I read once that the higher the octane the more resistance to burn, which made me understand why cheap gas had a tendancy to diesel because of glowing carbon on the piston, right?

Exactly right.
Low octane burns hotter and faster. But can produce less heat volume.

Hold a lighter under your hand. For a brief time it won't burn you. But hold it long enough and you can have 3rd degree burns. By high octane burning longer due to the cooler burn, it transfers more heat volume, but at a lower temp.

Heat temp and volume are two different thing.
Think of a furnace and a cutting torch. The 9000 degree torch will cut steel, but won't heat a room. High temp, no volume. The furnace will heat the room, but will never cut steel. Low temp, high volume.

AND super heated air is what pushes the piston down. The more heat we can transfer into the air, the more power due to air expansion pushing on the piston, and the more power out of the engine.

But if the octane is too high, it won't burn properly, thus not much heat volume. If the octane is too low, the burn is very hot, but very fast. Not enough time to transfer the heat into the air, and no power. It's a balancing act. The engine design and control system determines which is best for any application.

dude, your like a professor

kstyer said:But if the octane is too high, it won't burn properly, thus not much heat volume.

Does this mean that the piston completes it's stroke before all the mixture has fully ignited, and therefore releasing an unusual amount of unburned fuel out the exhaust port? That would make for a funky sounding engine.

JR

Yes, it does mean that. But it does not sound funky. The result is high Hydrocarbon and Carbon Monxide emissions, as well as a loss of power. It's something you very much want to avoid. It not only translates to pollution and power loss, but actually poor fuel mileage. You push the throttle further to get the power you would have with less throttle, and use more total fuel air mix, and drop mileage.

I'm not a professor, but I teach automotive at a technical college. Before that I fixed cars for 25 years and have 24 ASE certs. That and .60 get me a coke.

jredding said: Does this mean that the piston completes it's stroke before all the mixture has fully ignited, and therefore releasing an unusual amount of unburned fuel out the exhaust port? That would make for a funky sounding engine. JR

and this is also why you set your timing more advanced with higher octane fuel.. by firing earlier it gives it more time to complete the burn..

That's what I call 110 octane car knowledge. Ken & Ben...heckuva 1-2 punch.

JR

one thing you can do if you want to run very high timing and max out your power is run a water injection system.

this is an air charge cooling technique used on some older aircraft motors and in forced induction applications.

but it can benefit high compression normally aspirated engines also.

it not only cools the intake air but it also reduces combustion temp.

its also very good at cleaning your engine as it goes as the water turns to steam to break loose and prevent carbon-buildup. of course the amount of water used is very very small.. too much would prevent combustion and foul your oil..

the water does have one drawback and that is that it takes up some space.. ie it reduces the amount of fuel and air.. so to compensate they mix it with alchohol 50/50 to provide additional cooling and compensate for the fuel loss.

I know some of you will probably think im smoking crack.. so heres some links..

http://www.noswizard.com/water.php
http://users.frii.com/maphill/wi.html

Pretty wicked systems...a little out of my realm.

cthulhu said: I know some of you will probably think im smoking crack..

Naaahhh!!! I'd probably expect to find a NOS line out the base of your skull, though.

JR

Hey Ben, if your crack smokes, wipe slower!


Years ago some NASCAR teams used water injection. Then it was outlawed, it worked too well.

I had installed a water injection system on an old Hornet. It worked for about a week, then someone ripped it off from under my hood. Had to be someone I worked with. No one else knew, and it was taken during lunch time at work.

You do not want to use a water injection system on a computer car with an oxygen sensor. The water releases oxygen when in the combustion chamber. The extra oxygen is great for the car, but will fool the oxygen sensor and make the car run rich.

You can make your own water system easy and cheap.
Install a bottle under the hood. Make sure you have a sealed cap. Install an air intake with filtered air to the bottle. Run a line from the bottom of the bottle to pick up water. Use a small orifice in line, then use an adjustable valve. From the valve tie into the PCV hose with a tee, between the intake manifold and PCV valve.

The vacuum from the PCV will pull water into the intake. The PCV is a center located vacuum for the manifold. Adjust the water flow with the adjustable valve. This will take some trial and error. Look at the formulas in the above post for volume, and adjust the flow to match the rate based on fuel used.

Keep in mind, the bottle can be too big, and not fit, or too small and need filled several times per tank of fuel. It's nice to match one bottle per tank if possible.

A little experimenting and a few things from the hardware or parts store, and you can have water injection for less then 20 or 30 bucks.

Yes it does work. You can use window washer fluid. Pre mixed for winter use. Won't freeze. And you may find straight water works well in warm weather, but the mix may be better then as well.

|UPDATED|7/31/2004 7:21:12 AM (AZT)|/UPDATED|