Chris Knott Insurance - Competitive quotes for forum members
  • Hey Guest💡👉 We have just launched our new Dealer Directory and review service Find out more now

MAF flowrate - velocity - someone check my calcs

ibizacupra

Jack-RIP my little Friend
Jul 25, 2001
31,333
18
glos.uk
Code: 
mass flow rate g/s	density	velocity m/s	Area	Diameter mtrs			
0.225	1.168	43.604094	0.004417865	0.075		Air 25degrees 100kPa

cant get it aligned right - sorry

225g/s, thru 75mm MAF = 43.6 mtr/sec velocity (example of a chipped LCR airflow)

this look about right in velocity terms? - wilko?
 
Last edited:
m0rk said:
isn't the area 0.004418m^2? not 0.075

PI*R^2?
Click to expand...

mislabeled I think... should be diameter.
will check.

Code: 
mass flow rate g/s	density	velocity m/s	Area	Diameter mtrs				
0.225	1.168	43.604094	0.004417865	0.075		Air 25degrees 100kPa		

mass flow rate g/s	density	velocity m/s	Area	Diameter mtrs				
0.302	1.168	38.89542884	0.00664761	0.092		Air 25degrees 100kPa		

mass flow rate g/s	density	velocity m/s	Area	Diameter mtrs				
0.302	1.168	32.92109097	0.007853982	0.1		Air 25degrees 100kPa		

mass flow rate	density	velocity	Area	Diameter				
0.302	1.168	58.52638394	0.004417865	0.075		Air 25degrees 100kPa
 
Last edited:
some exmaples of "pegged" MAF on mine and tube sizes....
'if' velocity thru a chipped LCR is a reasonable 'maximum' velocity, comparing other tubes sizes for same massflow rates (presumes maf's read same airmass for the same 0-5v they output (maf sensors differ)
 
ibizacupra said:
some exmaples of "pegged" MAF on mine and tube sizes....
'if' velocity thru a chipped LCR is a reasonable 'maximum' velocity, comparing other tubes sizes for same massflow rates (presumes maf's read same airmass for the same 0-5v they output (maf sensors differ)
Click to expand...

I'm been thick Bill, surely the only variable here is the tube size :confused:
 
ibizacupra said:
some exmaples of "pegged" MAF on mine and tube sizes....
'if' velocity thru a chipped LCR is a reasonable 'maximum' velocity, comparing other tubes sizes for same massflow rates (presumes maf's read same airmass for the same 0-5v they output (maf sensors differ)
Click to expand...

Bill
I've had a 75mm od maf(69 id) read as high as 275g/s with no maf scalling, so even if this is at 5V, 200g/s from a chipped lcr is no where near maxing it out, and have seen 190g/s through a 70mm od (64mm ID)

I've seen 245g/s through a 86mm od (79mm ID) maf when scalled for a 69mm id maf, so theoreticaly 320g/s. This suggests that i'm running a similar velocity through the s4 maf on 18G as I was through an s3 maf on VF34.
Neither set up maxed the maf, and neither had problems with maf longevity.

Now bearing in mind that the compressor max flow is currently 300g/s, I think you have to look at free area of the maf, and take the sensor and screen area into account, so it's slightly more complicated than just maf diameter.

Cutting to the chase, you need a 95-100mm maf (ID) for 60lb/min flowrate.
 
Wilko said:
Bill
I've had a 75mm od maf(69 id) read as high as 275g/s with no maf scalling, so even if this is at 5V, 200g/s from a chipped lcr is no where near maxing it out, and have seen 190g/s through a 70mm od (64mm ID)

I've seen 245g/s through a 86mm od (79mm ID) maf when scalled for a 69mm id maf, so theoreticaly 320g/s. This suggests that i'm running a similar velocity through the s4 maf on 18G as I was through an s3 maf on VF34.
Neither set up maxed the maf, and neither had problems with maf longevity.

Now bearing in mind that the compressor max flow is currently 300g/s, I think you have to look at free area of the maf, and take the sensor and screen area into account, so it's slightly more complicated than just maf diameter.

Cutting to the chase, you need a 95-100mm maf (ID) for 60lb/min flowrate.
Click to expand...

John, do you think I could be maxing out my 70mm o/d MAF at 196 + g/s ?
 
DPJ said:
I'm been thick Bill, surely the only variable here is the tube size :confused:
Click to expand...

it is in my calcs for effective airflow, but I am not convinced 180g/s through an LCR MAF is the same signal level as 180g/s would be through a golf/Ibiza/leon sensor. the sensor elements are different where a lcr one in an ibiza does'nt run right.
 
Wilko said:
Bill
Cutting to the chase, you need a 95-100mm maf (ID) for 60lb/min flowrate.
Click to expand...

Thats the figures I have in mind (and with Forge to make)
wondering what low velocities will be like in resolution/stability terms off boost on a puny 1900cc motor tho. On boost it will have measurable velocity and reading, but the non linear MAf output graphs I can recall seeing never get to 5v as airflow rises to infinate... Guessing there's an A to D cut off/scale applied which gives a "reported" g/s number for a given input voltage.

Whats 60lb/min in g/s??
 
Bill
60lb/min, divide by 60 to get seconds, so 1 lb/s, and then divide by 2.204 to get kg/s, so .454kg/s, or 454g/s

As you say, they are not scaled linearly, as if 300g/s on mine is say 4.5V. 2g/s on tickover would be 0.03v, and wire/contact resistence would become a major issue.
I guess this is one reason that at lower flows, the maf is fairly stable, and at higher flows, its + or - 5 g/s

As for the sensor elements being different, I've had golf, tt, lcr, and s4 sensors in the same maf tube, and they read the same. I think it's just scaling that is different on the ecu's, to match maf diameter.
 
Last edited:
Wilko said:
Dave if a 69mm id maf will read to >250g/s, a 70 mm maf should read to >220g/s, assuming that the sensors are the same.
Click to expand...

Cheers John, you answered the question I was just about to ask. :)

You don't think with the smallest MAFs that fluid dynamics would play a more significant role (more drag near the walls) and limit this further - (have a proportionately lower limit)?

You can see I'm struggling to explain why I'm on my 10th MAF. :cry: :rolleyes:
 
Just been doing some reading on this subject and just want to confirm my calcs.

2871r turbo max compressor flow rate of ~40lbs/min.

So thats 302g/s - (40/60/2.2.04x1000 as per wilkos calc above.)

So on a 76mm od maf vs 70mm Ibiza maf that g/s reading of 302 needs to be reduced by ~8.1% to give a max flow rate?

So would work out at ~277g/s.

So apply the 1.32 figure to get ~366bhp?

So if said turbo was running at 1.3bar and shifting 240g/s working backwards would you say that the maf was reading correctly for this boost and pulling 330bhp on the dyno?


The car in question is running lean as hell and i want to check that its not the maf readings that are incorrect and causing the lean condition. To me that MAF figure sounds about right for the power/boost levels but on full boost its seeing 14:1.
 
PhilW said:
Thanks bill, just wanted to make sure i was in the right ball park.

I think the map might be way off if thats the case. CC3 btw, 2871r ibiza.
Click to expand...

its needs a wideband on it.... airflow is low, and afr would follow, so mechanical things need to be confirmed first. It should not run lean, CC3 run things too rich generally, not lean. pumps ok?
If he needs it looking at you know where I am - unles its Jamies
 
291g/s from the 2ltr 2871/0.86 max - 1.8bar peak, 1.5bar top end
284g/s from the 1800cc 2871/0.63 - 1.8bar peak, 1.5bar top end ( I see a log of 280g/s at 2350mb

max figures off logs i have here if that helps as a comparison
 
Last edited:
Im not really too hot on this subject. My car pulled 260g/s at 1.8 bar last night. The maf im using is an rs4 79mm id unit, thats not been scaled yet from the lcr 69mm id one i used to have. What would that make my true g/s?

Cheers, Alex
 
You must log in or register to reply here.
Adrian Flux insurance services - discount for forum members.
Top Bottom
Back