Super Unleaded 98ron - wow!

[LostKiwi]

So not only do you fail to get any performance gains, it will only reduce the build ups of soot?

Octane rating and additive packs are two different things.
You could have a low octane fuel with an additive pack designed to keep the engine clean and a high octane fuel that allows carbon deposits to form. Soot will only form when an engine runs rich (unless it's a diesel) and with closed loop feedback from lambda sensors controlling mixtures factory spec maps just don't allow this as excess fuel damages catalytic converters.

 

[oigle]

So not only do you fail to get any performance gains, it will only reduce the build ups of soot?

Yep. Sorry. The egr muck will still buildup at the same rate too which is the biggest problem in the long run.

 

[KeithJG]

@Capra
This is info that I have found regarding premium diesels. Seems that performance can be maintained by keeping an engine clean rather than seeing an increase.

"Because diesel engines don't ignite fuel to create power (fuel is added to the air that is compressed instead), premium diesel doesn't usually feature a higher octane rating. Instead, this more expensive super diesel will feature chemicals in its mixture that are designed to shift soot deposits and other oily build-up from within the engine's fuel system"

So that is what you read.........

Diesel engines must ignite the fuel because that what gives the bang?........they do it through compression ignition and not spark ignition as in petrol engines.

Diesel fuels do not have an Octane Rating as Petrol Fuels do they have a CETANE Rating and it differs in Premium Diesel Fuels to the basic diesel fuel which is why Shell Nitro is superior to most diesel fuels.

 

[Capra]

@Capra
This is info that I have found regarding premium diesels. Seems that performance can be maintained by keeping an engine clean rather than seeing an increase.

"Because diesel engines don't ignite fuel to create power (fuel is added to the air that is compressed instead), premium diesel doesn't usually feature a higher octane rating. Instead, this more expensive super diesel will feature chemicals in its mixture that are designed to shift soot deposits and other oily build-up from within the engine's fuel system"

So that is what you read.........

Diesel engines must ignite the fuel because that what gives the bang?........they do it through compression ignition and not spark ignition as in petrol engines.

Diesel fuels do not have an Octane Rating as Petrol Fuels do they have a CETANE Rating and it differs in Premium Diesel Fuels to the basic diesel fuel which is why Shell Nitro is superior to most diesel fuels.

Cheers, I know the basic difference of how a petrol and diesel ignite fuel. The area that we disagree on is where you said that there was a performance increase from using premium diesel. Can you read up on that??

 

[mancman]

The OP knows his own car like we all do, so if in his opinion if he feels like it runs better who are we to doubt his thoughts, poor guy won't post again,personally I think it runs better cos it's too hot and all our brains are fried.

 

[John Laidlaw]

I think you’re right- certainly didn’t want to chase him away!

 

[Botus]

Never ever noticed a difference except on a car designed for 98 where filling with 95 negatively affects power.
This discussion has been had many times and there is NO technical reason your car should be any better in 98 than 95 unless the car is designed for 98.

my latest bike is designed to run on 98, never knew, but two others with same engine said it does and makes a big difference. Got the manual out and it says use 98, if not available use 95 with reduced power and fuel economy

well yes there a difference ! now it has a massive flat spot around 4 to 6 k I guess running 98 it moved the ignition curve and one feels a bit more up to the point knock sensors wind it back and I now have this stupid flexible throttle cable sensation.... instead of instantly responding to my throttle input exactly as I want it... its feels like it adds stretch to the cable and responds a bit less and a bit after I wanted it ! which is awful...

rather oddly I got opposite affect in Europe.
over there my experience has always been the cr*p they sell e85, makes the bike run like a dog, with lumpy idle, no power and a rough / vibrating engine at all revs. You don't notice straight a way as you are on a part blend and getting used to terrible drivers on the wrong side (and the hell that is northern France Belgian motorways). But when one gets back to blighty and you fill with proper petrol it goes all smooth and the front wheel keeps coming off the ground when you accelerate

but on this bike going down to the tunnel my fingers didn't like the harsh vibration from the bars... then (as supposed to run 98) I got e100 when over there and the bike seemed quite happy and responsive and I didn't notice the flat spot and forgot about harsh vibration in the bars. Then I got back filled with 98 and its all harsh and nasty again. Not yet noticed the flat spot but not been exercising it as was 2 up when I last rode.

What I'm thinking is UK 98 is rubbish and not 98 whereas e100 has so much methanol (??) that it allows the bike to run as was designed. Probably as Ethanol allows up to 15:1 compression ratio the bike's getting less detonation and maintains a higher state of tune for longer (the bike is a 4 pot 16v 1300, makes 160 BHP and red lines at 9k - although they make a faster version with 2 air intakes and 175 BHP - Lotus or Riccardo helped play with it for BMW (as they didn't know what they were doing !)

 

[LostKiwi]

it moved the ignition curve and one feels a bit more up to the point knock sensors wind it back

This is exactly what happens.
On an engine designed for 95 octane the ignition curve is mapped for that fuel and will retard ignition if knock is detected. Of course this should happen rarely. Using 98 will not advance timing as the map is set to only retard from the optimal 95 settings.
If the map is set for 98 the knock sensor will detect more instances of knocking and retard ignition to suit, reducing power. Over time it will learn the new settings and adjust the adaptations to suit, hence why it can take some time after a change of fuel for the engine to 'recover' it's smooth running and power.
Not all systems behave exactly the same however and some may not tweak adaptations.
In many ways it's a pity they aren't designed to dynamically adjust timing both ways from the map settings and optimise timing across the rev range irrespective of the fuel the engine was designed for but I'm guessing there are good reasons for not doing this.

 

[KeithJG]

So as LostKiwi says above more power is obtained using a higher Octane / Cetane fuel but with diesel no advance or retard of a spark?

BUT if a cleaner burn happens then the bang gives more power ....even if it can`t be measured.....some of us have are more into car`s and therefore have a more sensitive bum!

Adding 2T gives a better burn because of the higher cetane rating it add`s to the diesel......none of you can argue unless you try it?

 

[LostKiwi]

So as LostKiwi says above more power is obtained using a higher Octane / Cetane fuel but with diesel no advance or retard of a spark?

BUT if a cleaner burn happens then the bang gives more power ....even if it can`t be measured.....some of us have are more into car`s and therefore have a more sensitive and bum!

Adding 2T gives a better burn because of the higher cetane rating it add`s to the diesel......none of you can argue unless you try it?

No advance of spark in a diesel is correct however exactly the same effect is obtained by advancing or retarding the point when injection starts.

Diesel is also not a bang but a comparitively slow burn (especially compared to petrol) as most of the fuel is injected after combustion starts unlike petrol where all the fuel was injected before combustion starts. This is part of the reason diesels don't rev.

There is no way you can feel power that can't be measured. A Dyno is far more sensitive and accurate than anyone's bum!

 

[Botus]

the new BMW map in my GS (the other bike) has a flat spot now ! one "fix" was to increase the sensitivity of the knock sensors (I was hoping this would help the high heat, high abuse over the top knock control at 6500 rpm) but now they have just given me no power at all at 4600rpm so it feels very nasty. Pulls like hell till 4500 stops for 500 RPM then wakes up again and carries on till 9k

I tried super unleaded thinking it must help, as I guess it can only be knock control "turning the key off at 4600 rpm for half an hour", but it made NO difference at all ! I'm going to slip 5% methanol in a tank of 95 and see if that cures it.... or somehow I'm going to have to get the old map back again !!!

 

[Craiglxviii]

No advance of spark in a diesel is correct however exactly the same effect is obtained by advancing or retarding the point when injection starts.

Diesel is also not a bang but a comparitively slow burn (especially compared to petrol) as most of the fuel is injected after combustion starts unlike petrol where all the fuel was injected before combustion starts. This is part of the reason diesels don't rev.

There is no way you can feel power that can't be measured. A Dyno is far more sensitive and accurate than anyone's bum!

That last bit made me laugh. Placebo effect is the very definition of “you can’t measure that kind of power!”

Another point to note, although I’m no powertrain expert I did do lots of work with military piston aero engines. Those were designed to run on anything from 83 to 130 octane fuel. Once fuel went over 100 octane the piston rings required changing to a higher rated type as the compression ratio (and thus temperature) went up enough to cause the original rings to fail in under an hour of running.

So, I’d be interested to know what physical differences an AMG engine has over its non AMG equivalent that aren’t related to boost pressures and engine maps.

 

[John Laidlaw]

It’s all about the nanoglide....

 

[Botus]

Another point to note, although I’m no powertrain expert I did do lots of work with military piston aero engines. Those were designed to run on anything from 83 to 130 octane fuel. Once fuel went over 100 octane the piston rings required changing to a higher rated type as the compression ratio (and thus temperature) went up enough to cause the original rings to fail in under an hour of running.

Compression can't change due to fuel type. High octane fuel burns slower, it allows the burn to start too early or in the wrong place (knock) without things getting out of control too fast. An engine with a high compression ratio and a lively ignition curve running low octane fuel, will shatter the rings, blow holes in the pistons and generally make it run bad

 

[Vintage Racer]

Must be my age.............maybe try 'go faster stripes'.

 

[LostKiwi]

blow holes in the pistons

Did that once. Full race 1275 mini engine (big valve head, ported, 300 degree duration cam, 45 DCOE carb etc) and skimmed the head to raise compression. Miscalculated it and instead of getting 13.5:1 ended up with 15:1....
Even with Xylol in the fuel at ridiculous levels it knocked a little. After not long it blew a hole the size of 10p coin straight through the top of no3 piston. The smokescreen was impressive to say the least!

 

[Craiglxviii]

Compression can't change due to fuel type. High octane fuel burns slower, it allows the burn to start too early or in the wrong place (knock) without things getting out of control too fast. An engine with a high compression ratio and a lively ignition curve running low octane fuel, will shatter the rings, blow holes in the pistons and generally make it run bad

That’s interesting, the manuals (British, American, German & Italian) all specifically stated that higher compression rings (and in the case of the D-B engines, different pistons and valves) were required due to compression increases.

 

[LostKiwi]

Compression ratio is a fixed value (except in some special variable CR engines).
It's defined as (S+C)/C where
S=swept volume (displacement of a single cylinder)
C=combustion chamber volume

In variable CR engines they vary the height the piston goes up the bore (thus increasing C whilst S remains constant.
If S is varied it's a variable displacement engine.

Different pistons may well be required to increase CR as pistons can be made with various sizes of dish in the crown. 1275 mini pistons were available with flat tops, 6cc dish or 12cc dish. The bigger the dish the lower the CR. In some cases forged pistons may also be required in order to better cope with power increases.
High compression rings are often chrome faced to better resist heat (as opposed to the standard cast iron ones).
Normally no change in valves is necessary though in some cases sodium cooled exhaust valves may be used to assist with heat dissipation.
The more CR the more heat as Botus said.

 

[Oldspanners]

Did that once. Full race 1275 mini engine (big valve head, ported, 300 degree duration cam, 45 DCOE carb etc) and skimmed the head to raise compression. Miscalculated it and instead of getting 13.5:1 ended up with 15:1....
Even with Xylol in the fuel at ridiculous levels it knocked a little. After not long it blew a hole the size of 10p coin straight through the top of no3 piston. The smokescreen was impressive to say the least!

Had near enough the same set up on my Mini 1293 S 13.5 CR and had a distributor set up to match which unfortunately went faulty and resulted in the same hole in the piston. Later we ran a Evo 2 RS 200 engine which shoved out 690 bhp on the dyno and we used a toluene mix not to give it an more power but to keep it together, didn't have to worry about fuel samples in those days.
Here I have changed from using 98 to 95E10 and have noticed no difference in power or mpg, L/100kms at all. Just reading in Auto plus about the conversion to run on E85 at €0.67 a litre against €1.48 for 95 E10 and €1.54 for 98. Won't really matter now the 80kph limit has come in!

 

[oigle]

Had near enough the same set up on my Mini 1293 S 13.5 CR and had a distributor set up to match which unfortunately went faulty and resulted in the same hole in the piston. Later we ran a Evo 2 RS 200 engine which shoved out 690 bhp on the dyno and we used a toluene mix not to give it an more power but to keep it together, didn't have to worry about fuel samples in those days.
Here I have changed from using 98 to 95E10 and have noticed no difference in power or mpg, L/100kms at all. Just reading in Auto plus about the conversion to run on E85 at €0.67 a litre against €1.48 for 95 E10 and €1.54 for 98. Won't really matter now the 80kph limit has come in!

E85 is the compulsory fuel that our Oz Supercars have to run. Seems to be OK. Plenty of power.