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931 FUEL OCTANE

 
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AGD931  



Joined: 17 Mar 2003
Posts: 290
Location: Athens, Greece

PostPosted: Mon Apr 07, 2003 11:39 pm    Post subject: 931 FUEL OCTANE Reply with quote

Guys,

Can anyone advise as to the fuel I should be using. My non-cat Euro spec 931 which has the digital ignition, has been up and running for the last two months. The only problem I have is that using 96 octane leaded fuel, the car occasionally pinks. Can I use constantly 98 octane unleaded that we have here in Greece?

Thanks for any help and advice.

Arthur
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Peter_in_AU  



Joined: 29 Jul 2001
Posts: 2740
Location: Sydney, Australia

PostPosted: Tue Apr 08, 2003 12:26 am    Post subject: Reply with quote

it will run happily on 98 unleaded (no cat needed).

That "96" leaded is probably a lot less than 96 octane. I thought that leaded fuel was restricted by EU countries 2 years ago.
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1979 924 (Gone to a better place)
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1982 924 (As featured on Wikipedia)

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AGD931  



Joined: 17 Mar 2003
Posts: 290
Location: Athens, Greece

PostPosted: Tue Apr 08, 2003 1:05 am    Post subject: Reply with quote

Peter,

Thanks for your help. You are right, it was restricted about two years ago, the new stuff has apparently a very low lead content, it is in effect lead replacement petrol, the 931 does not seem to like it very much (pinking, flat spots etc) but funnily enough one of my other cars (1980 Ford Capri 2000) with a 2 degree timing retard has no problems.

Arthur
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Peter_in_AU  



Joined: 29 Jul 2001
Posts: 2740
Location: Sydney, Australia

PostPosted: Tue Apr 08, 2003 8:32 am    Post subject: Reply with quote

the lead replacement they sell down here is very low octane something like 92 or 93 despite the "super" tag. I ran my car on lead replacement for a while but had problems with pinging, changing to 98 unleaded fixed that.
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1979 924 (Gone to a better place)
1974 Lotus 7 S4 "Big Valve" Twin-cam (waiting)
1982 924 (As featured on Wikipedia)

Learn to love your multimeter and may the search be with you
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Lizard  



Joined: 03 Nov 2002
Posts: 9379
Location: Abbotsford BC. Canada

PostPosted: Tue Apr 08, 2003 8:48 am    Post subject: Reply with quote

why would you run Leaded fuel in your cars
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Peter_in_AU  



Joined: 29 Jul 2001
Posts: 2740
Location: Sydney, Australia

PostPosted: Tue Apr 08, 2003 9:25 am    Post subject: Reply with quote

all 924s outside North America / Japan ran on leaded from new. Australia only mandated unleaded for new cars in 1985 (I think), Europe around the same time. The engines run happily on leaded or unleaded. As far as I know only North America / Japan cars were fitted with cats.

Real leaded fuel only disappeared from the pumps here and in Europe about 2 years ago.

If you're doing your bit for the planet, running leaded fuel is less toxic than running unleaded without a cat (at least that's what I've read).
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1979 924 (Gone to a better place)
1974 Lotus 7 S4 "Big Valve" Twin-cam (waiting)
1982 924 (As featured on Wikipedia)

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Lizard  



Joined: 03 Nov 2002
Posts: 9379
Location: Abbotsford BC. Canada

PostPosted: Tue Apr 08, 2003 9:43 am    Post subject: Reply with quote

If I remember correctly the 944 got the same readings with and without a cat
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CMXXXI  



Joined: 05 Nov 2002
Posts: 1939
Location: Vicksburg, MS

PostPosted: Wed Apr 09, 2003 5:54 am    Post subject: Reply with quote

Lizard, let's see if this helps...

The lead that used to be in all gasoline was there as an anti-knock compound. For practical purposes it raised the octane rating, without actually having to add more octane to the blend. I beleive that it also had some lubrication properties as well, something akin to a "dry film lubricant".

Octane is a simple 8-carbon molecule that won't detonate when compressed and is used as a measuring standard. I don't know what the octane scale actually runs to/from, but the scale (in very simplistic terms) "equates" to the proportion of octane and octane-like components in the fuel. Other hydrocarbons in fuel will and do detonate when compressed (think diesel engine), so when you mix the fuel with octane and other anti-knock chemicals you can change it's tendency to detonate under compression. The higher the octane rating, the less likely the fuel is to detonate when compressed.

In addition to removing the lead from fuels for environmental reasons, it also destroys Cat converters by coating the catalyst compounds preventing them from behaving in chemical reations.
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numbbers  



Joined: 05 Nov 2002
Posts: 1910
Location: Highlands Ranch, Colorado

PostPosted: Sat Apr 12, 2003 11:11 am    Post subject: Reply with quote

All of the cars, Euro or US will run fine on unleaded. The lubrication properties of leaded applies only to the valve seats, and all of the cars have the same seats. The issue is octane. The bottom line is, run the highest octane that is available. if you still ping, use an octane booster.
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AGD931  



Joined: 17 Mar 2003
Posts: 290
Location: Athens, Greece

PostPosted: Mon Apr 14, 2003 5:58 pm    Post subject: Reply with quote

Following the posts in this forum, I started using 98 octane unleaded in my Euro 1981 931. To be honest, the difference in engine performance is very noticeable, the engine is smoother and most importantly the pinking I was experiencing at about 4K whilst on boost, has gone.

As unleaded did not exist in Europe in 1981 when my car was built and in order to get it from 'the horses mouth' so to speak, I emailed the Porsche factory quoting VIN and engine number. Their immediate reply (excellent customer service) was basically that I should use only 98 octane unleaded with a lead additive. Their reply is quoted below.

"You must only use petrol of the rating of min. 98 Octane in your vehicle.
Fuel of a lower octane rating will cause pre-ignition (pinking) which in turn will seriously damage the pistons.
The engine of this vehicle will also require a lead additive if you have to
use unleaded fuel. This is also an absolutely necessity otherwise the valve seats in the cylinder head will become irrepairably damaged within a short time as they are not armoured in your car.
There are special additive manufacturers on the market (like Castrol) who
offer both the lead replacement additive and the octane booster in one bottle. The specific amount of additive needed is given on the bottle and is according to the quantity of petrol put in the tank. It must be added with every fill up."


I followed the above and now use a lead additive approx. 250ml per tankful, just to be on the safe side!!!
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numbbers  



Joined: 05 Nov 2002
Posts: 1910
Location: Highlands Ranch, Colorado

PostPosted: Wed Apr 16, 2003 12:34 pm    Post subject: Reply with quote

Anybody find a different part number for European and US model valves?
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Smoothie  



Joined: 01 Jan 2003
Posts: 8029
Location: DE (the one near MD, PA, NJ)

PostPosted: Thu Apr 17, 2003 1:22 am    Post subject: Reply with quote

I'd always heard it's the seats, not the valves that are specially hardened for unleaded gas use. This is in general - I don't know specifically how Porsche handled the situation, but it's probably safe to assume they started putting hardened seats in with the introduction of unleaded gas. Whether they put them in all engines at the same time or just those for specific markets, who knows..
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