Grade of gas in old flathead 6

[Guest Redbox]

One of the cars has a '37 flathead 6 and the other has a '53 flathead 6.

 

What grade of gas and type of additives are you using?

Thanks,

Steve

[nvonada]

These are low-compression engines and will run off just about anything.  Some old rubber parts do not react well to alcohol so you may want to avoid ethanol.  90/10 ethanol gas also does not age well so don't let it sit forever without using the gas. 

 

I rebuilt the carb on my '41 Champion and replaced the fuel pump and all the rubber hoses.  It has been running straight 87 octane 90/10 pump gas for years now.  On the other hand I just resurrected a Jeep Jeepster that had been sitting for 30 years and almost immediately had the accelerator pump and a couple of seals fail in the carb.  That could have been the ethanol or could just have been age, no way to tell.  But it also seems to be running great on regular gas now with a rebuilt carb and new rubber throughout.

 

[Stude Light]

I suggest lowest octane you can find with least amount of ethanol and no additives.

Scott

[starlightcoupe]

These are not that fussy like modern engines. One additive I would recommend you use is Marvel Mystery Oil. It's been a staple for a century. It cleans, lubricates and compensates for the ethanol in modern fuel.  Add a couple ounces before each fuel fill-up.

Edited October 19, 2016 by starlightcoupe (see edit history)

[JFranklin]

MMO 4 oz to 10 gallons non ethanol regular gas.

[Stude Light]

At a mix ratio of 320:1 in fuel, I never really understood how MMO really helped. I know there are a lot of folks that swear by it but from an engineering point of view, I was never convinced. I use it in my air tools and have used it at a 5:1 ratio in the crankcase to help clean the inside of an engine. It certainly won't hurt and is pretty inexpensive.

Scott

[JFranklin]

They wouldn't put mystery in their name if you were meant to understand how it works so well, but it does smell great!

[drdon]

I hope I am not screwing up my engines, but I use non-ethanol premium available at select gas stations here in Western Colorado.  Costs a pretty penny but I hate the ethanol enough to go with it. Anyone out there think this is dumb- the 91 octane I mean. PS: also use MMO.

[1927Chevy]

i use no ethanol have some fake lead additive once and awhile , and now and then put in some lucas upper cylinder lubricant carburetor cleaner

[JFranklin]

91 octane won't hurt anything. We can buy regular non-ethanol in our town so that is what I use.

[Spinneyhill]

We only have 91 and 95 pump octane. I use 91 in the 1939 Stude and 1930 Dodge.

 

The higher octanes burn slower than lower octanes, so the exhaust gets pretty hot as the fuel has barely stopped burning when exhausted.

 

Putting oil in the fuel is a bit of overkill. The "upper cylinder lubrication" is really only required, if at all, on startup.

 

I used lead additive for a while in my DC dodge. The plugs lasted 1000 miles, then would not spark. All eight failed more or less at once. So no additives any more.

[1927Chevy]

lucas is an injector carb cleaner also, when i had a  1923 t bucket 450 horse 383 stroker with daul quads and tunnel ram after it sat for a while it would stall and run real rough at idle, it had a huge cam with roller rockers so it idled rough already but after lucas would not stall.  primarily i use it early season after they sat for a while.  i only drive them about 300 miles a year each n more than 500.  heres pic of the bucket, thats my blue 27 chevy also

 

 

 

Edited October 25, 2016 by 1927Chevy (see edit history)

[C Carl]

Hi , Don , with your being in Colorado , do you have access to 85 octane high altitude gasoline where you are ? Your old low compression cars will run a little bit better , get a little bit better gas mileage , it will be a little bit easier on your engine , and the gas will be a little cheaper. Sounds like a win/win/win/win proposition to me. Particularly if you are driving at a few thousand feet elevation.  Ideally you would want 60 - 70 octane for compression ratios of 6 or 7 at sea level. Octane requirements are aprox 10x the compression , again at sea level. Reduce octane more as you increase altitude , as the atmospheric density decreases. Way , way down yonder in the great lands of almost free gasoline of my youthful driving , two wonderful octane gasolines were available. Sea level was well up in the 90s. High altitude was in the 70s. Much of the population lives around 10,000 feet or more , with passes up to 16,000'. Fuel management was critical , particularly if you were climbing or descending many thousands of feet. My flight engineers training of almost 50 years ago corroborates this also.  Safe happy cruising to you !  - Carl

[drdon]

Sounds like I need to find lower octane non ethanol gas. Will look around. Any Colorado/Utah people out there who know some is available. Most gas here is 85/87/91.

[Guest Redbox]

This may help.

 

http://www.pure-gas.org/index.jsp

 

[RPrice]

I don't have a choice regarding ethanol gas.   That's the only regular gas that we can get here on Long Island.   It hasn't been a problem in my Lark VI, which I've owned over 25 years.   I do,however, use Marvel Mystery Oil in my gas plus I always put some Stabil in the tank, since modern gas doesn't hold up well over time.   No problems so far.

Rog

[1927Chevy]

I remember working at the auto parts store in the mid 70's when the salesmen at the store would call some of that stuff, Valve Job in a Can

[keninman]

I know I am resurrecting an old thread but considering this problem, has anyone tried lowering the octane of 87 fuel by mixing with diesel? From what I have learned mixing 4 gallons of 87 octane gasoline with 1 gallon of diesel should lower the octane to about 77. The article warns about doing this for modern high compression 120 psi+engines not these old ones with 70 psi of compression. 

 

Putting Diesel into Gasoline

Now, let's look at the reverse – you’re mixing a higher flash, heavier fuel into a base fuel (gasoline) that’s lighter, more volatile and burns at a much lower flash temperature.  Despite these differences, putting diesel into gasoline won’t cause nearly as many problems as the reverse.

The biggest concern is the reduction in octane. Thinking about how gasoline burns in an engine, octane rating is the measurement of gasoline’s ability to ignite at the right time – not too early.  Gasoline with lower octane rating will ignite too quickly once it is injected into the chamber. The gasoline ignite and explodes, but the piston is still on its way up and the resulting pressure wave collision gives you (at best) a knocking sound and (at worst) damage to the piston and rod.  In a sense, octane slows down combustion, it delays it.

Gasoline needs to have an octane rating of 87-91 to fit today’s car engines. Diesel fuel has an octane rating of 25-40.  Mixing 2% diesel fuel into gasoline will lower the overall octane rating by 1 point. Getting 10% diesel contamination  lowers octane by 5 points, which is enough to create problems in most engines. The octane depression rises linearly with increasing percentages of diesel fuel in the gasoline.

So higher levels of diesel contamination will damage the engine and give you blown pistons and cracked heads.  More moderate diesel contamination will give you dirty combustion and can damage the engine over time if something isn’t done.

[Grimy]

Ken, the only times I've cut the gas with 10% diesel in my low compression engines is to prevent vapor locking--specifically on 4-day tours based at 4,400 ft elevation and going to 7,000 ft--in 95+ degree weather.  Bottom line: don't do it to lower octane, do it only to lessen volatility.

 

More info on your other thread.

[Stude Light]

I've experimented by using kerosene to lower the octane in my 4:1 compression ratio 1923 engine. It ran slightly better vs the standard 87 octane fuel. It's not very practical if you enjoy touring, so instead I just use 87 octane gas and advance the timing. I'm fortunate regarding the ethanol content....Nothing in my fuel system is affected, otherwise I would be looking for ethanol free from specialty stations or marinas.