Noisier on higher octane fuel ?

[Rory525]

Hi Folks,

Ive been running my 525i on Shell V Power for the last couple of months and found it to be really good. I get more torque over more of the rev range especially under 3k where the 525i needs it most. Allied to the chip I have a good fuel transforms the car, makes it feel very gutsy.

My question is - does anybody else notice the engine note is louder on higher octane fuels? It seems to be more gruff on them, although I feel more power.

I put 97 octane super unleaded in today instead of V power and went a drive, and as with 95 octane the engine is smoother and quieter but a little less gutsy.

Am I the only one who notices this?

Rory

[Fetch]

Unless the the higher octane fuel (which has more detergents in it) cleaned your engine, it won't increase the engine's power.

If you have a chip that requires the higher octane, than putting in lower octane could trigger knock sensors (does your engine have those? I don't know sorry lol) which would, in short, lower the power your engine makes.

Octane is a measure of how easily detonated the gas is.

[BillionPa]

as the ecu advances ignition timing in response to higher octane, there is increased violence in the combustion, which should result in more noise.

[Alexlind123]

Unless the the higher octane fuel (which has more detergents in it) cleaned your engine, it won't increase the engine's power.

If you have a chip that requires the higher octane, than putting in lower octane could trigger knock sensors (does your engine have those? I don't know sorry lol) which would, in short, lower the power your engine makes.

Octane is a measure of how easily detonated the gas is.

That is untrue, the engine will advance the timing in response to the higher octane fuel, making it produce more power.

[Claude]

That is untrue, the engine will advance the timing in response to the higher octane fuel, making it produce more power.

Is it also true with 535-1989 ? How the ecu detect what is the octane # of the fuel ?

[BillionPa]

occasionally it will slowly advance the ignition till knock is detected, then dial it back within safe limits. higher octane allows more advance. more advance = more power. more power = more noise.

ALTHOUGH.... what fetch said is mostly true. if you have a chip that "requires" high octane, its base timing map starts at a point where standard gas will cause knock....so dont put that in there.

octane is indeed a measure of how easily combustable the gas is, the higher the number the more resistant to ignition. however when it does ignite, at the same ignition advance, any octane petrol will produce about the same amount of power. only by modifying the fuel with expensive chemicals like neopropane acetone and a chemical called speedtec can you produce more power at a given ignition advance.

all E34 models use motronic DME systems and all should have knock sensors (im pretty sure on that)

if using standard gas with the stock chip is causing knock, then you have carbon problems, as the system is able to compensate with a working engine.

[Anton CH.]

91 525 uses Motronic 3.1 which does not have a knock sensor. According to factory you should be running premium grade octane anyway. So it doesn't care about knock.

occasionally it will slowly advance the ignition till knock is detected, then dial it back within safe limits. higher octane allows more advance. more advance = more power. more power = more noise.

ALTHOUGH.... what fetch said is mostly true. if you have a chip that "requires" high octane, its base timing map starts at a point where standard gas will cause knock....so dont put that in there.

octane is indeed a measure of how easily combustable the gas is, the higher the number the more resistant to ignition. however when it does ignite, at the same ignition advance, any octane petrol will produce about the same amount of power. only by modifying the fuel with expensive chemicals like neopropane acetone and a chemical called speedtec can you produce more power at a given ignition advance.

all E34 models use motronic DME systems and all should have knock sensors (im pretty sure on that)

if using standard gas with the stock chip is causing knock, then you have carbon problems, as the system is able to compensate with a working engine.

[Qsilver7]

all E34 models use motronic DME systems and all should have knock sensors (im pretty sure on that).

NOPE...not all e34 models have knock sensors. The M20 & M30 engines do not have them...regular 87 AKI or 91 RON fuel is all that is required (anything more is a waste unless the car is "chipped").

I'm not sure about the 1991-92 M50....but the M50TU (1993-95) & the M60 (530i/iT/540i) DO have knock sensors.

[Qsilver7]

no...the M30 engine does NOT have knock sensors...so it can not advance timing. Unless you have a "chip" anything more than regular fuel (87 AKI in the USA)...is a waste of money because the engine has no way to take advantage of higher octane fuel.

It's not that the engine detects what "octane" the fuel is...the engine will adjust timing based on fuel ignition within the cylinder.

[BillionPa]

does the S38 have knock sensors?