Where I am is in below my avatar.

I bet my engine will self destruct in a cataclysmic fashion since it is programmed by the Japanese engineers to do so if it senses that it is fed anything below 87.000000001 octane.

 

Simple physics increased ignition timing results in more Horsepower (up to a point). Basic 101 internal combustion engine for dummies.

 

I think the point is imperceptible in our Fits, or Honda and a crap-load of car-wogs outside of message boards would be shouting the benefits higher AKI in cars that don't need it, not to mention the oil companies.

I'm glad you can tell a difference on your scanguage.

 

According to a client who's an engineer for Texaco fuels there is no difference in their fuels other than octane number. The detergents, conditioners, etc. are all identical levels in each grade. The same applies to Chevron fuels. He has no direct connection to any other brand but suspects major brands such as Exxon, Shell etc. are similar. The difference is only the octane level. He also says there is no gain to running higher octane than what the engine needs to run ping free. He has no reason to bs me and nothing to gain so I believe him.

 

But what about an adaptive ECU that will increase timing until the motor pings?

I had a few carb'd cars that I made myself have to run 91 because I advanced timing too much they were small motors but you could definitely tell the difference.

:devil:

 

I believe the theory is that the timing might change but it won't really change anything since the system is a sort of a giant lung, air in and air out. The timing may change but the air volume can't change without changes to intake/exhaust to allow greater air flow. I'm not an engineer though, I just listen to them on occasion.

 

Read:

What Happens When the Timing Is Advanced

It is true that it does not put more air through the pump, it just changes how hard the pump turns.

 

All ECUs today react. All cars today have knock sensors.

The question is how often knocking occurs and timing is retarded, and for how long. It would be silly to retard timing for long periods and suffer reduced performance if knock isn't detected. Honda designed their engines for maximum performance using 87AKI gas. Sure this performance is degraded momentarily when knock is detected; but Honda is also very good at preventing knock through engine designs: cylinders, heads, cooling (although it would benefit from direct injection). The performance degradation isn't noticeable or Honda would recommend higher octane for better performance (they do this on their performance cars, and on Pilots/Ridgelines when towing).

However you said "adapt." This implies the ECU learns and advances timing until knock is detected. I don't think the Fit's ECU does this. GM's factory turbo engines (LNF) can (as I'm sure other high performance engines do), but that's a horse of a different color.

 

Seems like it would be fairly simple to write code to do that under WOT only

If I could do it with a hand tool and my ear anyway...

IDK if the Fit's ECU can do that, but i'm interested to find out if/how it works.

 

Better bone up on this subject. Air volume can and does change according to engine RPM you might be thinking of volumetric efficiency and most normal engines (not highly prepared race engines) run at about 60 % efficiency.


But and it's a big one here we are talking about power from advanced ignition timing at any cylinder loading.

Once the cylinder charge is loaded (no matter the ratio or volume of air) anything that effects the length and or efficiency of the burn INCREASES the power exponentially.

So in this case we have a full cylinder and the burn is initiated by the spark plug.

But the engine isn't static so if the burn is disrupted by the exhaust valve opening your combustion gasses have an escape path and the STILL EXPANDING GASSES go out the exhaust port instead of pushing on the piston top making power.

So in this scenario the only thing we are going to look at is advancing the ignition timing right?

What happens if you advance the ignition timing you ask? The answer is very simple (even for the engineers reading )

With NOTHING ELSE CHANGED except the timing of the ignition event what happens is the burn is STARTED EARLIER IN THE ENGINE CYCLE SO THE EXPANDING COMBUSTION GASSES PUSH ON THE TOP OF THE PISTON FOR A LONGER PERIOD OF TIME before escaping out the exhaust.

The end result being more power. Simple enough even for engineers to understand isn't it.

So the answer to your question has been answered and even if you ask your engineers they will have to admit in this particular scenario a NON-ENGINEER is correct.

 

Incorrect the ECM in a Fit DOES keep advancing ignition timing until knock is sensed. Any system using a knock sensor uses it to adjust the timing to knock. If it wasn't there would be no reason to have one.

And FYI Honda doesn't "recommend" 87 it says it is acceptable to use knowing most people buy the Fit for economic reasons and will opt for the CHEAPEST fuel they can find.

If you want more power and efficiency higher is better as I have outlined in the post above.

 

There is yet another "reason" to use higher octane if you care about performance and are not a cheapskate.

As you should by now know from reading threads like this that higher octane fuels also burn slower. So if you have a correctly working ignition system that "adjusts" to knock (like the Fit) and you advance the ignition (with no other changes) the same amount of higher octane fuel burns longer and converts more potential energy from the fuel by combustion into heat real energy.

This longer (more efficient) burn consumes more of the same amount of fuel resulting in increased combustion pressures which in turn PUSH HARDER DOWN ON THE TOP OF THE PISTON WHICH EQUALS MORE POWER.

Depending on how you drive one may even get an increase in fuel mileage using higher octane because there is more complete combustion of the same amount of fuel from the longer slower burn using higher octane resulting in more power which should result in less fuel needed to produce the same power over lower octane.


I know Steve 244 doesn't believe this or any other "internet chatter" what I would suggest is he get a scan gauge and use it on the ignition timing setting first with lower octane then after a couple tanks of high octane and see the difference.

And there are plenty of accounts in the scan guage thread reporting advanced ignition timing using higher octane but since you believe everyone of them is lying see for yourself.

Here ends today's lesson in automotive mechanics 101.

One last point LOL. Look at any Aviation engine that is internal combustion used in airplane and you will find in every case (in modern engines) they use the highest octane ratings they can normally above the 100-115 octane range. Why would one think they do this?

Because they get a more efficient burning engine producing more power using the same amount of fuel. For a plane the less fuel you have to carry the less weight there is which means the farther you can go for the same weight of higher octane because it is more efficient.

 

Honda not only recommends 87 (or higher as stated in the owner's manual), it's the "required" fuel.

Feel free to quote a source stating otherwise. Not interested in personal anecdotes.

 

LOL is that all you can come up with??? No comments from your vast knowledge of auto mechanics on the rest?

First I would like to know which "source" you consider adequate for you.

You dismiss threads and posts on this very site as "internet chatter" but yet come up with some lets just say "interesting" unheard of theories you had to pick up from the internet somewhere.

What criteria do you use for what is credible and what isn't using the modicum of knowledge you had to have gained from the net seeing as you are not a mechanic?

And the site YOU linked to says: "Required Fuel Regular Unleaded" while my owners manual says "87 octane OR HIGHER" that is the MINIMUM requirement because we know "some people" would put in 80 if they made it and it was cheaper.

 

Avgas is 100 octane low lead. And aviation engines are vastly different from car engines (as well as being mostly 40 year old technology)- they are designed to run near max RPM (which is still only around 3000) for long periods of time, at varying pressures (air's a lot thinner at 14,000 feet) and temperatures, with the main goal being that it never, ever, ever stops running. Compared to that, power and efficiency are secondary design considerations. Oh, and almost all of them have a mixture control- the pilot controls the air/fuel ratio. When was the last time you turned a red knob on your dash while watching an exhaust gas temp gauge?

Regardless, the relevant question here isn't "Does higher octane gas change how the engine runs" but "How much does it affect power output and fuel economy?"

 

Ha this good enough for you or not LOL?

Go to engine section then fuel required.......

Design Specifications (KT)

 

And why would using higher octane gas accomplish the goal of main goal being that it never, ever, ever stops running over lower octane if there was no benefit other than more efficiency pray tell?

Cars don't need a mixture control they have a computer to do the adjusting for them.

And I answered that question you call relevant extensively already go back and review.

 

That's a 1.3 liter engine, I thought our Fits have a 1.5. And the octane number there is research octane, not the (R+M)/2 measurement that we use in this country.

So no, it's not good enough for me, since it's not our engine, not our fuel...

 

Oh, I was not saying that higher octane gas has any bearing on never, ever stopping. I was saying that looking at aviation engines to compare them to car engines, simply because they use 100 octane fuel, isn't relevant to the discussion.

And yes, cars have a computer adjusting the mixture. Yet another difference between car engines and aircraft engines.

 

Cute but it is the same thing don't try and confuse the issue with red herrings. It has the same compression ratio and engine just smaller therefore needs the same octane fuel. I will convert it for you or you can use an online converter. 91 ron is the equivalent of 87 American measured octane.