What Octane Fuel to Use?

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Janius
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What Octane Fuel to Use?

Postby Janius » Mon Sep 21, 2015 11:57 am

I have a 1969 Alpine GT with a transplanted 1967 Alpine V engine (twin carb, aluminum head etc.). What octane gas should I use? High octane or the middle octane? I have been using the High Octane (92 or 93). Any suggestions?

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Re: What Octane Fuel to Use?

Postby 65beam » Mon Sep 21, 2015 9:05 pm

I usually use 89 with lead additive since most places only carry 87 and 89.

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Re: What Octane Fuel to Use?

Postby Mark1A » Mon Sep 21, 2015 9:44 pm

How original and stock is the engine? ... hardened valve seats? ...any trace of knock/ping if you use less than the 92/93 octane?
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Re: What Octane Fuel to Use?

Postby hartdm » Mon Sep 21, 2015 10:42 pm

The octanes were higher back in the day. Go with 93 if you can. Ethanol free if available. Higher octane gases should have less ethanol. In the mid-atlantic region, most every station has 93. Maybe that isn't the case in other parts of the country.

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Re: What Octane Fuel to Use?

Postby ImpBarn » Tue Sep 22, 2015 6:22 am

+1 for ethanol free.

Find the place nearest you.
http://pure-gas.org/
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65beam
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Re: What Octane Fuel to Use?

Postby 65beam » Tue Sep 22, 2015 5:35 pm

here in ohio we have no choice but to use a 10 % blend. there is no gas without ethanol except for 90 octane recreational gas sold only for marine or on water use. I have found a few places near the state borders that carry conventional gas but they bring it in from surrounding states. I've been in the oil/ fuel business for many years. I think it's only a matter of time before conventional gas goes away. several states have changed the taxes ,etc around and it won't be long before it will not be a good financial decision for the majors to refine two different blends of gas. my 69 has the original engine but it was one of the engines that were rebuilt at Chrysler's expense due to production problems. it was only driven in the D.C area for a short period of miles after the rebuild that the car was parked for the next 34 years until I bought it in 2006. I do use lead substitute and considering how little it gets driven I have no problems. there is a photo of my car in this months hemmings sports and exotic magazine.

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Re: What Octane Fuel to Use?

Postby Mark1A » Tue Sep 22, 2015 6:45 pm

FWIW - I've been using additives to [suppsedly, at least] prevent ethanol troubles. there is no "real" gas available anywhere near us.
My understanding of the need for lead is if you don't have hardened valve seats and if you are operating under high loads and/or high.rpm.

And "Congrats" Bob on getting into Hemmings!

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Re: What Octane Fuel to Use?

Postby 65beam » Tue Sep 22, 2015 10:32 pm

thanks, mark.
if an engine is built to have high compression it requires a higher octane fuel. low octane fuel will ignite under compression prior to spark in a high compression engine and that is what is referred to as "knock". lead prevented the valve seat erosion . hot valves would stick to the head and as it opened it pulled off small bits of the valve seat and that brought on recession of the seat. with the removal of lead there was a reason to use hardened valve seats. that's why I use the lead additive and there are many brands. it works ok for me. ethanol is an octane booster. that's why the refineries use a sub grade gas (84 or 85) to blend with ethanol to get an 87. they use an 87 with the ethanol to blend the 92 or 93.

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Re: What Octane Fuel to Use?

Postby vintagesportscars » Fri Dec 30, 2016 10:59 am

AV gas if you can get it! Has lead and none of the funky pump gas additives.


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