87 Octane versus 92 Octane? What's the diff?

[PonyBoy90]

Guys, I have a buddy of mine that's being eaten alive by escalating gas prices on the premium 92 Octane he fills into his BMW.

He asked me a question what would happen if he were to fill up on 87 instead of the usual 92. I asked him what his owners manual tells him to fill up on but the guy is not "car knowledgeable" and probably hasn't even cracked the book open.

I've heard about stuff like engine knocking/pinging may occur, rough ride, backfiring, gumming up the injectors, etc etc. I've told him these things yet he needs more info.

I believe all BMW's are high compression engines, so I'm assuming they need at least a 91 Octane. Those in the 80's tend to be for low compression engines mainly.

Could he damage his engine running on 87 Octane? How about filling up on 87 Octane on every second fill-up????????

Thanks guys



Will running 87 damage his engine?

 

[illwood]

The knock sensors would probably pull enough timing to get away with running lower octane fuel, but that should only be used in a "stranded" scenario. I would just check the manual and run what it reccomends.

BTW, he's being eaten alive by gas prices, but can afford a BMW?

 

[PonyBoy90]

BTW, he's being eaten alive by gas prices, but can afford a BMW?

Yeah, exactly. Actually the BMW is leased and he's trying to cheap his way out of saving a few bucks.

Would running the 87 show on a tune-up? I mean, say he runs on 87 for a year and goes for a tune-up as per his lease agreement. Would the dealership know he was running low octane based on the state of the spark-plugs and carbon build-up??????????

 

[9mm]

After putting your word problem thru a series of advanced algorithms on a supercomputer in an M.I.T lab i think the difference is 5 octane points.

 

[PonyBoy90]

After putting your word problem thru a series of advanced algorithms on a supercomputer in an M.I.T lab i think the difference is 5 octane points.

Man, you's good in math! Now I can go to my buddy and tell him this most valuable info.

 

[LX302]

Illwood is right about the knocksensor.
If he doesn't experience any knocking or pinging, he can get away with 87 and not really hurt anything. But he will suffer some performance for it.

 

[Look Its Aaron]

the difference? only about 2.00 or so when he fills up. It's not that much.

 

[HISSIN50]

Yep, if he does not stand on it much and does not enjoy the extra power, the piezos should knock timing out of it.

Tell him to note milage though - some folks get better milage with the higher octane, which can go towards negating the extra cost.

I have to run premium in the '94 GT - that gets expensive.

 

[QDRHRSE]

I have my wife put middle grade gas in our BMW although the BMW computer will adapt to 87 with no problem. As much as I love Mustangs, a Mustang is a POS compared to just about any new BMW. The fuel/computer systems are way better. Tell your cheap ass friend that 87 will be fine. The things he cannot skimp on are the fluids. All BMW fluids are synthetic and expensive as hell but the cars really benefit from it. oh yeah, like Hissin said, the mileage will go down a little with cheap gas.