turbo fuel ????'s

[rocket5979]

Well, unless there has been some revision in the laws of physics since I was at university, maximum power, regardless of induction type, is derived with an A/F ratio in the 12.5-13.3 range. Less than that and your loosing power and pissing fuel away.

Running a 12.5-13.3 AFR @ WOT in a boosted setup is asking for trouble. Much too lean. There are more factors that come into play than just power and fuel economy here. Now if you were recommending those AFR's on a N/A vehicle then that would be ok.

 

[Dave R]

There are more factors that come into play than just power and fuel economy here.

Factors such as?

 

[rocket5979]

Factors such as?

Engine safety and detonation to name a few. Running that lean of an AFR at WOT in a boosted vehicle will lead to a much much higher chance of damaging engine internals or at the very least lifting the heads and blowing a gasket. If you are running a lighter vehicle then you can usually get away with a little leaner of an AFR due to less load being placed on the engine but not quite the range of high 12's to low 13's though. Like I said, the AFR's you mentioned would be good for a N/A vehicle but not a boosted one where the engine is more prone to detonation. The "extra" fuel in the boosted engine will keep things cooler and allow much less chance of detonation.

One other thing worth mentioning is that leaner does not always equal more power in an internal combustion engine. I have tuned vehicles before where going a few more points lean would not do anything for power gains.

 

[Evil Ranger]

Factors such as?

Directly from Garret's website...

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.

 

[Dave R]

Thanks dave.

 

[mxracer652]

Hello guys, I'm new here, but regarding the OP's question, I do not think 19s will suffice for 7psi and here's why:

Even though this is the SOHC, the laws of physics & chemistry still apply. I was seeing into the 80s% duty cycle (80% being considered maxxed out) with the 24s that came stock on the SOHC & only 5psi boost, BUT 68psi fuel pressure. The high fuel pressure makes those 24s function more like a 28. With fuel injectors, err on the high side, and don't listen to anyone who says big injectors don't idle. I'm running 39.5s now on E85, and it fired right up yesterday morning when it was 5 degrees. If I were you, 36s.

Edit: That is ASSuming the rest of the system is up to par and you're talking about a 6cyl.

 

[rocket5979]

With fuel injectors, err on the high side, and don't listen to anyone who says big injectors don't idle. I'm running 39.5s now on E85, and it fired right up yesterday morning when it was 5 degrees.

100% true. The "big injectors don't idle" stuff is a thing of the past. My 60's idle and drive like stock too.