EvilBevel

Since we seem to have a broquet/optimax/ecotek revival, I was wondering about this and tried to look at it from a different angle.

I'm not saying product x works and y not, and I'm not after a debate about the merits of these products. The same would go for the difference between NUL and SUL.

What a I wondering about is: how is it possible to get a "better" MPG in technical terms? AFAIK the fuel that is injected into our engines (with a fire hose ) is directly related (I'm talking standard Scoobs) to the amount of air that is coming into the engine, and the boost/load site. There may me other parameters, but I think those 2 are the main ones.

So, even if the efficiency of the engine would improve, how would the ECU know to "squirt less" ? Would it go "ooh, damn, the engine is purring nicely, let's lean out the mixture" ? I can't imagine that.

OK, I can imagine the answer being "since it runs more efficiently, I don't have to push so much", but that is a "human" factor.

In short: does the ECU alter fuel mixtures in relation to the combustion efficiency ?

Theo

EvilBevel

Have to add one thing (talking to myself again ): let's assume that there is no ignition retardation, i.e. there was no det.

mook

My car (not scoob, not standard) has numerous engine sensors that between them are able to tell that the spark is brighter and can indeed move to a different part of the fuel mapping in the ECU and squirt less in. The ECU dosen't need resetting either which is a major plus. When switching from UL to SUL I went from approx 270 miles per 45 litres to 285/90 per 45 litres, moving to Optimax now sees that rise to around 300. I think a major factor in turbos is the fact that higher octaine fuel reduces the chances of detting which then prevents the over fueling needed as a 'coolant'. AFAIK

mook

I didn't see you additional bit then!! I reckon the 'benefit' is less noticable on an n/a car, but I may well be wrong.

DavidRB

If a higher-quality fuel produces more power per piston stroke then you can use less throttle to produce the same speed, hence you will see better fuel consumption.

Jza

Part of the previous millions of threads commented that the only way to test this properly would be to take an engine into a lab, and run it on a "before" and after basis.

Otherwise there are so many factors that can alter results. If you drive into a wind for example, it reduces MPG, so your results are out by a factor of wind, if you follow.

No one from the Broquets people were (at the time) going to conduct such a test, for whatever reason.

So anyone who claims they noticed a difference when using their car can only base this on their perception, not actual fact.

Jza

EvilBevel

Hmmm... It's still not completely clear in my head ... David, OK, so you would get a difference at cruising, I can see that. TPS would be lower for the same speed, which would help as long as you are off boost ( i.e. lower than 100 MPH on a flat road)

But at the same time, more efficient combustion = more exhaust gasses = quicker turbo spool up = quicker injection of said fuel. Would this mean (I'm just trying to think my way through this) that you might get worse MPG when you do short squirts, but better when cruising ?

Jza, I'm sure the answer *must* be what David said: the driver adapts to the more efficient engine. I can't imagine that the engine itself would use less fuel, it just wouldn't make sense (I think).

Final thought: fuel with higher RON/MON ratings are not per definition more efficient ... I thought it was even the other way round, but can't find the link to that right now. "Det resistance" is the main goal for using these fuels I thought ?

Jza

Evil,

Thats just it, there are to many factors to account for to be able to prove a "must be" comment like you make. Its just David opinion, and glad we are of it. Take is as that and your ok

What David says is possible and likely, but not a proven FACT. Its just one of hundreds of factors that influence MPG!!!

Jza

EvilBevel

With all due respect, but I think you are mixing two issues: I'm not asking "does product x improve MPG", I'm trying to find out how the improvement (provided it exists) would work technically.

We can discuss until we are blue in the face (in fact, we did that about 50 times on this bbs ) IF they work, but it's not productive IMHO. I'm sceptical, but I don't have strong feelings about those products one way or the other. Even if the improvement reported by some was to be due to "perception" ... most of our inputs is perception, so if it makes one happy, why not. People fit non recirculating dumpvalves for "perception" They even "feel" the turbo spools up quicker with them... hum.

However, that's not what I'm trying to discuss, I'm trying to get a clear view on just how the ECU would react on "more efficient combustion".

Mook mentioned a sensor looking at the flamefront ... what car is this ? I'm sure the only thing a Scoob would sense is the non-existance of det (knock sensor).

Jza

Fair point mate....

Jza

mook

Evil > I've got a Rover 220 turbo, the manual (at home) has a full list of sensors but there's allsorts such a knock sensor, lambda, various temp sensors in engine/oil/water etc, timing sensors, boost levels and so on, that all feed into the ECU. I could dig them out if you really want them. All the various factors mentioned above, such as wind, flat road, the weather, how much you dump your right foot, etc will affect what the sensors read and act upon.

Not sure if I'm going off on a tengent here, but does saying that different grades of fuel don't really affect economy/MPG mean that you would expect no change in performance/economy from a performance air filter/stainless exhaust. You are, effectively, changing the characteristics of the engine by putting the different grades of fuel in, so they will make a difference. Of course, as mentioned, for proof you would need to perform proper tests on a test engine.

FWIW - On the Shell site, they make mention of a test engine which they adapted to run half on normal UL and half on Optimax. They ran it for a number of thousand miles the stripped it. The Optimax 'side' of the engine had nice clean valves, whereas the UL was gunked up. I guess with the likes of Optimax it's more a case of keeping the car in 'from the factory' condition instead of slowely wearing out and loosing power over it's lifetime.

Does that make any sense, or shall I go back to the Hutch??

EvilBevel

>there's allsorts such a knock sensor, lambda, various temp sensors in engine/oil/water etc, timing sensors, boost levels and so on, that all feed into the ECU.

OK, so far nothing different from a Scoob then ... mind you, apart from the knock sensor, there is nothing so far in that list that would cause the ECU to change it's "fuel strategy". Lambda only works in the lower load region ( < 0.2 bar on Impreza), boost is used for timing/overboost detection etc ... Not trying to be argumentative, just going by what I understand so far from how the car works: the *amount* of fuel is only relative to air mass and load site (rpm/boost). Knock sensing is used to retard/advance ignition.

BTW: yes, would be interested to see if there are any sensors in your car that are not in the Scoob, so if you have a spare moment ...

>>Not sure if I'm going off on a tengent here, but does saying that different grades of fuel don't really affect economy/MPG mean that you would expect no change in performance/economy from a performance air filter/stainless exhaust.

I indeed don't expect the economy to change from air filter or exhaust mods. I do expect better performance - probably related to a bit more boost/lower intake air temp - from a decatted exhaust. Air filters don't do much IMHO, and I personally went back to the original Subaru paper job. The better performance will also mean worse MPG BTW, as you will a) be using that performance and b) when your car uses more air, it will also use more fuel (hopefully) up to a point.

Also: bear in mind that the Impreza at high loads dumps in fuel like mad, not for burning, but for cooling purposes. I can't imagine the type of fuel or whatever gizmo you fit would affect that ECU strategy ?

>>The Optimax 'side' of the engine had nice clean valves

Hmmm... this all sounds a bit too much like Shell is trying to claim that they are the first to do additives ... On the continent, it is a known fact that the base fuel from most of the big names is identical (they even have pipelines to each others refineries ...), but their main difference is their (highly secret I might add) mixture of additives they put in.

Best way to clean off the gunk is giving the car a good trash BTW, burns it off nicely (stay under the speed limit though LOL)

>>Does that make any sense, or shall I go back to the Hutch??

Hutch it is for you then m8 lol, just kidding.

Theo

Diablo

Is it not as simple as this:-

Higher octane = more advance (or should I say less retard) = more efficient combustion process than lower octane.

Greater efficiency = less energy required.

As the main energy source is fuel, fuel consumption is lower.

Its not IMHO a case of getting better mpg on super, as getting worse mpg on regular, if you get me.

This is a very simplified version of events. You'll need a physisist to explain the technicalities.

D

AlexM

Hi,

I have noticed that the amount of throttle needed to maintain a high speed cruise will vary quite a bit. I can see this both from the manifold vacuum at a given speed, and the difference in speeds that can be reached at a given vacuum.

This can be observed readily on outward and return trips with the same tank of fuel, but different weather conditions e.g. fine weather outbound / rainstorms back.

There are too many other factors to seperate out the effect of fuel / broquet or other minor influences in isolation unless you've established repeatable test conditions IMHO.

Cheers,

Alex

mook

Evil > *lol*!!

As far as extra bits on engines, such as filter/exhausts, go, I appreciate they will lower MPG if more air/fuel passes through the engine in any given time span.

*drop of shoulders* I'll dig out the manual when I get a chance then

Re - dumping of fuel for cooling purposes. I would have thought that by running a higher grade of fuel which in turn prevents overheating, this would prevent so much fuel being added as a coolant and thus improve your MPG?!?

Regarding the sensors effecting how much the ECU decides to squirt in, I think it might be a better analogy to say that it just gets more out of what it suirts in so your right foot makes the compensation - as said above, it more a case of the car running less efficient on UL than more efficient on SUL/Optimax.

Point about Shell website, you're probably right there! I have my suspisions that the label of Optimax is just a packaging ploy with Shell shipping there standard European SUL to the UK too, but that's pure conjecture.

Here's a slight digression - as Scooby engines are of the boxer veriety, are they also then quad cam? I assume so.

mook

Okay then - had a look at the manual and it states the following are all input into the ECU -

* Crankshaft sensor
* Manifold absolute pressure
* Coolant temp sensor
* Inlet air temp sensor
* Oxygen sensor
* Throttle potentiometer
* Knock sensor
* Battery supply
* Ignition supply
* Diagnositc input
* Fuel temp sensor
* Power earth
* Sensor earth

I don't know what half of them do, but there you go. It then states the following are output from the ECU -

* Ignition coil
* Injectors
* Stepper motor
* Temp gauge
* Fuel pump relay
* Main relay
* Diagnostic output
* Oxygen sensor heater relay

Again, some of them are beyond my knowledge, but it can obviously set fueling and ignition which I take it ia how it manages to return better MPG with Optimax than UL

Floyd

iTrader: (9)

Air filter and exhaust mods have got to reduce pumping losses, right? It improves power released and ecomony.

The less restrictions mean that the engine is producing more power for a given throttle position.

F

EvilBevel

OK ... D: OK, I agree with the knock sensor bit, but I did say I was working from a situation where ignition retardation was already at 0 in the ECU (MY01 would be a different situation)

Alex: yeah, I noticed that too ... some days, the car stays off boost at 100, the other at 103 mph (German Autobahn OK) ... same roads, so probably a question of colder/denser air (closer to optimal charge temp I mean). You would see a difference in mpg when driving constantly.

Mook: ok, thanks for the list. I'm not a mechanic, but from that list, I would say that your car's fuelling will be driven (at boost) from the MAP sensor (probably corrected by intake temp sensor), whereas a standard Scoob would use the MAF (Mass Airflow) sensor. Oxygen = Lambda = used when off boost.

I guess I'm mostly arguing with myself actually ... I do understand that a better MPG is possible, but it would always be a reaction of the driver to not use the extra power, but to do the same speeds with less power. In other words, the MPG seen (or not seen) would almost entirely depend on the driver ... in my case I would probably just conclude the car feels "nippy" and consume just as much - unless I would be doing long boring stretches of highway I guess.

DavidRB

Exactly, a higher quality fuel's primary reason for existance is the ability to deliver more power. The most noticeable result of this is better acceleration and a higher top speed. Improved MPG is a result of artificially restraining the car at a constant speed for long distances (on the road) and would not normally be seen when flat-out acceleration was always being used (on the race track).

I'm convinced that it really is quite simple!

mook

That makes sense to me , you still cruise at the same speed down the motorway, as opposed to suddenly doing an extra 4-5mph after you've put the better fuel in

dowser

Hi Theo

An example: when I removed my induction resonator, not only did throttle response improve, so did economy.

I scratched my head over why, but figured it's the time thing - prior to removal: I put my foot down, ecu instantly squirts fuel but the air takes a fraction longer because of the resonator restriction to airflow....so car's running rich for a split second.

After removal: air arrives quicker, mixture correct quicker, less fuel used.

This ties in with increased throttle response as well - everything happens quicker. I also found because things happened quicker I started using part throttle, instead of full throttle, to get the same performance...I guess this is also a factor.

Just my tuppence worth

Richard