Fuel Question

[MikeB]

What are the thoughts of running a 50/50 mix of premium gas and 100Low Lead avaition fuel in my '69 T-bird. It has the original 429, never been opened up.

[vince]

If your worry is the need to run leaded gas, the collective wisdom of mechanics and machine shops I have talked to is you don't need to worry. If the engine has not been opened, the lead deposits on valves and seats from the years of running leaded gas protect the engine. You do not have to continue to use leaded gas. You can go for years with impact on your engine.

Of course once you do a rebuild of the heads, you have to harden the seats. An then run unleaded gas.

If your worry is octane, and you may know this, the current '93' octane no lead rates much higher if the '60's method of calculation is used. So, you should be in spec for your engine. I guess if you are getting some pinging and all the other tune up specs are fine you might mix in air craft or racing fuel. We have a couple of stations here that carry the latter and its rated at 110, pricy though.

[MikeB]

Yes, it's the octane i'm looking for. Right now I 've got the timing so far retarded to prevent pinging, it runs hotter than I like on the highway. Around town it the temp gauge rund right on the lower leg of "M". On the highway, it'll run between M and P on the gauge.

[mike harmon]

What's the milage and condition of your engine? A carbon build-up will also cause pinging, due to reducing the combustion chamber volume (raises compression ratio) and to also acting like a glow plug. Aviation fuel, according to an FAA ground school and flight instructor I know, has a higher heat or energy index than auto gas- it burns a lot hotter. Run it straight in a non-aircraft engine and it may burn holes in the pistons as well as do other damage. It can be run in diluted mixtures, but you can only guess as to what the resulting octane is. If the pinging is from carbon buildup, avgas probably won't help much, particularly in relation to the cost of the stuff.

[MikeB]

It just turned over 70,000. I'm also leaning towards the carbon build up. Around town I have no problem with it pinging no matter how long I drive it. However, if I'm on the highway, after I get off, it will ping under accelleration. What can i do to see how much carbon is built up in it, and how do I get it out? When I do drive it, it's mainly to and from work. About 15minutes at 65mph. When I stop for gas, I'll run Shell, or another "quality" fuel through it. i also put a can of SeaFoam in the tank.
Thanks

[vince]

One other possibility is the vac. diaphram at the distributor is starting to fail.

[mike harmon]

That milage isn't high enough, normally, to have much of a carbon buildup unless the car has been driven only short trips and never warmed up, and never on road trips to blow the junk out. Of course, there's the possibility the clock's turned over at least once, but then the rest of the car- interior, etc., would show some wear and tear. Short of looking inside of the combustion chamber there's no sure fire way I can think of to see what's in there. Something way in the dark recesses of my fading memory I almost think I can recall reading something about some sort of a small surgical-like tool (scope) that one could inspect the inside of the cylinder with, but it's only a faint recollection. Other than that or trying to deduce something based upon circumstances, I think the head's got to come off. Before you do something that drastic, you can try chemical carbon removers- I think GM may have one (their Northstar V8 is a notorious builder of carbon in its rings), as may other auto manufacturer's. I wouldn't try any of the over-the-counter stuff from parts stores. Also check the oil consumption, using the recommended viscosity for that engine- preferably on a couple of trips of a couple of hours or more. If it's using more than a qt. in 1000 miles, it's a smoker- and is piling up the carbon deposits. Also check the distributor's breaker plate for easy movement. If it's sticky or even stuck, it might not be able to retard enough under acceleration to avoid the pinging.

[MikeB]

I will look into the distrubtor. Last year I went round and round with Pony Carbs. They rebuilt my 4300 and I could never get it to lean out. It ran so rich I wound up replacing the fouled out plugs in less than 500 miles. I now have a Holley (80457s) on it now and it runs a lot better. The plugs I'm running are Autolite Platinium 45. They are gapped towards the narrow side of the range.

Oil consuption is good. I change it twice a year, and it's at the full mark when I change it. I'm averaging 1,500 to 2,000 miles a year. I do think the valve guide seals are going though. After the car has been sitting for a few days or a week, I'll get some grayish smoke when I start it. I'll see it under acceleration until it warms up. After that I don't see it anymore. It smell like a mixture of fuel and oil.

Mike, The tool your talking about is a boroscope. It's used to look into places that you can't see with a naked eye.

Thanks for you input,

[Blown306]

Just FYI, here is the formula to calculate octance rating when mixing fuel:

T=Tank size in gallons
H=High Test fuel octane rating
HQ=High Test fuel quantity in gallons
L=Low Test fuel octane rating
LQ=Low Test fuel quantity in gallons

H*(HQ/T)+L*(LQ/T)=Mixed Octane rating

Example: Octane rating when mixing 1 gallon of 112 octane with 93 octane for 20 gallons of fuel.

112*(1/20)+93*(19/20)=93.95 (i.e. one octane point)

[mike harmon]

That's it- a boroscope- a proctoscope for machinery. You could be right about the valve guides/seals. When the engine sits for awhile, some oil will seep past worn guides/seals & go down the valve stems into the intake area. It usually burns off in a few seconds or so. Similar things can happen with oil control rings on worn engines- when cold, the worn rings sometime won't seal properly, but once hot, things expand and they seal better. This usually isn't so noticeable on most auto engines (I've seen it more on Fords than other brands), but it is very noticable on larger such as big truck diesels and locomotive diesels. When first starting, or cooled down from idling for a long time, it's not uncommon to see older ones blowing blue oil smoke.

[bnrautobrokers]

Hi,
Have you tried using a lead substitute? I buy it at my local parts store and mix it with the gas. I use it in my 71 Bird with no problem.
Thanks,DAR

[MikeB]

I had my carb rebuilt by Pony Carbs, and they said not to run a lead additive. As metioned earlier in the threads, there are enough lead deposits, so no need to worry. Unless one would drive the car extremely hard. Pony also said the lead additive would "gum" up the carb.