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Old 06-15-2009, 03:20 AM   #31 (permalink)
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If you force air in the engine, absolute pressure in the manifold will increase with increased pre throttle body pressure (throttle position being equal).

Higher pressures before the throttle plate have negligible effect on fueling in open loop ( or closed loop) unless you exceed the highest mapped pressure, the ecu will still be reading from the same section of the map tables regardless of how much air you cram in the intake tube. No correction beyond normal fluctuations would be required by the ecu.

Closed loop, different story. I think you are referring to a 350Z? WOT operation will never be 14.7, but between high 13's to high 12's. As far as most management systems go, closed loop is only triggered by throttle position, but I imagine some are pressure and/or rpm. There normally is no correction for open loop other than referencing manifold pressure and rpm, everything else is simply a multiplier of sorts, coolant temp, intake air temp, ect.

Granted, all this is in reference to a manifold pressure density type system, mass airflow system is a bit different

I must be falling behind, there is a system out now that has a correction based on egt's? Wonder how they pulled that one off...

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Old 06-15-2009, 08:33 AM   #32 (permalink)
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The only difference in open and closed loop is. . .the ECU gets data from one location or multiple. Open it gets data only from the MAP(MAF) and then plugs the data in and recovers how much fuel is needed. In open mode its more conservative and adds a little more fuel than it needs(I'm not talking 350z) to make sure it stays outside of lean. In closed it does what I just said and then the ECU takes data from O2 sensors(and nowadays alot more) and tries to get closer to what its mapped for. Eco cars are going to try to get right at 14.7 whereas sportier cars are going to hover around in the rich region and just have a tighter AFR band.

As far as the topic at hand is interested though a RAM air could theoretically improve FE, but I can't say for certain because I haven't tried it myself. I can't recall which user it was that has done it, but I believe them. WAI like I said is just a big restricter plate that pushes your driving tendencies towards ecohabits(unless you have lean burn and it has a required minimum AIT, then its a restricter and a system hack).
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Old 06-15-2009, 12:02 PM   #33 (permalink)
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why don't we all just get a diesel so we don't have to worry about throttle plates?

I have a new idea... In all new cars, take a coil spring from a truck, and use it for the gas pedal spring. Americans are lazy, and would rather work less and drive slower than push the pedal with lots of might to go 75mph. Seems like a crazy, might work plan to me
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Old 07-17-2009, 06:34 PM   #34 (permalink)
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I think the point being discussed is that WAI's suck, it's basically reducing your WOT HP potential of your engine.
If you have a ram air setup, it's irrelevant because the throttle body will just be open a little less to provide X-HP worth of air to cruise the car down the road.
Btw 14.7:1, while being the "optimal" fuel number, isn't always so.
When I had my ECU chipped and tuned for my Civic, we were running a wideband and got the cruise AFR to 16.0:1 before it started to lean pulse. That's 8.8% better efficiency right there, and I saw an increase in cruise mpg of 2-3 MPG.
Now if I had a crappy WAI I'm sure I would have ran into detonation before that point and would be running a more 14.7ish AFR...

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