Is leaded gas required in my 1977 911S 2.7l CIS
06-16-2008, 11:46 AM
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Is leaded gas required in my 1977 911S 2.7l CIS
I am wondering if leaded gasoline is required in my 1977 911S 2.7l w/CIS? It has no smog pump and no cats and it used to get leaded gas until they banned leaded gasoline. There is a sticker in the fill pocket that states that it requires leaded fuel. Are the valve seats hard enough to run 91-93 octane unleaded. If I want to drive in a spirited manner should I fill with leaded race gas?
Can anyone recommend a lead additive that is save for CIS? Or a race gas concentrate that is save for CIS?
Thanks!
Can anyone recommend a lead additive that is save for CIS? Or a race gas concentrate that is save for CIS?
Thanks!
Last edited by CORNER CARVER; 06-16-2008 at 12:18 PM.
06-16-2008, 02:34 PM
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Yes. I have read good authority (http://www.early911sregistry.org/for...9&postcount=14) that 911s have always had hardened valve seats obviating the need for the build up of lead oxide on the valve seats for cushion. In the old days, the tetraethyl lead helped cusioned the soft steel valve seats and prevented them from needing resurfacing as often. We shouldn't have to worry about that.
In 1977, the automanufacturers knew that the lead was on the way out of gasoline and designed the engines with lower compression ratios on that account. The only thing about the gasoline currently available that should concern you is the ethanol in it and its effect on the components of your fuel system.
In 1977, the automanufacturers knew that the lead was on the way out of gasoline and designed the engines with lower compression ratios on that account. The only thing about the gasoline currently available that should concern you is the ethanol in it and its effect on the components of your fuel system.
06-16-2008, 03:01 PM
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Thank You!!! I thought I had read that all the seats were hardened. I will be getting her out of the garage after installing an 11 blade fan. Wanted to make sure I was not harming the valve seats. 
06-17-2008, 03:13 PM
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Keep in mind that the 1977 911S was originally equiped with the thermal reactors and was designed to use leaded fuel. With the loss of leaded fuels you should have no problem with running unleaded. Porsche has been using hardened seats for some time. I would think that your 1977 has had the top end overhauled (valves) and you have the more modern, harder seats.
Good plan on the 11-bladed fan. Why they switched to silly 5-blade was always a mystery to me although I read some time back that Porsche did it only because of sound. They were quieter than the 11s. You need all the cooling you can get on that 2.7 liter with magnesium cases!
Suggest you locate some Octane 104 to boost your octane a bit. I used to use it a lot. Not even sure if it's still available,--goodgle?
Good plan on the 11-bladed fan. Why they switched to silly 5-blade was always a mystery to me although I read some time back that Porsche did it only because of sound. They were quieter than the 11s. You need all the cooling you can get on that 2.7 liter with magnesium cases!
Suggest you locate some Octane 104 to boost your octane a bit. I used to use it a lot. Not even sure if it's still available,--goodgle?
