93 octane gas only?

[pteam]

Originally Posted by porscheracer

This is a damn ass thread... especially from a guy who owns a yellow Lambo and Ferraris. Pteam for Poseur Team?

hmm I just noticed this reply porscheracer, thats a pretty F'ed up reply. If you notice all I did was ask "Does the boxster / S require 93 octane gas only?" because I havnt owned a boxster in about 6 years and that was a non - S version. Especially since my girlfiend is driving it everyday right now I need to make sure that the proper gas is going into the car.

Maybe CJ Boxster was on the right path about you when he asked if you forgot your Vagisil???

[Peer]

JackG wrote:
> In an engine optimized to burn 87, you don't make or lose HP by
> using 93. You just pay more money.

Well, actually the best matching octane/timing would be a compression that's just on the limit to ping. However, since pinging is bad for the engine, the manufacturers are usually exaggerating the recommended octane rating just to be on the safe side.

-- peer

[trube78]

For high compression high reving engines, advancing timing just before ping occurs is great for steady state driving on the flats. Anti knock sensors are inserted to ensure there are no instances where knock actually occurs in the transients although the use of High Octane gas ensures a reasonable engineering margin of safety. Continuing to retard timing to prevent knock will adversely affect both power and MPG. For many cars the computer will log instances where the anti knock sensor retards timing. Dealer Repair shop use it for troubleshooting to see if there is an engine management problem. In BMWs if there is consistent indications of knock onset without an accompanying engine problem they will assume low octane fuel is used (BMW also logs over-rev situations on their cars and has used the data in warranty claims in the past.) I do not know what the new Porsche computer logs but it does log more than they did in the past. Under current EPA rules and automotive engineering standards. Exagerating Octane requirements in order to squeeze additional performance is prohibited. The Mazda RX-8 performance was downgraded due to engineering sleigh of hand by mazda. When independent testing was conducted, the output was downgraded and Mazda had to compensate their new RX-8 owners. My personnel experience with high octane/high performance engines. Expect a decrease of about 10% in gas mileage and similar HP decrease from using regular vice the recommended premium gas. So you will loose in the end plus possibly put your engine's long-term life at risk during hard acceleration. while my 'test" were not scientific other folks experience concurs.

ATB,
Tom

[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

[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