fuel question

[4380r]

Getting to know my new/old 1974 TC. What's the story for fuel. Should I use a lead additive?

[EuropaTC]

I use a combined lead replacement & octane booster additive over here in the UK. When we first went to lead-free petrol it was considered essential but since then I've heard contradicting reports and how some folks manage quite happily without it.  The argument seems to be that for low mileage cars which are driven gently, you can get away with regular fuel. If I could get 98 or 99 octane fuel locally I'd probably try it without any additive, I'm not convinced about the theory of "lead memory" but I can see that after a few thousand miles the seats could easily have work hardened enough to work with modern fuels.

Over that side of the pond I have no idea, but Trevor has just driven a few thousand miles when he popped out to meet up with a few mates, so he should be able to answer that one 

Brian

[cal44]

I use Shells' highest and do not have any problems.  Last year I sold a '70 Boss 302 I could not get to run well no matter what was done to it.   The Texan that bought it said he used Texas gas and it ran great............so go figure.

mike

[YellowS4DHC]

First, I would stay away from any ethanol blends if you have rubber fuel lines.  Watch for stickers on the pumps that say "May Contain Up to 10% Ethanol."  I think this notification is required by law in the US.  Availability varies by region:  I don't see ethanol blended gas in CA, but it's everywhere in ID.   

Second, it is my understanding that twin cam valves and seats are sufficiently robust to tolerate the absence of lead (as a lubricant), so lead, per se, is not essential IMHO in that regard.

Third, if you need a high octane rating to get the car to run properly, consider blending non-ethanol regular (87 oct) with racing gas (100 oct or higher).  I personally don't care for octane boosters as I understand that they (or at least some) leave nasty deposits on the valves.

I can't find anything higher than 91 oct in CA and my S4 (CR 10.5) doesn't run well on that.  So, I run a 93 + octane mix of racing gas and 87 oct regular gas.   Get on the internet to find a Sunoco racing gas dealer.  To get the correct ratios, there is a handy octane calculator here:

http://www.csgnetwork.com/octanemixcalc.html.

Note that octane rating can't be derived by simply doing a weighted average of the two fuels.  Using the calculator, you will find you need approx 2.8 gal of 87 octane gas for each gallon of 110 octane fuel for a 93 octane mix. 

The only downside to this approach that I've experienced is that you have to go to two pumps and plan a bit ahead.  On a long trip I carry a small 2 gal plastic fuel container in the boot so I can get home with decent gas.

Hope this helps.
Rick

[YellowS4DHC]

Correction to the above post:  the fuel calculator I linked to DOES appear to simply to do a weighted average. 

When I initially checked it (thinking that was the case), I got a different answer than the calculator so I assumed that there was something more esoteric involved.  Going back, I suspect I double-hit a number key doing the math.   Easy to do on my old laptop keyboard

Sorry if I mislead anybody.  If you use a simple mix ratio, you can do a weighted avg in your head and not need a calculator of any sort.

Rick