I really hate to be a wet blanket but that is not what octane does or how it works. to quote the people at how it works website...
"If you’ve read How Car Engines Work, you know that almost all cars use four-stroke gasoline engines. One of the strokes in the compression stroke, where the engine compresses a cylinder full of air and gas into a much smaller volume before igniting it with a spark plug. The amount of compression is called the compression ratio of the engine. A typical engine might have a compression ratio of eight to one.
The octane rating 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 plug, it causes knocking in the engine. Knocking can damage an engine, so it’s not something you wanna have happening. Lower octane gas, like regular 87 octane gasoline, can handle the least amount of compression before it starts igniting.
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 links. These different chain links 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, and butane has four carbon atoms chained together. Pentane has five, hexane has six, heptane has seven, and logically, octane has eight carbon atoms chained together.
It turns out that heptane handles compression very poorly. Compress it just a little, and it ignites spontaneously. Octane, on the other hand, handles compression very well. You can compress it a lot and nothing happens. 87-octane gasoline is gasoline that contains 87 percent octane and 13 percent heptane or some other combination of fuels that has the same performance as 87-13 combination of octane and heptane. It spontaneously ignites at a given compression level and it can only be used in engines that do not exceed that compression ratio."
the reason why car running E85 fuel or fuel that's mixed with Ethanol, which is a type of alcohol, is there is considerable less energy in 1 gallon of ethanol then there is in 1 gallon of gasoline. you can take any gasoline powered car and fill it up with straight gasoline and it will get much better fuel economy and have much more power than a car running on a blended fuel.
keep in mind many many race cars run on alcohol based fuel but that is different than our blended gasoline E85. I really don't think that the people at NASCAR give a crap how many miles per gallon the cars get on the track.
for us normal people that drive our cars on the street we must deal with the gasoline that is available and octane ratings that available to us. as you know the higher the compression ratio the higher octane you will need in order to keep the car timed correctly and get all the horsepower out of your engine that you can.
I hope that clears up the octane/horsepower/compression ratio equation a bit. as well as why blended fuels versus straight gasoline get different miles per gallon on the same car with different fuels.
Eric
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I have a 3:55 gear in the backend, my tire size will be different than what they are now ( haven't decided for sure yet ), and I don't know the exact weight of the car.
Jeez ... this is harder than when I picked out the cam for my poly ... just used what Gary P said to use :-)
Thanks,
Brian
On Monday, September 17, 2012 2:20:44 PM UTC-4, Roger Pettigrew wrote:--I would suggest holding off on the cam selection until you find out what your going to end up with for CR (pistons),,,, your gearing, tire size, and total weight are also considerations that need to go into cam selection.413 pistons are not everywhere, and usually more expensive than 383-400-440, I believe that some have found it cheaper to have block sonic checked and bored to 440 specs.In a message dated 9/17/2012 12:53:16 P.M. Central Daylight Time, hzf...@xxxxxxxxx writes:I'm rebuilding a 413 and am looking for some help selecting a cam.
Muscle Motors did their race-prep service on the block, bored it .030 over.
The 452 heads have been prepped by a local machine shop - milled the heads, new valve guides, hardened seats.
Looking for a mild street cam as this is a daily driver during the nice weather months with an occasional trip down the track.
I also need to find some pistons ( or have some built ) - help with that process would also be appreciated.
Thanks in advance,
Brian Safford
'62 Dart 440 4-door / Poly 318
2010 Challenger R/T
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