A Nissan Sentra Forum banner
1 - 20 of 21 Posts

·
Registered
Joined
·
13 Posts
Discussion Starter · #1 ·
Hi everyone, my car's a 2003 spec v with CAI, headers, balance shaft chain cut, motor mounts inserts and yes I have loctited the butterfly screws. I purchased an ELM327 wifi interface and I logged disappointing results. My maximum airflow with the CAI was 105 g/s at around 6000 rpm. My hypothesis is that the maf I use (stock Altima one) was designed to work with a 2.5 inch diameter tube and that the air flow measured is smaller because of the 3 inch diameter of the assembly. In fact, if I use a thumb rule with the surface of the tubes I get that the 3 inch pipe covers 1.44 times more surface than the 2.5 inch one. So, if I multiply the 105 g/s by 1.44, I obtain 151.2 g/s, which sounds better. I think that the ECU takes the smaller value and applies that factor to send the correct amount of gasoline. That's only what I think! I'd like to have your opinion on those readings I get and my way of thinking. I based that on my friend's 168 hp 2.4 liter Mitsubishi lancer gts that scored a nice 142 g/s! Thanks a lot everybody!
 

·
Registered
Joined
·
3,069 Posts
first of all you shouldn't be using 3" maf housing n/a on a stock motor
 

·
Registered
Joined
·
175 Posts
Are you sure the frequency/resolution is enough to record the proper g/s at 6000rpm? I'm not asking to be a dick, asking to make sure.I know the resolution on my OBD reader compared to Osiris is night and day. Can you get voltage readings at idle/WOT?

In any case you would be comparing volumes not area so taking a 1" cross section the volume of the 3" pipe would be 7.0685in^3 and the volume of the 2.5" pipe would be 4.9807in^3 . The ratio of the larger to smaller would be 1.419 respectively. Giving you a result of 149.01g/s. <- all from speculation my math skills seem to get muddled in old age. lol So it seems you calculations are close or we just used different ways to get the same thing.

The ECU uses the voltage numbers it gets from the "Hot Wire" MAF to look up in a g/s table what amount of fuel to inject into the cylinders. People have been using larger housing to lean out their values for years. Infact I think the nismo second gen CAI was a bigger diameter. With the amount of volume you have added you could be loosing power, going too lean causing detonation, or right at the sweet spot where the table is returning a g/s amount that results in an approximate 13.1 AFR under WOT. The only way to really know though is with a wideband.
 

·
Registered
Joined
·
7,401 Posts
Isn't this the same reason the VQ TB wouldn't work correctly on the QR?
 

·
Registered
Joined
·
175 Posts
Isn't this the same reason the VQ TB wouldn't work correctly on the QR?
Same reason different direction. VQ throttle body flowed too much at idle = too high a voltage for the ecu to understand. This created the stupid fluctuating idle we have all seen or heard about. His issue is reverse.
The larger housing is decreasing the voltage the ECU sees.

For a while I was telling people to use a larger housing to get the VQ TB to work. I never tried it but was told it didn't work. I'm going to try it with uprev tuner by editing the MAF/voltage tables. If life ever gives me some time.
 

·
Registered
Joined
·
1,736 Posts
first of all you shouldn't be using 3" maf housing n/a on a stock motor
Whats wrong with 3 inch maf
As long as theres some safc tuning its fine
 

·
Registered
Joined
·
1,736 Posts
I love my elm 327
But the data transfer is slow. There could def be an issue there


Also 3 inch maf will run lean up top without compensating somehow
 

·
Registered
Joined
·
3,069 Posts
but there isn't. It's throwing off his maf readings which is why this thread was started. Besides that if he's running full 3" intake he's going to be fucking up his stock tune in all sorts of ways but he's not. He's running a strange homemade cai last I saw

Whats wrong with 3 inch maf
As long as theres some safc tuning its fine
 

·
Registered
Joined
·
13 Posts
Discussion Starter · #10 ·
but there isn't. It's throwing off his maf readings which is why this thread was started. Besides that if he's running full 3" intake he's going to be fucking up his stock tune in all sorts of ways but he's not. He's running a strange homemade cai last I saw
I have a 2nd gen NISMO cold air intake adapted to fit with the 03 maf sensor. With the cai I obtained 92 g/s and with the stock housing and air box with a k&n drop-in air filter, I obtained 105 g/s. as far as i know, the piping of the cai has a 3 inch diameter. Thanks to everyone for the reply! My obd2 interface reads at about a 3 Hz frequency and i made 3rd gear pulls so i get about 20 values from 2000 to 6200 rpm! I recorded the data
 

·
Registered
Joined
·
13 Posts
Discussion Starter · #11 ·
My mistake was to think that the stock maf housing had a 3 inch diameter. I'll measure it this weekend!
 

·
Registered
Joined
·
13 Posts
Discussion Starter · #12 ·
So, do someone know what's up with the low values I have obtained? Are they normal according to you guys?
 

·
Registered
Joined
·
13 Posts
Discussion Starter · #14 ·
Yes, i perfectly understand that, but what I am trying to figure out is the actual normal readings I should expect. I'll check in the fsm, but if someone knows it, I'd appreciate it a lot
 

·
Premium Member
Joined
·
11,452 Posts
The difference between the stock MAF housing and the Nismo gen2 pipe is minimal. I had to make zero tuning corrections when I switched over to a full 3" OD pipe with integrated maf.
 

·
Registered
Joined
·
175 Posts
The only MAF values the FSM has are at idle and at 2500rpm. 02 MAF idle = 1.1-1.5v (1.0-4g/s) 2500rpm = 1.6-6v (4.0-10g/s)
 

·
Registered
Joined
·
13 Posts
Discussion Starter · #18 ·
With the nismo CAI in short ram mode, I obtained a 97 g/s peak. Which is 5 g/s more than in the CAI configuration and 8 less than with the stock housing. It sounds weird, like it is the opposite of what it would be supposed to be. Now, do some of you guys know about our Throttle Body and if it is supposed to be opened at 100% at WOT. The problem I have here is that my throttle position sensor says, when I floor the gas pedal, no more than 87% and the value is 87% from a few inches before the floor to the floor(as if the last inch was useless in getting more throttle opening). I'm really curious about these numbers and I'd like to clear it out! Thanks
 

·
Registered
Joined
·
3,069 Posts
I remember reading something about this throttle body thing somewhere.... damn idk. It was something like it doesn't matter how you are pressing the gas there is a sensor that is controlling things based on pressure....
 

·
Registered
Joined
·
13 Posts
Discussion Starter · #20 ·
okay, as if your foot on the pedal would control the percentage you use from the available torque or something like that?
 
1 - 20 of 21 Posts
Top