The Truth About Gasoline

[mattycakes]

the truth about gasoline is for ca people it has mtv-e in it and its going to give us all cancer becuase of lame-*** nafta. sick!

[curtis73]

Originally Posted by 534BC

Now that I think about it, I am wondering if any cars are normally "on the edge" od detonation enough that they are relying upon the knock sensor for timing control?

In other words the timing is not normally being retarded because of knock sense so that increase in octane will not advance timing any.

The factory computer sets an optimum ignition curve. It leaves it fully advanced to that point unless it senses detonation. So, if your owner's manual recommends 87 and you put 93 in, it won't continue to advance, it will just use the default map in the memory.

So, no more power or economy will come from more octane unless something is out of whack with the engine. As a normal operational thing, a stock engine will rarely retard ignition on the recommended fuel.

[curtis73]

Originally Posted by drew300

Yes, octane rating is the resistance to detonation. With a higher number, the car can advance it's timing, and increase fuel economy. It's worked on every car that I could change the timing on, but now I have to let the computer do it.

Advancing the timing past optimal lead for your combination will hurt power and most likely economy with it. If your car makes best power on a dyno at 35* total advance with 87 octane, switching it to 37* and 93 octane will lower power. The key there is flame front. Since you haven't changed the flame front speed, you build too much pressure 2 degrees sooner in the chamber, meaning the rising piston has to fight more pressure. The result is lower power.

Proper advance doesn't change with octane, its fixed given the mechanical operating parameters of the engine. This is the exact reason why you need ENOUGH octane and adding more won't make more power.

Adding more octane won't "let" the computer do anything. It won't go past optimum lead. You have to physically program the computer for more timing, which, like I said, will most likely hurt power and economy. The right combo is the best combo. More is not better.

[drew300]

Curious.
My VW GTI required premium fuel. The manual said it would run on regular, but at reduced power.
An old car with breaker points, I could manually advance the timing with premium, and get better mileage, but that timing would would cause knocking if I put regular in it. And that really hurt performance.
My present car, the manula suggests premium if I'm towing, or using the car in very hot weather.

[curtis73]

Originally Posted by drew300

Curious.
My VW GTI required premium fuel. The manual said it would run on regular, but at reduced power.
An old car with breaker points, I could manually advance the timing with premium, and get better mileage, but that timing would would cause knocking if I put regular in it. And that really hurt performance.
My present car, the manula suggests premium if I'm towing, or using the car in very hot weather.

Exactly what I was saying with the VW... its timing curve, compression, and other properties are optimized for premium. Reducing octane kicked in the knock sensors, retarded ignition, and reduced power.

Conversely, my 73 454 is optimized for 87. If I advance the timing and run 93 it just knocks and pings because the flame front is smacking the top of the piston way too early. Power and economy suffers greatly. I'm using more of the crank's rotation fighting the early ignition.

All I can suggest on the points car is that it was timed conservatively in order to prevent overheating, reduce NOx, or it was an HD application where detonation was a potential problem

And your present car... they're just covering their butts on warranty repairs in case you're one of those tow drivers that just puts their foot to the floor and hopes

[Derby]

Interesting discussion, but I like to make a comment.

a stock engine will rarely retard ignition on the recommended fuel.

The thing with the ecu is that is programmed in a room with a constant temperature and constant humidity. In normal driving conditions the ecu will retard ignition. High temperatures, heavy load or high altitude have influence on the combustion. So using fuel with a higher octane number can increase power. Or like BMW likes to do two different ignition maps for two different types of fuel.

Derby

[Reg Saretsky]

To give you bettter miliage form higher octane fuel.

This woudl idicate a slight timing problem,I believe? Otherwise, the miliage would not change

Lower volume engines require higher compressiuon ratios, hence higher octane to allow ignition at the 'optimal power moment'. That is why racing engines need high octane ( max power @ high compression).

Its the reason that the lil Merlin engine gave 1,650 hp in your Grampas' Mustang on 100/130 octane, while your Grammas'
Lavochkin needed a heavier engine ( higher volumetric) to keep up...

[Reg Saretsky]

Best layman's explanation of Octane vrs power curve I've seen in long time!

Now, about your Gramma's Lavochlin...
http://pratt.edu/~rsilva/index.htm

[MishaA]

Originally Posted by Derby

The thing with the ecu is that is programmed in a room with a constant temperature and constant humidity. In normal driving conditions the ecu will retard ignition. Derby

Who told you this?

[Derby]

Nobody told me.
I worked at a company for a while that programmed ecu's for LPG systems. And the base maps were created in a office. And off course the ecu can interpolate the data and has a certain freedom of choosing the right timing, but that is for a reason.
What is your point of view on this matter?

What I wanna say is that the engine never runs on the limit of knocking/no knock.

Derby

[MishaA]

Don’t know what is LPG, sorry…

I left engine R&D in the mid 90th, and at that time everything in engine design (including ECU software) were first designed and put together in the office and then checked and tested in the field, and corrected accordingly, in several iterations. In terms of base maps it means the first version was definitely created based on static dyno data, and then it was modified based on the subsequent field tests. I do not have any reason to think the procedure changed to worse since those times.

[Reg Saretsky]

Actually, CNG, compressed natural Gas , is more likely.

LPG is used in vehicles used confined spaces due to low emissions( mines, malls, etc.)
Thx
Reg

[MishaA]

Oh, yeah, and the second part, sorry
My take is that engine is tuned to run optimal ignition timing whenever possible - this is the only way to have highest possible power and highest possible efficiency simultaneously; and engine is designed so that optimal timing is pretty close to the detonation limit on full throttle – again, this is the only way to get maximum out of the given engine. Of course, recommended octane rating assumed.

[Derby]

@MishaA. Reaction on your first comment,
You have no reason to think the procedure has changed since then, but you give the answer yourself. Testing. Testing is expensive. And the only thing that counts these days is emission regulations. Fuel economy isn't of any interest.

LPG (liquid petrol gas) is a common fuel in europe. It can be found at most gas stations through out europe. CNG is something else, and is a lot harder to implement in vehicles.

I have reason to believe what you say but on the other side I keep wondering about exhaust gas temp. (catalyst temperatures) in combination with high CR's. And BMW definately run better on high octane fuel then on normal octane.

Someone with more info about that?

Derby

[grego101]

someone gave me a half a bottle of iso-octane. what can I do with it. I am interested in knowing if I can use this in my truck. like put about 4oz to a tank of 87 octane. What will that do.