ditka550

Station not far from me sells racing fuel and I was wondering if it was safe to use in a stock BMW 550i?


If not a complete fill up maybe half and half. Just a thought to cleaning it out a bit instead of buying injector cleaner or all that other stuff.


Thoughts?

abe76247

Octane and cleaning are not at all related. Cleaning is due to detergents added to the fuel and the racing stuff may have less of it than regular unleaded at the normal pumps.
Octane makes fuel harder to burn so that it has reduced tendency to ignite in cylinder from pressure and any local hot spots as in glowing carbon deposits. You're likely throwing away money and at worst it may be hard to start cold and run rough until it runs a minute or less.

If you have a two valve per cylinder Detroit iron motor with really high compression ratio then that is the fuel you need.

zach1328

It's not going to clean the engine out by any means. Definitely do NOT use only 105 octane - that is way too high for a 550i. Maybe do a 40/60 mix of 105 octane and 93 which would average out to about 97-98 octane.
The 550i has a 10.5 compression ratio compared to my 535i which has a 10.2 compression. However, since the 535 is turbo'd there is a lot more pressure in the cylinders to burn up the higher octane fuel. Regardless, I've never run higher than 99 octane in my 535i.

paul-g

people are very mislead by octane becareful

FormerE30Owner

So many myths about the Octane Index.

Octane is not a substance added to fuel. It is an index used to compare the anti-detonation property of a fuel to that of Octane if it were used as a fuel.

There is absolutely NO benefit from running higher octane fuel in an already clean well running engine. That being said, running a higher octane fuel will not do any harm, except IF it does not contain the additives that normal octane fuels have, which might be the case for this racing fuel.

BTW, a 50-50 mix of 93 and 105 will give close to a 102 octane equivalent, not the 99 as one might think. The mixing of different octane fuels is not linear in effect.

Bottom line - don't waste your money using higher than specified octane fuel.

Salut, Bob P.

ditka550

Thanks everyone for the clarification and replies!

u3b3rg33k

FYI, higher than normal octane-rated fuel will NOT cause starting/running problems, nor will it damage your engine.

UNLESS that octane rating comes from lead (some racing fuel has lead), or you're using methanol/high ethanol fuels with a different fueling requirement. lead will damage (deactivate) your catalytic converter, and ethanol/methanol fuels are not approved for use by BMW.

FWIW, iso-octane is an actual chemical:
http://en.wikipedia.org/wiki/Isooctane
Higher octane rated fuels aren't harder to burn, they're harder to detonate.
For an extreme, and somewhat off-topic example, take C-4 (the explosive). burns like a candle, but doesn't explode unless you hit it with a monstrous pressure wave.

high octane/harder to start myths come from fuels that differ significantly from normal gasoline - ethanol has an octane rating of about 108 AKI, but is harder to ignite when cold than "gasoline" (which is not, as you may have gathered, a specific chemical).

Booyaazaa

+1

OP - it would be a waste of money for you to run anything above 94 octane. Only real time it might benefit you is if you are doing a track day or running your engine hard for long periods of time on a hot day. Otherwise save your money for some cool mods.