Joe very nicely done. I have always wondered about the energy value of fuel.. and the fact people always were telling this burns faster, slower. Until now I had no weapons in my fuel database..

Thanks
I will continue to research this topic...

Francis

 

Glad to be of service Mr. Jellyfish.

 

Great explanation, Cowboy, it definitely puts all the Octane factors into proper perspective! [sm=smiley20.gif]

I'm sure, though, that there are people that will swear by their experiences with regular/premium gas. Octane is the easy difference to point the finger at to explain their experiences, but your explanation pretty much puts most of those issues to rest. What other aspects are there that would account for those experiences (e.g.: detergents/additives, "water in the gas", brands, etc.)? I'm sure that all gasolines are not created equal!!!

Mike

 

Turbo or supercharger does not increase the compression ratio. One has nothing to do with each other.

BTW, usually when turbo or blower is installed by the factory, a lower compression piston is usually used

 

The only thing that changes your octane requirements are increased temperature in the combustion chamber as I stated in my previous post.

The act of increasing compression in itself does not increase the octane requirement. Usually when the compression ratio is increased, the temperature in the combustion chamber increases as well, hence possiblyl requiring higher octane. A diesel is a good example of this. Diesel combusts from the heat generated from the extremely high compression ratio(around 20 to 1)

 

I caught that too. I think he meant the dynamic compression ratio or cylinder pressure. Static compression is not changed by a power adder.

Somebody was paying attention lol.


Only me again

 

That is exactly what I meant, hence I stated "mechanical compression" in #1 and used the word "effectively" when dealing with forced induction. Yes, it does not increase the compression ratio but it increase the volume being compressed. That is why when installing a turbo or supercharger, you usually use a lower compression piston. If you do not, your compression ratio will be too high for the volume being compressed.
And you are correct when you talk about heat but the heat is caused by pressure. The pressure is created by compression of the fuel/air mixture.

You say six, I said 1/2 dozen...... no need to argue here.

 

Dang, I'm sorry I missed this thread! One of my favorite subjects.

Cowboy, you obviously have had some racing experience too! Nothing like finding that .01 of a second will teach you about engines!

I can remember when I was working on a crew for a CF/D back in the 60's. We had a small block chevy running nitromethane. Before each run we had to make sure the timing was set. The car ran best with a static timing of 56 degrees before top dead center! Nitromethane is very resistant to ignition, but will make a lot of power once ignited. BTW, we were running 14 to 1 compression in that motor!

The higher the octane the more POTENTIAL to make power! You need to have an engine that is capable of converting that kinetic energy in that fuel to power. If you don't you burn it just like the lowest octane you can put in your bike.

Now, the engines in our KLX's do not have the sophisticated engine management systems that some of the high dollar cars do. We do not have the ability to advance the ignition timing to use all of that power. Since you must ignite a higher octane fuel earlier in the combustion cycle to get the most power from it, the sophisticated engine management sytems will keep bumping the ignition timing up until it sees pre-ignition (pinging) happening. That is why when you have a car with that fuel, it will run very well on that fuel but not on a lower octane fuel. If you ever tinkered with a car, the first thing you did was to advance your timing, the car just ran so much better. You can do that on the KLX, but it does take a bit more work than moving the distributor.

The "Effective Compression Ratio" is something that can also be changed via camshaft timing. If you have valve timing that is open after bottom dead center on the compression stroke, that will reduce your "Effective Compression Ratio" on you.

Now, let's talk about something a bit more interesting - Top Tier Gasoline.

I found out about this because I am also riding a bike with EFI. To keep the bike running it's best, it needs certain additives to keep the fuel system clean. I was given a site that lists all the suppliers of Top Tier Gasoline. You might want to take a look at Top Tier Gasoline.

Myself, I run 87 in my KLX and it runs just fine! If I were to advance the timing, I could effectively use 89, 91 or even 93. However it is NOT a race bike and I don't think spending the extra money on fuel warrants it.

Just my opnion of course.

 

OK I concur.

 

I read like a month ago that a mag.... (dirtrider i think) did a dyno test starting with 87 and went all the way up to 97 with additives.

there was a 7 horsepower gain at 9000 rpm.