That has so little filtration area, that might be enough airflow for a 100hp motor

 

The supercharger inlet pressure sensor is what I am referring to. I imagine yours was showing a negative pressure at WOT.

 

Oh I think i understand. You mean to say there would have been a higher value of vacuum (lower psi reading) on the scip than normal with a restrictive filter?

 

Anyone know what an average normal scip reading at WOT should be?

 

I have the same filter on my 150hp miata, now I'm beginning to wonder if I'm restricting it too haha

 

Try running it open filter or with just a screen and see if there is a difference (just the miata not the cobalt)

 

Are you asking or telling? Air pressure behind the throttle body should rise to atmospheric pressure at WOT. If your showing a lower pressure than atmospheric you have an inlet restriction.

 

I guess I'm telling. It seems in theory the engine is always acting as an air vacuum pump even at WOT so I cannot see the scip ever reading exactly the same as atmospheric pressure at WOT especially with a supercharger/turbocharger that pulls in more air (more vaccuum). But yes I understand and agree that a restriction would show more vacuum (lower psi) on scip.

 

a slight vacuum on the scip sensor at full throttle is normal, but by slight i mean a couple kpa. its impossible to have absolutely no restriction between the blower and air filter. i rarely look at my scip but anytime i have there is a couple kpa difference. keeping an eye on this is a good way to tell if you need to clean your air filter.

that doesnt surprise me that filter was causing that much of an issue. cheap filters dont flow well to start with, and that has so little surface area.

 

The best way to understand pressures and the sensors that measure it is to remove Vacuum from your vocabulary. There's a reason why it's called a "Manifold Absolute Pressure" sensor. On an N/A engine, there is air pressure or the lack of it. On a forced induction engine it can go above atmospheric. Vacuum is measured in a very crude way... Inches of mercury. Even when we calibrated the crossfire injected engines in the Dealership we used a slack tube manometer which used much lighter dyed water.

At WOT you should be as close to atmospheric pressure as possible. Had GM set the perimeters on the inlet pressure sensor tight enough, they could have used it to detect dirty air filters and you would have set a code.

 

I have seen large K&N filters retreated with motocross foam filter oil... That stuff that is worse than fly paper when it cures. It would actually crush them on supercharged V8 engines.

 

I believe we are saying the same thing. Manifold absolute pressure is just a fancy way to measure vacuum (inHg) using psi units. Anyways thanks everyone for the input, just glad the car is back to boosting. Until next time...

 

The early sensors were separate, Vac and Baro. Now, most engines run just a MAP and look at Baro during KOEO and 85% throttle opening.

I was trying to get you to go back and look at what you did that may have caused this.

Did you still have good boost pressure before doing this?