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Over the years so much has been written about fuels and fuel requirements that we shouldn’t even have to waste this space with additional discussion. Well, it’s my space to waste and I’m not satisfied that most hi performance enthusiasts or even many racers have a handle on the situation.

The short version is that you should use the lowest quality fuel your engine will run on. You can’t believe how many people run expensive premium unleaded when regular unleaded will do just as well if not better. OLD WIVES TALE NUMBER 1: Premium fuel is better for your engine than regular. NO! What is best is the least octane fuel that your engine will run on and act right. By that I mean that starting is easy, and engine shut off is instant. Also that the engine doesn’t detonate or “ping” or “rattle” under load in high gear. This load can be simulated by riding with 2 or 3 extra passengers at 50 MPH in high gear and STANDING on the throttle. If you hear nothing, that’s the best fuel. If it pings, you should try the next grade higher, or even Regular again but maybe a different brand. If it pings but not badly you can still use the lower grade of fuel UNLESS you load the car or increase the demands by wide open throttle. Further fancy tuning could find a blend between low and medium grades> The important thing is to get as close to detonation as possible without actually getting there.

I DO NOT LIKE NOR DO I RECOMMEND FUEL ADDITIVES. Every one I have tried through the years has one or more drawbacks that are in our opinion UNDESIREABLE to say the least. These drawbacks can be gumming up the combustion chamber, dangerous to breathe or contact with your skin, impossibility to maintain constant mixtures, cost, ineffectiveness, unavailability at the worst times and just a pain in the butt to be a slave to. Do your fuel tuning with FUEL.

Let’s look at some basic facts concerning fuel. Fuel (gasoline) is a complex hydrocarbon consisting of carbon, oxygen and hydrogen. It’s ability to resist detonation is stated in its octane rating. That rating in short relates to the speed of the burn upon ignition. Regular unleaded burns fast (almost to the extent of explosion) and premium burns slow. As you might expect, the lower the compression (or effective cylinder pressure) the faster the burn time allowable without causing engine damage. As the compression is increased and cylinder pressure is raised, the burn time must be slowed down. An “explosion” or fast burn will cross the top of the piston BEFORE it reaches TDC and the shock becomes knock.

In other words it’s a timing thing. The burn time must be coordinated with the position of the piston to gain the best power. Ignition timing plays a part although smaller than the rate of burn of the fuel used since it is completed in a mille-second, and the fuel has the final say in length of burn. So the trick is to get it just right. Not to fast and not too slow. Every engine is different and even the weather becomes a factor. Hot summer days opposed to cool autumn nights cause the requirements for burn time to change. It is a constant and continued quest to stay on the ragged edge for the greatest fuel economy and power gain. Add to this the fact that oil companies continually change the content of their fuels to accommodate changes in climate. There is winter gasoline and summer gasoline. They each have different additives to assist at compensation for temperature ranges of a hundred degrees. Winter fuel has de-icing agents and summer fuel has anti-boil additives. Some engines on the cusp may need a better grade of fuel in the summer and low grade in the winter. But the LEAST octane rated fuel your engine will run on, the better the power and the economy.

Let me tell you a story about how I discovered these anomalies. It goes back to racing in the 60’s.

Back then Sunoco had the famous blend-o-matic gas pump that had 8 different grade fuels. They numbered them 190 (which was below regular) 200 which was their regular, then 210, 220, 230, 240, 250 and of course 260. All of us ‘racers’ used Sunoco 260 of course. We ran a 63 Dodge Aluminum Front end Wagon, 426 Cubic inch Wedge rated at 415 HP. It sported 11.0-1 Compression and everyone thought that it needed the best fuel available.

I can’t remember the guys name that got me thinking about fuel, but he had an old Studebaker race car called the “Crockagator” which had the head of a Alligator and the tail was the head of a Crocodile. He said the reason it was so mean was because it couldn't poop! Anyway we both gassed up at the same time once and while I was pumping the good old 260 into the Wagon, he was filling his tank with 190. Wow a race car using below regular gas! I asked him why and he said it simply ran better. To make a long story short, each week after that I dropped one number. 250, 240, 230….each drop resulted in gains of a few hundredths of a second. I stopped at 220 just out of fear, but not before I gained a tenth and a half (that’s a lot) from my experiment. And it was a lot cheaper. I remember the 260 to be .399/gallon. Highway robbery.

Same today. I use VP C13 which is a blend of C12 and C14 in my high compression engine (12.5-1) and straight C12 for the low compression engine (11.75-1) Getting it just right makes so much difference you can’t believe it. In a 10.88-1 engine, C10 was worth 15 horsepower over C12.

Right is might! Forget better, worse, big, small and like all things in this business strive to find those things that are “JUST RIGHT” If anything, we all have a tendency to over do it, thinking more is better. It isn’t. Use your head, have a better finished product, make more power, last longer and save a few dollars to boot.



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