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?

[Paul in NZ]

i find the opposite,with my 535 all i need to use is 91 ron,but the engine runs smoother and seems more civilised(and quieter) on higher octanes,If i am inclined i willl use 95(recently downgraded from 96.I dont notice any difference with 98(from 95 or 96 i mean)

[CharlesAFerg]

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.

Yes, finally someone without plugs in their ears...
Hey I think I saw you on the E38 board... My dad just picked up a black 740i sport from San Fransisco back up here to Portland, OR... gooorgeeouuusss!! :p :) :) :)

[Claude]

Basicaly what's the operation principal of the knock sensor. Where are day located and what do they look like ?

[DaveVoorhis]

Basicaly what's the operation principal of the knock sensor. Where are day located and what do they look like ?
A knock sensor is a essentially a piezolectric microphone, generally mounted to the block or head, that is tuned to pick up the characteristic high frequency sound of pinging or detonation. The ECU uses this to retard timing to where pinging just stops, as this is the point where maximum power and efficiency is produced. They usually look like a biggish bolt with a lead coming out the top.

A brief explanation can be found at http://www.autoshop101.com/forms/h38.pdf, including a quiz at the end to see if you've learned anything. :p

[Qsilver7]

...I think I saw you on the E38 board... My dad just picked up a black 740i sport from San Fransisco back up here to Portland, OR... gooorgeeouuusss!!
probably...I'm all over the place...;) and I hope he enjoys his 7 as much as I do mine. ;)

[Claude]

A knock sensor is a essentially a piezolectric microphone, generally mounted to the block or head, that is tuned to pick up the characteristic high frequency sound of pinging or detonation. The ECU uses this to retard timing to where pinging just stops, as this is the point where maximum power and efficiency is produced. They usually look like a biggish bolt with a lead coming out the top.

A brief explanation can be found at http://www.autoshop101.com/forms/h38.pdf, including a quiz at the end to see if you've learned anything. :p

Thanks very much Dave, top notch explanation for me.

[Digita1 Ecstasy]

Where do all of you live? The highest offered octane here (northern illinios) is 91-93

I would love to feed my car 96, 97.

[///Metal]

there is increased violence in the combustion

any gratuitous sex and nudity in there at all?

[BillionPa]

well of course there is!

and also, with the compression ratio of E34 engines, octane over 96 really wont do much good. the gas that gives the most power is the lowest one that will run without knock. LOWEST OCTANE!..... at the most advanced timing the engine management system has to offer.

now if you stick a turbo on without lowering the compression ratio, then high octane gas does a world of good. otherwise you are gonna get some unstable idle.

[bigtisas]

OK folks. I just bought a 92 525 M50. Should I use 89 or 91 octane fuel?

The owner manual says use premium gas only, but which octane number is premium?? I put a tank of 89 to it and it seems to run fine. Not sure about knocking or not. According to Consumer reports fuel test, octane number is like shoe size. Bigger number won't get you run faster. So I want to use the lowerest number octane gas (cheaper) as possible.

[BillionPa]

on a BMW engine with knock sensors you will get more power with 91 than with 89. and if you get an EAT chip you will get more power with 93 than with 91.

with a chevy truck engine on the other hand, you will generally have no power gain by using higher octane fuel.

and if you get knock and "need" higher octane gas to make the engine run better, you have severe carbon issues and the money you would spend on high octane should be put to better use fixing the problem.

[JerseySi]

Just to add my 2p's worth... :D
With my 535i, I do notice if I run it on Super (98 octane) for even just one tankful, it feels noticably better - although overall power is probably no different..
As Rory says, it just feels nicer to drive - and yes, it does sound more 'healthy' :D
It's even more noticeable when I've been using decent petrol & put cheap 95 octane stuff in - the car feels flat & unresponsive..
It makes the difference between willingly squeaking the tyres when pulling out of junctions on good stuff, to wondering whats wrong with it on cheapo stuff..
(car is standard 535i, only 'mod' is cold air feed into std airbox, no chip or owt)

p.s. - Hi Rory - seen you around on bmw5.co.uk too :D

[BillionPa]

the formulation of the gas does make a huge difference, although the "octane" rating on the pump can be something totally different depending on how the weights and measures of your country calculates it.

in the US we use AKI, which is the mean value of the RON and MON values of the gas. RON is the higher number, and generally a 93 octane "super unleaded" here equates to 98 RON & 88 MON, or something similar.

the gas grade you are getting is probably listed by its RON value, because 98 AKI fuel is almost racing fuel and would have to be formulated with either large amounts of ethanol, which would NOT make the car feel better, or it would be almost twice as expensive as "regular" gas.

also other factors influence the way it feels. the higher the altitude gets, the less important the octane level becomes. that has do do with the density of the air. the additive package also will have long term impact on the feel of the car. and of course the ethanol content of the gas has a massive impact on both drivability, economy and power.

as for getting better fuel economy from higher octane gas, more refined gas generally has slightly (1%) better economy than standard if the car will run it properly, and if your car will get power gains from higher octane, then less fuel will be required to produce the same amount of power, resulting in less fuel used (less than 5% usually)

[Rory525]

Hi Si , good to see you here too :)

I find the same as you , if I go back to 95 from 97 + the car feels really sluggish and unresponsive. Im sure its more than a placebo effect, its that noticeable.

Ive actually been at the point of being fed up with the car and thinking I should sell it for something faster, then put higher octane fuel back in it and remember why I liked it in the first place !



Just to add my 2p's worth... :D
With my 535i, I do notice if I run it on Super (98 octane) for even just one tankful, it feels noticably better - although overall power is probably no different..
As Rory says, it just feels nicer to drive - and yes, it does sound more 'healthy' :D
It's even more noticeable when I've been using decent petrol & put cheap 95 octane stuff in - the car feels flat & unresponsive..
It makes the difference between willingly squeaking the tyres when pulling out of junctions on good stuff, to wondering whats wrong with it on cheapo stuff..


p.s. - Hi Rory - seen you around on bmw5.co.uk too :D

[DaveVoorhis]

if I go back to 95 from 97 + the car feels really sluggish and unresponsive. Im sure its more than a placebo effect, its that noticeable.
Baffling. I tried alternating between 95 and Super in my bike, and didn't notice the slightest difference. I think I'll pour a tankful of Super in the car and see what it does.

[Ross]

The rating here in Illinois is an average of research and motor octane numbers. I think the posters here are refering to RON(research octane number) which I believe is the higher number for thr same fuel.
Look at the label on the pump, it explains it.

[Jake Casson]

Us here here in the UK have much better fuel therefore more powerful cars, than you yanks, right?

[Paul in NZ]

Us here here in the UK have much better fuel therefore more powerful cars, than you yanks, right?

No its been explained in this thread already.The US octane rating are AKI which are RON+MON/2 whereas those of us in the UK and Aussie and NZ refer to our octane ratings as RON