Would 87 octane pure gas + octane booster be OK?

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Jim Ed
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Would 87 octane pure gas + octane booster be OK?

Post by Jim Ed » Sun Jun 26, 2016 11:58 am

Hi.
I found a Conoco station that sells pure gas but, it is 87 octane (USA pump gas rating). I think that cross references to 91 RON.
I was thinking that it would be suitable if I added an octane booster.
A long time ago I was using 104+ Octane Booster in an old Ford Fairmont. I gunned the engine on the highway and it blew a head gasket. For this reason I am concerned about using that product in my 1973 VW Beetle even though it does not have a head gasket but, it does have thick copper spacer rings between the heads and the tops of the cylinders.
Can anyone recommend a safe octane booster?
TIA!

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Marc
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Re: Would 87 octane pure gas + octane booster be OK?

Post by Marc » Sun Jun 26, 2016 1:48 pm

Unless your engine has a higher-than-stock compression ratio there should be no need for octane booster. 87 (R+M)/2 octane is adequate at sea level, and the requirement goes down as the elevation goes up.

I also doubt that it was the 104+ that caused your Ford's head gasket failure.

In general, the only additives that actually raise the octane by more than a trivial amount are not technically street legal - read the fine print on the bottle. One such product that has received good reviews is Royal Purple Max Boost. It's claimed to raise octane by "up to" 3. At ~$11 for a pint, which treats 25 gallons, you're adding 44 cents per gallon to the price of your fuel at the recommended dose. Surely you can buy pump gas with an octane number 2 or 3 points higher for under .44/gallon more than the Regular...if you do really need it.



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Re: Would 87 octane pure gas + octane booster be OK?

Post by aussiebug » Mon Jun 27, 2016 8:03 am

I agree with Marc. Your bug engine was designed to run on 91RON, which is equivalent to 87AKI in the USA. There should be no reason you need to use an octane booster, especially if you have copper rings on top of the cylinders - these would reduce the compression ratio, meaning a LOWER octane fuel would probably be sufficient.
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Re: Would 87 octane pure gas + octane booster be OK?

Post by Piledriver » Fri Jul 08, 2016 1:43 am

Also note that the "points" the octane boosters call out are generally 1/10th of a point of octane if you read the fine print. (the RP may be real, but read the fine print)

So your expensive bottle of magic juice would typically get you from 87 to 87.3 octane.
A bottle of rubbing alcohol would probably help as much.(if 100%, aka drygas)

E85 is ~102 octane, if its actually 85%, and can be higher if you blend your own with race gas.
It would probably not agree with your solex carb tho.
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Re: Would 87 octane pure gas + octane booster be OK?

Post by Marc » Fri Jul 08, 2016 1:07 pm

Piledriver wrote:Also note that the "points" the octane boosters call out are generally 1/10th of a point of octane.
I was hoping to avoid that confusion In my last post. To clarify I was referring to "gross" points - Royal Purple Max Boost can raise the actual octane number by 3 (i.e. 30 "points" in the advertised claims). Unlike some competitor's products, RP makes that quite clear on the front of the label. But yes, always read the fine print.

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Re: Would 87 octane pure gas + octane booster be OK?

Post by Piledriver » Sat Jul 09, 2016 1:52 am

That stuff (The RP booster) maaay make sense if you are racing and knock limited, and pump premium almost works, and you don't want to spend $6-8 a gallon on the 100 octane boat gas. or similar for avgas.

Most of the junk "octane booster" sold gives you 3 "points" meaning 0.3 added octane==in the noise.

A tank of midgrade or premium fuel is a much better bang for the buck, until recently premium was about 17 cents a gallon more, seems to be much more these days as modern engines cars can actually use or require it and can actually get a real performance advantage.

A stock T1 should never need anything but regular anyway, and it really shouldn't run a lick better on premium...
May actually run worse due to slower burn, but you'd probably need a good dyno to even see that.
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Re: Would 87 octane pure gas + octane booster be OK?

Post by Marc » Sat Jul 09, 2016 2:23 am

Piledriver wrote:A stock T1 should never need anything but regular anyway, and it really shouldn't run a lick better on premium...
May actually run worse due to slower burn, but you'd probably need a good dyno to even see that.
The energy content per gallon is virtually identical in all grades of gasoline, a higher octane number just indicates better resistance to self-ignition from the heat of combustion before the sparkplug fires - pointless unless the compression ratio is high enough to create peak cylinder pressures/temps that'll cause preignition. The burn rate is essentially the same in any grade of gasoline. Long story short, running higher octane than the engine requires doesn't really do any harm, other than unnecessarily lightening your wallet.

I haven't messed with this stuff since the late `70s when I was campaigning a 12½:1 1300 on a ⅕mi oval track. Back then the go-to octane booster was 104+, which I found to make plug readings very difficult because of the way it would discolor the insulators...it also gave disappointing results so something better was needed, and the class rules specifically prohibited using "racing fuel". You could still buy leaded pump Premium at a few places then, eventually I ended up using a 50/50 mix of that and 100/130 unleaded AVgas with 15% methanol (using a Type III electric pump to recirc the tank to keep it in suspension). No idea what the final octane number of that witch's brew was, but it stopped the detonation ;)
Tetraethyl lead was used to raise octane numbers more cheaply than could be done by more refining alone, and its effect was not linear - the improvement from adding "X" amount of it to gasoline fell off quickly beyond the initial dose, so if you mixed a high-octane fuel 50/50 with a lower-octane fuel and either one contained lead, the gain from the presence of the lead in the mix would more than offset the loss due to the presence of the lower-octane fuel.

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Re: Would 87 octane pure gas + octane booster be OK?

Post by aussiebug » Fri Aug 12, 2016 2:13 am

Piledriver wrote:
May actually run worse due to slower burn, but you'd probably need a good dyno to even see that.
Thanks for your post above Marc.

Not critising Piledriver, but as Marc says, the octane rating has nothing do do with the burn speed of the fuel - all gasoline has essentially the same burn speed.

But even Marc has one part which needs clarification. Detonation usually occurs AFTER the spark, but BEFORE the flame front has raced all the way out from the spark plug (some unburnt fuel still remaining). In the 2-3 thousandths of a second that the fuel needs to burn, temp and pressure increase dramatically and the unburnt fuel starts to decompose. Some of the decomposition compounds might auto-ignite, resulting in an opposing pressure wave, a hammer blow to the piston and the characteristic harsh clicking sound of detonation.

The octane number simply describes the ability of the fuel to resist that detonation -auto ignition - so that the flame front races out to the walls of the cylinder and burns all the fuel as a steady burn.

Pre-ignition (ignition before the spark) CAN cause detonation, because it results in over-advanced timing which means the piston has not started its descent, so the pressure rise can be extreme, but it's not the primary cause.

The compression ratio is the primary method of controlling detonation - a low compression needs only a lower octane fuel, and a higher compression ratio (which results in higher temperatures during the fuel burn) needs a higher octane fuel.

I could add more, but that will do for now.
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Re: Would 87 octane pure gas + octane booster be OK?

Post by Piledriver » Fri Aug 12, 2016 4:08 am

Absolutely no offense taken, I have been where you are coming from, so to speak...

...But mote the caloric content and specific gravity of "gasoline" theoretically is always the same too, but its isn't.
What comes out of a fuel pump and reference iso-octane bear little>no resemblance these days, and can vary day to day.

Modern "gasoline" today is about as close to "traditional gasoline" as most "yogurt" you can buy in the supermarket is to actual yogurt.

Its just an unscientific observation, and it may have nothing to do directly with the octane rating of the fuel...
...but some motors seen to like regular a little better than premium.

Given the witches brew that modern pump "gasoline" has become, ~all guesses as to why are open.

Maybe they like being on the edge of detonation... Heck, at one point, NASCAR folk built combustion chambers that were designed to create late-in-cycle detonation ---an extra kick just for efficiency... May still.
Blame Larry Widmer.
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Re: Would 87 octane pure gas + octane booster be OK?

Post by aussiebug » Sun Aug 14, 2016 6:23 am

Yes the chemical content of gasoline is a lot more complex today that it used to be. In the past it was almost entirely hydrocarbons, but these days there are many other compounds in there too.

As stated above, TEL - tetra ethyl lead (plus a bromide scavenger so lead did not build up inside the cylinder and exhaust) was the best octane enhancer. But it's a nasty pollutant. You can get better octane numbers by using more benzine compounds in the fuel, but they are carcinogenic so fuel companies try to reduce the amount used. MTBE (methyl tertiary butyl ether) was tried for a while, plus other similar compounds ETBE and TAME, but these days it's mostly ethanol used to boost the octane rating. Pure ethanol has an octane rating of about 120.

But ethanol contains almost 40% of USED oxygen which reduces the energy content of the fuel, meaning that E10 (10% ethanol and 90% gasoline) has about 4% less energy per litre/gallon.

No problem for modern computer controlled fuel injected engines, they adjust the mixture on the run - they just burn a little more fuel.

But it's a big problem for carbureted engines like our bugs, because carburettors mix a VOLUME of fuel with the air, with no regard to its energy content. So the engine runs lean, that means hot, which can result in the need for a higher octane number to stop detonation, or else you use richer jetting in the carb to get the mixture back into balance (stoicheometry).

It's a complex problem, but the octane number remains just a number to describe the ability of the fuel to resist detonation - it's nothing more than that.
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