recognise a change and modify its respective behaviour in respect of timing and boost.
So what I see, is very little difference in performance between the two. You might observe that the top speed on Conrod for the 102 was higher, but this was only because I had backed off on the 98 run because of traffic - so the 70 - 230 portion of the run is what is relevant.
So I guess its was interesting, and in some ways disappointing, but given the fuel cost differential, it becomes a "no brainer" as to which fuel to use - at least for simple club sprint events.
I'd be interested in other members comments and experiences....
04-17-2010, 11:06 PM
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I run Sunoco 260GT 100 octane in my 993TT, 930 and 944 Turbo. I have never dyno'd the cars with different fuels, but they run much better on the 100 octane. It seems to make them feel much more "crisp"... or maybe its the $8.00 USD that make it feel better for me...
04-18-2010, 02:44 AM
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Malcolm
It is difficult to read the data on these pictures. Maybe if you can adjust the scale from min 60 to max. 230kph it will help see better the lines. You migh talso need to smoothen the long Gs to 0.2-0.5s to remove the peaks.
Depending on your programming your engine can benefit to a larger extent from higher octane.
It is difficult to read the data on these pictures. Maybe if you can adjust the scale from min 60 to max. 230kph it will help see better the lines. You migh talso need to smoothen the long Gs to 0.2-0.5s to remove the peaks.
Depending on your programming your engine can benefit to a larger extent from higher octane.
04-18-2010, 07:37 AM
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Altered Plot axis
Jean, here are the plots with the Y axis altered. Hope these are easier to read.
The Long G data up hil (Mountain Straight) looks reasonably stable and usable. But the data on the down hill run on Conrod Straight looks rather odd and of questionable reliability.
Blue/Black - 98RON
Red/Pink - 102RON
The Long G's up hill look pretty similar. Down hill, there might have been more during the 4th gear run between 3900 and 4100m. The wild swings in 6th gear from 4450m I think must relate to the suspension and engine being loaded entering the rise and then unweighted and unloaded cresting the rise.
The Long G data up hil (Mountain Straight) looks reasonably stable and usable. But the data on the down hill run on Conrod Straight looks rather odd and of questionable reliability.
Blue/Black - 98RON
Red/Pink - 102RON
The Long G's up hill look pretty similar. Down hill, there might have been more during the 4th gear run between 3900 and 4100m. The wild swings in 6th gear from 4450m I think must relate to the suspension and engine being loaded entering the rise and then unweighted and unloaded cresting the rise.