I have a Honda Hybrid 2003. In the past I purchased High Test and found I get less mpg (about 5 less) than when I use regular. This has happened on two different occasions.

Strange... What is it about this engine and/or fuel injectors that causes this to happen?

Thanks... Jim

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Dear Jim

It all depends on what gasoline the engine has been tuned.
High octane gas only provides better performance if the engine has been tuned to the requirements for that type of gas.

The same goes for starting burning lower octane fuels : first retune the engine to the requirements for that gas, before you can benefit of the lower cost of the fuel.

Success

There's more energy is regular gasoline, which has more volatile molecules (more explosive power) than high test. The additives in high test promote a more uniform burn, in order to reduce engine knock. The results you observed are most apparent on long trips at steady highway speeds.

Quote:

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Originally Posted by txgreasemonkey

There's more energy is regular gasoline, which has more volatile molecules (more explosive power) than high test. The additives in high test promote a more uniform burn, in order to reduce engine knock. The results you observed are most apparent on long trips at steady highway speeds.

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With other cars I would get higher mpg to justify the greater expense of the higher octane fuel. Do you know why the hybrid civic would be different?

Would it have anything to do with the fuel air mixture?

Jim

High octane fuel is designed for high compression engines. The higher the octane, the more the air/fuel mixture can be compressed in the cylinder before it is ignited. A lower octane fuel would detonate due to compression, and then re-detonate with the spark (knock - in a high compression engine).

If you drive a Camry, or a Civic or any other car that does not require 91 octane or higher and you are paying for high octane fuel: you are wasting your money

I see... that makes perfect sense. I always wondered why..

Quote:

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Originally Posted by Credendovidis

Dear Jim

It all depends on what gasoline the engine has been tuned.
High octane gas only provides better performance if the engine has been tuned to the requirements for that type of gas.

The same goes for starting burning lower octane fuels : first retune the engine to the requirements for that gas, before you can benefit of the lower cost of the fuel.

Success

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The next question is how does one tune the engine. Is there a resource on the web I can go and check? Is it a matter of adjusting the MAP sensor and fuel injectors?

I suppose I should explain a bit more why I am interested in this.

I am installing a Hydrogen System into the car that will inject Hydrogen through the air filter. This will create more horsepower if I leave the fuel air mixture the same. I would like to lean down the fuel for gas saving. My goal is to increase mileage from the 55mpg to 70 mpg by increasing the efficiency of the gasoline engine by 30-40%.

Hope this puts things in context.
Jim

That sounds like a neat project... I know that there are a variety of programs that allow you to plug your laptop into your car's ecu and actually use it as a diagnostic/engine management tool. This is very popular in the tuner market with people who are looking to squeeze the most performance out of their engine modifications (intake, exhaust, bigger injectors etc... ). These programs allow you to advance your engine timing, and control fuel injection just to name a few

I unfortunately don't know much about spraying Hydrogen into the intake manifold :(

Thanks for the information. Hopefully I will not have to advance the timing... way beyond my expertise.

A friend expressed concern that if I lean down the air fuel mixture too much, I will fry the valves. He did so decades ago with a carb run vehicle. If I pull the spark plugs out every few days to see the condition, will that tell me what I need (whitened powder) since I am bypassing the MAP sensor.

Thanks.

I have another post on this so I hope I do not cause trouble with putting the question in 2 places...

I have installed the Hydrogen Generator. That part was easy. It is pumping out the hydrogen and is currently cleaning out my engine and valves but I am not seeing any mileage increase.

The MAP senser I found is located on the fire wall. I have a Potentiometer attached to the center wire that I believe is the signal wire (Pink). I am supposed to be able to reduce the signal to the computer (thereby leaning out the mixture to let the car running more on the hydrogen.

The car is not responding per the manual. It is as if there is no modification of the signal even when I turn it to full resistance.

Is there another MAP sensor or a MAF sensor? What manages the fuel to air ratio?

Any help would be appreciated.

Jim