Fuel used in your 1965 to 1970 911.

[NV Stig]

What type of fuel are you using when you drive your old Porsche?
Do you use the 91 octane with lead substitute and octane boost to get the 98 octane recommended?
Does anyone mix Avgas 100LL with 91 to get this result, or is that considered to be taboo? Appreciate any input.
Scott

[ttweed]

I ran the piss-poor 91 octane pump gas that passes for high-test here in CA for years in my 2.0S engine with no ill effects. What 98 octane recommendation are you referencing here? Is it a RON octane rating, or MON, or the Road Octane Number (RdON), which is the common US standard, and equals the average of the two, or (R+M)/2.

Lead substitute and octane booster added to 91 octane pump gas in the usual retail quantities will not get you anywhere near a 98 octane equivalent. You would have to mix 7 gallons of 100 with each 2 gallons of 91 octane to render a 98 octane mix, but it would be a waste of money unless you are using a high compression race motor.

TT

[LeonardZ]

With TT,

I've had cars sit for months with regular pump gas with no ill effects. Not that I would recommend it but I've started cars on gas that sat for a year and they have always started. To be on the safe side Tom's advice is probably the best route though.

That said, there is a 100 low lead available at most airports which has stabilizers which is $5.00/ gal. At least that's the price here. As mentioned there is always the lead substitute that most Wal-Marts carry.



Leonard

[NV Stig]

I got the 98 octane from the old 911 book (pamphlet) It just says recommended octane is 98 octane. Got to love the era, simple and to the point. No 3 page disclaimer with conversions for 50 countries and the like. I don't really know what kind of increase you get with the octane boost additive, but I just figured 91 octane with boost and lead substitute got it relatively close.
I used to get guys with 60's era cars showing up with 5 gallon drums when I fueled airplanes back in college. I heard stories going both ways on the subject. Didn't have the right additives to lubricate valve guides, burns too hot, etc. Then I heard it was the greatest thing since sliced bread. Just wanted some insight from people with practical experience with Porsche engines. Thanks for the input guys. I really appreciate it. Sounds like 100LL will work.
Has anyone ever done a no lead conversion to their 911? Is it possible? Does the car lose its teeth in the process? I never heard of anyone doing one before, but that doesn't really mean anything.

[tfiv]

The cars and bikes can sit all winter and will start every time even after 4 months of down time. The gas doesn't go bad and the carbs stay clean

I run it in my chainsaw that gets used very occasionally. I think it's been on the same tank for three years now!

[LeonardZ]

Has anyone ever done a no lead conversion to their 911? Is it possible? Does the car lose its teeth in the process? I never heard of anyone doing one before, but that doesn't really mean anything.

If the original valve guides and valves were replaced with new guides and stainless valves lead, or lack there of, wouldn't be an issue.

[kenikh]

Pump premium; never any problems. US 92 octane = 98 Euro octane. If using crappier gas, dial the timing out a bit.

[jcarpio]

NV Stig,
Like Tom said above, and Kenik reiterated, I think the pamphlet/owner's manual refers to RON (Research Octane Number). What you see labeled on the pump is actually the average of the RON and the MON (Motor Octane Number). Sorry if you already knew this. Here, have a blast reading this: http://en.wikipedia.org/wiki/Octane_rating.

Short answer is, it's OK to load her up with 91. Now, the manual that came with my 72T says that I can get away with regular (RON of 93, IIRC) or 87 (R+M)/2, but I fill it with California's finest 91 and all's well so far.

Jorge

[SandyI]

Owned my car about six years, run 91 Octane for almost 40,000 miles, plus about a dozen POC track days. No gas related problems.

[tfiv]

Also, our cars also do not have any where near the compression listed in the spec books. When my 67S was rebuilt we measured the CR and it worked out to less than 9:1. The new Mahles were just slightly higher.