Should I be using Octane booster? - Impala Tech
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post #1 of 8 (permalink) Old 12-30-2011, 04:45 PM Thread Starter
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Should I be using Octane booster?

I have a 1967 Chevy Impala with a 327 V8 engine.
It takes in unleaded/regular gas right now, I could go to a higher grade like plus or premium but gas is expensive these days.
It also takes in Lead substitute like every older car needs.

Should I be using Octane Booster? I was hoping they had a mixture of Lead + Octane booster to hit two birds with one stone but I don't think they do.
What type of Octane booster should I buy? and How many people here use it?
I don't have the car manual so I can't really answer my own question.
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post #2 of 8 (permalink) Old 12-30-2011, 06:26 PM
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I always fill with 93 octane and use the lead additive in my 69 327. Runs great.

Ape Out.

Make: Chevrolet
Model: Impala Custom
Year: 1969
Doors: 2
Engine: 327 V8
Trans: Powerglide
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post #3 of 8 (permalink) Old 12-30-2011, 07:58 PM
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A 275 horsepower 327 SBC (the base engine) was rated at 10.25:1 compression ratio when new. The "when new" part is important because odds are it isn't any more. Wear in the rings and piston skirt allows the piston to cock in the bore which keeps the worn rings from sealing as well as they did when new. That wear also removed metal from the cylinder wall as your cast iron rings are just as hard as the cast iron cylinders; so each wear away at about the same rate. As the cylinder grows the spring tension in the rings relaxes allowing even more cylinder pressure to escape into the crank case. So though your flat top pistons have picked up about 0.005" of lead deposits on the top of the cylinder increasing the static compression, the wear has lowered your static compression rate even more.

Back in 1967 regular leaded gas had an octane rating of 94 octane for the cheap stuff. That is a full two point above what most gas stations pump today though where I live 93 octane is the norm at the premium pump. In Georgia and LA (lower Alabama) many of the gas pumps have one that is locked except on Friday and Saturday night. That is the 104 Octane race gas pump that they have to have to fill up all of the cars going to race at the short oval, the long oval, the high banked, and the dirt track that is in every open area around the Southeastern part of the US. You still can not put it in your car; because there is no road tax paid on the gas sold (of course if you pay the road tax, or about the equivalent of 12 16 oz cans sold in the big blue box with a familiar beer logo on it) to the clerk or the clerk's boy friend who is hanging around because he has no beer money and he hasn't anything else to do, he will pump it for you).

Lead additives are still available on the shelf at auto-parts stores; and it will raise the octane of the gasoline as well as lubricate the upper cylinder. Tetraetyl-lead is made today in Germany instead of Louisiana, but it is imported to this country and sold in 30 gallon drums at any chemical supply house. It is highly carcinogenic and poisonous which is why it was removed from the gasoline supply in 1978 (three years later than intended). It will raise your gas to any octane you could desire, when mixed in the correct ratio with the fuel.

Back in 1967 all gas was received in your home town as regular and lead was blended into the stock supply at the distribution point to make the other two octane ratings you found at the pump (mid range and high test). You shouldn't be adding octane booster (which is just Toluene or lacquer thinner) if you are also adding tetraetyl-lead. As I said Toluene is sold as octane booster but there is so little for such a high price as to be a waste of money. Add a one gallon can of lacquer thinner instead to 20 gallons of 92 octane gas and it will raise the contents of the tank to about 95 octane, which is more than enough. Unfortunately adding more Toluene won't raise it much more than that; as it isn't linear as to how it works. To get to 104 lead free gas they use about half gas and the other half consists of other exotic aromatic compounds to raise the octane, including Toluene. As you might expect with a tankful of aromatic chemicals they will quickly start to evaporate out of your tank so do not mix up more than you can burn, as after a few days all you have left is the 93 octane gas you started with.

Big Dave
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post #4 of 8 (permalink) Old 01-08-2012, 11:45 AM
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Use 91 (or 93 where available). You don't need a lead additive.

Two doors, four doors, wagons, and ragtops.
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post #5 of 8 (permalink) Old 01-09-2012, 08:13 AM
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all this talk about octane has me wondedring what the 10% ethanol is doing to the higher compresion engines. i noticed it at every gas station in Maine this past summer. all gasoline contained 10% ethanol. here in NS, Canada we don't really have anything like that but i'm sure the day is coming. i am curently using Shell premium gas only with the octane boost in my 400 cid 10.5:1 compresion.

i also didn't notice any shell stations there here in canada,well Nova Scotia, everyone seems to use shell gasoline in their big blocks. its actually recommended to help deal with the higher compression
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post #6 of 8 (permalink) Old 01-09-2012, 09:13 AM
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We use the 10% ethanol here and there's talk of 15% coming. One thing Ive noticed on my 65 is that the flexible fuel hoses at the tank and fuel pump dry rot pretty quickly. Also Id imagine its not doing the carb much good either. If your using ethanol mixed fuel, better check your fuel hoses for cracks as that can start a fire. Most auto parts stores now sell a ethanol safe hose.
As for additives, I use them sometimes. I usually don't put enough miles on the car to justify there use ,as Dave says they evaporate. I always use 92 or above octane fuel as the 396 wont start with anything less.
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post #7 of 8 (permalink) Old 01-09-2012, 10:14 AM
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Good news is the alcohol subsidy to General Mills and other mega corporations to grow corn for gasoline instead of corn flakes has expired (and with everyone looking during an election cycle it won't find it's way back into the pockets of big agribusiness until after the election when no one is looking), so don't expect the alcohol content to rise any time soon. Fourteen percent of the current jump in fuel prices is reflected in the additional cost to buy the mandated alcohol content without the federal subsidy, so expect it to stay at it's current ten percent level.

You are correct about one thing though. Any car built before Ronald Regan became president isn't able to use gasohol. It was Jimmy Carter who mandated the change back in 1973, but it didn't go into effect until 1978, and even then no one was in complete compliance because there wasn't any gasohol to buy. So an old car doesn't have a stainless steel tank and hard lines or the plastic lined rubber gas lines to prevent the acid content of alcohol from causing corrosion and dehydration of the rubber parts.

Big Dave
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post #8 of 8 (permalink) Old 01-09-2012, 03:33 PM
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I think it should be noted that ther are two issues being discussed here; lead/no-lead fuel and octane ratings.

Aside from being a cheap 'anti-knock' agent, Lead in gas offers a cushion between valves and valve seats, specifically on the exhaust side. Unless you're planning on running Hi RPM's or driving long hours on the highway with your antique Chevy you really don't need lead. Today's fuels have better alternatives in terms of anti-knock agents (such as ethanol). However it should be noted that unleaded fuel burns hotter and therefore can be an issue with exhaust valve seats. Again, it goes back to your usage. Most antique vehicles that have mild performance engines without hardened valve seats won't see an issue under normal driving conditions. Hi performance engines that are planned to use unleaded fuel should have hardened valve seats installed.

As far as octane rating, yes, your older engine with compression ratio's above 10:1 should run 93 octane. If you want to run 87 octane and save a few pennies you can avoid possible pre-ignition situations (pinging) by pulling some timing out of your engine. You will lose performance as a result though. Check your plugs for detonation; Detonation shows up as little black specks on the porcelain.
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