Supercharger Performance and Engine Performance Parts

When manufacturers didn’t have tight control (or a solid sensor reading) of exhaust gas content, then in order to prevent the engine from running dangerously lean under high demand and damaging the motor, they were forced to default to adding in a margin of safety worth of fuel, running the motor well into the rich range with a healthy dose of fuel per the air ingested.

Now although this richer mixture (and sometimes excessively rich) was bad for emissions and mileage, it did allow cars to have better throttle response, produce smoother wide open throttle acceleration, and respond better to bolt-on modifications.

Now when it comes to power enrichment tuning (for high load and full throttle operation) there are basically two different philosophies :

The Rich Life:

In this philosophy the engine is tuned for a target between 13.5:1 AFR and 11.5:1 AFR depending on the total amount of combustion pressure in the engine (Compression, rod ratio, boost, squish…etc) . With this richer mixture, there is a lot of energy (in the form of fuel) to be harnessed out of the mixture timing is generally advanced to start the combustion early to take advantage of this power rich charge of energy.

Sure some fuel is wasted, but if you wanted to save fuel you wouldn’t be running at full throttle now would you ?

Lean is Mean:

In this philosophy, the engine is tuned for a leaner 14.7:1 AFR to 13.5:1 AFR at full throttle depending on the conditions. As the mixture is leaned out from the power happy theoretical value 12.7:1, the leaner mixture has less fuel cooling and higher combustion pressure, where cylinder pressure builds more rapidly after the initial spark event which gives a more complete and cleaner burn for the air and fuel charge.

However, this hotter burning mixture can spike cylinder pressure too fast, and force us into pre-ignition and pre-ignition caused detonation. So, to compensate, timing advance at full throttle under the lean is mean philosophy is reduced to counter-act the affects of the heat buildup.

Retarding the timing in this manner delays the initiation of the combustion process, which reduces the amount of air and fuel burnt inside the cylinder and increases the amount of air and fuel burnt in the exhaust system. This raises exhaust gas temperatures (EGT’s) which improves the performance of catalytic converters and lowers emissions. However, having a larger portion of the air and fuel charge burning OUTSIDE of the cylinder in the exhaust system means that ultimately we are throwing away energy that could have been harnessed inside the cylinder to produce more power.

OEM manufacturers are coming under pressure to produce cleaner and greener vehicles, not just at idle and cruise, but through-out the entire operating range of the engine. Because of this pressure, manufacturers are more commonly opting for the Lean is Mean mantra of tuning, by trading off some performance and power for higher combustion efficiency and better catalyst performance.

The main problem with this mantra is not only in that the car is not tuned for peak power in stock form, but rather that with additional modifications to the engine, the ECU will always try to maintain that same lean mixture holding back further power increases or even lose power with modifications.

How can you lose power with modifications ?

It’s a commonly known fact that combustion pressure increases , the more air and compression you put into your motor. Modifications that help the motor breathe better deliver more air to the combustion chamber which results in higher combustion pressure when the mixture is ignited. This higher pressure increases the speed of flame front propagation more so than it already is accelerated (due to the lean is mean tune) which can cause pressure spikes and pre-ignition / detonation. The ECU will detect this engine knock and severely retard timing to save the motor and with the retarded timing , even more of the combustion process will occur outside of the cylinder, further reducing power.

So with this style ECU it is not only likely that may not gain power with bolt-ons. It is also likely that you will LOSE power with mods, unless you get the car retuned to a richer mixture.

The Other Problem:

The other problem with these ECU’s is that until recently, they were untuneable. With traditional style piggy back fuel and timing controllers, you used to be able to lie to your ECU about the amount of air entering into your engine by intercepting and modifying your air metering signals, which forced the ECU to run a richer or leaner mixture at full throttle depending on how you tuned your controller.

With the newer wideband equipped ECUs; the ECU is able to accurately read the final air to fuel ratio in the exhaust using the wideband oxygen sensor. Now that the ECU knows that you have altered the incoming air metering signals, and now that it has detected that the final air to fuel ratio is not where it was intended from the factory, the ECU applies a correction known as a ‘fuel trim’ to correct the final air to fuel mixture back to where the OEM engineers had set this target to be. By doing this, the ECU cancels out your tuning efforts and returns power levels to stock.

Until very recently, these cars were un-tuneable short of ripping out the entire engine management system and installing a standalone aftermarket system and tuning from scratch. This however is a drastic measure that is not fathomable for anyone with light modifications or even a bolt on supercharger system.

So what is the new concept ?

The new concept in tuning these ECU’s is to use a smart piggy back controller to intercept the Oxygen sensor signal (rather than the air metering signals). These new piggyback controllers allow you to alter the target air to fuel ratio that the ECU is looking for by adjusting the oxygen sensor signal to correspond to the 14.7:1 air to fuel ratio when YOUR DESIRED TARGET mixture is reached. This way, when the oxygen sensor is reporting 12.5:1 AFR to the piggyback, the piggyback will relay that to the ECU as 14.7:1 and the ECU will be happy with what it ‘sees’ and the car will produce the power that we want.

Moreover, now that we have setup this adjustment in the computer’s feedback control system, the ECU will now make adjustments to stay as true as possible to this new target, just as it did to the OEM target even if conditions change. Which means the ECU will re-tune itself to the proper target AS YOU APPLY MORE MODIFICATIONS to always keep you in-tune.

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