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Installation and Review: Psychosled "Bridge" Fuel Controller

christopher

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UPDATE:

After having the Bridge installed for a season or two now I FINALLY got around to installing a GOOD gauge package.

I now know I am producing 9.5lbs of boost!

My AFR run from a low of 11.2 on very hard acceleration to a high of around 13 other than at idle, with most of the time spent at 12.2-12.5 and the "Rich" warning lite going off on my gauge.

Clearly the Bridge is adding a significant margin of safety to my Nytro by ensuring it NEVER GOES LEAN!
 
M

MotoPsycho

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"Rich" is a relative term.

Stoichiometric is a "perfect" combustion measurement. When an engine is running as hard as these boosted sleds do, there are other factors involved... There isn't a vehicle on this earth that runs stoich when it is running hard... It is too lean, and just doesn't work. We have that covered.


Sent from Moto's iPhad
 

christopher

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While 14.7 would be dead nuts on, if we have to "ERR" I sure as heck want it to be on the RICH side and NOT on the LEAN side!

I have no doubt but that with a little tuning we could pull it up a bit more and squeeze out some more power from a better Air-Fuel Mixture rating. But I am not sure its worth it.

===
http://www.turbobygarrett.com/turbobygarrett/airfuel_ratio_tuning_rich_vs_lean

Why lean makes more power but is dangerous

When discussing engine tuning the 'Air/Fuel Ratio' (AFR) is one of the main topics. Proper AFR calibration is critical to performance and durability of the engine and it's components. The AFR defines the ratio of the amount of air consumed by the engine compared to the amount of fuel.

A 'Stoichiometric' AFR has the correct amount of air and fuel to produce a chemically complete combustion event. For gasoline engines, the stoichiometric, A/F ratio is 14.7:1, which means 14.7 parts of air to one part of fuel. The stoichiometric AFR depends on fuel type-- for alcohol it is 6.4:1 and 14.5:1 for diesel.

So what is meant by a rich or lean AFR? A lower AFR number contains less air than the 14.7:1 stoichiometric AFR, therefore it is a richer mixture. Conversely, a higher AFR number contains more air and therefore it is a leaner mixture.

For Example:
15.0:1 = Lean
14.7:1 = Stoichiometric
13.0:1 = Rich

Leaner AFR results in higher temperatures as the mixture is combusted. Generally, normally-aspirated spark-ignition (SI) gasoline engines produce maximum power just slightly rich of stoichiometric. However, in practice it is kept between 12:1 and 13:1 in order to keep exhaust gas temperatures in check and to account for variances in fuel quality. This is a realistic full-load AFR on a normally-aspirated engine but can be dangerously lean with a highly-boosted engine.

Let's take a closer look. As the air-fuel mixture is ignited by the spark plug, a flame front propagates from the spark plug. The now-burning mixture raises the cylinder pressure and temperature, peaking at some point in the combustion process.

The turbocharger increases the density of the air resulting in a denser mixture. The denser mixture raises the peak cylinder pressure, therefore increasing the probability of knock. As the AFR is leaned out, the temperature of the burning gases increases, which also increases the probability of knock. This is why it is imperative to run richer AFR on a boosted engine at full load. Doing so will reduce the likelihood of knock, and will also keep temperatures under control.

There are actually three ways to reduce the probability of knock at full load on a turbocharged engine: reduce boost, adjust the AFR to richer mixture, and retard ignition timing. These three parameters need to be optimized together to yield the highest reliable power.
 

christopher

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