Unleaded Fuels

911 and Porsche World

When we started to convert to unleaded fuels here in the United States in the late seventies everyone was concerned about what was going to happen to our cars with out lead to lubricate the valve guides and cushion the valves on the valve seats. 

One of the first things that I did was check with Porsche and they said that all of the cars from the SC forward had sintered iron seats made of a material that they call Pluko. They said that all of these cars would be fine and that they weren't sure about the earlier cars, but that if there was a problem the could provide Pluko seats for the earlier cars as well. 

Next I checked with a friend, Tim Wusz, who was the Senior Engineering Associate Fuels Technology, Unocal Science & Technology Division then, and who is one of the authorities here in the US on what the effect would be when they took the lead out of the gas over here in the late seventies and early eighties. Tim Wusz said that the only cars that would have problems with the removal of lead were some early American cars that used the cast iron of the blocks or the heads as the material for the valve seats and had very soft seats. Wusz assured me that our cars would run fine on the unleaded fuels that would be available and suggested that I have our valve seats tested for their hardness. 

Unleaded fuel is really no problem at all - lead was the work of the Devil. Lead did do a few things for us, but it may have actually done more harm than good. Lead in gasoline contaminated our oil, it fouled our plugs and it loaded up our oil control rings. Modern cars that run on unleaded fuels last longer, run better, and go further between services. We often see the modern Porsches of the unleaded era run for well over two hundred thousand miles without requiring major mechanical work. 

However, besides acting as an octane booster tetraethyl lead acts as a shock absorber between the exhaust valves and valve seats. The concern we enthusiasts have is for the potential of excessive valve seat recession or pound-in because of being run without leaded fuels. The reason that lead is so important to these older cars with "soft" seats is that the lead acts as a lubricant between the valves and the valve seats, cushioning the valve each time it seats to prevent exhaust valves and/or seats from recessing or pounding-in. In older Porsches, with their softer seats and valves there is some cause for concern. The newer cars, from 1977/78 on were designed so they could run on unleaded gasoline. In 1978, when Porsche started to use catalytic converters to meet the emissions standards requiring the use of unleaded gasoline, they changed the valve seat material to an sintered iron material that they call Pluko. Just how hard are "soft" seats and how hard do they have to be to prevent recession or pound-in. Really soft seats are cast iron seats with a hardness of from Rockwell 12 to 25. Seats with a Rockwell hardness of 45 to 50 are probably hard enough in most cases to provide for satisfactory protection. 

I have hardness tested the exhaust seats used in a number of our different Porsche cylinder heads. I checked the following heads with the following results:

1. 1966 911 head RA 65
2. 1969 911 head RA 54
3. 1976 911 head RA 64
4. 1.8 914 head RA 59
5. 1.7 914 head RA 44
6. 1962 356 head RA 64
7. 356C/912 head RA 58

None of these seats can be considered "soft" seats and as such they should not cause any problems with unleaded gasolines. Additionally all of the Porsche engines built since 1964 have some form of valve rotators. Their favorite is to use the ATE style keepers which do not hold the valve tightly, so that the valve is free to rotate. This has served them well and only the 924 engines had a separate valve rotator. So we should be able to use unleaded gasoline without any additional changes. However, the best way to keep track of what is happening until we are sure, will be with more frequent checks of the valve clearances. Obviously, if the valve clearance changes over a short period of time, some changes will have to be made to the exhaust valves and/or seats. 

It is also interesting to note that when lead was introduced to gasoline in 1923 there was very similar concern about the effect on the engine's valves and valve seats because of the addition of lead to gasoline as there is today with the removal of lead from the gasoline. At the time the engine designers felt that the lead caused a serious service problem with the spark plugs and exhaust valve damage caused by the corrosive effect of lead oxide. The designers forged ahead and used lead as an additive because of leads superiority over all other antiknock additives of that era. With higher octane gasoline the engine designers could use higher compression ratios to achieve major gains in both power and fuel economy. During this period of automotive history the designs and materials used in high-compression engines made tremendous improvements over a very short period of time. These included special alloy exhaust valves, and seats and sodium cooled valves all to combat valve and valve seat erosion, caused not by the removal of lead, but the addition of lead to the gasoline. With the introduction of lead to gasoline the octane number was increased from about 50 to todays 90+ for high octane unleaded gasolines making possible a boost in compression ratios from 4 to 1 up to the 9+ to 1 used by all of our modern Porsche engines. Because of advanced catalytic cracking methods and other octane boosting additives the gasoline companies find it easier to make high octane unleaded gasolines today than they did sixty years ago so the removal of lead from our gasoline hasn't caused much problems. 

Engines that are run on unleaded gasoline burn cleaner and will run much longer between tune-ups than cars that are run on leaded gasolines. All modern normally aspirated Porsches (4, 6 and 8 cylinders) have a recommended service interval of 15,000 miles including the oil change intervals and the turbocharged cars have a recommended oil change interval of 7,500 miles. Bosch has 30,000 and 50,000 mile spark plugs and the unleaded fuels are largely responsible for these extended service intervals. It also looks like engines that have been run on unleaded fuels will last longer than those run on leaded fuels, it is not uncommon for 911 SC engines to run for 175,000 to 200,000 miles without requiring any major maintenance. 

I have offered to write an article for 911 & Porsche World, which would include most of the above information, but Chris didn't seem too interested, perhaps I should ask the Post. 

Porsche never really wanted to say much beyond what I mentioned about the seat material. PCNA has never really said anything about the potential effect of unleaded fuels. Here in California the leaded fuels have been gone for most of this decade and we have really seen no negative effects are a result of the absence of lead. 

To your point about the amount of power used, my expert said that the only to examples that he could think of where people might have problems were Power boats where you run at full power for extended periods of time and possibly with one of the old VW busses heavily loaded pulling a very long very steep grade. Everyone will worry about the potential problem until sometime in the future when it dawns on everyone that everything has gone on as normal and that the cars have had no problems. Everyone will pretty much have to experience that for themselves as they have over here. Young people over here don't know any better and think unleaded fuels are just fine.