A friend of mine is looking to buy an 87 GT and he asked me what the speed density system is and how it differs from mass air. I know ford changed over after 1988 but mechanically I don't know the difference other then most people like mass air better.

 

I think mass air detects the temperature of the incoming air and then the computer adjusts air/fuel ratio and/or timing/spark from that. Also, I think mass air is more mod friendly. With speed density the car is optimized to run at a specific air intake temperature and is more difficult to get optimized fuel/air... I think thats how it works but its best to get an answer from someone who knows for sure, but I do know that california mustangs were mass air from '87 I believe, whereas the rest of the country got mass air in '89.

 

the Mass air is based off of Air density. The hotwire is cooled therefore the car can increase its a/f mixture for more power. The IAT is what measures air intake temps (and can increase or decrease timing based on these temp readings.) I've never had experience with Speed Density, but I believe HotRod is correct, it is calibrated for a certain setting and each mod has to have it retuned or calibrated.

Mass air cars you can add mods or make changes and the car will normally adjust itself for peak performance. Adding things like n2o or a supercharger still need to have tuning done to the ECU.

 

yeah i had an 86. basically, simple bolt ons are not problem. but once you start moving into head and cams etc with S/D the computer doesnt know that it is now getting more air and fuel. so it cannot adjust to modifications. where mass air measures constantly the temp and amount of air passing the MAF and adjusts everything for you. where S/D you have to make the changes youself. tell him if thats a problem to find an 89-93 car

 

You can convert a speed density car to mass air for about $200 these days, if you shop carefully. You'll need a new computer, mass air meter, wiring harness, bracket, and some ducting.

 

SD systems are mapped with the understanding that at X manifold pressure and Y air tempurature with the throttle open Z amount, the volume of air moving through the engine should be this much since it cannot physically measure how much air is actually moving through the engine, The only clue it has is when the 02 sensor says that it is to lean or to rich.

 

yea my 88 dosent have mass and it stinks.... i just dont have the money for a 600 dollar converstion kit... and i cant go to the junkyard and pull one because I dont know what to pull... any help?

 

Tech Article on speed density (SD) vs mass air (MAF). I'm in the process of converting my 87 vert over to MAF. I dont have any immediate plans on major engine mods, but I do want to see what "extra" I get out of the engine. If your friend plans on adding NOS, he might want to keep the SD....
Lots of info out there on the subject. The Search function on most forums can be your friend.....

 

As Ember said If you shop carefully. You can bid on a MAF meter, bracket, and ducting . An A9P computer or an A9L. (A9P is what most people are after.) And a MAF conversion harness. Make sure the MAF meter is correct for the size injectors you are using; 19# or 24#.

Tech article 1 and Tech article 2 for mass air conversion.

I would suggest spending the extra $$ for the conversion harness to the MAF meter. I posted earlier about where to purchase a couple of EEC pins to complete a partial harness...... :notnice: ....its was a no-go.

 

If you're mechanically enclined it can be a lot cheaper. all you would need is the MAF meter, (with about 6 inches of harness on it), computer, and a schematic for a mass air car and you can wire it up yourself.

 

I just finished the conversion from SD to MAF. The tech articles listed above were a HUGE help in the process.
I spent the extra $$ for the mass air conversion harness, instead of building one. (I had difficulty finding 5 EEC pins to build a harness, and spring is fast approaching... . I wanted it done and back on the road.)

The hardest part for me was getting the computer back up into the plastic hold-down and re-attaching it's harness with the additional wires. Ford did not provide a whole lot of room for hands and arms up alongside the heater/blower box..... :notnice: .

Anyway, the conversion went without a hitch, so far. Haven't had it back on the road yet, but I must say that the car starts easier and idles better.