By using High Octane Gas in the 38 should this cause difference in the timing adjustment?
Bruce W
How high is high? Do you mean "premium" available at the pumps or something else? As it is, modern gas is much higher octane then when the car was new.
IMO. Unless you have "shaved" the heads for higher compression, I cannot think of a single reason to use high octane fuel in that low compression engine. To quote from the shop manual of another brand of vehicle that I am working on right now ---
"Rough idle, poor throttle response, induction backfire, and stalls during cold start and warm up may be caused by the poor volatility of some high octane premium fuels. When compared to regular grade unleaded fuel, high octane premium unleaded fuel may cause long crank time."
If you have a high compression engine, use high octane fuel. Using high octane in a low compression engine is a waste of money and may actually do harm.
Modern high octane gas is certainly much more volitile than the 30s gas. I cant see it harming anything, but, no original L head (flat head) engine, shaved or not, needs high octane gas. The compression ratios are no where near an overhead valved engine.
If the car sits idle for long periods - like many of our old cars, you may consider using premium fuel, as it evaporates better and does not leave residues or gum like some regular gasoline does.
I entirely solved my sticky valves issues in my unrebuild 1947 by switching to high octane .
A Packard collector from the USA told me exactly the same thing - he always put premium in his rarely driven classics.
High octane is more volatile than premium and so is more prone to percolation or vapor lock.I have experienced this too, in my 1932.
On the other hand, if your engine generates too much heat to be cooled by the radiator circuit, advancing timing to the max will greatly help - this is again where high octane becomes a necessity in some cases, since a low compression engine will knock if the timing is too advanced.
The owners manual of my 1940 LaSalle cautions owners to use 72 octane fuel. In my part of the US, regular fuel is 87 octane.
I can't see any reason to use anything more than regular, since our regular would have been super duper premium back in the thirties.
Of course, outside of North America, the fuel sold might be very different from what we use.
Due to low compression, high octane gas will not completely burn, and leave carbon deposits in the engine.
Do what you like , but that's the truth.
Roy
Quote from: Alan Harris CLC#1513 on December 29, 2013, 08:47:03 AM
The owners manual of my 1940 LaSalle cautions owners to use 72 octane fuel. In my part of the US, regular fuel is 87 octane.
I can't see any reason to use anything more than regular, since our regular would have been super duper premium back in the thirties.
Of course, outside of North America, the fuel sold might be very different from what we use.
Not only that, but the 72 octane in the 30s was by the research method, today it is the average of research and motor methods. That means todays gas would have an even higher number.
The number has nothing to do with whether the gas is capable of a clean burn in an engine. It is only a measure of its ability to resist an uncontroled burn (knock).
In the UK, i run my 49 on our "super unleaded" it makes the car feel better, its hard to describe its sound better, picks up faster for what it worth :)
in my manual for the 59' tripower states if i can get 100 octane or higher i have to retard the timing as well... where the hell am i getting 100 octane from is beyond me... i dont own a rocket, it just looks like one....
Dwayne,
You can use Av gas, it's 100 LL.
I use it for long term storage of my hit & miss engines and our 39 Caddy. Stopped the gumming up of check valves in the hit & miss engines. In the Caddy I put some in it in the Fall and run it thru the system for a couple of rides. Then the car sits until May in the basement and starts right up.
On the first ride of the Spring I fill the tank up with 87 unleaded. Once in a while during the Summer I fill it with REC 90 that has no ethanol which is what I run in our quads, chain saw and other gas powered equipment.
Lou Quirch
good to know Lou, if i can avoid any trouble with gumming up , i will pay the extra... its easier to pour gas in the tank then to have to take carbs apart....thanks
Bruce,
The "gasoline" that was available for your car in 1938 bears little resemblance to the "gasoline" of today. Octane is just a number that is the fuel's "resistance" to auto ignition or "knock". If nothing else changes in the fuel but the octane rating, an engine can use any grade fuel that has at least the octane rating the manufacturer (of the engine) recommends. There are many, many reasons for fuels to perform better than others under specific conditions, and typically fuel distributors "blend" their brew several times a year for seasonal (temperature and humidity) changes as well as emissions during specific high emissions promoting conditions.
"Leaded" fuel is primarily a product of WW-II and the need for high octane ratings for aircraft engines where compound superchargers were used. These ratings went up to (I believe) about 140 octane. A by product of the addition of lead to motor fuel was the effect it had on valve seats, in that it helped protect them in higher compression engines. Cadillac saw the end of leaded fuel coming in the mid 60's and started installing hardened valve seats in the motors.
That said, IF you use 87 octane regular and it is clean and blended to a "neutral" state in the seasonal mix, you should be able to run the same timing your factory service manual recommends for the car.
Greg Surfas
A little reading.
http://www.automedia.com/High_Octane_Fuel/ccr20050501ok/1
Also an interesting read on spark plugs and additives.
http://www.autohausaz.com/html/spark-plugs_spark-plug-wires.html
I would like to thank everyone for their reply it was much appreciated,
Bruce W