What octane are You running?

[catalyst.]

Hey all.. im 16 and own an e36 325i

Anyway my question is,what are the effects of using 87 octane gas in an m50 powerplant? (this is the main question feel free to stop reading here)

My beleif is that the m50 powerplant was built to run on higher octane fuel and for the past 6 months of me being the owner of the car ive been using 92 octane.

My moms volvo recently took a shit and im at boarding school so shes been driving my bmw.. when i found out about this today the first thing i asked was what fuel shes been running it on.. and yea shes been using 87.

In my opinion the notorious m50 valve tick is most likely caused by running low octane fuel, since my car has no tick and has 130k on it, ive been assuming the po's ran 92 its whole life. Anyway any comments would be great.

[Julien]

honestly i don't think fuel octane grade has anything to do with valve tick... running some nice synthetic oil will quiet your engine downt though.


Julien

[uofom3]

if its an octaine problem you're hearing deonation, not valve tick. I would suggest running 92 octaine gas at all times. Your engine will run better, cleaner, and more efficiently on that gas IMO. I have to run 2 gallons of "super 98" per tank of supreme, but that is with high compression pistons and cranked up timing (thus prevents denation, to an extent). Unless you have modified internals, you obviously wouldn't need to go this far and i **might** not have to either, its just a safety thing. Run supreme! As far as valve tick goes, run synthetic oils and make sure the pump is in good working order. My s50 ticks slightly at cold start on really cold mornings, but goes away very quickly. I don't know if there is a valve adjustment procedure for the m50/s50 family, but after i did that to my s14, it quieted down a lot.

[catalyst.]

Thanks for the info, yea i was thinking about the causes of valve tick, and i realized the gas your running would have no effect on it.. heh :oops:

[Ryan Stewart]

You arent on the best forum but. what year is the motor?

On the M50s there are hydraulic lifters. They often sound shitty if there isnt sufficient pressure built up, often they will tick until pressure is built up but it goes away almost immediately. They are self adjusting, unlike the M20/S14.

There shouldnt be knock, it has knock sensors to retard the timing if you are using a low octane fuel. An M50 doesnt require 92 unless the timing has been advanced.

Find someone with a code reader and see if it has detected knocking. Save that you can sometimes hear it if you load the car up at low speeds. Like putting it in 5th gear at like 30mph and slowly try to accelerate. The engine will rattle like a diesel if its knocking.

[uofom3]

Like putting it in 5th gear at like 30mph and slowly try to accelerate. The engine will rattle like a diesel if its knocking.

most cars will rattle like a diesel if you do that.... and that is seriously, seriously bad for your engine. If it's knocking under normal load in the first three gears you have a serious problem... if it's knocking under load in 4th or 5th at very low rpm's (lets say sub 1800 rpms) and you have a chip that is not shocking, and that is a fuel related issue. My s50 is not chipped, and it doesn't knock at low rpms in 4th with supreme gas. My s14 will knock at 2.5k rpms in 4th if I burry it. Point is, throttle position and gear selection are huge factors in this. regardless, running supreme gas can and will help. I also found that with a new o2 sensor low RPM's were improved, go figure as now the sensor is mixing the proper amount of fuel. On a side note: it was mentioned in Roundel this month that s50's build up carbon deposits on the pistons very easily if you are running anything less than supreme fuel. I understand you're not tlaking about the s50, but the m50 is not a hugely different minus displacement, cams, and stroke... something you might want to be aware of given that you've been running non-supreme gasoline...

[Mystikal]

There shouldnt be knock, it has knock sensors to retard the timing if you are using a low octane fuel. An M50 doesnt require 92 unless the timing has been advanced.

Ah, but the non-Vanos '92 motor does not have knock sensors. I think.

[Ryan Stewart]

My S50 has no problem pulling itself at 30mpg, it doesnt stall out like you describe. At 30 Its so quiet I can hear the intake whistle. I have used, and seen this used to detect audible knock on engines many times. I am not talking going so slow as to stall out the motor, just to increase the load to a point but still be going slow enough so you can hear something. And yes, its often caused by fuel issues common with chips.

About whether or not the 92 had no sensors, what was the first question I asked?

[Mystikal]

About whether or not the 92 had no sensors, what was the first question I asked?

I noticed. But proceeding to give a definitive response without knowing the answer to the question renders the knock sensor claim incorrect, if you don't state exceptions.

I'm just messing with you at this point. I'm still right though. :P

[M-technik-3]

If I remember you are here in Mass correct? I have a Peake tool and can read it for you if needed.

[calypso]

In south africa i run 97 leaded. But we pay about R4.50 ($0.75) a litre now.

[finch]

i run 98 (apparently)

[silversleeper]

I run 87, maybe that is why my shit ticks like a bmx bike with a card stuck in its spokes.

[Ryan Stewart]

no, ticking in an M20 is valve adjustment time.

[seqo]

i run 98 (apparently)

Whenever I can be bothered to pull into a BP I'll run 98 as well... Not many BP's on my daily routes though, so I go Mobil Synergy or the Caltex Premium (I believe they are both 95 RON).