Wait, the 3.2 can use 87 octane with a stock DME chip??

[sugarwood]

I've been doing some light reading on the Motronic DME, and came across this.

Porsche programmed the ignition maps of the Carrera to run on 87 CLC octane fuel (standard U.S. pump rating, equivalent to 92 European RON octane). While this may be sufficient for a poorly maintained vehicle running on low octane fuel, it is far from optimum in terms of power and efficiency. With most drivers operating their 911s on 91+ octane fuel, optimizing the ignition maps for such increases the engine's horsepower, torque, response, and fuel efficiency.

SWChips.com - Ignition Maps - Porsche 911

[autojack]

It says that right in the owners manual. I was surprised too.

[stlrj]

No surprise to me, but I often wondered why I seemed to be the only one who was using regular on my Carrera. Could it be that most of us do not have the owners manual since many of us are not the original owners? Or maybe the fact that the 911 is such a high performance car, we assume it requires premium gas?


Cheers,
Joe
87 Carrera

[rnln]

umm... I wonder if anyone, who has used 87, can see the difference between 87 and 91? including performance and gas mileage? I am too chicken to try

[michael lang]

In the winter months (Jan/Feb) I get a lot of my clients complaining about check engine light and running rough on their Mercedes Benz. It seems to be a consistent pattern of misfire at start up. I explain that the issue has to do with internal engine temp not being in the set range the M.E. Is looking for so it thinks there is a problem and bings the check engine. The rough running usually only last until the warm up cycle is done and then the vehicle runs normal. When I ask them what grade gasoline they use get all tell me they put the premium octane. I advise them to go with the 87 octane during the coldest months. Most are surprised for me to tell them that. I don't have any physical data to prove it but it seems like the lowest octane level have the lowest percentages of ethanol added so in essence, is the least "watered down" gasoline and as a result, minimizes misfire at start up and check engine light issues.
Ironically enough, if you go to buyrealgas.org and look at the gas station list that sells true gas, all the gas that does not have ethanol added is 87 octane.

[jlynch1960]

I have an '84 and use 93 here in the states, but spend summers in the Canadian bush where 87 is the norm and I have to drive a good distance to find 91 (forget 93). With 87, cold starts can be a little rough (erratic idle for a few moments/possible stall if the air temp is cool), but once the engine warms up, I'd be hard pressed to notice much of a difference - perhaps just a slight lag in acceleration. Fwiw, per Mr. Lang above, the station I fill up at only sells ethanol free fuel.

[darrin]

I've always viewed detonation as the "problem" solved/addressed by high octane gas. Since our 3.2 engines lack knock sensors and knocking/pinging is difficult to detect while driving, running high octane gas is relatively cheap insurance when once considers the harms caused by preignition.

Also wonder whether the 86 octane requirement remained in '87, when software changes bumped power by 10(ish) hp

[Concestor0]

For normal driving I use 87 but avoid really pushing it. When on the track (been a while now) I fill up with 91 or 93. I haven't noticed any difference with the different octanes but neither have I ever used maximum power or been above 4,000 rpm while using 87.

BTW, could anyone tell me if engine knock/detonation is reliably noticeable to the driver or could you be damaging your engine without noticing it. I have a stock 3.2 in my '86 Carrera.

[911tracker85]

my 85 3.2 has a chip programmed to expect 93, used to run her at DE but she is now retired from the track.

and I tend to drive her fairly hard out on country roads. love to hear that shriek at the top end.... and do not drive her hardly during the winter. so far no issues running 93.

[911tracker85]

opps. forgot to mention I always use 87 in my '84 928S. low compression US spec so seems totally happy with 87.

[KNS]

Originally Posted by Concestor0

BTW, could anyone tell me if engine knock/detonation is reliably noticeable to the driver or could you be damaging your engine without noticing it. I have a stock 3.2 in my '86 Carrera.

It is hard to detect but you can sometimes hear it. In my (long gone) '80 SC and my 993 I can sometimes hear it when accelerating hard along side a wall next to the driver's side window. Clackity, clackity...

The 993 has knock sensors but their not as sophisticated as more modern ones. Where I'm at (Arizona) all we have is 91 octane and pushing the car on hot days (if I have a high wall next to me) I can hear it.

Steve Weiner has stated that the 993 3.6 was really designed to use 93 octane and I believe it. He's gone on to say that if you live in a hot climate and push the car during summer or track it you should be running 93. He's right, when I mix in a little race gas with the 91 to bring it up to 93 - no more noises.

[stlrj]

Originally Posted by rnln

umm... I wonder if anyone, who has used 87, can see the difference between 87 and 91? including performance and gas mileage? I am too chicken to try

No difference as far as I can tell so there must be a psychological reason that keeps us from using regular.

[sky1jord]

From my 88's Owner's Manual, interpret as you choose

[Fly911]

I have never understood why people are concerned about fuel consumption or fuel prices on their Porsches! If fuel cost is a concern, you should buy a Prius or something. You are driving very expensive cars, and are risking thousands of Dollars to save a few pennies. I don't get it!

I get 100 smiles per gallon, and would always buy the highest octane gas possible.

[911pcars]

You should be okay with lower octane fuel if your operating conditions are not aggressive (i.e. part throttle cruising speed, street or highway). Listen for threshold pinging and act accordingly.

However, detonation can be an issue during high load engine conditions (e.g. full throttle acceleration, hill climbing, engine lugging, etc.). This is exacerbated by high ambient temps and altitude. If you can hear the engine detonate, good for you - back off the throttle and/or downshift. High speed detonation can occur undetected, but your pistons/rings will know.



Sherwood

[ischmitz]

Octane rating doesn't change HP performance. It enables changing the engine or mapping to allow for more power. So switching fuels alone doesn't change power output on a 3.2. It is a commonly accepted fact that Porsche left some HP on the table in favor of engine longevity when tuning the 3.2 engine. This is especially true for the U.S. spec models. That's where chipping comes in.

Knocking depends on many factors such as ambient temperatures, driving style and overall condition of the engine. A newly rebuild engine might not knock where an older engine with lots of carbon deposits in the combustion chamber starts knocking. Further you have to consider that more modern platforms have knock sensing and adaptive ignition retard. The 3.2 doesn't have this feature so it was tuned to be safe under worst conditions.

In the end it's up to everybody how much risk you'll want to take by reducing gas quality and pushing performance by chip tuning. Being very conservative you'd fill up with the best gas you can get while leaving the timing stock. That's what Porsche did. They built in ample safety margins for crappy gas here in the U.S. The European models have different timing to take advantage of the higher octane fuels commonly available over there.

Bottom line. 87 octane is fine with a stock U.S. chip and the manual says so. Once you go to 91 there is some headroom for a reasonably tuned chip. However, as the engines age its tendencies to knock could increase.

Ingo

[sky1jord]

Originally Posted by ischmitz

Bottom line. 87 octane is fine with a stock U.S. chip and the manual says so. Once you go to 91 there is some headroom for a reasonably tuned chip. However, as the engines age its tendencies to knock could increase.

Ingo

Sorry, my bad, I missed the page in the manual that says 87 octane is fine for a 3.2. Can you show or reprint it? Or maybe just the page number?

TIA

[Nick Triesch]

I think some of you guys are wrong. Just checked my 85 Carrera's owners manual and it says under technical data in the back to use 92 rating in USA pumps premium unleaded fuel only.

[Arne2]

The manual for my '84 is different than the '88 posted above. Mine states the minimum is 87, but 92 is recommended. See snap below.

FWIW, I've always run 92 in it, both with the stock chip and the 91 octane SW chip that was in it when I bought it. I removed the SW chip in part because it was prone to ping a touch even with 92. No sign of detonation with 92 and the stock chip.

[Nick Triesch]

In fact, it says to use premium in several places in the owners manual. 87 is not premium.