Advice sought – mapping session and fuel to use

[Nick Bassett]

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!

[Dave Hardcastle]

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.

[Nick Bassett]

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!

[MattB]

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

[StevehS3]

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...?

[oilyhands]

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

[Billy.Whizz]

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.

[Nick Bassett]

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.

[StevehS3]

Interesting topic. Is the reason because that with higher octane fuel the ignition can be further advanced (resulting in slightly more power)?

[MattB]

#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

[jbcollier]

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.

[Beagler]

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.

[Nick Bassett]

Beagler - no worries, glad it has been of interest!

Perhaps I provide a brief write up of my mapping experience next month...

[John Vine]

#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

[revilla]

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.

[oilyhands]

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.

[rgrigsby]

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.

[ECR]

Surprising!

 "all other things being equal, 95 octane has the potential to produce a smidgen more power than 99 octane." 

[Beagler]

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.

[SLR No.77]

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.

[anthonym]

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