93 octane gas only?

[JackG]

Originally Posted by Peer

trube78 wrote:
> Expect a decrease of about 10% in gas mileage and similar HP decrease from
> using regular vice the recommended premium gas.

A ping-free engine will not gain any power by increasing the octane rate.

-- peer

You're missing the point. If an engine is designed to use, and benefit, from 93, it will most definitely lose power when using 87. The engine management computer will detect pinging, and will retard timing, enrich the fuel mixture, etc. to stop the ping. It will be ping-free, but will be down on power and will use more fuel on 87.

Running 93 will gain you power in this case.

[clickman]

So I'm trying to understand what octane rating I really need here in the great white north:

My manual says:

1. "Your engine is designed to provide optimum performance and fuel economy using unleaded premiuim fuel with an octane rating of 98 RON (93 CLC or AKI).

Porsche also recognizes that these fuels may not always be available. Be assured that your vehicle will operate properly on unleaded premium fuels with octane numbers of at least 95 RON (90 CLC or AKI), since the engine's "Electronic Oktane knock control" will adapt the ignition timing, if necessary."

2. On the fuel filler door of my Box it says "Minimum octane RON+MON/2 = 93"

Some quick net research tells me that AKI (Anti Knock Index) is the same as (R+M)/2.

Therefore the manual and the fuel filler door don't agree, and I'm left wondering if I really can run 91 or 92 instead of the much pricier and rarer 94 I'm currently using.

It sounds some of you are running 91 without any issues, but I'd like to know if that's more universally the case before I switch.

And I'm also curious if USA cars have the same label on the fuel filler door that I have.

[nola mike]

not necessarily. even if the engine specifies 93, it won't gain hp/mpg UNLESS pinging actually occurs when using 87. this won't always/usually happen, unless you're driving hard, up steep hills, hot weather, etc. my saab specifies premium also; it's a bit different that it's low compression, but the turbo is much more likely to detonate than a streetable high compression engine. instead of retarding timing, it reduces turbo boost. so i can actually see when the computer kicks in by watching the boost gauge. surprisingly, this only occurs in extreme heat, a/c on, up steep hills, with the pedal floored. otherwise i always get full boost.

Originally Posted by JackG

You're missing the point. If an engine is designed to use, and benefit, from 93, it will most definitely lose power when using 87. The engine management computer will detect pinging, and will retard timing, enrich the fuel mixture, etc. to stop the ping. It will be ping-free, but will be down on power and will use more fuel on 87.

Running 93 will gain you power in this case.

[Peer]

nola mike wrote:
> even if the engine specifies 93, it won't gain hp/mpg
> UNLESS pinging actually occurs when using 87.

Exactly, and this has been my point all along. As stated in my first post, I believe there would be less confusion in regards to octane ratings if it wasn't represented numerically along with some superlatives:

"The term "Premium" is extremely misleading when it comes to gasoline. People assume that when they buy "Premium" they are buying the best there is to offer. This couldn't be further from the truth. 87 octane has more potential horsepower than 93 (or higher) octane. Octane is a rating. It is a calculation that predicts when pre-ignition will occur in any given engine. The lower the octane number the more volatile the gasoline -- by comparison, the higher the octane number the less volatile (combustible) the gasoline. Then why do racers use higher octane? Simple, the higher compression and more ignition advance an engine has, the more likely pre-ignition will occur -- hence, they need high octane fuel to prevent this from happening. If you want your engine to run the best possible, then run the LOWEST octane that you can without pre-ignition (pinging). If different terminology was used to distinguish grades of gasoline, people would think more accurately about it -- for example, instead of calling it "Regular" call it "Highest Volatility" and instead of "Premium" call it "Least Volatile"

-- peer

[JackG]

Originally Posted by Peer

nola mike wrote:
> even if the engine specifies 93, it won't gain hp/mpg
> UNLESS pinging actually occurs when using 87.

Exactly, and this has been my point all along. As stated in my first post, I believe there would be less confusion in regards to octane ratings if it wasn't represented numerically along with some superlatives:

"The term "Premium" is extremely misleading when it comes to gasoline. People assume that when they buy "Premium" they are buying the best there is to offer. This couldn't be further from the truth. 87 octane has more potential horsepower than 93 (or higher) octane.
-- peer

While I agree that the term "premium" is slightly misleading to the uninformed, it is also appropriate. The numeric system confuses you, so it's not perfect either.

Higher octane fuel is better behaved. It doesn't detonate in high compression or turbo/supercharged engines as easily. It's necessary in many high performance engines that would simply self-destruct running "regular". It has highly desirable burn characteristics compared to "regular". It is indeed "premium" fuel. It is indicated as such by the higher octane number.

The lie you continue to propagate is "87 octane has more potential horsepower than 93 (or higher) octane". That is simply untrue. Both regular and premium have the same energy content, and therfore the same capability to produce power. They do have different burn characteristics, making the premium fuel necessary in some engines that require it.

Many modern engines that require premium will not ping when fed regular. The engine computer adjusts to compensate for the less than ideal fuel. You may not see it until the boost gauge gives you an indication (which is likely a last-ditch effort to save the engine, not the first), or you may not notice it at all. The engine management computer is doing its job. The manufacturer has nothing to gain in requiring premium fuel if it wasn't needed. They do it for a reason, and it's not to give a liberal arts poetry writer something to argue about, on a subject matter in which he seemingly doesn't have a clue. It's because the engine was designed to take advantage of premium fuel, thereby producing more power, and it requires it.

Take a freakin' engineering class...

[nola mike]

Originally Posted by JackG

While I agree that the term "premium" is slightly misleading to the uninformed, it is also appropriate. The numeric system confuses you, so it's not perfect either.

i'm not confused; numerals refer only to the volatility of the fuel.

Originally Posted by JackG

Higher octane fuel is better behaved. It doesn't detonate in high compression or turbo/supercharged engines as easily. It's necessary in many high performance engines that would simply self-destruct running "regular". It has highly desirable burn characteristics compared to "regular". It is indeed "premium" fuel. It is indicated as such by the higher octane number.

how is it better behaved? does it ask permission before pre-detonating? it doesn't detonate as easily, that's it. look into your own advice as to what the numeric system means. it has nothing to do with the quality of the fuel. how about diesel engines? the "premium" tendency to not detonate would be opposite what you'd want in that case. in fact, once detonated, the flame front is governed by the combustion chamber, not the octane of the fuel. the only undesirable burn is pre-detonation, which is an unorganized explosion--hence the engine knock. what are these "highly desirable burn characteristics" you're talking about?

Originally Posted by JackG

The lie you continue to propagate is "87 octane has more potential horsepower than 93 (or higher) octane". That is simply untrue. Both regular and premium have the same energy content, and therfore the same capability to produce power. They do have different burn characteristics, making the premium fuel necessary in some engines that require it.

agreed, except for the "necessary" part.

Originally Posted by JackG

Many modern engines that require premium will not ping when fed regular. The engine computer adjusts to compensate for the less than ideal fuel.

that's the point of the thread.

Originally Posted by JackG

You may not see it until the boost gauge gives you an indication (which is likely a last-ditch effort to save the engine, not the first), or you may not notice it at all. The engine management computer is doing its job.

what would be the "first" ditch effort to save the engine? no, this is the first and only adjustment made in response to pre-detonation. if i (and the knock sensor) don't notice pinging, then it ain't happening. and agreed, that's the engine management system doing its job--preventing potential engine damage.

Originally Posted by JackG

The manufacturer has nothing to gain in requiring premium fuel if it wasn't needed. They do it for a reason, and it's not to give a liberal arts poetry writer something to argue about, on a subject matter in which he seemingly doesn't have a clue. It's because the engine was designed to take advantage of premium fuel, thereby producing more power, and it requires it.

Take a freakin' engineering class...

the manufacturer specifies it because under some circumstances, you won't get as good performance, and possibly fuel economy, on lower grade fuel. not always, not even usually. they specify it because it gives an extra margin of safety which may or may not be needed. it's quite possible that the engine detunes under some circumstances when using lower grade fuel. is that dangerous to the engine? no. does it degrade performance under these circumstances? yes. which engineering class explained to you the differences between premium and unleaded fuel and their effects on sports car performance? right, that's what i thought. if yer gonna flame, maybe you should have some facts or references to back up your bs?

[JackG]

This is getting out of hand, but I'll play one more time...

Quote:

"i'm not confused; numerals refer only to the volatility of the fuel."

Unless you're peer posting under a different handle, I wasn't referring to you. My post was a follow-up to his post. Are you peer?


Quote:

"how is it better behaved? does it ask permission before pre-detonating? it doesn't detonate as easily, that's it."

Bingo. It is better quality (better behaved) because it doesn't detonate as easily.

"how about diesel engines?"

Non-sequitur.

"what are these "highly desirable burn characteristics" you're talking about? "

Resistance to pre-ignition.



Quote:


""making the premium fuel necessary in some engines that require it.""

"agreed, except for the "necessary" part."

Really? You know more than the OEM's? Cool.

A high compression or turbo engine "requires" high octane gas. You own story about your boost gauge proves that. The protection that the OEM builds into the engine management is just that... protection. The engine wants/needs/requires premium to operate in its design performance envelope. The OEM tells you that. You're smarter than they are?



Quote:

"that's the point of the thread."

Actually, the thread was started by someone asking if 93 was necessary. You replied "allegedly (it's recommended). i'm sure there'll be disagreement, but i don't think you'll blow up if you run 87. you most likely won't be as fast, and i probably wouldn't flog the car through extreme heat/mountains/etc."

Actually, it is recommended, not just "allegedly". You don't "think" it will blow up. That makes us all feel more secure. You agree it will lose power. That's my point... thanks.


Quote:

"what would be the "first" ditch effort to save the engine?"

Retarding timing, enrichening the mixture, cutting fuel/spark are some that come to mind. You do realize that the boost is produced by exhaust gases, right? It could be you are seeing the results of other adjustments when you see boost drop. Kill spark, kill fuel, reduce exhaust gas, boost drops.

"no, this is the first and only adjustment made in response to pre-detonation. if i (and the knock sensor) don't notice pinging, then it ain't happening. and agreed, that's the engine management system doing its job--preventing potential engine damage."

Did you write the software that runs the engine computer? Are you completely sure that the turbo boost is the only response that it has? Cite? Besides, the knock sensor can hear pinging before you do.



Quote:


"the manufacturer specifies it because under some circumstances, you won't get as good performance, and possibly fuel economy, on lower grade fuel. not always, not even usually. they specify it because it gives an extra margin of safety which may or may not be needed. "

Is it performance, or safety? You bounce around in your thought about why they specify premium. And you also wrote that you "don't think you'll blow up if you run 87", but now it's for safety? What exactly is it you do think?

"it's quite possible that the engine detunes under some circumstances when using lower grade fuel. is that dangerous to the engine? no. does it degrade performance under these circumstances? yes."

No... it's a fact that it detunes. The OEM's state that is exactly what they do.

"which engineering class explained to you the differences between premium and unleaded fuel and their effects on sports car performance? right, that's what i thought. if yer gonna flame, maybe you should have some facts or references to back up your bs?"

I'm waiting for your cites, references, and engineering classes to back up your BS. If you require them for me, surely you have them for your own BS, right?

BTW.. I didn't flame you. You seemed to take it personally. Maybe you should learn to read a thread, and remember what you said back in post two of this thread, " i'm sure there'll be disagreement". There is, and you're surprised?

BTW... pony up for a shift key. Capital letters... what a concept.

[Peer]

I wonder why some people on this forum often resort to personal attacks, as if they were struggling with a self-esteem issue that brings an animosity towards other forum members (who they obviously have never met, or know).

F.ex, while everyone in this thread stuck nicely to the issue at hand, JackG decided to go off on some frivolous personal attacks:

> They do it for a reason, and it's not to give a liberal arts poetry
> writer something to argue about, on a subject matter in which he
> seemingly doesn't have a clue.
>
> Take a freakin' engineering class.

I'm not sure if the above was addressed to me, though, I'm fairly certain that JackG knows little to nothing about what classes his fellow forum members have taken over the years.

-- peer