ChaseN

So, for the 99% (I hate that term now) that don't have a means to test fuel density every time we fill up, octane is the best indicator we've got, which to me means run the highest available. I know you aren't saying anything to the contrary...just clearing things up I guess.

With Motronic, wouldn't the motor have to knock in the first place for it to pull timing? I don't think the car "knows" that you filled it up with 89, it just knows when the engine isn't running like it should...

ChaseN

Does this decrease efficiency, decrease power, or both? What I mean is you have a combustion chamber full of X amount of air being combined with Y amount of good, high density gasoline. Say your next tank of gas is a lower density. If it still combines Y amount of gas (by volume) with X amount of air, the mixture would ostensibly be leaner. I'm no expert, but it seems to me that a sufficiently advanced EFI system (Motronic would seem to fit the bill) would detect that leaner mixture, and now introduce Z (a higher volume) amount of fuel to combine with X amount of air, in order to sufficiently enrichen the mixture to stoich or whatever AFR it looks for - Thus, in my admittedly non-qualified brain, producing the same amount of power, but increasing fuel consumption thereby reducing efficiency?

When speaking of fuel density as related to performance...would filling up in the early morning when the outside air is at its coldest be beneficial? Fuel is denser when cool, correct?

Agreed on the ethanol issue. I sat through a talk given by T. Boone Pickens about the issue two years ago...the forces at work behind ethanol in gasoline are almost criminal.

Indycam

If you want to say that denser gas of lower octane will put out more btus then thinner gas with a higher octane , then I will say you might be correct but when you do a real world test you will find that the thinner high octane will get you down the road quicker in a 964 .

Ethanol fuel (E100) 76,100 btu/gal
Gasoline (conventional, summer) 114,500 btu/gal
Gasoline (conventional, winter) 112,500 btu/gal
Gasoline (reformulated gasoline, ethanol) 111,836 btu/gal
Gasoline (reformulated gasoline, ETBE) 111,811 btu/gal
Gasoline (reformulated gasoline, MTBE) 111,745 btu/gal
Gasoline (10% MBTE) 112,000 btu/gal
Gasoline (regular unleaded) 114,100 btu/gal

Diesel is denser than gasoline , its "Specific gravity" is greater than and it has more btu/gal .

E85
http://en.wikipedia.org/wiki/E85
http://www.topspeed.com/cars/ethanol-cars/ke327.html

Ethanol = 22.27 kWh/gal
http://www.carmagazine.co.uk/Green-C...enigsegg-CCXR/
"A green Koenigsegg? Surely some mistake?
For those who find themselves a little underwhelmed by the 806bhp power output of the Koenigsegg CCX, check out the new CCXR. Unveiled to a stunned Geneva audience, the CCXR packs a barely believable 1018bhp and - get this - it runs on environmentally friendly E85 biofuel. 'Our engineers couldn't quite believe the figures when we tested the car,' Christian von Koenigsegg told CAR Online when he showed us the car. 'Apart from a few minor changes to the fuel injection system, fuel lines, upping the supercharger boost pressure from 1.2 to 1.5 bar and changing the piston rings, the engine is the same as that in the CCX,' he explained."
"The engine tune in the CCXR is more powerful than that of the CCX, putting out 759 kilowatts (1004 bhp) at 7200 rpm and 1060 Newton metres of torque at 6100 rpm, 25% more power than the CCX.[2][3] Christian von Koenigsegg said that "Our engineers couldn't quite believe the figures when we tested the car".[4] The increased power is a result of the cooling properties of ethanol in the engine's combustion chambers allowing for a higher pressure in the cylinder and the biofuel having a higher octane rating of 113 RON compared to 95 RON for petrol in North America and 100 RON for petrol in Europe..."

Less kWh/gal than gasoline , Ethanol = 22.27 kWh/gal / Gasoline = 33.41 kWh/gal , and the fuel gives higher performance ? That does not line up with what you are saying , in fact it shows that what you are saying is not real world .

http://www.buyrealgas.com/

Makmov

becarful there. It is not the fuel that is doing it. The fuel choice allows you to, but the increased cylinder pressure from turning up the boost.

Remember octane rating is the number that the fuel will detonate at x cylinder pressure.

On a standard 964 you do not have that ability the cylinder pressure is fixed. It's not a apples to apples comparison.

Lorenfb

"If your car isn't knocking, then higher octane will basically yield little to no power increase."

Actually, in most cases one will never become aware of knocking, given the
knock control system used in the 964 DME ECM. What really happens is that
the ECM will retard the spark and eliminate the knock immediately and on
a singular cylinder if that's the case. The retard remains until the knock is
eliminated, e.g. less engine load. With a retarded timing the torque is reduced
and thus performance.

So when using lower octane fuels the engine will produce lower torque,
i.e. It results in a higher probability of the knocks and the knock control
system retarding the timing. Furthermore, when using the so-called 'performance'
chips, the probability of knocks (because of the 'pushed' timing) is increased
resulting in actually reduced torque (performance) under some driving conditions.
So using a 'performance' chip could be considered another zero-sum-game.

Makmov

Correct. I had already made metion of that fact.

Lorenfb

"but it seems to me that a sufficiently advanced EFI system (Motronic would seem to fit the bill) would detect that leaner mixture, and now introduce Z (a higher volume) amount of fuel to combine with X amount of air, in order to sufficiently enrichen the mixture to stoich or whatever AFR it looks for - Thus, in my admittedly non-qualified brain, producing the same amount of power, but increasing fuel consumption thereby reducing efficiency?"

The Porsche 964 DME ECM does not use power (HP) as a feedback element to tweak its output.
It's only feedbacks are; RPM, O2, load (AFM), cam timing (Hall sensor), temp (air/head), and
knock signals. So the the ECM never knows it actual power output. Although the O2 sensor
does help it maintain close to the ideal AFR for peak torque.

Indycam

So you fail to address that a lower fuel density fuel can produce more hp and torque than a higher density fuel . You dodged it by pointing to the boost .

That's not the whole story , it's much more interesting if you look into the reality .

The pressure is constantly changing . And is changeable .

This is another subject that you don't quite get .
"A little knowledge is a dangerous thing"
Your "advice" is "funny" and dangerous .
Anybody who follows your advice will put their engine at risk of great damage .

Indycam

Is there any system on any car that looks at HP ?

I've been meaning to contact you , I picked up a auto force efi 8400 .
Have you ever used one ?

Lorenfb

"Is there any system on any car that looks at HP ?

I've been meaning to contact you , I picked up a auto force efi 8400 .
Have you ever used one ?"

Please call sometime. The number is on my website.

Makmov

No I think it's you that is not getting it.

It is NOT the fuel that is making the increased hp and torque. The fuel is allowing the engine to make increased hp and torque by increasing boost in this case. The fuel is just allowing them to do it.

And actually no, there is not a whole lot more that needs to be said about octane.

Tell me exactly how the cylinder pressure at detonation is changing in a 3.6 964 motor. The only way to effectively do that is variable valve timing and or boost, which this particular engine has neither. So tell me smarty pants how is that happening.

Lastly I have not given anyone advice on what fuel to put into their car. I only pointed out that octane is somewhat meaningless in assessing fuel quality, and an explination of fuel density in relation to performance.

Show me where I said you need to run this fuel or else. The closest thing was a suggestion to use the best quality fuel which would likely come from a name brand supplier. How is that putting anyone's engine a great risk, moron.

Makmov

Not really the case at all. In the case of the 964 the mapping of the factory chip was intentionally lean for better fuel economy and emissions.

So a good performance chip remaps the fuel trims increasing power and performance.

Lorenfb

"Not really the case at all. In the case of the 964 the mapping of the factory chip was intentionally lean for better fuel economy and emissions."

The AFRs are so close to the ideal range (within a 2 point range) that tweaking the fuel maps
yields basically NOTHING for a stock engine. That's the TOTAL hyperbole (and snake oil) of those
that sell the so-called 'performance' chips. It's all about how much the timing can be 'pushed'
that yields a torque change. There's no real knowledge required. It's simple; for every one degree
change of timing, a three to four ft-lbs change in torque results at the peak torque point.

"So a good performance chip remaps the fuel trims increasing power and performance."

Sure? Let's see the data where JUST a fuel map change has yielded a torque gain of any significance
without tweaking the timing for a stock engine!

Bottom line: Another one that 'bought' into the tuning B.S.!

Makmov

I think you will find all the data you need here http://www.911chips.com/index.html.

And sure there might be some ing timming envolved but your argument was a chip was net zero.

Lorenfb

"I think you will find all the data you need here"

Please! How about some REAL and UNBIASED data?
Doubt that there are any or if so won't provide any because it indicates the ZERO effect of AFR tweaking.