Need a dead maf for an 86 !

usfromflorida · 07-02-2008, 05:23 AM

I am looking to temporary relocate my Maf to the the S/C intake. I am getting surging and want to eliminate the Maf location as the issue. If anyone has a dead one to borrow or sell please let me know.
Mark

MarkRobinson · 07-02-2008, 05:29 AM

Yes, surging a common report for blow-through MAF's on the 928. Relocating to the inlet of the blower (give it some distance, 18" min. I'd think to prevent swirling inside the MAF, keep the screens), and use a recirculation valve after the blower & re-route to after the MAF but before the blower, ala factory draw-through applications.

usfromflorida · 07-02-2008, 05:46 AM

I have been banging my head against the wall with this issue. My Lm-1 Data logger data is fine as far as A/F ratios go etc. When I do a gradual acceleration it surges ever so slightly. It dawned on me that any S/C application always placed the Maf in the intake. It seems that the Maf cannot compensated for the quick air volume/ heat changes as fast as needed with 86 technology. I also believe the 90 degree bend is causing a swirling of the intake air, I will see once I get his done.

MarkRobinson · 07-02-2008, 06:40 AM

I'd bet it's the proximity of the 90d & swirling. My turbo 928 spools incredibly fast, makes a lot more rwtq than the average SC application & has never surged even once: drives as-stock.

MAF's are extremely sensative to air coming through them: I place the MAF equi-distant from the Air filter & the turbo, & place the BOV relcir. bung as far away from the MAF too, to prevent turbulence, swirling, etc. Never an issue, even during development. However, the 3 MAf blow-through 928's I've had/driven all had some sort of wierd surging at times: blow-through will not yield an as-factory smoothness. Even on a stock MAF 928, remove the air box lid & filter, & the car will run odd/unhappy as air around the MAF is not stablized by the air filter. Go for a drive this way, it'll stall on you too.

Mark.

Danglerb · 07-02-2008, 08:42 AM

What good would a dead MAF be?

BTW the MAF is the same for all years including the 84+ Euro.

usfromflorida · 07-02-2008, 10:18 AM

A dead Maf is used in place of the good one for testing, saves on fabricating a replacement tube and finding out it did not make a difference on the surging.

MarkRobinson · 07-02-2008, 11:06 AM

and, 3.75" piping to use as a mock MAF is very, very hard to find.

usfromflorida · 07-02-2008, 11:29 AM

I know hope someone has a dead one for me!

usfromflorida · 07-02-2008, 11:30 AM

Hey Mark what did you set your cam timing to, I just checked mine it's 0/0.

John Speake · 07-02-2008, 11:38 AM

Quote:

Originally Posted by usfromflorida

I know hope someone has a dead one for me!

If you just want a MAF body (casting) , I can give you one for cost of postage, about 20USD.

MarkRobinson · 07-02-2008, 11:39 AM

I have an unknown condition MAF i'll loan you. Send me $5 for shipping via paypal & I can use Paypal to autmatically generate the label for me.

Stock cam timing: my car was over 300+rwhp/tq before my turbo kit: just clean tuning & AA timing chip profiles.

Herr-Kuhn · 01:41 PM

Blow through is no problem...works really well as a matter of fact.

Bypass or blow-off valve should be placed as close to the throttle as is possible. All the air stored in the system when the throttle plate is closed should not have to back up to get out of the system.

usfromflorida · 07-02-2008, 03:19 PM

Where are you recommending to connect the BOV?

usfromflorida · 07-02-2008, 05:34 PM

I am starting to get the parts together to relocate my Maf due to low acceleration surging.
Here is a prototype to allow the Maf to be placed on the intake of the S/C. I have Kevin from Injection labs making a Maf pigtail to extend the harness and working on getting a dead Maf to allow to reconnect the intake correctly.
This should put the surging issue to bed or make me crazy not sure if thats that hard.

Now to work on getting a radiator now that mine is destroyed!

Herr-Kuhn · 07-03-2008, 03:02 AM

The best place for the bypass valve is always as close to the throttle plate as possible...but if you are using a draw thru MAF then you have to pump that air back into the system again...it cannot simply go to atmosphere as it could with a blow thru. If you draw thru and then boos the air and then let that boost off to atmosphere the car will go rich...you should never meter the air, order the fuel and then dump that air...it's bad practice.

With a lot of cars running blow thru I'm surprised you are having these issues. Many people prefer blow thru. My preference is draw thru, but with the packaging constraints inherent in the 928 I designed my system to be blow thru...but with that said a lot of time was spend making the plenum box which feeds my MAF. The car runs and drives very smoothly and I can rest assured I have the quickest possible throttle response out of the system, because there is little distance from the MAF to the cylinders.

If you are just looking for a space holder for the MAF area, why not just a piece of pipe? That way you can have it bead rolled for hose retention.

usfromflorida · 07-03-2008, 11:05 AM

John Speak has kindly provided me with a Maf core for $20.00 for shipping cost only, what a guy!

Now I need to find a good place for the Bov !

Herr-Kuhn · 07-03-2008, 01:26 PM

You'll need a better transition from that pipe to MAF. The airflow through the MAF has to collect and then rush through. If you have a small pipe and then transition right at the MAF you will introduce turbulance into the system and it won't read correctly. They can be very sensitive to transitions, specifically right before the sensor.

usfromflorida · 07-03-2008, 02:40 PM

I have a room issue and I am going from a 3' air feed to a 4" maf. I don't know of another location to mount the air filter. It is under the passenger fender near the brake duct. If you have an idea please speak up.
My problem now is with the Maf in the T/b location I am getting surging under partial load.

usfromflorida · 07-04-2008, 05:17 AM

I am getting some mixed messages as to my set-up, it was brought to my attention the by using the 4” to 3” reduction at the in and out of the Maf is going to cause turbulence. I have very little space to work with is there some type of formula as to how much straight 4” feed the Maf needs on both sides so not to disturb the air flow.

Herr-Kuhn · 07-04-2008, 09:45 AM

Are you sure it is the MAF causing the problem? I guess you had an elbow right before the MAF and I could see where that could be cause for concern. How about splitting out the air from the Supercharger and then running into a plenum box like my car runs?....this way the air is given a chance to expand out, then it has to re-collect through the outlet hole and through the MAF. My car is very streetable with this setup.

Or...consider building a charge cooler for the car and collecting the air right out of the charge cooler to then feed into the MAF.

If you are insisting on moving the MAF like that you will need a gradual transition...something with as slight a taper as possible...a diffuser is what you need. If you use those step hoses the flow will never get to fully laminar when it passes the wires...the air needs more distance before it passes the hot wire sensor. Most places will tell you 6" or so...or collecting right at the base of an airflow box is acceptable....the issue with going from small to large like that is that the air velocity coming in is greater than what it needs to be through the sensor...it's a pAV equation...the density is fixed (atmo) and your area is increasing rapidly....therefore the flow velocity has to follow and slow down...but since you are asking the air to slow down and fill in that large area over a very short distance...well it just ends up jetting through the sensor...sometimes hitting the wires as you want, other times not and you are stuck with a repeatibility problem. Not fun! Can you place the MAF right at the air filter? That would likely work very well....then step it down after the sensor.

If you are interested in the plenum box let me know...if you can figure out how to split the outlet of the SC and run it over top of each bank and then into the plenum box I think it would work well...and in addition your engine ends up with a bit more aesthetic flair.