Racing Fuel as an Additive?

[Doug Axelrod]

Folks,
Have a 408 stroked 351Windsor which nominally runs premium unleaded. I've been told that we've got winter gas for another couple of weeks here in Ohio and the winter gas can make the engine a bit logy. The marathon folks here sell "Marathon Blue" racing gas, which I understand is higher octane and leaded. My hot rod friend says that adding maybe 25 percent of the racing fuel to the premium unleaded would help with engine response without hurting the engine which has no catalytic converter.
Comments?
thanks!

[Jeff Frigo]

Doug Axelrod:

Don't waste your mone, there is no reason to do that. Its been proven that you may actually loose horsepower when you use a gas that has more octane than you need.

[Bob Parmenter]

Hey Doug,

The difference between "winter" gasoline and "summer" gasoline is Reid Vapor Pressure. Winter gasoline has more "light ends"(of the distillation range) that will vaporize more readily for lower temperature starting. This should have virtually no effect on octane rating.

I'm not familiar with the term "logy" so I have no idea what you mean by that, but octane rating (e.g. 91 or 93) has to do with whether or not your engine knocks(or pings if you prefer that terminology). If nothing has changed in your tune up, and your engine doesn't ping, then higher octane alone won't do anything to improve anything. You can potentially get more performance from a higher octane fuel if you change your tune up to take advantage of the higher octane rating (more resistance to knock). Generally that means changing timing.

Fact of the matter is, knock should be less of an issue in lower temperature months since you are getting a denser charge and lower cylinder temperatures with the cooler air. Knock (and the operational knock level) is basically a function of temperature all other conditions being equal.

Mixing leaded fuel with a premium unleaded fuel will result in a higher octane, but the effect will vary depending on mixing ratio, and lead volume. My guess would be, even in a racing fuel, the lead content today is pretty light, which would mean only marginal improvement. But again, if you don't have knock on the unleaded premium, then you're just spendin' money. If you do change your tuneup to take advantage of the octane boost, and the perceived improvement is worth it to you, then spend away.............it's your dough.

[Jeff Frigo]

Bob:

You are correct in what you said, but increasing timming does not necessarily mean more hp.

Pro-Stock engines only run 30 degrees of total timing. The more efficient the engine, the less timing it needs.

[a427sc]

Maybe Doug is referring to Oxygenated fuels, used to lower emmissons in cold weather. Not available in all parts of the country, generally in areas like the Northeast where we have to deal with the bad air blown on us from the mid-west. Vehicles will see a distinct difference in performance and mileage between "winter" and "summer" gas.

My guess is 15 gallon tank, 20% = 3 gallons @ $4.50, vs 3 at 1.95, and doing it maybe once or twice till the fuel changes back. Not enough of an expense to bother with. You probably spend more on wax. The other plus not mentioned is the great smell race gas has. Just another sensory spike when you open the door.

Don

[CMansfield]

Doug,
I am not sure what Loggy is, but if it refers to rough idle, gas vaporizing when you stop the engine and then start it a while while later it sputters when accelerating until you get fresh gas through the carb., and other general nastiness, I have the same problem. I have a 351 / 396 and had it back to the Olthoff's two weeks ago, they blamed the performance issues on winter gas. I bought some VP Red (106 octane) and mixed 2.5 gallons with about 15 of 93 and WOW what a diference, the car idles better, accelerates more smoothley (and seems faster) starts more easily after sitting, and just seems much happier. To me the difference in preformance is worth the cost.
Best, Chas

[petek]

There is always home-brew: http://www.gnttype.org/techarea/misc/octanebooster.html

(Haven't tried any of it...)

[Mr.Fixit]

Octane requirements are based on the static compression ratio of the motor for the most part. Too little "octane" and the air : fuel mixture explodes prematurely. Mixing octanes of gas should result in a averaging of their octanes, given equal volumes. However, it can turn out slightly better that that because the octane boosting additives in the fuels are different respectively, and also added beyond the point of diminishing marginal returns. Mixing them brings the additives into concentrations with higher marginal knock-reducing capibiblity.


Furthermore, in winter, the air is more dense, hense more available oxegen to burn, so without carburation adjustements, you'll be too lean and knock. This extra gas is needed to absorb heat from the combustion chamber to prevent detonation. Higher octane gas in a slightly lower stoichiometric ratio won't knock and an be run at the proper A : F ratio.