Do you need tune for a test pipe?
07-20-2012, 05:28 AM
#21
07-20-2012, 06:35 PM
#22
Running a test pipe is NOT going to change the AFR (Air Fuel Ratio for the newbs), the fuel map is already set in the ECU and besides that the cat is after the primary (pre-cat) O2 sensor so even while normal driving the O2 is adjusting the AFR, while under WOT the ECU is going to dump the same amount of fuel its programmed to into the cyls with or without a testpipe. If anything your going to get a CEL for "catalytic insufficiency" which wont affect anything (like put your car in limp mode, etc)
There are several standard ways to improve volumetric efficiency. A common approach for manufacturers is to use larger valves or multiple valves. Larger valves increase flow but weigh more. Multi-valve engines combine two or more smaller valves with areas greater than a single, large valve while having less weight, but with added complexity. Carefully streamlining the ports increases flow capability. This is referred to asporting and is done with the aid of an air flow bench for testing. Another major aspect of design is to use a crossflow cylinder head, which has become the standard configuration in modern engines.
Many high performance cars use carefully arranged air intakes and tuned exhaust systems to push air into and out of the cylinders, making use of the resonance of the system. Two-stroke engines take this concept even further with expansion chambers that return the escaping air-fuel mixture back to the cylinder. A more modern technique, variable valve timing, attempts to address changes in volumetric efficiency with changes in speed of the engine: at higher speeds the engine needs the valves open for a greater percentage of the cycle time to move the charge in and out of the engine.
Many high performance cars use carefully arranged air intakes and tuned exhaust systems to push air into and out of the cylinders, making use of the resonance of the system. Two-stroke engines take this concept even further with expansion chambers that return the escaping air-fuel mixture back to the cylinder. A more modern technique, variable valve timing, attempts to address changes in volumetric efficiency with changes in speed of the engine: at higher speeds the engine needs the valves open for a greater percentage of the cycle time to move the charge in and out of the engine.
sources: http://en.wikipedia....tric_efficiency & How to Tune and Modify EMSs
This is essentially saying that if you increase the efficiency that an engine passes air you are in fact increasing its Volumetric Efficiency. The result of this is an actual 'leaning' of the engine itself. The air exiting the engine acts as a vacuum of sorts is what I perceive is happening.
However, I have one caveat. I would argue this. At normal operating aka cruising, the stock ECU does in fact operate in what's referred to as "close-loop". During this phase it's my belief that the ECU would in fact adjust accordingly because it's reading from the 2x o2 sensors (1 on header and 1 on TP). However, in WOT (wide open thottle), like SpinningHigh04 stated, the ECU goes into open-loop and gives zero shits about the exhaust o2 sensors. This is when I would argue the leaning occurs.
I looked for dyno comparison of before and after AFR measurements when only adding a TP or TP and exhaust and I can't find any respectable ones. If someone else has one it may be somewhat helpful.
--Matt
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