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  1. #1
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    What gas brand has the highest octane gasoline?

    I've been chasing a poor performance problem for awhile with my old car (1960), as it really loses power on hot (95F-100F) days in August-September and sometimes even pings or misses with wide open throttle. I'd been checking through all the usual things and narrowed it down to ignition (still using original single-points type distributor) or maybe just fuel as my compression should be just slightly higher than the 9:1 original value because during the rebuild to take out an 0.040 scratch due to a broken ring, a little skim was also taken on the cylinder head.

    So, rather than go to the trouble to switch in some other ignition, I bought a bottle of octane boost, and wow, there was definitely a lot more power to be had in there and all my problems disappeared. Octane boost is ridiculously expensive, so now I wonder who is selling the highest octane gas at the pump so I can test a tank and see if that's enough, or if I need to continue to pour in a little octane boost when I want max power. I can usually find 92/93 labeled octane rating, but I wonder if anyone is selling 96 or 98?
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    Chepooka StupidlyBrave's Avatar
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    Here is something you can research further: http://www.sunocoinc.com/site/Consum...UnleadedFuels/

  3. #3
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    Do you go to car websites and ask what the best flavor cliffbars are and what the best after-ride recovery drinks are?

    Seriously though, octane availability varies wildly around the country. It does you no good to know that I can get 101 octane unocal 76 at the pump at sears point raceway in sonoma. You're going to need to call your local "speed shop" and ask them if they know any stations in your area that sell higher octane fuel.

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    Chepooka StupidlyBrave's Avatar
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    I have given bicycling advice on a car enthusiast forum. However, when someone posted that they "Need a Cat!", my advice to simply go to a shelter wasn't well received.

  5. #5
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    It doesn't matter what type of ignition system you have, it is the compression ratio and combustion chamber design, and possibly the air/fuel mixture from your carburetor, that is causing the spark knock.

    Modern cars sometimes ****** the ignition timing if they detect spark knock. This is one advantage of a computerized system but you can do it yourself just by retarding the timing of your distributor. Then in cooler seasons you can advance the ignition back to where it was.

    It might be possible to find a water injection system that would help a bit, or even a cold air intake system so you are pulling 95-100F air into the carburetor instead of much hotter air that is under the hood.

  6. #6
    Senior Member DannoXYZ's Avatar
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    Quote Originally Posted by Wilbur Bud View Post
    So, rather than go to the trouble to switch in some other ignition, I bought a bottle of octane boost, and wow, there was definitely a lot more power to be had in there and all my problems disappeared. Octane boost is ridiculously expensive, so now I wonder who is selling the highest octane gas at the pump so I can test a tank and see if that's enough, or if I need to continue to pour in a little octane boost when I want max power. I can usually find 92/93 labeled octane rating, but I wonder if anyone is selling 96 or 98?
    First, you need to recognize that the little bottles of octane boosters will boost your octane in "points". As 0-point-3 or 0-point-4. So your 91-octane tank goes to 91.3 or 91.4 octane maximum. Read up on this article comparing octane boosters.

    If you have a race-track nearby, you can always get 98-102 octane fuel for about $9/gal. Then mix it 50/50 with regular pump gas for a 94-95 octane mix for about 1000% improvement over the little bottles. I usually do this and turn up the boost a couple of psi and add a couple degrees of ignition when at the track.

    Other best value for the money is toluene at 114 octane. It gives you largest octane boost per tankful than any other stuff. Available at paint stores for about $10-15/gal (Sherwin Williams, Frazee, etc.). Xylene is 117 octane, but more difficult to obtain and cost per octane-boost, so it's not as good as toluene. If this is a long-term thing, best bang for the buck is getting VP-100 or VP-110 race-fuel delivered in 55-gallon drums. You'll need to verify EPA storage rules for your area.

    On the hot intake-air, look for the hose under the air-filter housing. It sucks in hot air from above the exhaust-headers to help vapourize the fuel when the engine's cold. There's a valve that shuts off this intake when the engine's warmed up. If the valve's broken, you'll be sucking in hot air full-time, not a good thing. You can also run a hose from the end of the air-filter housing to the fender for outside air. But above a certain speed, 25-30mph, there's sufficient turbulence and swirling that under-hood air-temps are the same as outside air.

  7. #7
    derailleurs are overrated bigbenaugust's Avatar
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    They won't let you do it I bet, but is 100LL/AvGas from the local airport an option?
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  8. #8
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    I always figured the only reason the bottles of typical auto shop shelf octane booster do any good is all the solvents they include in them. It gets the carbon deposits off your piston tops and then with fewer "hot spots" you don't get the pinging.

    FWIW, as far as actually boosting up the octane, you can get the best bang for your buck on octane boosters by getting Lead Supreme 130, now known as octane supreme 130. I used to get it delivered by mail from Utah since it wasn't available in california, and used it in my dino that had a 10.4 compression ratio.

  9. #9
    Senior Member DannoXYZ's Avatar
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    Quote Originally Posted by bigbenaugust View Post
    They won't let you do it I bet, but is 100LL/AvGas from the local airport an option?
    The problem with 100LL is that it's of lower-density than auto gasoline. This causes the engine to run lean without re-jetting carbs or re-programming the EFI. I've seen many a hi-perf engine destroyed by running 100LL.

  10. #10
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    delta sonic (carwash chain) used to sell 100 octane racing fuel. Last time I saw it is was over $5 a gallon (regular was about 2 then)
    sigless at the moment....

  11. #11
    derailleurs are overrated bigbenaugust's Avatar
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    Quote Originally Posted by DannoXYZ View Post
    The problem with 100LL is that it's of lower-density than auto gasoline. This causes the engine to run lean without re-jetting carbs or re-programming the EFI. I've seen many a hi-perf engine destroyed by running 100LL.
    I figured it would blow up the engine.
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  12. #12
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    Thanks everyone, part of the joy of asking non-cycling questions in Foo comes from the tangential responses, so that's why I ask here instead of in a car forum.

    Just to be clear, my problem is not knock or pinging, it's performance. On top of that, no PVC valve or any other blending or air controls in this one outside of a manual choke cable, it's prehistoric (but still fun to drive). There is a small crankcase vent to one carb, but it's not controlled and other than that, everything just flows straight in and straight out, no ductwork on any of the intakes, just compartment air. English car, SU carbs, etc.

    We do have a local municipal airport and I've a friend who rents hangar space for his cars, but so far no success in getting aviation fuel, plus there is the volumetric and energy density complication.

    We also have a racetrack or two, but if I have to drive across town to gasoline alley or out of town on the others side, it sort of negates the value of the trip as I'll have used a fair bit of it for the trip. I can try to find a co-worker willing to exchange 5 gallon containers, but as I commute to work by bike, not sure I want that on my rear rack.

    Fun idea to buy a drum, I do have a qualified storage location at work, but probably won't ask to store one there, nor at home, too much volume for me to take the risk.

    Anyhow, many thanks, you've given me some new options with which to proceed.
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  13. #13
    derailleurs are overrated bigbenaugust's Avatar
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    Is it a Lotus Super Seven, and if so, can I borrow it?
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    Haha, no, nothing like that. Big Healey.
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    Just to be clear, my problem is not knock or pinging, it's performance.
    Octane is a measure of resistance to pre-ignition, but has absolutely nothing to do with performance (BTU content of the fuel). If your car will run on 87 octane with the same ignition settings as 93 octane, then it will have the same performance on 87 as it will on 93. (Some modern cars will adjust timing with different fuels and will give better performance with higher octane fuels.) If you have a performance problem at high temperatures it is because the air is less dense and you get less of it into the engine. Anything you can do to prevent underhood heat from getting into the intake will help a little bit, beyond that you would have to go with some kind of forced induction.

  16. #16
    Senior Member DannoXYZ's Avatar
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    Exactly. Higher-octane fuels does not combust any faster or generate any more power under the same conditions. It just allows you to make mods like increase-compression, increase boost, add more ignition-advance that will generate more power. This requires using the higher-octane fuel 100% of the time. If you are able to run lower-octane fuels, then higher-octane will not generate more power.

    Also without air-density measurements and compensation, the car will run rich under high-temperatures. This is a common problem with carburetor autos. This rich mixture causes a drop in power. One of the old hot-rodding expressions was, "lean is mean". Of course, there's a smaller safety margin as well. Highest theoretical BMEP is at 12.5:1 in lab-environment. In real-world testing, about 13-13.5:1 yields highest power in non-boosted engines.



    Here's an article I wrote a couple years ago: What is Octane?

  17. #17
    Senior Member no motor?'s Avatar
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    This guy was in the last motorcycle club I was in, and knows more about gasoline than most of us need to know. If you look long enough he should be able to answer whatever linger questions you may have on the subject.

    Those big Healeys were cool too.

  18. #18
    aka Phil Jungels Wanderer's Avatar
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    Join Date:Aug 2008
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    Posts:169Just to be clear, my problem is not knock or pinging, it's performance.
    Octane is a measure of resistance to pre-ignition, but has absolutely nothing to do with performance (BTU content of the fuel). If your car will run on 87 octane with the same ignition settings as 93 octane, then it will have the same performance on 87 as it will on 93. (Some modern cars will adjust timing with different fuels and will give better performance with higher octane fuels.) If you have a performance problem at high temperatures it is because the air is less dense and you get less of it into the engine. Anything you can do to prevent underhood heat from getting into the intake will help a little bit, beyond that you would have to go with some kind of forced induction. Reply Reply With Quote
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    10-11-10 10:58 AM #16 DannoXYZ
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    Posts:10,304Exactly. Higher-octane fuels does not combust any faster or generate any more power under the same conditions. It just allows you to make mods like increase-compression, increase boost, add more ignition-advance that will generate more power. This requires using the higher-octane fuel 100% of the time. If you are able to run lower-octane fuels, then higher-octane will not generate more power.

    Also without air-density measurements and compensation, the car will run rich under high-temperatures. This is a common problem with carburetor autos. This rich mixture causes a drop in power. One of the old hot-rodding expressions was, "lean is mean". Of course, there's a smaller safety margin as well. Highest theoretical BMEP is at 12.5:1 in lab-environment. In real-world testing, about 13-13.5:1 yields highest power in non-boosted engines.



    Here's an article I wrote a couple years ago: What is Octane?


    These two are the correct answer.....

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  19. #19
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    Thanks again, I'll be sure to keep reading until I have the science firmly in mind. That said, I must be solving a problem I didn't know I had (lower power than capable) while also finding out how to solve an occasional problem that only started bugging me enough to do something about it recently (preignition on WOT when too hot). This engine is still fairly fresh and I haven't driven it regularly like the one before such that I really know its characteristic performance yet, all I can say is that with higher octane fuel (and an 85F day not a 100F day) the ten to whatever time was way more fun on wide open throttle than the other times I can remember, plus the aggravating mis-performance while hot disappeared. Maybe it was just old lawnmower gas on a hot day, and for sure it runs blistering hot sitting at a red light for 30 seconds, especially with intake and exhaust on the same side. I haven't wanted to pay the money yet to get on a dyno with a set of needles and decide how rich is rich enough until I get through these other teething problems and probably install a more modern ignition. Even then it'll be next August before test conditions will be the same.
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  20. #20
    Chepooka StupidlyBrave's Avatar
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    Your description has some of the symptoms of vapor lock.

  21. #21
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    filled up tonight, delta sonic had 100 at 6.59/gallon!! ouchie.
    sigless at the moment....

  22. #22
    holyrollin' FlatTop's Avatar
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    I'm curious about your ignition's advance. Not only in respect to the timing, but the advance curve. A bit of tuning in this department, and checking that your carburetor jets are centered (needles not dragging on the sides of the jets), plus mixture adjustment, might make a substantial difference in how the Healey responds.

    I've noticed a tendency to adjust SU carbs far too rich. What do the spark plugs say?

  23. #23
    You Know!? For Kids! jsharr's Avatar
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    Interesting read, not sure if any of this is applicable to your Healey, as it concerns an MG, but still a nice read for the gearheads that roll amongst us.

    http://www.teglerizer.com/dcoe/dcoe_...n_end_user.htm
    Last edited by jsharr; 10-12-10 at 07:35 AM.
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    Quote Originally Posted by colorider View Post
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  24. #24
    Senior Member DannoXYZ's Avatar
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    Quote Originally Posted by Wilbur Bud View Post
    I haven't wanted to pay the money yet to get on a dyno with a set of needles and decide how rich is rich enough until I get through these other teething problems and probably install a more modern ignition. Even then it'll be next August before test conditions will be the same.
    Dyno-time with carburetors is very painful and expensive. For that money, you can get your own wideband-O2 sensor system with datalogging. I've used the following with very good success:

    Innovate Motorsports LM-2
    Zeitronix ZT-2
    TechEdge WBo2 2Y - best value if you're handy with soldering iron

    Even then having the data on where in your 3D fuel-map you need to adjust is only partially there. You'll really need to customize the needles for your particular application. That means spinning them on a mini-lathe and customizing each section along the entire length. For that kind of time and effort, you may as well upgrade to programmable EFI. I've tuned customer cars in Europe remotely from California via the Internet in under an hour using MoTeC systems. Takes about 6-10 runs and I can make changes in under 5 minutes for another pass.

    MoTeC, Electromotive, even Link or Autotronic are overkill for a project like yours, unless you want to add turbos and take it endurance racing. Something simpler like MegaSquirt will work great.MegaSquirt started out as a freeware/open-source type of project and has evolved tremendously in the past decade giving you 90-95% of the functionality of those other systems. It'll give you significant improvements in performance. I don't even bother with carbs any more on anything simply due to EFI being so much more time-efficient and gives much more significant improvements. Hell, I even sold my friend on converting his 1927 Rolls to EFI. Now if I can only convince him to put in some turbos....

  25. #25
    Senior Member no motor?'s Avatar
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    It's kind of hard to believe that we used to use tools like the Uni-syn to balance carbs. And even harder to believe that I needed a mercury stick to synchronize the throttle bodies on my fuel injected BMW motorcycle.

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