I've got the answer - a little over 1 psi. The baro sensor in the MAF will measure the pressure drop in the vicinity of the MAF, and I consistently get about 1.2 psi pressure drop at peak power, but I decided to get an alternative reading well after the MAF to see the pressure drop is greater there. It was exactly the same as what I measured at the MAF.

At this point, I'm not convinced the 1 psi is even due to the MAF. It could be due to the air filter (that I cleaned about a month ago). At any rate, 1 psi doesn't seem like a lot. I'll eventually try SD without the MAF to see how much of a difference removing the MAF makes.

 

I'm back to maf. After understanding the ideas presented in measuring airflow directly vs calculating I don't see need for sd. On a stand alone that is ground up engineered that way I feel different though. Braces for 03white + more intellect and debate .

 

On a lower power setup maf is fine. One big advantage of sd is no issues if you pop an IC pipe in traffic or far from home! I have a maf on my 20G and SD on my 6262.

 

till what point is the stock maf efficient ? when switching to biger turbo, say 500+ hp, is the maf still able to make calculations of that increased airflow ?

 

Yeah, I keep a 10 mm socket in my car just for the t-bolt on the throttle body. Its the only one that ever comes off, and thankfully, I think I have it on there pretty good now.

 

At first I was thinking that getting rid of the 1 psi restiction would only get me another measily 1 psi of boost, but I thought it more last night and realized that it might be a bigger deal than an extra psi of boost. A 1 psi restriction means that the air density at the turbo inlet is about 93% of amospheric value. Based on my experience with the effect of air temperature on air density and hp (hot days suck for hp), a 7% reduction in air density seems significant. Reducing the restriction to only -0.5 psi should mean a 3.5% increase in air density and perhaps 3.5% more power. This lines up reasonably well with the kinds of power gains that people see when switching to SD.

 

Reminds me of this article from Motoiq.com:



http://www.motoiq.com/MagazineArticl...-and-More.aspx

 

LOL same here, lesson learned. Popped it off one day coming home from Lake Tapps when I was still on maf. Ended up using my shoelace to hold the oem uicp on the tb and stayed out of boost all the way home

 

If you have a decent sized filter, I'd be suprised if it is the filter causing the restriction. Just for refference, while my car was at 360WHP uncorrected, if you factor in air density of 4200', I had the same inlet volume flow rate as a sea level car making ~430WHP. I tested out removing the airfilter on my SD setup and I saw ZERO change to the car. It was one of the smallest K&N filters you can get too. Granted, I was not measuring inlet pressure, but there was no change in boost, AFR, power...nothing.

Like you said though, it's not about pressure, it's about air density at the turbo inlet.

That 1psi inlet loss also means your P/R at 30 psi guage pressure goes from 3.04:1 to 3.26:1 (neglecting IC pressure drop and an ambient pressure of 14.7psia). This means an increase in EBP and turbo shaft power, these are all secondary effects though to the density loss.

 

You will also always measure a vacuum is fast moving air pre turbo. The place to measure would be right at the compressor inducer which may be impossible to measure. I wouldn't worry about it.

 

Air passing a perpendicular port will pull a lower pressure signal regardless, is that what you're saying? That it's Rather difficult to measure high velocity air, pressure?

 

I think what he is getting at is by looking at the baro, you are not seeing the pressure loss associated with the intake pipe, just the MAF. You will also have a lower pressure here due to bernoulli's principle. He might have a decent point really as I seem to recall the baro reference actually being in the main MAF port. The MAF is designed to increase air velocity through the sensor section so the air velocity will be highest at the point where the baro sensor measures. You likely get some pressure recovery after the air exits the MAF sensor section and true pressure loss across the MAF might be less then the baro makes it look like.


System total pressure at the inlet is ultimately what matters, but static pressure at the inlet is still how the compressor maps are formed. Take a peak at FP's posts and you'll see a "pressure ring" that is the SAE type sensor used on gas flow benches used to map out compressor wheels.

 

If you guys want to test the maf etc for pressure drops, I own a sonic nozzle flow stand that can give you a 36 point curve for it

 

Mapping out an unmolested OEM MAF with air box with capturing MAF frequency would be pretty awesome for verifying some ECU mass airflow calcs.

 

yepper.