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Old 12-29-2004, 07:27 AM
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93 Octane / 110 Octane

this site is the greatest...

just got the new engine / blower combination put back into the car and i need to run higher octane then pump gas. my question is ... is it alright to mix 93 and 110 together or is it better to just tune the car to run on 110 octane. any help would be great

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Old 12-29-2004, 08:18 AM
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High Octane

There is no problem with mixing Different octanes of gas, for instance mixing 93 and 110 octane will produce, a theoretical 101 octane gas.
I used to do that for a race car I had. I mixed 91 octane pump gas with 101 octane Av-Gas. Worked great.
You might consider just using 104+ octane booster or a similar product to your fuel. Going to a lot higher octane gas than your engine requires is a waste of time and money, as it wont produce any more power.
I would suggest that you get with the maker of your supercharger, and run down all your numbers to them, your static compression, cam specs, psi of boost etc, and get their recommendation on what octane you should need. What is surprising is that quite often, your vehicle will run on the high octane quite well as long as your static compression isnt excessive. Example are the many street machines running superchargers with 8-9.1 compression with 6-10 lbs of boost and still live quite well on 91-93 octane gas.
Where is Camaroman when you need him? Hes got a lot of the inside scoop on this stuff.
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Old 12-29-2004, 09:05 AM
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I agree with Keith, mixing octane is fine and people do it all the time.

What makes you think you need higher octane than 93? I am not doubting you just curious. As Keith mentioned running higher octane that needed will only hurt power output. You want to run only enough octane to prevent detonation.

My blown 388ci SBC making 12lbs of boost, with 8.47:1 compression, runs fine on 91 octane fuel. I do have a boost retard to keep me safe (I know I am on the edge). I also have aluminum heads and I went with a large blower (8-71) so I could spin it slower and make more boost.

You didn't give any detail on your combination so I can't even guess as to wether or not you need race fuel. You do have to be careful because detonatin with a blown engine can be terrible (detonation with any engine is not good).

What type of blower are you running? How much compression? How much boost do you think it will make? (you will only know the answer to the last question once it is in and running).

If you are judging your octane rating from the charts on some off the blower sites, they are on the conservative side (for good reason).

Royce
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Old 12-29-2004, 10:14 AM
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royce, first off great looking car set up.
the motor was build for a blower set up. 9 - 1 383 cubic inch..
boost is around 12... car runs great up to 3500 rpm after that it starts pinging.. i have the boost retard on it and it is working. the blower is a 871 with dual 750's... it make piles of horsepower. almost scary... i have another question what type of fan you running on your radiator.. once i hit traffic it wants to run at 200 degree's i know that is to hot... i was looking at around 4000 cfm fan to try and cool things down.

thanks for you help

john
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Old 12-29-2004, 02:09 PM
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John,
Your combo is real close to mine. With 9:1 compression you are probably going to have to up the octane a bit or lower the boost. I did a few things when I built mine to avoid detonation (like quench) I am also using aluminum heads (not sure if you are) and polished the chambers. The cam also makes a difference.

Your sparkplug heat range can make a huge difference along with timing. I would have to go look at my notes but, I think I am runnning 18* initial and 16* mechanical (blowers love advance). I noticed that when running the timing much more retarded the engine would run warmer.

I used a Be Cool aluminum radiator and a Vintage Air fan. That is the biggest/most powerful electric fan available. It is 19" and moves a lot of air. I can look up the part number for you if you want. 200* is not too hot, if that is as hot as it gets even in traffic you are doing fine. If you said it was going up to the 220* range then I would say you need to do something.
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