Logged Air Flow Rate

[DSM_6SL2 Power]

I just did a log on my air flow, because I have been wanting to ever since I got my fp18g. I just did one in second, in town, a block away from my house.( I was Bored on my way home) I have the boost set to 12, but by the time it logs my highest rating it is creeping to about 16. The flow was 33.64.


Anyways, now for the question. I know for a fact that I have boost leaks even though I have not yet tested. So I was wondering if boost leaks affect air flow readings? Where does the reading come from, Im guessing the maf.(obviously)


I thought I read somewhere that boost leaks do affect the readings, but I searched and could not confirm this. The reason im asking, is because I do not really understand how it would have an affect. Since its reading at the maf, wouldn't it be reading before the boost leaks could have any affect? Some explantions would be great.

 

[Gstclipse69]

Well first you need to fix the boost leaks. If you have leaks your turbo is working harder than it needs to to build the boost level you have it set at. And yes the airflow reading is at the maf however your leaking pressurized air after the turbo so the airflow reading would be less than the given value. Fix the leaks first then go from there.

 

[CTP]

Yes, you clearly have boost leaks because I highly doubt you're flowing 33lbs/min at only 16psi on an 18g. Leaks make your airflow readings go up.

 

[DSM_6SL2 Power]

Can someone give a more in depth explanation of how it works, and how the boost leaks directly affect air flow readings?

Ive got two different answers here, but obviously boost leaks do have an affect though.

 

[MrBoxx]

The MAF may say you're flowing 33lbs per minute or whatever, but if there are boost leaks after the MAF, not ALL of that airflow is getting to the engine. It's leaking out. Same for boost. You may be running the turbo at a higher boost pressure than you're reading at the manifold due to leaks PRE-manifold. The turbo running at higher boost is going to draw more air past the MAF than if the turbo were working at the correct boost pressure, which inflates your airflow numbers.

 

[kenamond]

Sure thing.
The MAS on your car precedes the compressor. The MAS reads intake temperature, barometric pressure and air velocity. From that it can compute the mass air flowrate through the MAS (e.g. pounds of air per minute (lb/min)). This is what the ECU uses to determine how much fuel to use. If it takes the mass air flowrate and the speed of the engine (rpm), it can compute the mass of air entering each cylinder during their respective intake strokes (if you take airflow in lb/min, multiply by 454 and divide by rpm, you get grams of air per boom in a cylinder (g/rev) which is also called "load").

Now, the ECU gets all it will ever know about how much air is pumped through your engine via that MAS, so if any of it leaks between the turbo and the engine, the ECU doesn't know about it. As a result, it injects more fuel than is actually needed for the air that actually makes it into the cylinders.

Now the compressor is having to work to get that air into the motor. But if there's a leak, it has a bit of an easier time hitting, say, 16psi boost than if all of that air was going through the motor. So the amount of air it pumps goes up. It's very crudely like having a higher volumetric efficiency (VE) as far as the compressor is concerned. So with a boost leak, the turbo can flow more air at the same boost than if all that air had to be crammed through the IC, IC pipes, TB, IM, ports, and past those valves; some of it just goes bye-bye into the engine bay.

That good enough?

 

[DSM_6SL2 Power]

Great explanation, I fully understand now.