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spence88mph spence88mph is offline
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Join Date: Jan 2007
Location: Melbourne, Australia
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I have completed the turbo conversion and can speak from experience unlike your speculation above. I can tell you that many turbos blow oil through the intake, not good for an AFM, I can tell you the AFM's threads will thread very easily as it's made of crappy cast alloy so getting a good strong seal to it is a PITA unless you helicoil it which I ended up doing (no biggie).

Unless you modify the exit with a retaining flange there's a good chance you will blow off the elbow to the throttle body. This has happened to me and friends cars many times. All these issues would not be a factor with suck through, that is why I am saying it would likely be a better set up and it's not new I've seen it on a few cars with good results.

The only reason I'm not converting to suck through as I did contemplate it, is I'm converting to MAP in the next couple of weeks, as soon as I get a chance to install the sensor. I'll also be able to tell you all how soon the flapper maxes out which I'm predicting would be very early in the rev range like 2500rpm but it's speculation. You could test this by connecting a volt meter to the AFM signal and see where and when it hits 5.0V.

In the N/A configuration using the spring loaded barn door Motronic Air Flow Meter (AFM),,, it is placed close to the throttle plate. I think it is located there for a reason, its placement minimizes the volume of the connecting hose between the two so that this design of AFM will work efficiently.
Not correct, it measures flow not pressure/volume.

I don’t think the Motronic AFM was given design considerations to run in a boost application and perhaps that’s why they are modified by companies like Promotive. (I would like to know what is done internally?)
Oh ok, that's why Porsche used it in the 951 and hmmm wonder if they chose blow through or suck through, do some research....

you loose pressure through it, Yes you do lose a bit just like you do when you add an IC but the gains are greater than the losses of operating it from the intake side of the turbo.
And your findings here are based on?

Sick of the bench racers!!!
'89 911 M491+Turbo
'89 944 Turbo
'88 928S4
'18 C63S Coupe
Old 01-27-2009, 02:45 AM
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