Area Representative Nick Bassett Posted August 2, 2023 Area Representative Share Posted August 2, 2023 I have my 7 booked in for a mapping session next month post an engine rebuild at DVA over the Winter. Never done anything like this before, so looking forward to it.However I’m in a bit of a quandary over fuel type… I always try and run my car on Super-unleaded, but am not precious of fuel brand etc. However on occasions, it’s not always possible to get Super-unleaded – the fish n chip run for example, where I might end up with a mixed tank of 95/99 octane.So, what do I fill the car up with for the mapping session? I want the car to run at its best when being fuelled by 99 octane, but also to run safely on 95 when needs be. I’ve spoken to the RR company and they’ve suggested using only 95 for the RR session if I want it to run safely on that fuel. But that is only for a small proportion of the time I drive the car.Another thought I’ve had is to have it mapped on 99, but to carry a bottle of octane booster to use on occasions when I can only put 95 in. Could that be a viable solution?Would welcome others thoughts on this.Thanks! Link to comment Share on other sites More sharing options...
Dave Hardcastle Posted August 2, 2023 Share Posted August 2, 2023 I'd do the RR session on standard 95 fuel as per the advice you've received. Personally, I don't think it will make that much difference, it's not like any of us are after thousandths of a second on our lap times. Link to comment Share on other sites More sharing options...
Area Representative Nick Bassett Posted August 2, 2023 Author Area Representative Share Posted August 2, 2023 I've just contacted the RR company with my potential solution and they said it'll work fine, so that's what I'm gonna do! Link to comment Share on other sites More sharing options...
MattB Posted August 2, 2023 Share Posted August 2, 2023 I had the 2.0 Duratec engine in my MX5 rolling road tuned some years ago. The tuner said that using 99 octane wouldn't make a difference in a naturally aspirated engine, but he was surprised to find that he could add much more advance than he had on other engines, resulting in what was a better tune for me.I carried a bottle of octane booster in the boot, but never used it. It's now in the boot of the 7. The MX5 did, however, have a knock sensor.MattB Link to comment Share on other sites More sharing options...
StevehS3 Posted August 2, 2023 Share Posted August 2, 2023 Out of interest, when our 7s have a RR session what in addition to the fueling map is changed? Ignition map? Barometric pressure compensation? Cold start settings...? Link to comment Share on other sites More sharing options...
oilyhands Posted August 2, 2023 Share Posted August 2, 2023 Potentially just about everything depending on how close the existing map is, cold start calibration is quite hard to adjust at a RR as the engine will only go through warm up once and that is when the map is not yet perfected. Since the cold start settings are percentage adjustments against the regular map it's a chicken/egg situation. If the cold start adjustment table is obvious nonsense then some sensible estimates based on experience will be used. Idle adjustment is critical for good running and starting, throttle body balance and setting correct air throughput makes a huge difference to idle, progression and drivability.Baro correction is pretty much a standard set of adjustments.Oily Link to comment Share on other sites More sharing options...
Billy.Whizz Posted August 2, 2023 Share Posted August 2, 2023 I recently took my 420R to the two Steve's after having RBTB's fitted by CC to have a re-map and was told super unleaded was best but normal unleaded was ok but you must have the re-map done with the fuel you are going to use.Steve also said it's ok to fill up with u/l if you can't get s/ul but change back as soon as you can. I also did this on the F&C run and every thing was fine. Link to comment Share on other sites More sharing options...
Area Representative Nick Bassett Posted August 3, 2023 Author Area Representative Share Posted August 3, 2023 Just to add to this, my mapping company said that if my car is mapped on 99, it is OK to use 95 occasionally as long as full throttle is not used for a long period. Given my use is on the road only, then that won't be a problem at all. Link to comment Share on other sites More sharing options...
StevehS3 Posted August 3, 2023 Share Posted August 3, 2023 Interesting topic. Is the reason because that with higher octane fuel the ignition can be further advanced (resulting in slightly more power)? Link to comment Share on other sites More sharing options...
MattB Posted August 3, 2023 Share Posted August 3, 2023 #9 - yes. Higher octane doesn't give more power, but allows the map to be adapted to generate more power.If a knock sensor is fitted the ecu can reduce that advance if it senses knock, so filling up with lower octane fuel is even less of a risk.MattB Link to comment Share on other sites More sharing options...
jbcollier Posted August 3, 2023 Share Posted August 3, 2023 Just want to make sure that no no one thinks that more timing always results in more power. At a certain point, on some engines, it still won't ping but it will start to have some retarding effect on the piston. Also, increasing advance increases the heat load imparted to the piston crown. Link to comment Share on other sites More sharing options...
Beagler Posted August 3, 2023 Share Posted August 3, 2023 Didnt consider this when I sent mine for mod. Only use Shell Nitro but good point as rolling road will produce results on that fuel so important to continue. Thanks for this thread Nick. Link to comment Share on other sites More sharing options...
Area Representative Nick Bassett Posted August 3, 2023 Author Area Representative Share Posted August 3, 2023 Beagler - no worries, glad it has been of interest!Perhaps I provide a brief write up of my mapping experience next month... Link to comment Share on other sites More sharing options...
John Vine Posted August 3, 2023 Share Posted August 3, 2023 #11 Also, increasing advance increases the heat load imparted to the piston crown.Not to mention the exhaust valve(s), as I discovered many (many) years ago when I cocked up the timing on my Matchless G3LS!JV Link to comment Share on other sites More sharing options...
revilla Posted August 4, 2023 Share Posted August 4, 2023 I was recently involved in helping to map a single seater with a K Series engine at Northampton Motorsport (my input was the mapping software).Troy reckoned he could he cold hear the early signs of detonation so we retarded the timing - and got MORE power, not less as we expected. We then retarded again, and got another increase, but very small this time, so we left the timing at that - more power and much safer. Link to comment Share on other sites More sharing options...
oilyhands Posted August 4, 2023 Share Posted August 4, 2023 As a general rule timing is set to MBT(minimum best timing), fuelling notwithstanding, timing is advanced until torque is maximised, then backed off until on the cusp of torque falling back. This usually offers a safety margin. Higher octane fuels generally have a marginally lower calorific value so all other things being equal, 95 octane has the potential to produce a smidgen more power than 99 octane. Where higher octane fuels do make a difference is with forced induction where higher boost can be used as the fuel is more resistant to detonation. Link to comment Share on other sites More sharing options...
rgrigsby Posted August 4, 2023 Share Posted August 4, 2023 This may not help but some ECU's do support multiple maps, I'm running an Emerald on my Duratec and have a Super map that I use most of the time and a second map for regular 95 fuel if I need it. Simple toggle switch on the dashboard to switch between them. Link to comment Share on other sites More sharing options...
ECR Posted August 4, 2023 Share Posted August 4, 2023 Surprising! "all other things being equal, 95 octane has the potential to produce a smidgen more power than 99 octane." Link to comment Share on other sites More sharing options...
Beagler Posted August 4, 2023 Share Posted August 4, 2023 Higher octane does nor readily mean more power although it can enable more advanced ignition its more about anti knock properties associated with combustion of end gases in the combustion chamber. Link to comment Share on other sites More sharing options...
Leadership Team SLR No.77 Posted August 4, 2023 Leadership Team Share Posted August 4, 2023 My 7 was mapped on 95 but that was a few years ago when I couldn't guarantee getting SU on a regular basis. Times have changed and we're now looking at the added complication of E10 and E5, not just the octane rating. My own observation is that SU is now more readily available because of the ethanol content situation. If I was having it mapped again I'd have it done on SU simply because I'm now going out of my way to buy E5 rather than E10, my 7 is 1999 so I'm not happy feeding it with E10. Another added complication!Stu. Link to comment Share on other sites More sharing options...
anthonym Posted August 16, 2023 Share Posted August 16, 2023 Mine's (year 2000 K) just been mapped on 95, to my then horror. However, upon reflection and the more so reading this thread given I am road use only, the growing absence of 98 in Europe does make 95 less stressful when down to 0 litres remaining. Anthony Link to comment Share on other sites More sharing options...
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