Octane Rating

[bmwstephen]

I know the stock tune does not benefit from putting in any sort of gas higher than 87. The ignition maps on the stock tune will simply detonate as if 87 octane was in the system.

Because of this, will there be any negative effects when putting in 91+ octane (aside from pissing away money) since the excess potential is not utilized? I recall seeing something along the lines of clogged catalytic converters, improper mixture, leaning etc... can anyone verify?

Out here in California, the content of our gas is made of 10% ethanol so I've heard that mixing 91 every once in a while with 87 will do a bit of good since we do not have pure 100% unleaded 87 octane. Any truth to this?

[jlevie]

The only things that will happen if you use 91-93 octane without the ignition advance to take advantage of it is a slight loss of performance and an excess of unburned hydrocarbons in the exhaust. If the engine management system is working properly, the hydrocarbons should not hurt the catalytic converter.

[bmwstephen]

The only things that will happen if you use 91-93 octane without the ignition advance to take advantage of it is a slight loss of performance and an excess of unburned hydrocarbons in the exhaust. If the engine management system is working properly, the hydrocarbons should not hurt the catalytic converter.

interesting... quite concerning at the same time too because a lot of basic tuner chips out there like Dinan appear to only have maps for WOT but demand 91 octane just in case. Based on this, prolong use of 91 in daily driving/cruising seems harmful

but how does it result in loss of power?

[digger]

I know the stock tune does not benefit from putting in any sort of gas higher than 87. The ignition maps on the stock tune will simply detonate as if 87 octane was in the system.

That makes next to no sense at all

Because of this, will there be any negative effects when putting in 91+ octane (aside from pissing away money) since the excess potential is not utilized? I recall seeing something along the lines of clogged catalytic converters, improper mixture, leaning etc... can anyone verify?

it’s not worth worrying about, except the extra $$$. The changes will be small and the thing wont go up in a fireball. The higher octane stuff will keep the system cleaner though

[bmwstephen]

[QUOTE=digger;3827386]That makes next to no sense at all

it’s not worth worrying about except the extra $$$ and changes will be small. The higher octane stuff will keep the system cleaner though[/QUOTE]

How so?

[digger]

[QUOTE=bmwstephen;3827390]

That makes next to no sense at all

it’s not worth worrying about except the extra $$$ and changes will be small. The higher octane stuff will keep the system cleaner though[/QUOTE]

How so?

the higher octane stuff (in oz atleast) has additives which help injectors from clogging and less deposits in the engine.

[bmwstephen]

[QUOTE=digger;3827542]

the higher octane stuff (in oz atleast) has additives which help injectors from clogging and less deposits in the engine.

The top tier (76, chevron, shell) gas stations out here use additives in all grades of octane

[davesmystery]

This is good to know because I was planning on putting in 91+ to try and get it to pass emissions, good thing I didn't since it would have likely caused me to fail HC even more. Thanks!