SladeX

Noticed on 3rd and 4th gear pulls that im hitting the maf wall at 5600 rpm roughly. It still holds a\f ok, but the maf is bouncing till peak. Mods are 98 car with more or less a ls3 transplant, forged bottom end and mild 235-238 115+2 0.618/0.613 cam. I'd imagine I'd need a 100mm.

Barring anything major, id imagine it just like upgrading to the 85, insert 100mm maf table, tweak with logging, wot on dyno qith qideband right?

Think an air straightner may help the 85? Or is 100mm the better option?

jimmyblue

iTrader: (11)

Your PCM limits are 12kHz and 512g/sec. The Delphi 85mm
MAF hits 12kHz at about 459g/sec according to the factory
tables I've seen. Now, I have yet to see anything out of the
3xx g/sec range, on my setup and well higher RPM. So I
doubt you are hitting a "wall", and your description seems
more like instability (or electrical noise issues).

I did find, whilst hogging out a 85mm to try and get the
g/sec limit up to 12kHz, that the reading became unstable
somewhere over the course of shaving and finally removing
the main divider. And this was with a non-pulsating air
source.

Whether a 100mm piece would fix the problem, I guess
depends on the root of the problem. If airflow or its
distribution is, itself, oscillatory then the MAF can only
follow, or filter somewhat. If the MAF electronics is the
unstable bit, well, maybe designs differ in your favor.
Maybe.

I think if it were my problem, I'd be logging at as high a
data rate (few PIDs) MAF frequency, MAP and RPM, try
and dope out whether there is indeed bigh speed surging
and whether this is airflow (MAP*RPM) or the MAF and SD
air masses just do not hold any consistency at certain points.
A 'scope might let you look at MAF output jitter and gauge
whether there is something funky (like harness EMI) that just
happens to "beat wrong" with the output at certain RPM.

SladeX

I've noticed in the log that MAP readings are hovering in the 97-101 range, its showing a bit of decline as you start the hit then ramp up rpm. I will try cutting out the PID to see what I can get out of it resolution wise.

The MAF is a Z06 maf, no screen. I based my tables off the truck table, smoothed it out with lots of logging and did the final upper frequency on a dyno. Just looking at the MAP makes me think you may be on to something that it's gulping air in chunks since my MAF climb is not smooth on the log.

I've ordered a saxonpc air straightener already so I'll see in a week or so how it works out. SOTP feel is still nice, I can break the tires loose at 70 mph on a downshift to 3rd. Just the logs itself bug me

SladeX

Finally had a chance to log a bit of less PIDs. MAF and MAP are nice and smooth looking, no abnormal spikes indicating any problems. No chance for WOT runs, but will do some later once traffic dies down around here.