Q WTF is Speed Density?
The ECU has to calculate how much fuel to spray for every cycle. To figure that out, it has to know how much air the engine is inhaling.
The stock ECU uses a mass air flow sensor (MAF sensor) to figure out the air flow rate. It divides the flow rate by RPM to know how much air is going into each cylinder with each cycle. From that, it can figure out how much fuel to spray to match that air with the desired air-fuel ratio (AFR).
“Speed density” is an alternative to the MAF sensor. The ECU looks at RPM (speed), and manifold air temperature and pressure (density). It uses those tow things to look up the predicted air flow rate in a table (called a volumetric efficiency table). Basically, the VE table says “at this speed, and this density, the engine will pull in this much air.” And from that, the engine can figure how much fuel to spray to get the desired AFR.
Q What’s up with ATP’s EWG exhaust housings?
I think that one of the main benefits of an EWG is to vent unnecessary exhaust gas before it has to go through the restriction of the exhaust housing. Therefore, I am not fond of ATP’s EWG setup. I got my 3076 with the IWG option, and will probably add an EWG to my UP later.
The exhaust housing inlet is 1.75″ and it probably constricts a bit further before it reaches the spot where ATP puts the EWG. By putting the EWG on a 2″ up-pipe, I’ll only be forcing about half of the peak exhaust flow through the 1.75″ restriction. Putting the EWG on the exhaust housing means that at peak flow, 100% of the exhaust still has to go through that restriction. It just doesn’t make sense to me.
The IWG with the supplied actuator works well up to at least 23psi peak boost. Probably beyond, but my clutch started slipping when I turned it up further so I can’t say for sure yet.