O2 sensor hack

[Genie47]

More weirdness. OK effect of AFR.

 

What is the effect of changing the air-fuel ratio?

 

Traditionally, the greatest tendency to knock was near 13.5:1 air-fuel ratio, but was very engine specific. Modern engines, with engine management systems, now have their maximum octane requirement near to 14.5:1. For a given engine using gasoline, the relationship between thermal efficiency, air-fuel ratio, and power is complex. Stoichiometric combustion ( air-fuel ratio = 14.7:1 for a typical non-oxygenated gasoline ) is neither maximum power - which occurs around air-fuel 12-13:1 (Rich), nor maximum thermal efficiency - which occurs around air-fuel 16-18:1 (Lean). The air-fuel ratio is controlled at part throttle by a closed loop system using the oxygen sensor in the exhaust. Conventionally, enrichment for maximum power air-fuel ratio is used during full throttle operation to reduce knocking while providing better driveability [38]. An average increase of 2 (R+M)/2 ON is required for each 1.0 increase (leaning) of the air-fuel ratio [111]. If the mixture is weakened, the flame speed is reduced, consequently less heat is converted to mechanical energy, leaving heat in the cylinder walls and head, potentially inducing knock. It is possible to weaken the mixture sufficiently that the flame is still present when the inlet valve opens again, resulting in backfiring.

 

Shamelessly taken from here: http://www.faqs.org/faqs/autos/gasoline-fa.../section-1.html

 

Pretty good write up on that page also for those still insisting that higher RON petrol gives more power.

[Eching21]

So in theory the little o2 sensor "hack" should work.. since it moves the air-fuel ratio towards the maximum performance side. The only thing then would be the safety margin...

[Genie47]

Rich is safe. Lean however is risky except at lower RPM at around 2-2.5k. Since it runs it rich, so it should be OK. The website did say you will suffer in the fuel economy department.

[Eching21]

I understand that comparatively, lean is a lot more dangerous than rich. In fact, turbo engines and the like run rich to protect the engine.

 

But, according to the website that you posted earlier, it says that knocking is likely to occur at the 13.5:1 ratio or thereabouts. Although the article did mention that that is engine specific, but by following the trend of their analysis, a richer mixture may also result in knocking. Am I reading that part right?

 

If I am, then since our engines normally run at 14.7:1 A/F ratio, richening the mixture will effectively result in a <14.7:1 ratio (after normalizing to 1 part fuel of course), which means it goes closer to the 13.5:1 ratio.

 

If it goes too close, doesn't that suggest that knocking might also occur?

[Eching21]

Oh the other thing is the emissions requirements in Singapore.. Again I feel that we don't know how much it is richening the mixture by, so even assuming that it is safe, there might also be a possibility (though slim i admit) that we start coughing out black smoke due to unburnt fuel, isn't there?

 

Although if you don't care about fuel consumption, the price of the device indeed is tempting to experiment.

[Genie47]

Again more into the engine's design coupled with the compression ratio. Pretty jumbled up, huh?

 

So this can be solved easily. Use higher RON petrol.

[Eching21]

$ $ $ All in the name of more power..

[Genie47]

It is indeed tempting. But the beef is that Powerchip hack instead of the O2 sensor hack. At that price, it is cheaper than a Unichip and does not alter your ECU. 3 modes of operation from standard (normal ECU), to performance (rich) and economh (lean).

 

Tempting indeed. It is like tuning a carburetor on the fly while you drive.

[Genie47]

Nice thing about the Powerchip hack is that it can alter ignition timing and advance as well. Like the example I used, carburetor tuning on the fly.

[Eching21]

Yes indeed =) And it also works through closed loop operation.. no more ECU compensations, no more ECU resets.

 

Btw, I know the site mentioned that you can adjust the Powerchip thing while you're driving. But how do you get access to the chip huh? From the picture it looks like a small device which goes into your engine bay.

[Genie47]

I'm a little confused. They have dipswitches. Hmm..... They don't supply the switch? Maybe you got to get your own steering wheel thumbswitch.

 

Scenario:

 

AHA! WRX think you can bully my puny 1.4L DOHC car, huh! [Flick Arming switch] and hold for "AFTERBURNER", Swooooooosh!

 

Then driving daily grind driving to work. Flick switch, double click for fuel economy. [female robotic voice says: Economy option started].

Edited November 16, 2005 by Genie47

[Eching21]

I have a feeling that you have to tune it using the "potemeters" (potentiometer?) to whatever you like, and if you want to enable the device, flip on dip switch 2, otherwise, flip it off. I don't think they supply a way for you to turn it on and off on the fly, unless you connect the dip switch to your own on-off switch and somehow mount it in your dashboard/steering wheel.

 

Thing is, that is not going to be a trivial task since I don't think most people will want to peel off the red seal tape on the Powerchip and mess with the circuit directly. And even if you do that, I think it's not going to be easy to setup three configurations (lean, rich, standard) since those are essentially controlled by the "potemeters" through some kind of multiple state switch that you throw into your dashboard/steering wheel..

 

Ouch.. sounds quite painful did I get anything wrong?