VCCA Home Forums TECHNICAL - GENERAL Mechanical - Engine, Trans, etc Octane - 93 for me!

So... my 35 is like a woman.. never know what mood she is going to be in. :)

Anyways, thought I had it running well, when suddenly it seemed like I had lost power.... a lot of power It was to the point that when I tried to accelerate hard, I actually engaged the starter! I began wondering if there was something wrong with the accelerator? It was if I needed more play to get more gas.

I was driving this weekend and needed gas I remembered getting the last tank of 87 from an off brand station. I usually use a name brand (BP) and get 93. So, I thought, could it be the gas? Well it was!! I filled up with BP 93 and it is running like a champ. I mean it feels like I picked up 15+ HP!! And that is a lot!

Not sure what others have found, but my 207 seems to like the good stuff! :)

--John

If you are running lots of timing advance, you can notice a difference, especially if you always run the 93 and have tuned it up with this octane.

It could also be you got some really crappy gas. A friend got a bad batch of gas in a modern jeep and I drove it and it seemed to be down about 80% and it picked right back up after the next fresh fill. It was astounding the difference.

Hi Tim, I think it was the gas. I run 7-8 degrees of advance, but turned back to 0 and it still ran bad. Amazing how big a difference it made.
--John

You have another problem. The only thing higher octane does is make the gas burn slower. Your 1935 was designed to run on 70 octane gas. The higher octane gas is/was for cars with a higher compression ratio so under power the engine would not ping - with the higher octane gas.+

Hey Gene, thanks for your thoughts... any ideas what it could be?

Could be a fuel or eletrical problem.

Gas tank may have stufff floating around or gas line plugging-up. Fuel pump getting weak. Vent in gas cap plugged-up.

Coil or condenser breaking down when hot. Points set too close.

The only Engine I've ever needed 93 Octane was my 64 Super Sport with a 327, never in my 30's cars.

I agree with Gene.

You may have had some bad gasoline. That stinkin' ethanol again.

97 octane is just fine for all the old 207s and 216s. Anything higher octane means you are just throwing your money away and ignoring/masking the real problem.

If you really want to go see what high octane can do to an engine go out to the airport and fill up with 130/145 aviation fuel.

Best,

Charlie

I am thinking it must have been bad gas..

- gas tank - new
- fuel line - new
- fuel pump - rebuilt
- coil - new
- points - new and set correctly
- condenser - new

I put new gas in and it is running great. May be famous last words, but 93 for me... until the next thing! :)

ps. Charlie, as much money as I have thrown away so far, $0.30 / gallon is easy. If I get 10 mpg, I can drive 240,000 miles before I spend as much! :)

--John

Keep doing what you have been doing for a while to make sure the problem is gone. Don't want to jinx it lol.

Long term, whether it was some really bad gas or some other issue from Gene's list, it will actually tend to run best with the lower octane fuel. You can bump up your timing some more as well and experiment. As Gene said, the higher the octane, the slower the air/fuel burns so with a lower compression engine like these you want the fastest igniting fuel you can get as pinging is just not an issue.

Even with most modern cars, they will have more power and better mileage if you use the lowest level octane that the engine runs on without pinging.

Also recommend Tier 1 stations for all fuel and NEVER buy gas if there is a tanker on the lot as filling the storage tanks stirs up the layer of water on the bottom of the tanks.

Glad to hear that you seem to have figured out what happened. I do agree that there is more going on than just the octane rating. Our chassis dyno work with our race car showed that we got better power with lower octane fuels. We could not run high compression or highly advanced timing so knock was not an issue.

As Gene often notes in his posts we have to deal with the realities of gasoline with 10% ethanol in most of the US. These older cars seems to be able to handle that without too much trouble.

One "gotcha" showing up in our area is stations advertising "super unleaded 88". It is normally a few cents per gallon cheaper than 87 octane 10% ethanol fuels.

The trick is that it is 15% ethanol. That is what gives it 88 octane. Lots of cars have trouble with that, even those designed to handle 10% ethanol.

Last summer I did a study with the gas we get here in Dallas. What I learned was that if gas is allowed to sit for 1 month with any exposure to air (even the exposure it gets in a fuel tank or gas can), the quality of it goes downhill at a breakneck pace. It will still burn and still make a vehicle run (although very poorly), however it becomes amber in color and it burns slowly and with a copious amount of black sooty smoke...nearly like what is given off by a carbon black plant. It also leaves a much larger deposit which looks like varnish or burned sugar. And it smells horrible when converted to exhaust gas. 1 month was all it took for it to go bad. What caused me to do this was the lawn mower. 1/2 a can of gas sitting through the winter was so bad I couldn't get the mower running. Could be that's what you had a tank of...who knows?

Hey Jon,
Thanks for sharing. Poor quality gas could certainly be the reason. The station I bought a tank of gas from is not popular and could have had gas in the ground for a long time.

I have read up more on octane and the wise men on this site are of course correct... the octane should not be a factor. More likely is the quality of the gas.

I will fill up with 87 on the next tank from a reputable station and report back my findings.

Appreciate the feedback from all... as always!! :)

--John

As others have mentioned in this thread, the octane rating refers to the time that is required to burn the fuel. The higher the octane, the SLOWER it burns.

Why is this important?

Think back to your 7th grade science class, where mechanical advantage was discussed, normally with a system of ropes and pulleys. The more ropes and pulleys, the higher the mechanical advantage of the system.

The power of a gasoline engine may be analogized to the ropes and pulleys. The higher compression, the greater the mechanical advantage (ie torque). The slower burning fuel is necessary for higher compression to prevent detonation.

BE (before ethanol), gasoline contained 117,600 BTU/gallon. That figure applied to a gallon of 87 octane, a gallon of 91 octane, a gallon of 93 octane, or a gallon of av gas 100 LL.

One simply selected the minimum octane necessary for ones engine to prevent detonation.

Too low octane can cause detonation, with catastrophic results.
Too high octane can cause very hot running, with catastrophic results.

At the very best, too high an octane will cost more at the pump, and the unburned fuel will result in a loss of power and fuel economy.

This is my suggestion on how to choose the octane for your vehicle: OCTANE

Jon.

Hey Jon,
Thanks for the education.. good article. I am running a bit hot.. perhaps the 93 is contributing? Gotta get her out and burn off this tank to refill with 87 to see results (power and temp)
--John

Gene may even tell us that running a too high octane fuel may indeed trigger a need for hardened valve seats.

The fuel may be still be burning when it leave the combustion chamber and still be doing so as it goes by the exhaust valves; thereby heating them to a much higher degree temperature than the engineers intended.

Just a thought.

Charlie

Reviving this thread.

I don't understand how "Too high octane can cause very hot running, with catastrophic results."

In the instant case the question was whether 93 was too much. It's only 6 points higher than 87. So what? The engine in my '31 was designed to run on 65 - 70 but I run it on 87. That's 17 to 22 points higher than it was designed to run. It's hard for me to understand how another 6 points will make any difference to operation - to a bank account yes, but to the detriment of the engine - please enlighten me.

Can't see a jump to 93 causing anything that drastic myself.

I would think it would more of an absolute extreme situation - like someone running Av Gas with 130 octane, engine timing running more retarded than it should be, and at high Altitude at the same time. The engine power could be cut in half so I suppose if someone drove the crap out of it at wide open throttle under these conditions, it could do some damage since unburned fuel would be travelling and burning through the valves and exhaust system. Maybe some really nasty backfiring. Could get the same effect with some nasty stale gas I suppose.

Sounds like a "Mythbusters" experiment lol...

If the engine has insufficient compression and timing to use the slower burning high octane, then some of the fuel goes out the exhaust poet unburned (at least where it should be burned). This results in the engine running leaner than it should. Lean engines run hotter than they should.

Of course, if the fuel valve in the carburetor is grooved, resulting in a high float level in the carb, the carb could be supplying too much fuel, balancing the unburned fuel due to the octane, which might cause the owner to think the octane is just right.

Please note the post stated could cause catastrophic results. The post did not state that it would cause issues in all cases.

Did you hear the one about the gambler that left Las Vegas with a small fortune??? He went there with a large fortune.

Jon.

Two weeks ago, I bought a 1932 Chevy that is totally stock. Despite assurances that it had just been tuned up, it ran very poorly. I figured I would just let it be for a bit until I knew the car a bit better.

Last Friday I took my wife and went to WalMart, about a 10 mile drive. When we started home, the car just refused to start. I fiddled and piddled until I found a wooden measuring stick for the gas tank. Despite the fuel gauge showing 1/4 tank, the more reliable wooden stick showed the tank to be bone dry!

Called my best friend who said he would be right over with a couple of gallons. Once the fuel was in the tank, we dribbled about 6 drops of gas into the carburetor and "Virgil" fired right up. Yay! Best of all it was like the tune-up that was promised had finally kicked in. It was of course simply really bad gas. No telling how old it was.

Now "Virgil" runs like a brand new 1932 Chevrolet. In the words of the era, he now has lots of "pep" and "Pulls like a steam locomotive in 3rd gear. Etc."

Always check the obvious first!

Opa