Quote:
Originally Posted by digimattic
Forgive me if this is a dumb question. I am having some difficulty understanding the interplay of octane, IATs, and fuelling.
I am planning to flash BM3, stage 2. I would like to use the 93 map, but I understand that the gas in Ontario (even the 94) is not really great quality. I will be upgrading my intercooler, which should help keep timing up. But evidently that is not enough. I know some people turn to WMI, but I would rather not. Would an upgraded fuel pump like this help prevent timing being pulled in my situation? Or is the issue strictly one of octane and IATS?
Thanks!
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I can’t speak with first hand knowledge of Ontario 94, but if you’ve heard that there are issues from other users, then you might be right. The only way to know for sure is to take a look at logs.
Over the last few days I’ve been doing a lot of research on this topic, and have made a few posts on it in this thread:
https://f87.bimmerpost.com/forums/sh....php?t=1669225
It’s a complex topic, but you already know that the higher the IAT and the higher the boost pressure, the greater the chance of pre-ignition, and timing will be pulled to compensate. To some extent, adding more fuel can be done to cool the combustion, but this has a negative impact on power, so you may gain timing, but may not gain any power... assuming your fuel pump can keep up.
Oxygenated fuels like Ethanol in E85 can be blended and these improve the situation in 2 ways. 1) they lower the intake charge temperature as they change state from liquid to gas 2) they raise octane. More Ethanol volume than gasoline is required to achieve a stoichiometric burn, so this puts strain on the fuel pump as well.
Upgrading the fuel pump will allow you to run a stronger Ethanol blend and allow the DME headroom to pump in more fuel if needed to cool the charge, so it will help, but eventually you’ll run into octane limitations.
Octane in the US and Canada is rated in AKI, with the formula (R+M)/2 with R being RON and M being MON. Elsewhere in the world fuel is quoted as only the RON value.
I was able to locate the UK standards for ‘Regular’ and ‘Super’ unleaded fuels as follows:
Regular: 85 min MON; 95 min RON = 90 AKI; Sensitivity 10 (Sensitivity is RON-MON)
Super: 86 min MON; 97 min RON = 91.5 AKI; Sensitivity 11
And the CA standard:
Regular: 87 min AKI; 7.5 min Sensitivity = 83.25 MON; 90.75 RON
High Octane: 91 min AKI; 7.5 min Sensitivity = 87.25 MON; 94.75 RON
Recent research is showing that modern engines are operating in a state which is said to be ‘beyond RON’, meaning that the intake charge is at a higher pressure for a given temperature than the RON test or a lower temperature than the RON test for the same pressure. This is either because of intercooled forced induction (higher pressure for a similar temperature to RON), or because of efficient intake gas cooling from technologies like exhaust gas recirculating and just better airflow. This research is showing that the RON rating is not only more important than MON, but that a higher sensitivity (and therefore a lower MON) is also beneficial.
Taking a look at the standards above should show you that both the RON and MON values required for the CA Regular gas standard are lower than the UK, and that the sensitivity is lower as well. CA High Octane pump gas isn’t even as good as UK Regular - the RON is nearly as good, but the MON is higher so the sensitivity is lower, making the fuel worse for our modern engines.
WMI changes things massively... It cools the intake gases a lot... much more than an intercooler could hope to do, and increases octane. Cooling the intake gases moves the engine characteristics even more away from ‘RON’, so higher RON and higher sensitivity become even more beneficial. The increase in octane and cooling from WMI reduce the need for octane so much though that you can run CA pump gas with a high octane tune.
That’s probably more information that you wanted, but that’s it in a nutshell.