Speed density vs. mass air flow

[blackbuick87]

OK, TR's use a Mass Air flow system vs. the speed density system (manifold absolute pressure) used in TPI cars and SY/TY's, and trucks.

My question is, why did GM go back and forth? In the early 90's everything was speed density, then with the LT1 and LS1 and all the SFI motors (like my 3.1 Regal) they went back to Mass Air Flow?

I guess I just dont understand the advantages of Speed Density. Was the development of better MAF sensors the reason GM went back? Better ECM's? Now a couple MAFless speed density systems looks to perform better than our mass airflow systems. It keeps going in one big circle

 

[Sinful6]

MAF is a better system. Take it from the 5.0 guys, the most desierable years are 89-92. the 87-88 years had the speed density which after a certain level of power had to be converted, and the 93's had those darned hypereutectic pistons

 

[Steve Wood]

Both Ford and GM have been back and forth on this one, I believe.

Factory speed density systems are simpler which probably means cheaper. On the other hand, they are hardwired and do not respond to modifications to the combination as readily as do mass air systems. Reprogramming is required. Perhaps, more importantly, it may be that emissions requirements are better controlled thru a mass air system that is more precise in controlling fuel air.

On the other hand, after market speed density systems, that are aimed at high performance rather than daily drivers that must past emissions, are more readily programmable (and probably more expensive)

FAST, DFI, etc. are on the top end and may be had with wide band O2 feedback which can drive software to aid the user in developing fuel curves that work well with a given combo, or changes to the combo. Cheaper versions don't use O2 input.

At the low end, price wise, would be the ME-R which is programmable by the user to fit the combo but offers not the feed back to automate the procedure. It does not offer the precision of tuning as the high end systems but is much cheaper.

The simplicity of the programmable speed density systems may (maybe) make them better for all out performance by eliminating a complex link (the maf). It may not make them the best street performer when it comes to economy and emissions. It may also be better for those that don't want to get too deep into the tuning.

This subject may be a bit like religion...you got your choice of sprinkling or immersion...in the end, it only matters that you get there.

 

[GNVAIR]

A mass air meter (one utilizing a hot wire) as opposed to a vane meter (one using a flapper/door) is a more precise way of measuring air intake and condition. It allows more precise fueling/timing adjustments based on actual engine requirement. The speed density systems are at a disadvantage since they can only make their adjustments based on MAP (manifold absolute pressure) and TPS readings. Basically speed density is making its adjustments based on engine load (vacuum readings)
A mass air set up is definitely an advantage when you are talking about making air flow modifications to a car with production electronics. Changes such as camshafts and better cylinder heads can wreck havoc on a speed density set up since they affect engine vacuum.
The reason why manufacturers started installing them was for drivability and emissions. Ford started installing them on the 5.0 V8 Mustangs in 1988 (california) and then 49 state cars in 1989. It was for this reason the Mustangs were so easily modified.
Now GM did the reverse. Starting with Mass air on the 1985 TPI cars and going to Speed density in 1990. GM had a horrible time with the bosch mass air meters (same design as a GN)on those early TPI cars and it was most likely for this reason they switched. The main reason as I see it for the problems with the mass air meters failing was oil being spit out the intake on shut off contaminating the grid. In all honesty, GM's TPI electronics were very primitive compared to Fords EEC IV system. All TPI systems were batch fire whereas Fords EEC IV was sequential. Even the 92-93 LT1's were of the same batch fire system as the TPI cars. The fact that engine modifications required burning new proms put GM at a serious disadvantage to Ford IMHO.
Starting with the 1994 model year, GM finally introduced improved electronics that included a redesigned mass air meter. This allowed the LT1 cars to benefit from air flow mods without having to reflash the pcm. You will notice that starting in 1996 that almost all vehicles produced by GM and Ford have mass air meters. 1996 was the start of OBD2 electronics (as legislated by the government). As such, each manufacturer used mass air meters to precisely control fuel and timing adjustments.

 

[blackbuick87]

Thanks for the excellent answers guys

 

[bruce]

As the oems have shown it all depends.

MAF has alot of self filtering, with the way the MAFs are designed. The newer ones, being less "dampened". On the OBDII cars they use both. The MAF as the primary sensor, and then MAP for doing a sanity check on the MAF in compliance with the OBDII guidleines.

The MAP has one unmistakable advantage in that you can do ALL the filtering in software.

MAF in systems with large amounts of Reversion, can be troublesome to calibrate.

The MAFs in the GNs with the stock programming can be error prone. Since flowing 200 gm/sec can happen at a number of different throttle openings, vs boost conditions. A simple inclusion of using a Turbo link boost sensing input can work wonders on drivibility. But, that takes some work.

Going to a blow thru MAF (LT1/LS1) can eliminate the MAF as being much of a restriction in the system.

At WOT there is little difference between the two when both are done correctly, IMO.

 

[Nick Micale]

You asked lots of questions about MAF vs. speed density and received lots of good answers. The only one not asked or answered is "what is best for me?"

Each type system has its advantages and you did not specify any particular application. Since I am interested in better engine management, I have looked at many different systems and talked with various "experts" about this subject.

Here is my opinion, at least up to this point. If you want to change from a stock ECM which is MAF, the only reason is to maximize WOT performance. A street-driver T-R that is used sometimes at the track, can and should, do well with the ECM and a good chip or 2.

For a "race car", something more tuneable to the average person like me can do it better with an aftermarket system. So far, most of them are speed density. All the DFI tuners that I have met with also prefer speed density, as are the racers going the fastest.

Just go to the "DFI" section of this board and see what most are doing.

 

[red89notch]

MAF conversions for Stangs are desired usually after a larger cam install , otherwise those were the fastest out there *87 & 88 notchbacks w/ 5spd* Not sure on the GM deal though.