Air mass meter and turbo...

[SyKo]

this seems like bit of an idiot question, seeing as i fell i know a relative amount about turbo's and tuning with them (not enough as i would like though :( )

the air mass meter, can i put it AFTER the turbo as opposed to before it as it sits at the moment?

If not, i see cars with turbo's but no AMM on them ... they have MAP sensors, is this essentially the same thing just in a different way of measuring?

Would be grateful of the help!

Matt

[t5 pete]

Theres a couple of people in the us running the air flow meter in the intercoolers pipes but if there on the hot side i think it tends to mess with prongs/strips that hang down i the piping.

[dooby]

Hiya,

interesting question. If I remember right, the MAF in our cars is a hot wire type. Electronics tells us the resistance of a wire changes depending what temperature it is, so essentially what happens is 2 wires have a voltage across them. One could be covered (no air rushing over it) and the other left in the air stream. This would give you a voltage difference between them which could be calibrated into a wind speed.

Thinking about it, if you put this after the turbo all that would happen is the air is more densely compressed, and hotter (due to the compression). So, since the temperature of the air should have an effect on how much it 'cools' the exposed wire I guess maybe it is possible to make a type of MAF which could be calibrated to give the right signal with compressed, hot air rushing past it.

However, I don't know if it works in practice - the Bosch MAFs we use in our 850s are rated for up to 110 degrees centigrade continuous and I don't have a figure handy for post-turbo, pre-intercooler air temperatures. I think I was reading on another forum that temperatures in the 60 degree range are considered sane at the throttle body so if the intercooler is reducing from 110 to 60 (for sake of argument) then maybe it's possible.

No idea if having the MAF as an obstruction when the air is more dense has a worse effect on air flow.

Warning - I haven't done electronics in a long time, this is all from my hazy memory :-)

Would make an interesting experiment with a 2nd hand MAF if you fancied messing about with the pipe work!

Cheers, Pete

[SyKo]

excellent post! cheers for the info there ... what if i put it after the intercooler? the intercooler will have an electronic draw fan fitted which will be turned on when really giving it hell to draw cooler air over it reducing the temperature. i would have though placing it after the intercooler would be a better option ... although the existing wires wouldnt reach, which would mean me having to extend the wiring loom ... what do you think o n this?

Matt

[dooby]

Hi Matt,

if it were me, I'd be tempted to head down to a scrappy and pick up a MAF and its plug, and make an "extension lead" as it were, and have a play with putting it in the post-intercooler piping somehow.

I don't *think* you'd do any damage you couldn't fix by clearing the ECU codes or unplugging the battery over night but I'd probably also try and wire up an analogue multimeter to measure the voltage at the MAF before and after, to watch for wildly different signals in case the ECU gets confused. I probably also wouldn't absolutely boot it until I was sure the ECU was still fuelling right. If you have a wideband Air Fuel Ratio gauge that would make the experiment even safer I'd imagine.

Go carefully :-) Cheers, Pete

[p fandango]

i extended the wires on my MAF without noticing any problems, i used to run a dash mounted Apexi Neo which altered the signal from the MAF to the ECU (altho this didn't affect the WOT fueling as it didn't use the MAF signal for that)

[SyKo]

excellent, i do have an afr guage, its just not hooked up yet as the turbo is off the car and so is the manifold, downpipe, cylinder head etc..

I will test this when i get it all back together, but otherwise thank you for all the info you have provided. Very helpful!

Matt

[tomtyres]

Not sure about a maf?
But i've mounted my flappy box on the cold side and it's fine!
http://i87.photobucket.com/albums/k157/tomtyres/Image0527.jpg

Purly to make room for my little turbo,
(p.s. left = standard 740 turbo garret, right = holset h1c from 25 tonne cat dumper truck)

http://i87.photobucket.com/albums/k157/tomtyres/Image0513.jpg
http://i87.photobucket.com/albums/k157/tomtyres/Image0514.jpg

You will find your maf getting oily though and not picking up the airflow so well!

[dooby]

You will find your maf getting oily though and not picking up the airflow so well!

Ahh, good point - that's one good reason for keeping it before the turbo :-)

Cheers, Pete

[SyKo]

flappy box?

[dooby]

Think it's an alternative air flow measurement instrument. The air blows a flap open to a particular angle, which is proportional to air flow. The flap is hinged at one side only.

HTH, Pete