What grade and octane should I be burning?

[greybeard]

I've just purchased my first bimmer, an '87 325ic. The owner's manual specifies 91 RON, which is the European standard of measuing. I've found information on the internet that 91 RON equals 87 R+M/2, also known as the Anti-Knock Index (AKI), which is the standard of octane measurement in the US. That suggests I can safely run unleaded regular 87. The only information I can find about octane requirements is related to pinging: if it pings under acceleration or load, you need to run a higher octane. I've only run 3 tanks of gas through mine, all regular 87 , and get no pinging. Is there another reason I should be running a higher octane, perhaps 89 or 91, or is it okay to run 87?

 

[epj3]

I've been using 89. Older cars typically require or run better with higher octane gas to make up for the compression lost due to age. My car runs perfectly fine with 87, but just a little smoother with 89 - enough to warrant paying an extra $0.80/tank.

 

[frolf]

run at least 89, i run 92/93, sometimes 91, doesn't make a huge diff. But our rockstar Administrator had issues with his M3 when he ran 93, and now runs 91.

 

[wood_e]

89

 

[daihard]

I've just purchased my first bimmer, an '87 325ic. The owner's manual specifies 91 RON, which is the European standard of measuing. I've found information on the internet that 91 RON equals 87 R+M/2, also known as the Anti-Knock Index (AKI), which is the standard of octane measurement in the US. That suggests I can safely run unleaded regular 87. The only information I can find about octane requirements is related to pinging: if it pings under acceleration or load, you need to run a higher octane. I've only run 3 tanks of gas through mine, all regular 87 , and get no pinging. Is there another reason I should be running a higher octane, perhaps 89 or 91, or is it okay to run 87?

A bit OT, but do you have the link to that Internet site where they talk about the octane value conversion between RON and R+M/2?

Thanks,
Dai

 

[greybeard]

A bit OT, but do you have the link to that Internet site where they talk about the octane value conversion between RON and R+M/2?

Thanks,
Dai

Sure; here's the link:

http://www.type2.com/bartnik/octane.htm

 

[greybeard]

I've been using 89. Older cars typically require or run better with higher octane gas to make up for the compression lost due to age. My car runs perfectly fine with 87, but just a little smoother with 89 - enough to warrant paying an extra $0.80/tank.

Interesting... any idea how that works? Everything I read about gas grades and octane says that higher octane doesn't give better gas mileage, doesn't increase power, doesn't make the engine run smooter, etc.... that it's all and only about pinging..... A friend of mine who has one said bimmers need higher octane because they are "high-compression engines," yet when I asked him what that meant and why a "high-compression engine" needed higher octane, he didn't know. I'm not saying he's wrong, but I'd sure like to know why I should run higher octane if I'm not getting any pinging. Ive also heard explanations that higher octane grades have better additives and will keep the injectors cleaner, but nothing I can find in any articles suggest that. If octane creates higher compression, any idea how that happens? A couple of people actually have told me the opposite, that because my car is older and doesn't have as high a compression as when it was new, I can run lower octane. But again, when I ask them why, no one has an answer. I'd love to know why.... Any ideas?

 

[daihard]

Sure; here's the link:

http://www.type2.com/bartnik/octane.htm

Thanks!

 

[NICOLA]

Here's the deal:

Only the best for the best !!

 

[gizzy]

You use a higher octane to prevent detonation (pinging). The higher octane helps cause the fuel to burn smoothly when your cylinder tempetures get hot rather than exploding which can damage your engine over time.

 

[larry1718]

problem of pinging my be moot

the engine in my 2000 528i will adjust automatically if a lower than optimal octane (91 recommended) is used. according to the bmw manual, if a lower octane is used the engine will self compensate at the cost of reduced performance. at least this will protect the engine from pre-detonation damage. i don't know if this is true for other engines.

cheers