ez

i have noticed there are few options of which type and brand of MAF to use on a 1987 305 TPI. Mine had the Bosch hot wire MAF from factory. Since then i installed the Airfoil, KN filters, and cold air intake. Finally, the MAF died.

Here is what I did and noticed:

I orginally, installed the Gartinellia (sp) "film"adjustable maf. I noitced stronger power gains, and over all response was strong, vs sluggish (prior to the MAF change out). But no matter how many times i tuned the MAF, the car ran rough all around. I was not pleased.

I then ran down the infamous Wells RU-145 "film" maf, only to discover Wells themselves does make them. Instead, you get a wells box with a OEM new Bosch hot wire maf. Completely, looks like the old maf with newly updated hardware. Well, after speaking with Wells mgt regarding whats in the box topic. He advised, Wells stopped production as sales volume was low. Only selling 2 to 3 month. Now, they buy these MAF from a source (bosch or hitachiti (sp)) as there own....

I installed the Bosch. car runs like new again. strong, a little sluggishness, but all and all smooth. compared the above maf.

but, i feel the film has less restrictions, hence more air intake.

so, does one maf version hot vs film truly produce more HP over the other? Does one truly out perform the other???

I noticed napa and autozone sell a MAF per the board, that is perfect, but its the film.. i have no problem , returning a 2 nd maf and purchusing a 3rd provided, if the difference is noticable.

once i settled on the maf, i believe i need to tune this car. next step, PROM looks like the way to go vs a chip... I am thnking the PROM will smooth out all, and provide noticalbe gains.

anyone known how much HP a good PROM tune would provide based upon my set up?

thank you for all the help.
eddy

Vader

There are a few conventions that should govern your theories, and a few other observations:

The MAF measures intake air mass (not volume) and reports it to the ECM. The ECM does the actual fuel trimming based on this data, so incorrect data is likely going to result in incorrect ouput. Garbage in, garbage out. Because of this, you need a reliable signal from the MAF to assure correct fuel trimming.

The ECM disregards (but still monitors) the MAF input data once the throttle is opened above 80%. At peak power production, the MAF isn't even an issue in terms of fuel calculations. The only effect it may have is in its inherent flow restrictions. So while a less restrictive MAF may indeed allow more intake air and power at peak throttle, the sampling must be correct at low throttle angles so the mixture can be maintained in the correct range.

The stock (Bosch) MAF has a small sampling tube mounted in the center of the unit and screens placed at each end. These screens create some air turbulence so that the pasing air sample is relatively equal through the entire cross section of the unit. Thus, the sampling tube is regarded to have an "accurate" sample of the overall flow. Removal of those screens can introduce flow laminations and affect the accuracy. Similarly, removal of the heat sink fins for the internal electronics package will also affeect the sampling rate. The MAF output is calibrated to compensate for the flow restriction imposed by those fins.

The thick film sensors that I have studied have no such sampling tube. The air mass measurement is performed on a circuit card mounted in the center of the sensor body, and it still relies on an intake "screen" to mostly equalize flow across the entire diameter of the sensor. The sensor I have actually has a flat metal matrix instead of a round wire screen, so it performs that same function without presenting as much flow restriction.

Following a semi-scientific analysis of the two types of MAF sensors, I have determined that the aftermarket thick-film type (such as the Wells SU-145 used to be) has a significantly larger corss-sectional area and lower flow restriction than the OEM Bosch sensor. Between the dual round wire screens on the Bosch MAF, the intrusion of the heat sink fins into the MAF body, and the slightly smaller inside diameter of the Bosch 14094712 MAF, the available area in the MAF is about 5.965111 in². By comparison, the Wells SU145 MAF = 7.036153 in².

A "chip" and PROM are in essence the same thing. Purchasing a "cookie-cutter" PROM from an aftermarket company is not likely to provide any measurable gain. Altering the programming and burning your own custom PROM has a significantly greater potential for both power and fuel mileage increases. Rather than trying to adjust the output signal of the MAF, alter how the ECM reacts to the input. It's going to be a more reliable system overall.

For the cost of a single aftermarket PROM, you can get into burning your own, with most of the necessary equipment. You'll wonder why you didn't do it sooner. For example, a HyperTech Thermo Master 156332 lists for $201.99 (on sale!), whereas a TransTronics Pocket Programmer II lists for $149.95. Parts to build a serial data cable will cost you about $15. The software to datalog the ECM and alter the programs can be downloaded for free. Blank PROMS are about $8, and a PROM socket to convert your MEMCAL is about $6. For less than an aftermarket PROM, you cna be well into a far better program.

Once you start reprogramming, you can alter the MAF scalar tables to compensate for either type of MAF, and effectively tune out the low RPM problems, the hesitation, and maintain or even improve WOT power production.

RednGold86Z

iTrader: (1)

Vader,
Not to be nit-picky, but the MAF is used at full throttle. Only when the airflow measured exceeds 255 g/s (or greater than the "Max Airflow vs RPM" table) is the MAF disregarded, then it simply uses that max airflow + the PE% vs RPM. On a stock engine, the MAF is always used. On a mild cam 383, it can get maxed out easily, but the effect is compensated by the above mentioned action. Some people say there's Alpha-N, but to be more correct, it's just N (RPM). The alpha (throttle angle) is required (to get the airflow needed into the engine) but not required in the code. The Power Enrichment is excessive to compensate for the maxed out MAF.

Most chip burning guys will raise that max airflow vs rpms, and set them to 255 at the higher RPMs in order to prevent it from clamping the fuel sooner than the code can support.

ez

Vadder-- once again great write up. i have been reading your posts and they have been very informative.

we are on the same page on the MAF. bosch vs heat film. heat film is less restrictive with a touch more hp..

but the over all "tune" is wihtin the PROM. I agree, i need to purchuse the self PROM kit for the right tune.

I have installed the bosch self calb'd with no adjustments.

in your opinion, if i re tuned and reprogrammed all with new PROM settings here are my maf options: 1. stick with newly installed bosch over a heat film, would i be lossing much power>? or nothing noticalbe and leave the maf alone and focus on the PROM? 2. or pull the bosch and install a heat film.

thoughts? thank you sir and all.

Vader

Red/Gold,

I understand your point. I did mention that the MAF is still "monitored at WOT", only trying to simplify the explanation. In effect, that's all the ECM is doing since the tables have likely long since been effectively maxxed out. There's really little difference between 4.66 abd 5.12 MAF volts, but those values occupy nearly the entire Table 6.

Presuming that his '87 is still using $32B, a stock BIN, and a stock MAF, even the 305 is likely going to be at or about 4.66 MAF volts as soon as the engine hits about 3200 RPM and the throttle is even 75% open. At that point, fuel trim with the six MAF tables tuning is all but done, and the PE%vsRPM takes over ($622-$632). Notice how the factory L98 BINs just flat-line at or above 4000 RPM in that respect,and usually a little on the rich side. The 305 BINs flatten out as low as 2800 RPM, then go toward zero % PE. ¿Huh?

Further, at 2000 RPM, only 69% TPS sets WOT (open loop) condition.

In my oversimplification, I was merely trying to point out that MAF-based fuel trim is all but done as soon as the engine starts making any kind of power anywhere near WOT. PE%vsRPM is actually invoked well before the MAF is at 255g/S, as far as I can tell.

doc

Vader, As usual, great write-up..............

I like the part about the screens causing turbulence. I dont know how many times I had to inform people that the screens do just that,, screens do not create laminar flow as many have professed here.

And I like the part about PE % change to AFR vs RPM table. It is relatively easy to max out the MAF reading (not necessarily the MAF max flow rate) but just the reading of 255 gms/sec. Since the stock MAF flows 518 CFM at 28" of H2O (this converts to 293 gms/sec), the reading from the MAF is maxed out at 255 gms/sec at about 5,000 RPM. By the time this happens, the ECM has gone into PE mode and extra fuel can be added via the table mentioned above.

Tid-bit of info: The stock MAF with screens flows about 518 CFM,, which can support about 400 Hp at the flywheel. So, the point is, until you reach about 400 Hp at the flywheel (about 340 RWHp) you are good with the stock MAF. In order to break the 400 Hp barrier, the screens must be removed from the stock MAF. I have run with a descreened MAF for the last 8 years. And it is not a coincidence that I program my own Eprom chips.

More stuff on chip"burning": I think that there is a bit of mystery here. What we actually do when we say that we program our own chips,,, we are actually changing the entries inside the various tables. There is no real "programming" going on here, certainly not any Fortran programming. The "trick" is to know what tables need to be changed and make the suitable changes inside the table.

But now I have digressed from the topic of this post,, sorry.

Vader

Are you thinking it takes 5,000 RPM to hit the max MAF reading? Could be, on a 305, maybe? I suspected it was a good bit lower. Regardless, a little tuning is always a good thing. The '87 MAF tables are quite different from the later ($6E) tables, at least on the lower end, so even the factory may have recognized a bit of a discrepancy between the scales and their parameters.

You're right. We're not really "programming", per se, but simply tweaking parameters in an existing program. That alone can make all the difference. A few among us have actually programmaed, but that's a different world entirely.