[jphawk]

I have a 72 Lemans Sport Convert with a 455 and the highest octane I can get here is 93. I can't seem to get it completely solved. I was wondering if the octane boosts really work and if so which are best. Should I try different plugs?

[uneasyrider]

A cooler plug might help and backing the timing off a bit but I would think a '72 with stock heads would be ok on 92. I think the fuel requirement was 91. I think the fuel octane requirement is on the glove box and maybe on the fan shroud or under the hood someplace on a spec sticker. If you don't drive it hard or if the engine is getting tired you can get a carbon build up in the cyl. and it will cause that. If that is the case, take a spray bottle and put it on mist with some distilled water in it and lightly mist the carb with the engine running but don't mist it so hard you kill the engine and this will blow the carbon out of the cyl. and off the valves. OR just go ROD THE HECK OUT OF IT now and then.

[jphawk]

Thanks uneasy. This is not a stock 455. It is a rebuilt 70 with 69 ram air heads. Has a performance cam and carter afb. only has about 2000 miles on rebuild. I need to get more detailed info on specs from previous owner of what
exactly was used in rebuild. It does move verrry well tho.

[uneasyrider]

Ok, yep more info would be good. See if the guy has his build info and receipts. I would say that a step cooler plug and backing the timing off a couple degrees couldn't hurt in the mean time just to see.

[Hitman]

I tried a bunch of different boosters and none of them worked for me. I bought my car in the winter and it ran great and still does when it is cool out, but when the temp gets up there it will ping like crazy when you jump on it so I backed off the timing and it worked. This will be the other mystery I will try to solve after the suspension project.

[goatman-68]

One gallon of Toluene to 12 gallons unleaded. That usually works for a 10.5 iron headed engine. Don't get any on your paint.........

[myckee]

I too use toluene however 1 gallon to 12 gal gas is too little, for MY engine.

Assuming 93 octane gas is used, the result will only be ~94.6 octane. I can buy 94 at the pump and in my 10.5 iron headed 462, it is not enough. I need about 97.

Becasue the octane requirement will change on every engine due to the specs of the cam, the amount of quench, etc. etc., everyones specific combo will have different requirements. There are many engines with upwards of 11:1 compression running on pump gas.

You will just have to try for yourself. However, it is always best to richen it a lot and then work backwards to the ideal mix than it is to go the other way.

[johnsma22]

The octane of gasoline tells you how much the fuel can be compressed before it spontaneously ignites. When gas ignites by compression rather than because of the spark from the spark plug, it causes detonation or "knocking" in the engine. Knocking can damage an engine, so it is not something you want to have happening. Lower-octane gas (like "regular" 87-octane gasoline) can handle the least amount of compression before igniting.

The compression ratio of your engine determines the octane rating of the gas you must use in the car. One way to increase the horsepower of an engine of a given displacement is to increase its compression ratio. So a "high-performance engine" has a higher compression ratio and requires higher-octane fuel. The advantage of a high compression ratio is that it gives your engine a higher horsepower rating for a given engine weight.

The name "octane" comes from the following fact: When you take crude oil and "crack" it in a refinery, you end up getting hydrocarbon chains of different lengths. These different chain lengths can then be separated from each other and blended to form different fuels. For example, you may have heard of methane, propane and butane. All three of them are hydrocarbons. Methane has just a single carbon atom. Propane has three carbon atoms chained together. Butane has four carbon atoms chained together. Pentane has five, hexane has six, heptane has seven and octane has eight carbon atoms chained together. Octo = eight.

It turns out that heptane handles compression very poorly. Compress it just a little and it ignites spontaneously. Octane handles compression very well -- you can compress it a lot and nothing happens. Eighty-seven-octane gasoline is gasoline that contains 87-percent octane and 13-percent heptane (or some other combination of fuels that has the same performance of the 87/13 combination of octane/heptane). It spontaneously ignites at a given compression level, and can only be used in engines that do not exceed that compression ratio.

During WWI, it was discovered that you can add a chemical called tetraethyl lead (TEL) to gasoline and significantly improve its octane rating above the octane/heptane combination. Cheaper grades of gasoline could be made usable by adding TEL. This led to the widespread use of "ethyl" or "leaded" gasoline. Unfortunately, the side effects of adding lead to gasoline are:

Lead clogs catalytic converters and renders them inoperable within minutes.
The Earth became covered in a thin layer of lead, and lead is toxic to many living things (including humans).

When lead was banned, gasoline got more expensive because refineries could not boost the octane ratings of cheaper grades any more. Airplanes are still allowed to use leaded gasoline (known as AvGas), and octane ratings of 100 or more are commonly used in super-high-performance piston airplane engines. In the case of AvGas, 100 is the gasoline's performance rating, not the percentage of actual octane in the gas. The addition of TEL boosts the compression level of the gasoline -- it doesn't add more octane.

Sorry this was so long but I thought that the chemistry and physics behind this debate were important to know so that an informed decision on what you should do could be made.

[Robert Williams]

http://www.wauknet.com/douthitt/gas.htm

[pippintook]

I used 104 Octane boost and it definitely helped me. I had a 455 with about 9.75:1 (HC-02 cam), depending upon many variables (carb jetting, mech advance, initial advance, dist curve, outside temp, engine temps, etc), I would sometimes get mild detonation. I found a can of 104 OCtane boost definitely worked for my combo.

[uneasyrider]

johnsma22, there isn't a thing wrong with a long explanation when it's clear and correct and that one was very good for as condensed as you made it. I know you could have made it MUCH longer but you gat all the important stuff in there in a compact explanation of a complex subject, thanks.


Just to add my two bits, the shape of the combustion chamber and the quench area can have major effects on the detonation and preignition of the combustion gases also. Compression is the first factor in the "equation" though as john stated. For example, that is why the new "Hemi" isn't really a hemispherical combustion chamber (in the traditional sense) as it was in the original design (which was closer to a true Hemi) and is now false advertising as far as I'm concerned. The true Hemi combustion chamber and associated piston design don't lend themselves to modern low octane gas.

Here are a couple of things I found about the Hemi on the web. It's just some good basic combution chamber design facts.

"Throughout the 20 years Chrysler used the Hemi, the design changed very little. Unfortunately for Chrysler, society did. Chrysler's Hemi had one drawback, it didn't have a quench area. Quench allows for better chamber turbulence thereby achieving more complete combustion, which in turn results in a more efficient, and cleaner running engine. This was irrelevant till the late 1960's when the laws sanctioned by the Environmental Protection Agency (EPA) started to be enforced. As society demanded cleaner air and more efficient running engines during the gas shortages of the 60's and 70's, more attention was paid to the performance engines and their lack of compliance with emission standards. The Chrysler Hemi was a very "dirty" running engine, especially at low engine RPM and could not pass EPA tests. That coupled with the racing world's boycott of the Hemi because of it's unbeatable reputation, forced Chrysler to discontinue their use in 1971..."
-Unknown

This one is a bit contradictory as far as I'm conserned because of these two statements, "Chrysler had to find a way to increase power without increasing compression, which would require higher octane fuel." and "...and the rugged engine loved high octane gas." The lack of quench area is a major factor in the problem here. It either needs high octane or it doesn't and it does so I'm not sure how the two statements work together.

"Chrysler had to find a way to increase power without increasing compression, which would require higher octane fuel. The key was thought to be in the better designed cylinder head, perhaps hemispherical with conventional valve-in-head. Using hemi heads would increase thermal and volumetric efficiency, as well as provide a low surface-to-volume ratio (thus minimizing losses due to combustion-chamber deposits). Why was this design not used earlier in autos, seeing as it has been around since at least 1904? Complexity and high costs did not allow easy mass production, and the rugged engine loved high octane gas."


-Scotech Productions

Anyway, I'm not trying to debate the "Hemi" one way or the other, it's just an example of how the shape of the combution chamber effects the fuel quality demanded by the engine.

[BoinaVerde]

To answer the original question, yes, octane boost really works, just not as much as the manufacturers would like for you to believe. Most of them typically advertise that they raise the octane level by 3 to 8 points. This sounds great because most of us typically assume that if a bottle of octane boost is advertised to treat 10 gallons and raise it 5 points, it will turn 91 octane into 96 octane. This is far from the truth. If you read the fine print on most bottles you will find out that a "point" is actually one tenth of an octane, so that same bottle actually is only good for changing your ten gallons of 91 octane in 91.5 octane. Very misleading the way they advertise it if you ask me.

[Colin]

Try this........
http://www.torcoracefuels.com/catalo...x.php?cPath=22