high octane or regular?
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Freshman User
Joined: Feb 2006
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high octane or regular?
i was wondering if my 312V8 needs to run on high octane gas or is regular? ive heard its got a 9.7 ratio but im not sure, i dont hear a ping or any carb. problems with the regular. any advice?
Postmaster
Joined: Jun 2004
Posts: 4,190
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From: Riverside, So Cal
At 9.7:1, you could probably get away with mid-range (89 octane). The hi-test (91 octane) will also work and probably give you a little better mileage. It depends on how advanced the timing is. I wouldn't run regular in anything with 8.5:1 or less compression.
Logistics Pro
Joined: Oct 2002
Posts: 4,489
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From: Valley Center, CA
The best way to be sure is to first get the engine tuned correctly. Make sure that your timing and fuel mix are correct. Many carbs, especially Edelbrocks are lean which can lead to engine ping. After you are sure that your engine tune is correct, try regular. If it pings, then go to midgrade. If it still pings then you will need premium. Running regular gives you the hottest burn in the combustion chamber. This is good unless it is too hot and then you will hear the pinging sounds on accelleration. Running midgrade or premium just raises the octain rating which means the combustion chamber is burning the fuel at a lower temp. This is not good for power or mileage if regular is suitable. So try it out and see. I have a 272 and a 289. They both run great on regular. Jag
Postmaster
Joined: Apr 2004
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From: Santa Clarita
I remember one of my professors in college use to work for ARCO gas and was one of the chemist who formulated gasoline. He told us that the current octanes, 87, 89, and if your lucky 91 or higher are basically the same. The difference from 87 octane to 91 is so minimal, you can't tell a difference. Back in the old days when octane was 101, you would see a difference. He told us not to waste our money on premium. I've been running regular in all my cars and I have never had a problem so far.
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Senior User
Joined: Aug 2004
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From: Los Angeles
Imlowr2 is right, gasoline in this country is delivered via a shared pipeline. The only alterations to the composition occur at the distribution centers for each company. That's where ARCO adds water, Chevron adds their "Techron" etc.
In a related matter, has anyone ever heard that you're supposed to add a quart of Diesel fuel to each tank to compensate for the lack of lead in gasoline? I burnt up my old valve seats b/c they weren't the new hardened variety and someone mentioned that the diesel helps protect them.
In a related matter, has anyone ever heard that you're supposed to add a quart of Diesel fuel to each tank to compensate for the lack of lead in gasoline? I burnt up my old valve seats b/c they weren't the new hardened variety and someone mentioned that the diesel helps protect them.
Last edited by Larry_the_handyman; Feb 9, 2006 at 04:48 PM.
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Logistics Pro
Joined: Oct 2002
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From: Valley Center, CA
Larry, I never heard of that, but it sounds like another of those urban myths. I don't see how diesel would help replace lead. I think that the only sure cure is to get the hardened valve seats installed. A few months ago, there was a thread about adding acetone to your gas to improve mileage. It turns out that it does not help mileage and what's even worse is that it will eat up the rubber parts in your fuel system. 
Anyway, Ranch, let us know how you do with which ever octane rating you choose. I am also a big believer in plug color. Light tan/gray is best. It indicates a good heat range for the combustion. 
Jag
Anyway, Ranch, let us know how you do with which ever octane rating you choose. I am also a big believer in plug color. Light tan/gray is best. It indicates a good heat range for the combustion. Jag
Junior User
Joined: Feb 2006
Posts: 76
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From: El Dorado Hills, Ca
Originally Posted by Larry_the_handyman
Imlowr2 is right, gasoline in this country is delivered via a shared pipeline. The only alterations to the composition occur at the distribution centers for each company. That's where ARCO adds water, Chevron adds their "Techron" etc.
In a related matter, has anyone ever heard that you're supposed to add a quart of Diesel fuel to each tank to compensate for the lack of lead in gasoline? I burnt up my old valve seats b/c they weren't the new hardened variety and someone mentioned that the diesel helps protect them.
In a related matter, has anyone ever heard that you're supposed to add a quart of Diesel fuel to each tank to compensate for the lack of lead in gasoline? I burnt up my old valve seats b/c they weren't the new hardened variety and someone mentioned that the diesel helps protect them.
Elder User
Joined: Mar 2005
Posts: 828
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From: Indianapolis, Indiana
I would ask the CEO of Exxon/Mobil or may be Shell what is best. All joking aside, me and all of my buddies with hot rods just get the good stuff. Why-because I take care of my wife and do not feed her crap, so I dont feed my truck crap either (Unless the prices do not come down).
Kyle
Kyle
Senior User
Joined: May 2005
Posts: 102
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high octane fuel
The only reason to run high octane gas is to prevent pre-detonation, or engine knock. If you think its better or makes more power in an engine that does not require it, you are mistaken. I have dyno sheets from the last engine build I did. It was 542 ci. C$#@vy. We broke the engine in on the dyno and adjusted timing etc. with full 110 race gas. After a few pulls, we slowly started mixing in 91 octane amoco gas until we reached 100% with no knock. We knew this was going to be border-line, but wanted to see the results. Guess what, we got an exta 30 h.p. with the 91 vs. 110 for a total of 610 h.p. Don't waste your money on higher grades unless you need it.
Dan
Dan