My 72 350 by the book calls for 91 octane. Ethanol free is available near me however it is only 90 octane. If I run a 93 octane (10% ethanol) I can hear the fuel boiling in the carb. My question is this...do you all believe the ethanol free at 90 octane is suitable or should I run the 93 and deal with the consequences like everyone else does? Or is the ethanol free with an octane booster an idea? I believe it runs a bit smoother with the ethanol free. Just looking for thoughts/suggestions. Thanks, Mike

 

Try the 90 with a bottle or two of octane boost.

 

Do you hear any pinging/detonation on the 90 octane ethanol free? If yes, you could try running a ratio/blend of the two fuels to get up to or over the octane requirement, e.g., 75% 90 octane ethanol free and 25% 93 with ethanol.

If you live in a high humidity environment and the car sits for an extended period ethanol free is beneficial.

 

No pinging or detonation with the ethanol free. I had tried the 93 because I had some dieseling but that was cured with a timing and idle adjustment. Dieseling is gone now but this thought just ran through my head so I figured I'd ask for others opinions.

 

Having no choice about ethanol free in CA, I had to adapt my 455’s. Both my big blocks have stock-to-mild builds, nothing exotic, but I do like the HEI distributors. I’ve spent a long time getting timing right to avoid mid-throttle and WOT pinging.

The factory weights and springs for HEI’s didn’t work well for me. I alway had to dial back the timing at idle to avoid mid-throttle pinging (knock) which left them idling less well than I liked. I tried the variable vacuum cans that vendors sell, not right, or, well, not optimal. I tried springs, but light ones always made the problem worse. What helped was Echlin vacuum can 1838 which I think was for a Buick or Caddy and had a different (slower) timing advance profile.

6-9 months ago I came across Progression Ignitions Bluetooth distributors. I’ve installed 2. Thus far they’re solid. It replaces the vacuum advance springs & weights with a digital timing map you can control with your phone via Bluetooth. It still uses the vacuum input, but you can more or less infinitely adjust timing in realtime. Want more advance at idle? Sure. Want less at mid-throttle? Sure. Want to disable the ignition when you’re not in range? Can do. More or less timing at WOT? Sure.

The really big deal is they allow you to adjust your engine from your phone when you put in different grades of gas. You just figure out and save 2 different maps - say one for 93 with ethanol, and a different one for 90 octane without. Configure, test and save two maps and you can put in whatever you want.

Only 6-9 months in, I’m not certain of the longevity of these devices. All I can say is “so far, so good”.

Chris

 

That doesn’t sound right. 1972 engines were 8.5:1 advertised compression ratio (realistically around 8:1) and therefore should run fine on 87 octane.

Anyway, as noted above some of us have nothing other than 10% ethanol and our cars run fine on it, even in 110+ summer temperatures.

 

You can run the 90 octane ethanol free with no issues.

 

You can hear the fuel boiling, huh?
Do you have a 3 line pump and sender? Is it hooked up correctly? A return system should not allow the fuel to get hot.
As mentioned, that thing is low compression and should run on 87 if tuned correctly.
On a side note, the only people I hear complain about ethanol fuel are the ones that can get ethanol free in their area. The rest of us don't give it a second thought. It's not that big of a deal.

 

Agreed to all of these posts. You shouldn't have any problems. Might be something else.

 

^^^This!

 

A few things to consider.

Are you using rubber fuel lines under the hood? They hold heat vs metal lines.
Are your fuel lines close to or touching the block, rad hose or heater core hose?
I like mechanical fuel pumps, but they do make the system run hotter being attached to/and so close to the block. You could switch to an electric fuel pump and route all lines away from the block.

Also, is your car running hot?? That me be the root issue?

Just my 2c

 

Thanks everyone for the insight. Just for clarification I may be a little over dramatic lol. The car does run fine with either fuel, I just happen to think with the 93 the fuel is hotter. No issues other than most likely my paranoia. I'm sure it would run fine on 87 as you all have suggested, I just have never tried. This is why I was looking for opinions from experienced drivers. I know the owners manual states 91 but I figured the experience that I would find in this forum would give me real world situations. Thanks again!

 

I understand your desire to provide a little "headroom" for your engine. In my high compression engine(s) I use ethanol-free Chevron 94 and still use a bottle of octane boost in every tank for insurance, even though it's probably not necessary. However ...

This is just weird, because the whole idea behind GM's lowering of compression ratios in 1971 was to enable all their engines to run on regular low- or no-lead gas. AFAIK, 87 was considered "regular" then as it it now (although formulations between then and now obviously must differ). So I don't understand why the factory would be recommending 91, but it's been many years since I've seen a '72-vintage owners' manual. I would think that from the factory's standpoint 87 would be adequate for a car tuned to spec. Can you quote the passage from the OM that states octane requirements?

 

I agree...quite weird. Especially on such a low compression engine. Here's a picture from the OM along with the spec page that I had pulled from the GM Heritage center.

 

The octane rating that we are accustomed to is the average of Research Octane Rating and Motor Octane Rating.

(R+M)/2

The 91 Research Octane number noted in owner’s manual is not the same as our current “91 Octane.” I THINK it’s equivalent to our current 87 Octane.

…

 

The octane ratings were different in 1972 than they are today.
There used to be two methods of rating octane in gasoline.
The first was the "motor method" , where they used a motor with variable compression to test the "knock point " of a gasoline.
The second was the "research" method which established a theoretical octane rating.
The research method numbers were always higher, so they are the ones that oil companies used.
Sometime in the late seventies or early eighties (can't remember exactly when) the government decreed that both ratings were to be averaged.
And that was to be the stated octane.
The 1972 book requires 91 "research" octane which would be roughly equivalent to todays modern 87 octane.

 

Great information! I was unaware of this...you learn something new every day.

 

There is no reason you need high octane gasoline for that engine. Run the cheap gas and you will be just fine.


Just to sound old for a minute. I remember running to Vickers to get 94-96 leaded gasoline.

 

How about Clark Super 100.

 

We had a Clark station right down the street from where I lived in H.S. (1966-1970). I always bought the Super 100.

 

All we had was Chevron Custom Supreme.

 

That's all you could buy at a Clark station.
They offered no " regular " gas.

 

Sunoco 260 straight or blended at the pump using a dial on the side of the pump with 190 to make lower octanes.

 

Those dial an octane Sunoco pumps were something else. Used many back in the days. I worked at a Shell service station several years during & after H.S. Pumped a lot of gas & cleaned a lot of windshields.

 

Right you are. Not certain it was the best gas, but for the stated octane & price they got a lot of my $$

 

I have a 455 in my 64 F85. It’s a low compression smog motor from 1973. Runs fine on 87, does not ping at all.

 

Ha ha. Funny comments. We used to go to Vickers and get 99-100 octane gasoline. I remember in probably 85-86 ish gas dropped super low. I have my gas log still. We paid under fifty cents a gallon.

 

So, when the wheel was invented, did you guys ride around on an axle like the "B.C." comic strip?

 

Going back even further, to the sixties and early seventies, when our "muscle" cars were born .
Regular gas was 19 cents per gallon at the Midland Co-op, If you had an account there.
The most expensive gas in town was Amoco Super Premium at 28 cents per gallon. ( 98 octane)
The Arab oil embargo of 1973 changed all that.

 

The lowest I personally paid for gas was .29/gal (1964/65) mowing lawns ~14 years old. The lowest I ever paid while driving my Dad’s Buick Wildcat (1966) was .33/gal.

 

Mom was a home maker, but watched family spending like a hawk. While reconciling bills, paycheck at the dinner table on one of those giant mechanical calculators with the big buttons I recall her stating whatever it cost for a gallon of gas that’s what it cost for a loaf of bread.

 

I remember c. 1969-70 my dad had a hi-po (289/271) Mustang convertible. He decided to sell it because gas went from 0.29 to 0.33.

 

As a side bar conversation I recall during this time frame my interest in cars escalated when I bought my 1st car, 1967 4-4-2 (1969) and I first read about unleaded gasoline and hardened valve seats. I think that was my first subscription to Car and Driver.

 

Norm... wasn't that American at .19¢? I remember that for their premium!

 

Gas prices in the 60's was upper.20's to low .30's It hadn't seen .19 probably since the 1940's.

 

I think that's essentially most likely the average during that time period. I don't recall how old I was at the time, but I do know Dad was buying gasoline in the late 50's into the early 60's for 0.19/gal before I was old enough to drive. I recall very clearly him talking about it and seeing it on the pumps. Very formative years, for sure, as if I really knew the meaning of a dollar or how to read a gasoline pump and any significance derived from it. The one thing I do recall is his conversations regarding specifically the price he was paying for gas was 0.19/gal & he'd show me where that price was located on the pump. Speaking of pumps, those old pumps were something else, eh? My Uncles had these gigantic barrels (containers mounted on stilts) of both diesel and regular gas on their farms - some had vacuum pumps. I remember I bought gas from a vacuum pump service station in Plantation, FL (1970) for my '67 4-4-2 after driving from Naples, FL to what I believe is Andytown, FL today. The station was a Texaco station with this big Indian Chief statue either on the pump or at the station. I think I was riding on fumes along Alligator Alley - which at that time was a two-lane beaten down trodden piece of broken-up asphalt.

 

Off the subject, the cheapest I can recall gas bring in my driving lifetime was the early 90s at about 80 cents a gallon.

I’m too lazy to convert that to todays dollars, but I do remember vividly being happy with the price. My 85 cutlass got premium even though it didn’t need it!

 

Wow. I thought you were older than that!

 

Speak into my good ear please! Gotta make this quick, it’s dinner time and Matlock is on TV.

I’ll be 51 in September. That’s about the cheapest I can recall paying in my driving years.

 

For what it's worth, I wouldn't even consider ethanol doped fuel in either of my '69's. The S is pretty much all original and many rubber based parts in the fuel system will literally turn to a slimy mess after exposure to ethanol. The 442 is restored but I learned even stupid things like reproduction gas gaps aren't designed with ethanol resistant rubber. Non-ethanol octane rating around here is 90. No problem for the S but I do run an octane booster in the 442.