davidc1

Ok, so I've been told from reliable sources that our engines (I've got an AP1) have a tendency to run lean, especially at the track, and thats not good. Could lead to expensive engine damage.

I've been told that the best fix for this is an aftermarket ECU and tuning. But....I don't really have $2000 or so.

So, I was told by a few people, my mechanic, and some guys from the POC, that you can run higher octane racing gas when at the track to help.

But, I'm a little unclear on the relationship. I know that octane rating is simple a measure of the gas's resistance to detonation, pre detonation being bad. But, a lean running mixture is not the same a pre-detonation. Two different things. But are they related? I know that a lean mixture results in hotter temperatures in the combustion chamber. I know that hotter temps can lead to pre detonation.

So, is it the hotter temps themselves with a lean mixture that cause damage, in which case I don't' think high octane gas would make any difference? Or is it that the hotter temps from a lean mixture lead to pre detonation, which is what actually damages the engine, is which case a higher octane gas would help?

And if it's the latter, would an octane additive booster be as good as higher octane gas itself? ( because it pretty expensive).

Now, given all the above, are there any other ways of richening the mixture besides the expensive ECU route? For example, can you trick the O2 sensor to read a higher or lower voltage ( I don't know which way is correct), by simply adding a resistor in parallel or series with its wiring, and hook it up just for the track?

Thanks everyone.

VitaRenovatio

Another option would be to get a VAFC and add fuel. That would be a lot cheaper than a standalone ECU and full tune.

speedengineer

Running lean (actually a misnomer, by 'lean' most people mean running 'less rich') by itself doesn't harm the engine any. However, a less rich mixture increases the chance of engine knock (not the same as preignition). It also results in higher exhaust gas temperatures, which if too high, could be harmful to exhaust valves (wear).

The S2000 ECU is a speed-density system, meaning that fueling rates are determined by engine speed and manifold pressure. If your powertrain is highly modified (say exhaust, header, intake, etc), you will have higher volumetric efficiency, which means greater airflow, but since the MAP reading is the same, the ECU doesn't know the engine is actually getting more air, and won't know to inject more fuel, so it won't run as rich. Not sure if that is enough to make it knock, or to cause too high of exhasut gas temperatures (typically 'to high' is considered greater than 850 C). Heavy knock will eventually damage an engine, however, the stock ECU will use its knock sensor to retard timing and prevent knock, so I doubt that is an issue.

At part throttle, the engine runs in closed loop, meaning it uses the oxygen sensor to run at a stoichiometric AFR. At high load and high speed though, it runs in open loop, meaning it is not using the oxygen sensor to adjust fueling. Tricking the oxygen sensor will not work. You could use something like VAFC to control fueling rates though.

I know a number of high-mileage AP1's that have seen much track use and haven't had an issue. But some people do I guess.

yonson

What mods do you have? I know on my AP1 (2003) with my lambda installed before the cat it runs quite rich, I've only got fairly limited mods though, K&N FIPK, Berk Header, stock cat and Berk single 3" exhaust.

At Chuckwalla in 3rd gear at 6700 I'm running 12.2:1, 7700 11.8:1, 8700 10.6:1

VitaRenovatio

^ I run in the 11-12's with test pipe and exhaust. Mine is also a MY2003. I hear the later AP1's run the richest out of all models. I personally suspect this phenomenon is overrated, except maybe on the latest AP2's (CR's) that have a tendency to run lean (err, less rich) from the factory.

OP: why not go to a dyno shop and just get some baseline dyno's with AFRs? That should answer your question. Every car is a bit different. If you are in fact running lean, then VAFC would be the cheapest way.

yonson

Be warned if the dyno shop uses a tail pipe sniffer they are known to read a little leaner (~.5 - 1 AFR) than the car is actually running because of reversion and the sensor being after the cat. (if you have one).

yonson

I happen to have a VAFC with boomslang harness that I'm not using, never got around to installing it, now I can't run it because I'm out of points...

VitaRenovatio

If I recall correctly, the VAFC can only add fuel, correct? If so, I think we should make it zero points, since people cannot really utilize it to make more power. It's only real function would be to prevent harm to the engine. Is my logic correct, Chris?

s2000ellier

Thoughts on using an adjustable fuel pressure regulator to bump up the fuel psi?

psychoazn

Can you go further on this please? On the dyno, my car will read well over 14:1, and as high as 14.5, when untuned and with a headerback exhaust.