Octane Experiment

[The Melmaan]

Has anybody have experience switching from one octane to another? For the past couple of months, I have switching from 87 to 92 and back. I don't notice any problems with performance when I have the 87 octane for a couple of tank fulls. The gas tank door says that I should load up with Premium Gasoline only. Is there any bad issues if I continue to use 87 octane (cheaper) gas?

[MarkD]

Has anybody have experience switching from one octane to another? For the past couple of months, I have switching from 87 to 92 and back. I don't notice any problems with performance when I have the 87 octane for a couple of tank fulls. The gas tank door says that I should load up with Premium Gasoline only. Is there any bad issues if I continue to use 87 octane (cheaper) gas?

Have you got an M50 or M50tu (VANOS) motor? The M50 does not have knock sensors and should use 91 octane, the M50tu has knock sensors which will retard timing if knock is detected, but you will also have a reduced power output when timing is retarded. Depending on how you drive, you may not notice a difference. (if you don't accellerate hard)

MarkD

[Russell]

My car seems to run very well on Shell Vpower 93 and your chip. It also runs very well on Chevron 93 octane. Of course the 95 525iTU has the knock sensors that should take advantge of the highest octane.

Just an observation

Have you got an M50 or M50tu (VANOS) motor? The M50 does not have knock sensors and should use 91 octane, the M50tu has knock sensors which will retard timing if knock is detected, but you will also have a reduced power output when timing is retarded. Depending on how you drive, you may not notice a difference. (if you don't accellerate hard)

MarkD

[ryan roopnarine]

i know mark will likely have to disclaim what i am about to say, buuutttt....

i seem to have an average carbon buildup problem in my m50 (several here have said they have the same problem/symptopms)

as a "diagnostic" indicator, after doing any type of fuel injector cleaning, or about every 2 months otherwise, i'll put 5 gallons of the crappiest 87 i can find into an empty tank. ill put chevron 89 after i empty it again.

the engine is a 7/91 production m50 (1992 525i). obviously, it has no knock sensors. it is equipped with mark's chip.

never, on any occasion after doing this do i hear an increase in knock between 93 and 87 gas. not once. this doesn't mean that there isn't knock increase between the two, its just that it appears to have identical knock patterns across all octanes. on 87, the motor seems to have a smoother powerband, as well. i know enough organic chemistry to know why it would have more power on 87, i just don't know why it wouldn't knock more on it. i noticed in the manual for my mother's ford taurus that the duratec (1999) has a 10-1 CR, but only uses 87 (though it is obviously modern and has knock sensors). is the jump from the m30ish CR to the m50 one not drastic enough to cause too much observable ping?

[632 Regal]

in static compression (not mechanical). In order to visualize it the easiest way to describe what happens is take a stock engine with 10:1 compression. Crank it over for a compression check, say it reads 180 psi, knocks like hell with 87 octane.

Now replace the cam with one that has duration and overlap for racing and the compression would read close to 80-100 psi. With this lower number the engine will not have knock like its counterpart until the dynamics come into play and start loading the cylinders up in higher rpm range which you can regulate by retarding the timing and still getting much better performance.

I think the issue with your particular engine isnt just the carbon buildup but that the timing is far too advanced for economy or performance. There is NO WAY BMW designed your engine so that you have to run cleaner and clean the pistons so often if ever.

Your chip is the problem right now, why dont you ask Mark to recalibrate the chip or put the stocker back in and stop your whining. This is obvious to me because I understand the "cam" dynamics on an engine. All the knowledge in the world on fuel weights and octanes will never fix an engine that is over timed.

If anyone knows anything about swapping out camshafts on Detroit iron it is me, when the books didn't explain things and reasons I went out in the real world and figured out a lot of stuff that you wont ever read about. I was always the guy that picked a cam that was 2x too big, never had a detonation problem and kicked all the cars asses with similar combinations. A friend of mine with a 10:1 440 finally gave in and admitted problems...spark knock. We went through plotting ignition timing and couldnt resolve the problem, he gave me his cam card and it was so low in duration that I recommended a replacement (laughed in his face). With the same ignition timing no knock and the same power, then upped the timing almost 8 degrees and wham! that thing runs damn strong, picked up 1/2 second in the quarter.

Hope that somewhat makes sence, if not I'll be happy to blabber more about this issue.

[The Melmaan]

I have an M50 engine on my 93 525i. I don't drive like a race car driver, maybe that is the reason why I don't notice any change in the way the engine runs. Of course here in California, the highest octane that one can get is a 92. So far, my car is back on the premium gas (92) and so far it is still running the same.
Do I need to change the chip. BTW, I found some on Ebay that they are selling very less.

[MarkD]

in static compression (not mechanical). In order to visualize it the easiest way to describe what happens is take a stock engine with 10:1 compression. Crank it over for a compression check, say it reads 180 psi, knocks like hell with 87 octane.

Now replace the cam with one that has duration and overlap for racing and the compression would read close to 80-100 psi. With this lower number the engine will not have knock like its counterpart until the dynamics come into play and start loading the cylinders up in higher rpm range which you can regulate by retarding the timing and still getting much better performance.

I think the issue with your particular engine isnt just the carbon buildup but that the timing is far too advanced for economy or performance. There is NO WAY BMW designed your engine so that you have to run cleaner and clean the pistons so often if ever.

Your chip is the problem right now, why dont you ask Mark to recalibrate the chip or put the stocker back in and stop your whining. This is obvious to me because I understand the "cam" dynamics on an engine. All the knowledge in the world on fuel weights and octanes will never fix an engine that is over timed.

If anyone knows anything about swapping out camshafts on Detroit iron it is me, when the books didn't explain things and reasons I went out in the real world and figured out a lot of stuff that you wont ever read about. I was always the guy that picked a cam that was 2x too big, never had a detonation problem and kicked all the cars asses with similar combinations. A friend of mine with a 10:1 440 finally gave in and admitted problems...spark knock. We went through plotting ignition timing and couldnt resolve the problem, he gave me his cam card and it was so low in duration that I recommended a replacement (laughed in his face). With the same ignition timing no knock and the same power, then upped the timing almost 8 degrees and wham! that thing runs damn strong, picked up 1/2 second in the quarter.

Hope that somewhat makes sence, if not I'll be happy to blabber more about this issue.

Jeff,

I really can't tell from Ryan's post if he has much pinging, but one thing for sure, the chip is not designed to be used with 89 octane. It needs 91 octane at the least. If I remember correctly, that motor is supposed to run premium as delivered from the factory. Yes, some motors may not ping with lower octane and a chip, but there will only be a few like that and it could be due to various factors such as sensor tolerances and the (lack of proper) compression in the motor. I have shipped many of the same chip Ryan has and if there was a timing issue, (which I know there isn't) I would have heard about it.

MarkD

[MarkD]

My car seems to run very well on Shell Vpower 93 and your chip. It also runs very well on Chevron 93 octane. Of course the 95 525iTU has the knock sensors that should take advantge of the highest octane.

Just an observation

Hi Russell,

yes the m50tu can run quite well on 93 octane due to the knock sensors allowing timing to be further advanced than if there was no knock sensor.

Additionally, the 95 models with EWS have a new version of software which is more advanced than the 93 and 94 m50tu. (I found that out when I started working on the code, it's quite different)

I don't have any experience with the fuel you mention as it's not available here, but generally, 93 octane in that motor keeps it very happy. (we have 91 and 94 here)

MarkD

[ryan roopnarine]

Jeff,

I really can't tell from Ryan's post if he has much pinging, but one thing for sure, the chip is not designed to be used with 89 octane. It needs 91 octane at the least. If I remember correctly, that motor is supposed to run premium as delivered from the factory. Yes, some motors may not ping with lower octane and a chip, but there will only be a few like that and it could be due to various factors such as sensor tolerances and the (lack of proper) compression in the motor. I have shipped many of the same chip Ryan has and if there was a timing issue, (which I know there isn't) I would have heard about it.

MarkD

mark, i only fill the car up on friday-sunday, as those are the days that local gas stations price match their 89 and 93 octane gas. its also the day that almost all of the local gas stations get their tanks refilled, so i can pretty much rule out garbage gas. it doesn't get 89 as regular operating fuel, it only gets 4 gals of it after my periodic testing with 5 gals 87, which seems to only happen every 2 months or so (if i remember to do it).

[Bill R.]

buying gas on the days that they fill the tank, supposedly on the days that they fill you don't want to buy because it stirs up all the sediment and crap in the storage tank and mixes it into suspension, then you pump it into your tank and clog your fuel filter quicker... If you wait a day it gives it a chance to settle down to the bottom again....