Thanks, that is what I was trying to say earlier in the post, but you stated it much clearer.

 

In 1999 the Honda brochure for the Odyssey Mini Van read under performance specs "200hp with 87 octane and 207hp with 92 octane". That particular vehicle then equipped with the 3.0L V6 motor employed dual knock sensors to give the ECU information on how the gas was burning in order to adjust the timing.

It is my belief that the S2000 also has knock sensors to protect the engine from instances when less than optimal fuel is put in the car.

Based on my knowledge of ECU tuning that I learned from an accomplished engine tuner, ECU's contain a number of fuel/air/timing maps and based on information provided by the O2 sensor, knock sensor, temperature sensor, air flow meter, etc. The ECU chooses the appropriate map and away you go!

Now as I understand that and based on the statement made by Honda in 1999 about their V6, the ECU also has the option to ADVANCE timing if the car has higher octane fuel, thus producing better power. The ECU can work BOTH ways, retarding the timing for low octane and advancing the timing for high octane.

Now from my experience with 2 S2000's in California (a '01 and a '04) the cars took a hit in performance when California changed its policy and only allows a maximum of 91 octane. The cars started smoother, idled smoother and pulled stronger when 92 was available. I have since found a Union 76 station that sells 100 octane unleaded fuel. I have found, based on the 76 octane mixing chart, that running my car at 95 octane (5 gal 100 octane, 7 gal 91 octane) provides excellent results. The car once again runs smoother and pulls stronger.

More evidence was found when my friends S2000 had better lap times at the track when running 100 octane rather than the 91 octane, both available at the track. This tends to be better real world evidence than dyno numbers.

What I believe and propose is that the S2000 ECU, based on sensor readings, will advance timing to maximize power when higher octane fuel is present. This however does have a point of diminishing return once the ECU reaches the maximum octane for which it has maps. This I assume is 95 octane, since that is the maximum pump gas octane typically available in the US.

Now, when you start modifying your motor, forced induction, changed compression, etc., all bets are off. You probably have a custom engine management system and can dial in whatever you like.

I'd be really curious to hear what Woodwork has to say about this, since he has more than your typical insight as to what goes on in the 'black box' ECU of the S2000.

Andy

 

then we're definitely on the same page.

 

Before you go spreading this all over the forums, you may want to read the resonse UL gave in the UTH thread where you posted this same information.


While the S2000 has a very sensitive knock sensing, and is in some degree always pulling timing, this varies by car and conditions. While putting 100 octane in your car MIGHT give you slightly better performance, it might also not. The S2000 does NOT have a way to determine what kind of fuel has been put in. To my knowledge, no car does. It merely has the ability to read it's air/fuel ratios and use it's knock sensors to determine if it needs to pull timing.

The S2000 ECU will not advance timing if no knock is being detected. As UL stated, however, the S2000 tends to pull timing naturally even if no knock is necessarily being detected. This may be due to engine noise, etc.

So cliff notes. The s2k cannot tell what grade gas you put in. And the S2k may or may not see a slight increase in performance with 100 octane, only noticeable on a dyno.

 

This matches my empirical experience with a different car with the same high compression ratio. Slight differences that would not be noticeable in normal street driving are detectable on the track. I haven't had 100 octane in my S2000 yet, but perhaps at some point I will.

A couple other points:

For the 2005 model, the owner's manual says that engine damage should not occur down to 86 octane, but performance will degrade. This probably means the ECU can pull timing enough to compensate for octane as low as 86, but at that point reaches its limits. The problem with going below 91 is worse performance, not engine damage, as long as you stay above 86.

As for improved performance above 91 octane, there is a theoretical as well as empirical reason to believe that the car may perform a little better with higher octane.

The engine runs under a variety of load conditions, some of which are more susceptible to knock than others. The highest load conditions most susceptible to knock are probably low RPM high load conditions, such as wide open throttle when short shifting.

If you optimize the entire engine for 91 octane fuel under these limited conditions, the compromise is that you don't quite reach the engine's full potential in other conditions. It may be a better compromise to increase the compression ratio by a couple tenths of a point to get a little more power or efficiency in the majority of operating conditions, and accept a little bit of spark retardation under the highest load conditions.

If this is the case, putting slightly higher octane gasoline in will improve performance under the most limiting engine conditions, by making it unnecessary to retard the spark under those conditions, though it won't help the majority of the time.

I personally would go with the 94 octane if it were available in my area, as it isn't much more expensive. I suspect the 100 octane wouldn't be worthwhile - it's a lot more money with little additional benefit. I certainly wouldn't go below 91 octane, as the performance degradation would probably be significant.

In my area, premium is 92 or 93, and I do look for the stations that use 93 octane.

 

Your entire post was great, but this part was not necessarily correct.

Though the engine has the ability to pull timing when knock is detected, this is still not advised, and yes COULD cause damage. It's not likely, however if you put another consecutive tank of say 87 octane fuel, you drastically increase your chances something can go wrong.

It's a fail-safe on the car.... not something meant to be depended upon to put in low octane fuel. Damage COULD occur if abused.

 

The system has to see detonation before it retards the timing. Therefore, it will sense detonation over and over and correct for it. It's not as bad as an old car that you just let knock whenever you accelerate, but, still, it is not the ideal situation especially for a high revving close tolerance engine.