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Posted by: IronHillRestorations Jul 15 2019, 09:29 PM
The first time we had a Renegade Festival in Hot Springs (2nd mid west event), I lucked up and got a tech rep from BG Petroleum Products to give us a tech session. BG (was Wynn's Spitfire) makes fuel and oil additives. Their fuel additive is very effective for helping remove excess carbon build up. This is especially a problem in Japanese cars, or at least it was 20 years ago. He had quite a bit of technical data and, was there for a Toyota, or Honda tech summit of sorts. I saw him getting stuff out of the truck with a big BG on the side and started asking questions, and he graciously agreed to give us a tech session.
The guy did a cool "Mr. Science" kind of demonstration showing the difference between regular and premium gasoline. The demo showed that regular gas burns faster and cleaner than premium. He put a small eye dropper of each fuel on their own white Corell saucer. The regular burned without a lot of smoke and left a little residue. The premium burned slower, made noticeably more waxy like smoke, and left much more residue on the plate. Part of the point is to demonstrate that gasoline octane is the opposite of what most people think, "high test" or "the good stuff" is less volatile and has more additives. High octane fuel is the same fuel as regular, but with an additive package to lower the volatility, raising the octane for higher compression engines. He went on to say that you should use whatever your auto manufacturer recommends, and if no solid recommendation the general rule of thumb is to use the lowest octane you can, without getting pinging, or pre-ignition. Using high octane fuel in an engine that doesn't require it, can result in more unburned fuel, that can cause carbon build up in the combustion chamber, raising compression, and thereby requiring you to use a higher octane fuel that adds to the problem. Make sense? Are you tracking with me?
Most all of the guys there had questions, as well as their minds changed about the best fuel to use, in any car.
Someone posted on one of the 914 FB groups asking "what octane fuel should I use". My reply was based on my own experience, but mostly on the info from the BG rep: "Unless the mfr or engine builder says otherwise, you should run the lowest octane you can as long as you don't get pinging, or run on. Octane additives typically translate into carbon build up in the combustion chambers." Good grief, you'd have thought I said there's no Santa Claus, or our 914 is just a VW.
I've been around these cars for a while, and cringe whenever I get called an "expert" or "guru". Part of the great thing about our internet 914 community is we get to share insight and experiences both helpful and otherwise. Most everyone of us that's been elbows deep in a project has something good to share, even if it's "man I really messed up" But some people have to tell you how wrong you are, even if you aren't far off the mark, I don't get it 
Posted by: GaroldShaffer Jul 15 2019, 10:36 PM
Yep I seen that posting. How dare you call 914s a VW 
I agree with you on the fuel.
My autocross 914 demands higher octane, but I always used 87 /89 in my daily drivers with no issues.
Posted by: Larmo63 Jul 15 2019, 11:11 PM
So, should I 
try half a tank of regular?
Posted by: steuspeed Jul 15 2019, 11:11 PM
Great info! My cheap ass always runs the lowest octane that won't ping. Who would have known?
Posted by: Superhawk996 Jul 16 2019, 04:19 AM
There is no Santa Claus?
1) Facts don't often change peoples opinions. Lots of psychological studies on this. Sad but true.
2) We live in an age where even "experts" with the facts, can be shouted down by the majority (or social media mob).
3) Marketing from petroleum companies has convinced many that "premium" is better. How could it not be . . . it's Premium.
Brondo . . it's what plants crave:
https://www.youtube.com/watch?v=kAqIJZeeXEc
You did what you can do. Wind em' up and then let it go.
Posted by: 914Sixer Jul 16 2019, 05:52 AM
I know just enough to be stupid.
Posted by: bbrock Jul 16 2019, 08:01 AM
There is no Santa Claus?
1) Facts don't often change peoples opinions. Lots of psychological studies on this. Sad but true.
2) We live in an age where even "experts" with the facts, can be shouted down by the majority (or social media mob).
3) Marketing from petroleum companies has convinced many that "premium" is better. How could it not be . . . it's Premium.
Brondo . . it's what plants crave:
https://www.youtube.com/watch?v=kAqIJZeeXEc
You did what you can do. Wind em' up and then let it go.
Well put. Hard to believe the octane thing is still debated today, but we are indeed living in an idiocracy. I think I first read about what octane really does in the OLD VW-Porsche mag back in the early 80s. I've always run the lowest octane my car is designed for. I was bummed a few years ago when our Regular gasoline in this region suddenly jumped from the 85 octane appropriate for our high altitude up to 87 - the same as "low lander" fuel.
The petroleum industry would have us believe that high octane is like rocket fuel. Maybe those who buy the hype should try running a tank of actual rocket fuel through their engine and see how it works
Posted by: dr914@autoatlanta.com Jul 16 2019, 08:14 AM
excellent post, and in my opinion also dead on. I have always said to use the less expensive regular fuel in the 914-4 and the highest octane in the 914-6 for all of the below reasons. I can add one more thing that Classic Motorsports wrote about the other day: When storing a car, fill the tank with the highest octane you can find and add gas stabilizer. The high octane gas has a much longer "shelf life" than the low octane "stuff", and by additionally adding the gas stabilizer, the fuel could actually last a few years without turning
The first time we had a Renegade Festival in Hot Springs (2nd mid west event), I lucked up and got a tech rep from BG Petroleum Products to give us a tech session. BG (was Wynn's Spitfire) makes fuel and oil additives. Their fuel additive is very effective for helping remove excess carbon build up. This is especially a problem in Japanese cars, or at least it was 20 years ago. He had quite a bit of technical data and, was there for a Toyota, or Honda tech summit of sorts. I saw him getting stuff out of the truck with a big BG on the side and started asking questions, and he graciously agreed to give us a tech session.
The guy did a cool "Mr. Science" kind of demonstration showing the difference between regular and premium gasoline. The demo showed that regular gas burns faster and cleaner than premium. He put a small eye dropper of each fuel on their own white Corell saucer. The regular burned without a lot of smoke and left a little residue. The premium burned slower, made noticeably more waxy like smoke, and left much more residue on the plate. Part of the point is to demonstrate that gasoline octane is the opposite of what most people think, "high test" or "the good stuff" is less volatile and has more additives. High octane fuel is the same fuel as regular, but with an additive package to lower the volatility, raising the octane for higher compression engines. He went on to say that you should use whatever your auto manufacturer recommends, and if no solid recommendation the general rule of thumb is to use the lowest octane you can, without getting pinging, or pre-ignition. Using high octane fuel in an engine that doesn't require it, can result in more unburned fuel, that can cause carbon build up in the combustion chamber, raising compression, and thereby requiring you to use a higher octane fuel that adds to the problem. Make sense? Are you tracking with me?
Most all of the guys there had questions, as well as their minds changed about the best fuel to use, in any car.
Someone posted on one of the 914 FB groups asking "what octane fuel should I use". My reply was based on my own experience, but mostly on the info from the BG rep: "Unless the mfr or engine builder says otherwise, you should run the lowest octane you can as long as you don't get pinging, or run on. Octane additives typically translate into carbon build up in the combustion chambers." Good grief, you'd have thought I said there's no Santa Claus, or our 914 is just a VW.
I've been around these cars for a while, and cringe whenever I get called an "expert" or "guru". Part of the great thing about our internet 914 community is we get to share insight and experiences both helpful and otherwise. Most everyone of us that's been elbows deep in a project has something good to share, even if it's "man I really messed up" But some people have to tell you how wrong you are, even if you aren't far off the mark, I don't get it
Posted by: jd74914 Jul 16 2019, 08:43 AM
Well put. Hard to believe the octane thing is still debated today, but we are indeed living in an idiocracy. I think I first read about what octane really does in the OLD VW-Porsche mag back in the early 80s. I've always run the lowest octane my car is designed for. I was bummed a few years ago when our Regular gasoline in this region suddenly jumped from the 85 octane appropriate for our high altitude up to 87 - the same as "low lander" fuel.
The petroleum industry would have us believe that high octane is like rocket fuel. Maybe those who buy the hype should try running a tank of actual rocket fuel through their engine and see how it works
Its funny how people are about gasoline. Especially the misunderstanding that higher octane fuels are less thermally reactive (higher activation energies) which does not bode well for full burning.
I'm finishing my PhD; having spent the last 5 years studying combustion full-time and the prior decade part time. Much of the time looking at fuel effects, though usually for jet engines. People ask me all of the time when they find out what I do and then still argue with me about it.
Interestingly, any liquid rocket fuels which use an oxygen oxidizer would probably work in a T4. That's really only kerosene and liquid hydrogen, but still...
Posted by: Olympic 914 Jul 16 2019, 09:12 AM
I use the 89 octane in the teener with somewhere around 8.6 - 1 comp. No pinging with that.
The Cayman gets premiums as dictated buy Porsche.
I also had heard that the lower octane fuel burns faster.
Now days the cars computers will detect pinging and reduce the timing and maybe other factors to prevent damage to the engine.
Posted by: UROpartsman Jul 16 2019, 09:43 AM
With an older car that only pings when it's hot out, run the lowest octane Fall through Spring, and only buy the "premium" stuff mid-Summer.
Posted by: Superhawk996 Jul 16 2019, 10:51 AM
I'm finishing my PhD; having spent the last 5 years studying combustion full-time and the prior decade part time.
Ha! You’re a better man than I. I took a undergrad course on combustion. 1st day was cool. The professor was talking about fires, explosions, and engine combustion. The second day he started writing chemical formulas that ran the width of the calk board. 3rd day I dropped that class and added a vehicle dynamics class! Much better for me!
Posted by: SirAndy Jul 16 2019, 11:32 AM
The whole point of higher octane is to make it harder to ignite.
I thought that was obvious?
PS: The "burning slower" only applies if ignited under the same pressure when comparing to lower octane gasoline though. Or no pressure in case of the demonstration by the BG guy.
Posted by: Dave_Darling Jul 16 2019, 11:53 AM
Well, atmospheric pressure at somewhere near sea level. 
What's interesting is that the combustion speed is not dictated by the octane spec, so it is possible that premium could burn faster than regular. Vanishingly unlikely, and probably would require some PhD chemist specifically trying to make that happen, but it is possible.
Anecdote time: Once upon a time, they built aircraft engines specifically to use ~80 octane AvGas. Many years later, this became hard to find. Some folks just decided to stick 110 low-lead in their plane and call it done, because new engines cost a ton of money (and re-certifying your engine for car gasoline, which can be found with a reasonably acceptable level of octane, also costs a lot).
All of a sudden, there were a whole lot of burned exhaust valves showing up in those engines. Turns out the high-test stuff was still burning as it went out past the valve, heating up the exhaust valve and related bits (seats, guides) a lot more.
So those folks got to buy themselves new engines anyway... Oops.
I strongly suggest that nobody put 150-octane fuel in their stock 914... 
--DD
Posted by: bbrock Jul 16 2019, 03:02 PM
And to add to the mess... the only ethanol-free gas available around here is premium grade (91 Octane), so it seems we are forced to choose something that is not the best fuel for our cars.
Posted by: Chi-town Jul 16 2019, 05:57 PM
Combustion chamber design, spark plugs location, intake runner design, spark timing, spark length, etc.
All of these things come into play with combustion, detonation, and all the wonderful things that happen in our motors.
Saying "you should always run the lowest octane possible" is just a dumb statement without knowing the specifics of an engine or tuning done to it even on a basic production vehicle.
Modern cars are always advancing ignition till knock occurs and then making corrections to achieve optimum performance. This is a constant process and the ECU is always learning.
In an older static timing setup like a 914, your timing can only be advanced as far as the fuel will support. Hence why putting in 100 octane in a car tuned for 91 will usually net you no gain and may actually cost you power.
Then there's additive packages and oxygenation of fuel and what they do to burn rates and deposit buildup.
There's far too many variables to make blanket statements like he did
Posted by: bbrock Jul 16 2019, 07:04 PM
Saying "you should always run the lowest octane possible" is just a dumb statement without knowing the specifics of an engine or tuning done to it even on a basic production vehicle.
Is there an example of when running higher octane than is needed to prevent pinging for that particular engine would be advantageous? I thought the sole purpose of octane was to retard detonation for the purpose of controlling pinging. Not trying to be argumentative, just want to learn.
Posted by: tmc914 Jul 16 2019, 07:16 PM
Well, I remember back in the the early 70's when I was just a kid and my parents always complaining about the gas. They would shut the car off and it kept running. For years I thought it was an octane problem. Learned later it had less to do with gas and more to do with carburetors and heat. This thread brought back old memories. Sorry if I went off topic.
Posted by: jd74914 Jul 16 2019, 07:53 PM
Saying "you should always run the lowest octane possible" is just a dumb statement without knowing the specifics of an engine or tuning done to it even on a basic production vehicle.
Is there an example of when running higher octane than is needed to prevent pinging for that particular engine would be advantageous? I thought the sole purpose of octane was to retard detonation for the purpose of controlling pinging. Not trying to be argumentative, just want to learn.
That's not quite the right way to think about. Modern engine controls can operate up to the bleeding edge of what the supplied fuel can provide to maximize performance, efficiency, etc. It really depends where you are in the map (ie: low load, low torque demand, high engine speed you may be shooting for max efficiency vs. high load/torque demand where you want power). They maximize performance based on the fuel characteristics (and air, engine temperature, etc. characteristics for that matter)
When I say operate at the bleeding edge this means that they manipulate spark timing up until the point detonation occurs and then back off. That means that you could put 87 into your STi instead of 93, but it will retard timing to prevent knocking. Just pulling timing might be a somewhat simplistic way of looking at it-the controls may be changing ignition timing, valve timing/lift to modify cylinder pressure (higher pressure lowers autoignition delay times), boost levels, etc. This could all be based on a measured knock limit, with changes happening after one knock event is detected. Or a misfire, etc.
Hopefully that answered your question in a somewhat roundabout way.
Edit: Just some food for thought: When modern engines have a single misfire, they have "missed" emissions requirements for literally the next tens of minutes to hours. Just one. That's how tight the controls are. I wish I could find the presentation that showed these figures-fascinating for people who like numbers.
Posted by: 914-300Hemi Jul 16 2019, 08:47 PM
Always learn something new here. I always use what the car manufacturer recommends.
On my 2056 carb’d teener my mechanic recommends 91 octane.
Posted by: bbrock Jul 16 2019, 09:19 PM
Hopefully that answered your question in a somewhat roundabout way.
Well not quite. If I'm understanding, that's a great explanation of why modern engines are much more flexible in that they can perform optimally with a wider range of fuels. In other words, modern engines are able to adjust to maximize performance for whatever fuel they are supplied, within limits of course. I'm wondering specifically about when the advice to run the lowest octane possible would be wrong. Seems like that would mean that in some cases, adding octane above the lower limit needed to prevent knocking for a given engine would increase performance, efficiency, longevity, or reliability or reduce emissions. Given that lower octane gas is almost always the cheaper option, is there anything else that octane does besides reduce knocking?
Posted by: jd74914 Jul 17 2019, 03:35 AM
Well not quite. If I'm understanding, that's a great explanation of why modern engines are much more flexible in that they can perform optimally with a wider range of fuels.
The issue is that it's a local optimum; not a global. The global optimum exists around their design point
I'm wondering specifically about when the advice to run the lowest octane possible would be wrong. Seems like that would mean that in some cases, adding octane above the lower limit needed to prevent knocking for a given engine would increase performance, efficiency, longevity, or reliability or reduce emissions. Given that lower octane gas is almost always the cheaper option, is there anything else that octane does besides reduce knocking?
Octane is literally a measure of knock resistance (how this is referenced changes when talking about MON or RON). Assuming the same fuel type, each gallon has the same amount of energy in it. There can be some variance is how they ignite (single stage, dual stage ignition), but that's getting really complicated.
It's really all about what the manufacturer recommends as they've designed around it. Their recommendation in many cases is likely the minimum octane required to statistically prevent knock without intervention for their given baseline engine design. They decided a certain fuel was necessary either a) because they absolutely need it, or b) because it allows some engine performance characteristic which is worth more than the difference in cost.
Posted by: jd74914 Jul 17 2019, 03:40 AM
Ha! You’re a better man than I. I took a undergrad course on combustion. 1st day was cool. The professor was talking about fires, explosions, and engine combustion. The second day he started writing chemical formulas that ran the width of the calk board. 3rd day I dropped that class and added a vehicle dynamics class! Much better for me!
Yep, that is how it goes. I'm really more a chemical/systems engineer wrapped in a ME degree so those dynamics classes sail right over my head. All of that geometry was killer, somehow I have a better physical feel for chemical reactions and heat transfer. Wish we had been able to take VD classes during my undergrad though.
Posted by: Chi-town Jul 17 2019, 09:01 AM
Is there an example of when running higher octane than is needed to prevent pinging for that particular engine would be advantageous? I thought the sole purpose of octane was to retard detonation for the purpose of controlling pinging. Not trying to be argumentative, just want to learn.
I've seen a few dyno tests where non premium requiring cars have been fed premium fuel and picked up a few hp and ft/lbs once the Ignition multiplier in the ECU saw the ability to run more timing without knock.
In an older car without an ECU (or an ECU that can't correct timing) it would be a per basis testing. If you have knock and the timing is set correctly you need to check AFR as you probably have an over rich or lean condition. Octane won't help you there.
Posted by: jfort Jul 17 2019, 09:28 AM
There is a reason why they used to use lead as an octane enhancer. IT'S INERT. And there was a lubrication quality that I don't think has been replaced. I agree, lowest octane without knock. Anything else, as far as octane is concerned, is a waste of money.
The bigger issues today, for us, is cleaning additives, ethanol and lubrication.
I used to work for a major refiner. I think good cleaning additives and no ethanol are the desirables for our cars. Gasoline, at a wholesale level, is fungible and often traded. It get its unique characteristics at the bulk plant where it is loaded on trucks. My refiner used different additives for different brands, in part to avoid antitrust issues.
I used to have a 73S. Manual said 90 octane. I used 89 back then with no trouble. I used better brands to get the better cleaning additives.
Now, the 2.7 in my six is 10.8:1 so I use the high test, usually 93. I am going to try to buy ethanol free as often as I can.
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