Please help me understand MAF Frequencies?
06-08-2005, 04:38 PM
#1
Please help me understand MAF Frequencies? Ok ,My Problems are all in the MAF Table,such as start up surge and extremely -LTFT's.Now I have 2 tunes from my tuner one with my Breathless Performance ends that flow a little over a 1000 cfms and one with my 85 MM MAF.Now what I dont understand is why my stock with ends has a bigger airflow G/sec then a stock MAF and the 85 has a lower number?Is it the lower number the more air?I dont get it.Here is the MAF Tables I have for a 99 F Car.
Here is the 85 MM Table as follows
1.99 2.31 2.7 3.13 3.55 4.05 4.58 5.18 5.81 6.54 7.3 8.09 8.92 9.79 10.74 11.78 12.9 14.1 15.37 16.74 18.17 19.69 21.3 22.98 24.76 26.62 28.56 30.59 32.73 35 37.39 39.92 42.58 45.37 48.32 51.4 54.62 57.97 61.47 65.11 68.89 72.81 76.87 81.08 85.44 89.95 94.61 99.42 104.41 109.57 114.89 120.44 126.19 132.13 138.27 144.63 151.18 157.95 164.86 171.99 179.33 186.91 194.74 202.85 211.25 219.96 229.02 238.44 248.24 258.48 269.16 280.34 292.03 304.3 317.17 330.68 344.87 359.81 375.52 375.52 375.52 375.52 375.52 375.52 375.52
Now Here is my Stock with ends Table
2.44 2.84 3.32 3.84 4.38 4.98 5.64 6.37 7.16 8.05 8.98 9.97 10.98 12.06 13.23 14.51 15.89 17.36 18.94 20.62 22.38 24.26 26.23 28.31 30.48 32.78 35.17 37.67 40.31 43.1 46.04 49.17 52.44 55.88 59.51 63.3 67.27 71.4 75.71 80.2 84.85 89.68 94.67 99.86 105.23 110.77 116.51 122.45 128.59 134.95 141.5 148.34 155.41 162.72 170.29 178.12 186.19 194.52 203.04 211.82 220.86 230.19 239.84 249.83 260.17 270.91 282.06 293.66 305.73 318.33 331.5 345.26 359.67 374.77 390.61 407.26 424.74 443.13 442.8 442.8 442.8 442.8 442.8 442.8 442.8
Now Here is a Stock 99 factory
2.32 2.7 3.15 3.65 4.16 4.73 5.36 6.05 6.8 7.64 8.53 9.47 10.43 11.45 12.56 13.78 15.09 16.49 17.98 19.58 21.26 23.03 24.91 26.88 28.95 31.13 33.4 35.78 38.28 40.93 43.73 46.69 49.8 53.07 56.51 60.11 63.88 67.8 71.9 76.16 80.58 85.16 89.91 94.83 99.93 105.2 110.65 116.28 122.12 128.15 134.38 140.87 147.59 154.53 161.72 169.15 176.82 184.73 192.82 201.15 209.74 218.61 227.77 237.26 247.08 257.27 267.86 278.88 290.34 302.31 314.81 327.88 341.56 355.91 370.95 386.76 403.36 420.83 439.2 439.2 439.2 439.2 439.2 439.2 439.2
Now what I dont understand is why the 85 MM MAF is a much lower number than stock ,and why my 1000 cfm is a Higher number than stock?I am getting a new computer soon than I can share my tunes with you guys...Thanks for the help...
Scott
Here is the 85 MM Table as follows
1.99 2.31 2.7 3.13 3.55 4.05 4.58 5.18 5.81 6.54 7.3 8.09 8.92 9.79 10.74 11.78 12.9 14.1 15.37 16.74 18.17 19.69 21.3 22.98 24.76 26.62 28.56 30.59 32.73 35 37.39 39.92 42.58 45.37 48.32 51.4 54.62 57.97 61.47 65.11 68.89 72.81 76.87 81.08 85.44 89.95 94.61 99.42 104.41 109.57 114.89 120.44 126.19 132.13 138.27 144.63 151.18 157.95 164.86 171.99 179.33 186.91 194.74 202.85 211.25 219.96 229.02 238.44 248.24 258.48 269.16 280.34 292.03 304.3 317.17 330.68 344.87 359.81 375.52 375.52 375.52 375.52 375.52 375.52 375.52
Now Here is my Stock with ends Table
2.44 2.84 3.32 3.84 4.38 4.98 5.64 6.37 7.16 8.05 8.98 9.97 10.98 12.06 13.23 14.51 15.89 17.36 18.94 20.62 22.38 24.26 26.23 28.31 30.48 32.78 35.17 37.67 40.31 43.1 46.04 49.17 52.44 55.88 59.51 63.3 67.27 71.4 75.71 80.2 84.85 89.68 94.67 99.86 105.23 110.77 116.51 122.45 128.59 134.95 141.5 148.34 155.41 162.72 170.29 178.12 186.19 194.52 203.04 211.82 220.86 230.19 239.84 249.83 260.17 270.91 282.06 293.66 305.73 318.33 331.5 345.26 359.67 374.77 390.61 407.26 424.74 443.13 442.8 442.8 442.8 442.8 442.8 442.8 442.8
Now Here is a Stock 99 factory
2.32 2.7 3.15 3.65 4.16 4.73 5.36 6.05 6.8 7.64 8.53 9.47 10.43 11.45 12.56 13.78 15.09 16.49 17.98 19.58 21.26 23.03 24.91 26.88 28.95 31.13 33.4 35.78 38.28 40.93 43.73 46.69 49.8 53.07 56.51 60.11 63.88 67.8 71.9 76.16 80.58 85.16 89.91 94.83 99.93 105.2 110.65 116.28 122.12 128.15 134.38 140.87 147.59 154.53 161.72 169.15 176.82 184.73 192.82 201.15 209.74 218.61 227.77 237.26 247.08 257.27 267.86 278.88 290.34 302.31 314.81 327.88 341.56 355.91 370.95 386.76 403.36 420.83 439.2 439.2 439.2 439.2 439.2 439.2 439.2
Now what I dont understand is why the 85 MM MAF is a much lower number than stock ,and why my 1000 cfm is a Higher number than stock?I am getting a new computer soon than I can share my tunes with you guys...Thanks for the help...
Scott
06-08-2005, 05:36 PM
#2
Staging Lane
Join Date: May 2005
Posts: 54
Likes: 0
Received 0 Likes
on
0 Posts
I've been wondering this too. I keep hearing how my stock 75 mm MAF needs to be upgraded, but for any given output frequency on paper flow exceeds the stock 85 mm Z06 MAF. Seems to me if the flow of a 75 is say 100 at max frequency, I would expect the 85 to be greater than 100 assuming an identical max fr. Somebody's got the answer!
06-08-2005, 07:10 PM
#3
Moderator
iTrader: (11)
Join Date: Mar 2002
Location: East Central Florida
Posts: 12,605
Likes: 0
Received 6 Likes
on
6 Posts
Delphi 85mm have totally different geometry and
electronics than the Delphi 75mm. They are calibrated
different from the factory and the MAF table tells you
what airflow the output is supposed to represent.
The stock table for the '99 you may notice is gimped
out at the top end. It says, wrongly, that the MAF
frequency pegs out at 11kHz or so which is not true.
If you have a later PCM its upper frequency limit is
12kHz and the table index matches, and there's no
good reason for it to be populated with crap. But on
a stockish car you won't see that high a frequency.
There is a Holden table that has proper values all the
way out for the 75mm MAF. I know I've posted it here
before. The Holden table tops out at 512g/sec at 12kHz
both of which are also "hard limits" to what the PCM can
deal with. Funny coincidence, that.
The 85mm MAF will flow better, but its calibration is bent
lower because the vehicles it's used on just don't see the
high side of 450g/sec. I guess they went for resolution
and gave up range. The 1000CFM one (?) would be for
folks who have a different trade in mind. But the PCM
isn't really going to want to hear about 513g/sec.
Don't get all wrapped around the flow number axle.
A 1000CFM piece of pipe drops you, like, 15% less
pressure than a 750CFM piece of pipe (even supposing
they were rated on the same pressure basis, which is
a game you see played occasionally in the automotive
performance aftermarket.). Manifold pressure is what
it's all about. You're running a pumping-limited system
for the most part and not a pressure-limited one, as
far as the intake tract is concerned. Flow numbers look
impressive but the numbers don't mean, what they look
like they mean.
Look at (BARO-MAP)/BARO at WOT, top end. You're going
to see numbers like a couple of percent (NA). That's how
much you could gain, from where you are now, with a
zillion CFM MAF and a TB you can stick your entire torso
inside, a bellows so smooth the air can see its own
reflection and a lid that, well, is a real nice lid too. All
that stuff represents a couple percent problem. Unless
you already are doing some heavy breathing, then the
bar (heh) is raised.
electronics than the Delphi 75mm. They are calibrated
different from the factory and the MAF table tells you
what airflow the output is supposed to represent.
The stock table for the '99 you may notice is gimped
out at the top end. It says, wrongly, that the MAF
frequency pegs out at 11kHz or so which is not true.
If you have a later PCM its upper frequency limit is
12kHz and the table index matches, and there's no
good reason for it to be populated with crap. But on
a stockish car you won't see that high a frequency.
There is a Holden table that has proper values all the
way out for the 75mm MAF. I know I've posted it here
before. The Holden table tops out at 512g/sec at 12kHz
both of which are also "hard limits" to what the PCM can
deal with. Funny coincidence, that.
The 85mm MAF will flow better, but its calibration is bent
lower because the vehicles it's used on just don't see the
high side of 450g/sec. I guess they went for resolution
and gave up range. The 1000CFM one (?) would be for
folks who have a different trade in mind. But the PCM
isn't really going to want to hear about 513g/sec.
Don't get all wrapped around the flow number axle.
A 1000CFM piece of pipe drops you, like, 15% less
pressure than a 750CFM piece of pipe (even supposing
they were rated on the same pressure basis, which is
a game you see played occasionally in the automotive
performance aftermarket.). Manifold pressure is what
it's all about. You're running a pumping-limited system
for the most part and not a pressure-limited one, as
far as the intake tract is concerned. Flow numbers look
impressive but the numbers don't mean, what they look
like they mean.
Look at (BARO-MAP)/BARO at WOT, top end. You're going
to see numbers like a couple of percent (NA). That's how
much you could gain, from where you are now, with a
zillion CFM MAF and a TB you can stick your entire torso
inside, a bellows so smooth the air can see its own
reflection and a lid that, well, is a real nice lid too. All
that stuff represents a couple percent problem. Unless
you already are doing some heavy breathing, then the
bar (heh) is raised.
06-08-2005, 08:21 PM
#5
Staging Lane
Join Date: May 2005
Posts: 54
Likes: 0
Received 0 Likes
on
0 Posts
Good chit there and nice closing pun, Jimmyblue. Explains it well. And you are dead on regarding the Holden MAF--my calibration using Marcin's spreadsheet matched that curve perfectly and all is well in the 75 mm low rent district. I've yet to crack the 10 Khz barrier with a scan, even at 145 mph on the dyno with huge fans blowing.
This tuning stuff just sucks you right in if you're a curious techie bored with his day job
This tuning stuff just sucks you right in if you're a curious techie bored with his day job
06-08-2005, 11:32 PM
#7
Originally Posted by gametech
Going back to the original post, startup surge is not a MAF problem. On startup, the pcm uses the VE table.
Trending Topics
06-09-2005, 01:59 PM
#9
Moderator
iTrader: (11)
Join Date: Mar 2002
Location: East Central Florida
Posts: 12,605
Likes: 0
Received 6 Likes
on
6 Posts
At the very bottom it's all speed density. At the top,
above 4000, it's all MAF (when stable MAP). In between
the two are combined with weighting that varies, a
"sliding blend". At 2800Hz there's probably a little bit of
MAF data blended in and shaving on the MAF to make
it leaner, moved things a little. How much? Check how
much your LTFTs moved (presuming you are getting good
trimming, not narcoleptic O2 sensors etc.) for that 15%
on the one component of airflow. If LTFTs at the idle cell
moved (say) +3% for a -15% MAF scaling, that says the
MAF is 20% of the rolled up iar mass flow value and VE
table would move trims 0.8% / %.
Not sure how stable the MAF reading is at low flows. I
have seen the raw frequency wander a fair bit, on the
meter and in the logs; might be that the surging is to
some extent just following MAF instability (or vice versa,
or some positive feedback). Reducing the MAF value in
areas where it is already low weighted may preferentially
lower the unstable part, leaving the simpler SD stuff to
carry the weight.
Or something.
above 4000, it's all MAF (when stable MAP). In between
the two are combined with weighting that varies, a
"sliding blend". At 2800Hz there's probably a little bit of
MAF data blended in and shaving on the MAF to make
it leaner, moved things a little. How much? Check how
much your LTFTs moved (presuming you are getting good
trimming, not narcoleptic O2 sensors etc.) for that 15%
on the one component of airflow. If LTFTs at the idle cell
moved (say) +3% for a -15% MAF scaling, that says the
MAF is 20% of the rolled up iar mass flow value and VE
table would move trims 0.8% / %.
Not sure how stable the MAF reading is at low flows. I
have seen the raw frequency wander a fair bit, on the
meter and in the logs; might be that the surging is to
some extent just following MAF instability (or vice versa,
or some positive feedback). Reducing the MAF value in
areas where it is already low weighted may preferentially
lower the unstable part, leaving the simpler SD stuff to
carry the weight.
Or something.
06-09-2005, 04:29 PM
#10
Thanks Jimmyblue ,Well as gametech stated ,It was the VE!I put my MAF back to the one my tuner had put in there,Now car started very shitty.See my LTFT's are -12 to -16.So when I got it started again and warmed up where the surge was gone.I changed my VE for the 50 to 60 KPA for the required RPM range by 15% the car wouldnt start.So I changed it back and went 10% and the car ran great with no surge at Idle.So Gametech was right on that
I guess I got some serious tuning to do to the VE...Thanks again for the Help Guys...
Scott
I guess I got some serious tuning to do to the VE...Thanks again for the Help Guys...Scott
