Dave07997S

98 Ron is = to 93 US.

Dave

dasams

Usually but not always. The US spec is to report the ave of the research and motor octanes, hence the (R+M)/2, you see at the pump. If a gaso tests at 98 on the RON protocol and an 88 on the MON protocol, it's a 93. But if it's a 98 and a 90, then it's a 94. Get it? dave

dasams

Sorry, but this is not right. The car will run fine on high octane fuel. dave

dasams

Can you site a source that says the flame front propogation speed will be reduced, let alone reduced to the point that incomplete combustion is realized? dave

Jim (CIA PCA region)

I've been doing research on gas for a forthcoming article.

The U.S. spec cars (9x6 and 9x7) are 93 AKI (RON+MON)/2 MIN. Note the use of "MIN". The German cars use 98 RON MIN. Also note the use of "MIN."

Assuming I can get the attachments to work, the black car is a U.S.-spec 997.2, and the red car is a German-spec 997.2 GT3. (It's interesting that the GT3 sticker has a 996 part number on it.) I've also attached a pump shot from WI showing excellent labeling.

Now of course the cars *can* run on 91, as they're forced to do in some areas, but it doesn't meet Porsche's required minimum. Can-do and should-do are different things.

In Germany, the only gas I saw Porsche employees putting into the cars was 100 octane (RON) V-Power. As was pointed out in the thread, there's around a 10 point spread between research octane number (RON) and motor octane number (MON).

Using Porsche's own stickers as a reference, there's roughly a 5 point difference between RON and AKI, though 100 RON may be more like 95.5 or 96 AKI, as one of the posters pointed out, AKI may not be exactly 5 points less.

So if you're blending race fuel and premium pump fuel, in my opinion, you'd want to shoot for 93 as a minimum, but for optimum results you'd want 95 -- 96. That's what they use in Germany, so I figure that's the correct target number. For a track day, I'd certainly go for the higher number. Most race gas makers have blend charts on their website, so you know how much of each to mix.

As to how much difference it makes, Shell's German website cites a VW GTI (Mk III, IIRC) running 98 RON vs. 100 RON. The 100 RON gives it around 8% better horsepower than the 98. That's quite a bit of difference, in my opinion.

Given that Porsche is pretty strict on specs, if you use 93 AKI, then you should reach the spec horsepower. If you're stuck with 91, it's going to be lower. How much? A guess would be roughly 8%, based on the Shell data.

Would 95/96 produce better than spec HP? A good question for PAG which I'll ask some day. Even if it doesn't, I suspect the throttle response with 95/96 will be better. Using straight 101 AKI in a street Porsche, in my estimation, is unlikely to make improvement over 95/96 AKI. My reasoning is if they don't use it on the street in Germany, why have the advance range in the ECU be able to go higher than 100 RON?

I know in my car (986S) 93 is WAY better than 91. Better throttle response, and about a 2 MPG improvement in mileage. Going from 93 to 91 is like putting a down pillow over the gas pedal. Yea, it gets there, but everything is muted. I hate having to use 91, and wish I had a 100L tank for more range to find 93.

I did blend 93 and 100 once (100 is hard to come by out here), and wow, my thought was, "This is like being in Germany again." Super throttle response, and very quick.

So use or blend to 93 when possible, and 95/96 for optimum results.

HTH

dasams

This is good advice for a track day.
I've worked for Shell and I'd be skeptical as this sounds like marketing.
I'd be very interested in any response from PAG. Good post. dave

Macster

Cost is so low compared to other expenses I'd do it.

Several reasons: Track operation will have engine running hotter. The engine will be running closer and for longer periods of time at or near incipient detonation and the Ecu will likely be dialing back the timing, which increases combustion chamber temperatures.

Sure, upon hard acceleration Ecu can go open loop and feed engine a richer mixture which not only produces more power but is also more resistent to detonation.

OTOH, there will be times when the acceleration will not be hard enough for the above to occur.

Plus, an engine's octane requirement goes up as engine ages. Deposits and other factors work to raise this over time. Going to a higher octane gas at least in severe use conditions (track at least) will compensate for the engine's bump in octane requirement.

To me the peace of mind and extra margin against incipient detonation worth the few dollars the high octane fuel costs.

Sincerely,

Macster.

Macster

Can't cite source cause there ain't one. Flame speed of 86 to 93 gasolines is the same. (Energy content overlaps too) Engines have knock sensors not octane sensors.

The biggest difference is the higher octane gasolines are more resistant to developing pre-ignition compounds ahead of the advancing flame front.

The advantage is with a high octane gas (and of course an engine designed to require it which our Porsches certainly are) is ignition can be triggered sooner so the burning fuel imparts more push onto the piston at the most opportune time.

More usable power derived from the burning of the gasoline. But a side effect is this of course raises cylinder and combustion chamber pressures but the higher octane gas will still not ignite until the flame front reaches the remaining unburned fuel.

Running a lower octane fuel leads to detonation. The Ecu will of course detect this and retard ignition. This results in less pressure being deveoped in the cylinder/combustion chamber. A negative side effect is the fuel burns a bit later and some of its heat does not go into increasing pressure which pushes on the pistion but which does subject the downstream components to a higher heat load.

Engine output (torque) less, fuel economy less, and the engine is exposed to a higher heat from the delayed burning of the fuel.

Why anyone would use a lower octane gasoline thant specified -- or available -- in these cars is beyond me. Now in some areas we can't help it. 91 octane is all there is. 93/94 is available in some areas but this is still an octane point or two below what is available in Germany and UK and other European countries so those of us in the USA are at best only able to feed our engines gasoline that is at least 1 to 2 octane points lower than our counterparts elsewhere.

Sincerely,

Macster.

stevepow

Great discussion - thanks guys.

Dave07997S

Macster nailed it...ding ding ding...we have a winner.

Dave

Dave07997S

Thanks, I do get it..however...99.9% of the time though 98 RON is 93 (R+M)/2, this is just complicating things and really adding nothing to this discussion wether or not high octane fuel can help combustion. We just want people on this site to realize that when someone from the other side of the pond mentions they put 98 octane in the car (RON) it is roughly equivlent to 93 octane US.

Like I mentioned in a previous post...I saw a 06 997S run straight 100 octane and he gained over 13rwhp. He went from 317rwhp to 330rwhp!! That was the average of 3 runs.

I do feel that anything over 95 octane is wasted though as the improvements really diminish above that octane number.

From just going to dyno days here in Cali. most 997S's run in the 300rwhp range on 91 octane, yet I see east coast cars running 93 octane running in the 310-315rwhp range...has to be the fuel IMHO.

Good discussion guys...everyone may have a different opinion, doesn't mean anyone is wrong just different experiences.

Dave

Dave07997S

Great post Jim..

Pretty much what I have experienced as well..really 95 octane (R+M)/2 is awesome for these cars. Its just not for Porsche but BMW as well the DMEs are maxed out at around 95 octane. Anything above this and the gains are minimal unless you tune for the higher octane.

I run 3-4 gallons of F&L racing unleaded 105 octane in the car and I feel like its a different car...on just 91 octane the car feels lethargic.

Dave

stevepow

I have to disagree with this - anyone could easily be wrong. The discussion has been way over my head, so I'm a guy with an opinion - which may or may not be right. If I were an automotive engineer, engine tuner, etc., then I'd have the knowledge to know what I was talking about - at least, that's my opinion

A good technical explanation followed compelling tests (dyno for example) would seem to weed out opinion from useful information.

The most compelling test would be done under controlled conditions with the same car and would be repeatable for anyone with the right equipment - and I have to believe while most of us don't have that setup, gasoline companies, race car tuners, and car makers such as PAG certainly do.

stevepow

Here are a few articles with test results:

entertaining: http://www.hotrod.com/techarticles/e...son/index.html
boring and maybe marketing slanted, but interesting: http://www.motec.com/filedownload.ph...pdf?docid=2495

So back to the OP's original Q:

1 - no I have never tried 98 or 101
2 - seems like tuning is a big factor in whether or not it helps, as Dave and others suggest.
3 - I'd like to see some dyno results for our cars.

Macster

You have to be careful. Evo (UK published car mag) did an gas/octane test a few years back -- I have the article somewhere -- and found considerable differences between gasolines and considerable differences in engine output (turbo-charged VW GTi). Considerable. IIRC between best and worst was 40ftlbs of torque.

Same test run with BMW M6 and there was very little difference. The testers believe that in order to protect the BWM's drivetrain from the output of the engine the engine controller dialed back timing to soften the load the engine subjected the drivetrain to and thus there were no notable differences between the tested gasolines.

But with the VW the results clearly indicate there is power and torque to be had by running a quality gasoline that has the engine maker's octane rating.

Running a higher octane rated gasoline does not help, though some experimentation is needed cause of engine deposits and the possibility the engine's octane requirements have gone up.

However if one runs a quality premium grade of gasoline this will tend to keep deposits from building up. There is more to premium gasoline than just a higher octane rating.

Also, variations were noted between different fills of the same brand and octane of gasoline. This was attributed to staleness. Premium gasoline can go stale and lose some of its *punch*.

The advice was to fill the car's tank with the proper grade and octane rating of gasoline. This gasoline best bought from a name brand gas station and should be bought from a busy station, one that is least likely to have stale gasoline its underground storage tanks.

This last bit of advice can actually be an arqument against running racing fuel cause the racing gasoline may be stale given the turnover is light. Even so I find it hard to believe the gas would go so stale as to be no better than 91/93/94 gasoline, though 100 gasoline may not be 100, but a bit less if it is stale.

Sincerely,

Macster.