Fuel controversy rages

911jon · 04-03-2002, 07:00 AM

Hi Pelicanheads,

As a new-ish (and very happy) 911 owner (this is my first), I am wrestling with various issues relating to my car; here is one you may be able to help with.

My MY89 targa sport is euro spec at 231bhp - no cat. Like many UK owners of this model, I am using Shell Optimax 98.5 Octane super-unleaded petrol. It runs very nicely on this. I have no doubt that the valve seats are hard enough to cope.

My local independant Porsche specialist claims this will cause premature bore wear leading to an early rebuild. In the UK leaded petrol is now available again at specialist retailers at around 98-99 Octane, but is wildly expensive (£1.10/litre against £0.76 for Optimax).

Is there any real advantage to using leaded? Would an occasional tank of leaded, say 1-in-5 be beneficial? Or should I consider additives? The car is used daily, 1000 miles/month.

My car has 74K miles and has had no engine issues aside from the usual DME relay. Leakdown shows minor wear.

Thanks in advance for your comments.

Kahuna · 04-03-2002, 08:25 AM

One of the functions of lead was to cushine the valve as it made contact with the seat, soft seats without lead didn't last long. All 911 valve seats since the early 70s are hard enough for use with unleaded.

In addition oil and Oxy sensors will last longer with out lead additives.

71T Targa · 04-03-2002, 08:46 AM

So I should NOT add a lead substitute to my '71

Kahuna · 04-03-2002, 08:52 AM

I only had a '72 so thats the earliest # I memorized. I'll see if I can digout the original source of the info, which was in one of the early "Up-Fixen" series.

Wayne 962 · Wayne 962's Garage

The US has banned lead in gasoline since the 1970s. America is Porsche's largest market. We've been driving around now for more than 25 years on unleaded gas, with no ill effects to the cars.

I can't see any reason to add the substitute to your car. 356 and VW bugs run fine on unleaded here too...

-Wayne

Bill Verburg · Bill Verburg's Garage

I agree with Kahuna and Wayne, the interior of the engine, spark plugs and oil will remain cleaner for a longer period of time without lead.

As far as the seats go, they need a Rockwell hardness(RA) of 45-50 for use with unleaded. Bruce Anderson in his 3/86 Pano tech article reported the following

1966 911 RA 65
1969 911 RA54
1976 911RA 64

911jon · 04-04-2002, 01:28 AM

Thanks for your input, all.

I am aware that the valve seats are of sufficient hardness; the issue raised by the specialist I was in conversation with - a Porsche trained technical guy of 20 years experience and with his own successful business - was the bore wear/cylinder pressure loss issue which seems to affect many UK vehicles at moderate to high mileages.

His opinion is that unleaded might be a factor here, but this sounds unlikely given the experiences of the US market. It may be that concentrations of additives (benzene etc) used here differ quite widely from those used for the US market.

Top-end rebuilds seem to be a common requirement here - I would obviously wish to avoid this.... hmmn... 98.. or even 100mm cylinders... hmmmn.