dshepp806

That's my concern, and thanks Scarceller. A lot of the designers (tuners) won't really speak of their maps, but I got the feeling that Mr. Wong would tune a limit if requested. It makes sense that if the request is too high ( ie: higher than where he would push it--if he pushes it at all), he wouldn't then stand behind it. I'd like a somewhat conservative push but am sure of what would DEFINE this.,..especially with 93 octane, It may be that he's already AT a conservative value *whatever that means".

Timing may be "slightly" tweaked, with the fuel maps "slightly" tweaked. I do know this: He will put things where you want them (in terms of timing advances and rev limits), having had a lengthy conversation with him a while back. Very helpful fellow, quite communicative and educational,..and (get this) ,...all "done" with complete civility,respect,...no name calling or left-field assumptions (or should I say "presumptions"?). I'm almost there to get one...

How did you estabish 29 degrees as where you wanted it (rationale)?

......trying to learn more on this stuff...in fact, what is it in octane rating that allows for advancement of the timing? Time to play student..

Thanks!

dshepp806

Since the real answer lies beyond his final words, I can't help but beg rationality and help the ( apparently) aged kid (still) along.

Best,

Ed Hughes

Higher Octane actually 'slows' the combustion process, in a nutshell. Lower octane fuel will actually ignite quicker. With advanced timing, that would be the recipe for disaster.

It sort of seems contrary to what your instinct would tell you.

Lorenfb

"As far as Octane I really think the Porsche Design Team had to play it safe and assumed 93 octane would not always be run in the car."

Really! And where is this stated other than by the "tuners" to quell concern?

"Note: Per Porsche manual WKD 495 421 (911 Carrera) the fuel grade indicated
is 95 octane for the USA engine. The ROW engine required 98 octane. During the
late 1980s and early 1990s, 97/98 octane was the high grade octane and readily
available."

The max octane that's readily available now in SoCal is 91.

"My car has custom chip and does not exceed about 29deg advance."

That's the exception, as most/all chips exceed 40 degrees under various loads.

dshepp806

Damn! I didn't realize that in 1989, the fuel grade indicated was 95 octane!!!

As to the "exception noted",..is this less of an issue, as to dangers of advancing the timing and having bad results? (or the potential for dangerous results)?

old man neri

Are you talking about RON, MON, or AKI? I have a feeling that the numbers quoted the Porsche manual is not in the same units as what you see on the pumps in 'socal'.

dshepp806

If 95 octane was indicated,..and we advance timing while using 93 octane, is this the recipe you speak of?

Best,

imcarthur

Page 92 from a 1987 Owner's Manual.

Ian

scarceller

Hi Loren,

My point is that the Porsche engineers ALWAYS do there homework and in my PERSONAL oppinion I think they can RECOMEND a certain grade of fuel but the customer could use something lower in grade which is offten the case. So, I'm sure the factory would not want motors comming back damaged because the customer did not use the right fuel. Building consumer goods is often a balancing act and trading performance for reliability is often done. Once again this is just my view on this and I respect you can view things diffrently.

As for the timing values I'm well aware of the stock tables, when I mentioned 29deg advance I failed to say at what RPM and in what table. I was strictly speaking about the WOT ignition map. The stock 89 chip does not go past 24.5deg advance. But I agree with you that in the part throttle it goes as high as 40deg at some RPM-Load combinations.

Here are the maps from the 89 stock US chip for those intrested:

scarceller

Hi Ed,

Detonation occurs when the fuel in the cylinder ignites from or at 2 diffrent points. Meaning, the spark plug ignites the fuel at point A while for some reason the fuel also ignites else where at another point B.

This is a great article on this topic if you wish to get a high level view of these issues:
http://www.misterfixit.com/deton.htm

For some reason lower octane fuel tends to ignite on it's own under certain conditions. When this happens the 2 flame fronts soon collide with each other and the result is a huge amount of uncontolled energy.

I'm not a pro here but have done reading to better educate myself in this area.

Ed Hughes

I think that was the gist of what I was saying...I didn't elaborate much, and probably should've, and I'm sure your link provides the details.

Amber Gramps

I'm back. Did I miss anything? Gas is cheep in Phoenix....$3.09. What a deal.

dshepp806

Damn Scarceller! Thanks for the information.....I've an 89, too. This helps me better learn what's going on with the engine,...very nice

dshepp806

So,..this is quite a step in advancement in the 1760 - 2400 range. Does this equate to the dead spot mentioned on many 911'S? And, to get better partial throttle response, one would bump these stock ignition values a bit upward? (along with related fuel map changes, I'd suppose?) Is this very bumping upward to the high 30's world, say in the 3000 - 4000 rpm range what get's many worried?

What are the horizontal line entry titles? (pardon my stupid questions) Noworries, mates,..I'm NOT a tuner at all. Just trying to learn,..I'll have a read of the noted link.

THANKS!!

Amber Gramps

I have a quick question for the guys in the know: My car's date of production is 11/24/87. It was built to the first owner's specs. Scarceller says my chip is from late '89. I can tell I was the first guy to use a screwdriver to open the DME. So....A: The DME was opened and the chip was replaced in a way that didn't scratch, B: The entire DME was replaced, or C: The chip was around in November of '87. My guess is "C" 'cause nothing was ever done to this car. Did I say nothing? What do you think?