Mass Air vs Speed Density

RacerXGT · May 10, 2004

A little background here first. Im 33 and have been working on cars since I was 14. Everything Ive ever dealt with has been GM. Im a huge Pontiac Trans Am fan. I never owned a ford period until 2 months ago when I bought my 87 GT. I was loseing the lust for cars, and I thought a complete change of pace would shake me out of it. It has. I love the GT.

Now to my question. Through reading and so fourth its very evident that the Fords adapt much better to mods when useing mass air compared to speed density. The opposite is the case with GM's. The f-bodies started out as mass air and moved to speed density. Speed density is more adaptable to mods with GM's. Now the question.... does anyone here know why this is the case? Why does the ford like mass air while the gm likes speed density?

I know its not a very important question but for some reason its stuck in my mind.

5.0Droptop · May 10, 2004

www.50tech.com is the Ford SD guru site.

5.0Droptop · May 10, 2004

with ford SD the differnce is in how the eec reads the air coming into the motor and how it adapts to the changes. The ford EEC reads vacume at the map sensor and reads the 02 sensors and uses a preset table to adjust fuel. You can do heads cams intakes etc wih ford sd but you must be careful when you choose your cam with sd because of the preprogrammed tables you cannot get to rowdy with the cam or it will surge and run rich at low rpm and run lean up top. most guys who add a cam do it for the rowdy lope at idel and sd dosent like this.

88stangmangt · May 10, 2004

RacerXGT said:
Through reading and so fourth its very evident that the Fords adapt much better to mods when useing mass air compared to speed density

thats not always true there are some very nasty sd cars out there you can run big heads decent cam nice intake and a blower.

RacerXGT · May 10, 2004

thats not always true there are some very nasty sd cars out there you can run big heads decent cam nice intake and a blower.

does this mean if a s/c is in my plans that it would be in my best interest to stay sd?

ill check out that site also for some more info. thanks for the link.

88stangmangt · May 10, 2004

if just a s/c is in your plans i wouldnt bother with mass air. just get the blower i have tons of pics on my site of my re-build process and my blower and all the rest of my good junk.you could always also get a nice custom s/d cam from flowtech if you wanted to build your motor but are scared of s/d due to the cam limitations.

RacerXGT · May 10, 2004

thanks for the info...

pony gt · Mar 18, 2006

with ford SD the differnce is in how the eec reads the air coming into the motor and how it adapts to the changes. The ford EEC reads vacume at the map sensor and reads the 02 sensors and uses a preset table to adjust fuel. You can do heads cams intakes etc wih ford sd but you must be careful when you choose your cam with sd because of the preprogrammed tables you cannot get to rowdy with the cam or it will surge and run rich at low rpm and run lean up top. most guys who add a cam do it for the rowdy lope at idel and sd dosent like this.

I have an 87 with exactly this problem can i fix it with what i have....it has a .560 lift cam thats about all i know about it i bought it like that. or do i need to convert to mass air

i have exactly that problem, is it fixable or do i have to convert to mass air??

Tonys96Cobra · Mar 18, 2006

I guess you guys all copy and paste from the same place

DMAN302 · Mar 18, 2006

pony gt said:
with ford SD the differnce is in how the eec reads the air coming into the motor and how it adapts to the changes. The ford EEC reads vacume at the map sensor and reads the 02 sensors and uses a preset table to adjust fuel. You can do heads cams intakes etc wih ford sd but you must be careful when you choose your cam with sd because of the preprogrammed tables you cannot get to rowdy with the cam or it will surge and run rich at low rpm and run lean up top. most guys who add a cam do it for the rowdy lope at idel and sd dosent like this.

I have an 87 with exactly this problem can i fix it with what i have....it has a .560 lift cam thats about all i know about it i bought it like that. or do i need to convert to mass air

All you know is you have a cam with that lift? what about the rest of the car?What heads? I hope not the stock springs with that lift.

srothfuss · Mar 18, 2006

Fords version of SD uses a pre-programed system for fuel delivery based on vacuum. As long as you don't screw up the vacuum too much, the SD cars can be just as friendly to mod as MAF cars.

Heads
Intakes
bolt on
Super Chargers

all can be added without any issues. The cam is where you have to be carefull. As the other posters listed, there are some SD friendly cams out there but I don't know them off the top of my head.

BTW: The '87 cam is slightly more aggressive than any of the other years. www.mustanggt.org

seijirou · Mar 18, 2006

Ford SD is just very ridgid. For idle quality you have to have a cam that still pulls reasonable vacuum. When vacuum drops enough the eec assumes the throttle is being opened even if the tps doesn't show this. It adds fuel, car runs rich and like crap.
In an N/A car and a big cam like that, your limited by the factory maps. Vacuum drops to basically 0 at WOT, the O2 sensors are ignored at WOT, and the computer is basically running of a table. A table designed around stock stuff. If you're breathing more air, you're going lean. Doing the paperclip jumper to put the eec into diagnostic mode actually helps this because will actually look at the sensor inputs and try to correct the a/f ratio even at WOT. Even then however you're limited to the 19 pound injectors unless you _really_ know your stuff.

Going blower makes life a whole lot easier because of boost indexed fuel pressure regulators. You can get the extra fuel mechanically even when the computer's tune isn't correct.

troyGT03 · Mar 18, 2006

an stock sd car vs a stock mass air car= sd car is faster. all mods are no prob with sd. the cam duration is the breaking point due to vacuum changes. add heads,intake, charger, etc and it works great. it is still the old system so you can adjust with timing and fuel pressure adjustments. i kind of like the speed density simplicity. Going blower makes life a whole lot easier because of boost indexed fuel pressure regulators. You can get the extra fuel mechanically even when the computer's tune isn't correct.
__________________the sd cars actually run very smooth with a blower. you have to remember that paxton(sn89) and vortech used these cars to develop their blowers.

troyGT03 · Mar 18, 2006

i am running sd currently. see sig. the best sd cam to get is the crower 15511. it stays within spec for sd and vac stays good. 50tech.com is the place for sd setups.

seijirou · Mar 18, 2006

troyGT03 said:
a
__________________the sd cars actually run very smooth with a blower. you have to remember that paxton(sn89) and vortech used these cars to develop their blowers.

That's what I'm saying. Blowers make it alot easier to get the power out of a SD car because SD and blowers work so happily together. Trying to get the same power N/A with SD is alot more difficult compared to getting that power N/A with MAF.

FastDriver · Mar 18, 2006

troyGT03 said:
an stock sd car vs a stock mass air car= sd car is faster.

Yes, but why? The stock MAF was smaller than the stock TB. If I get a bigger MAF (say a 75mm, would my MAF 5.0 perform as well as the SD car? Is there something inherently different about the air/fuel curves that makes the SD car more powerful?

Chris

Daggar · Mar 19, 2006

seijirou said:
Ford SD is just very ridgid.

So very true. Wish I had a dollar for everytime I've tried to explain this to folks. Ford saw there way to effectively remove the inhearant versatility of speed density when they built this system. At first, I thought was an emissions thing and that the restrictions they'd put on it were the result of that. Come to find out, that wasn't it at all. Even the Holley race systems are tunable to much tigher tolerances. I suppose we just have to chock it up 70's technology being pulled off the shelf and dusted of for the purpose of the 86-88s.

FastDriver said:
Yes, but why? The stock MAF was smaller than the stock TB. If I get a bigger MAF (say a 75mm, would my MAF 5.0 perform as well as the SD car?
Chris

The point is that once you've done that, it's no longer stock anymore. hehe Seriously though... the SD cam's were a hair more aggresive than the later MAF cams.

RED = additional comment

seijirou said:
Trying to get the same power N/A with FORD SD is alot more difficult compared to getting that power N/A with MAF.

seijirou · Mar 19, 2006

Ah, good call Daggar, I should have been more specific.

IntenseBlue · Mar 19, 2006

SD cars, from what I've read, have slightly larger cams with faster ramp rates, no restriction in the inlet system (aka maf, no matter what size), and they also have more aggresive spark/fuel maps in the ecu.

Daggar · Mar 19, 2006

I'm already way too deep into current project to look back now but in the future (hopefully near future) I'll be looking to run something similar to this:

Commander 950 Multi-Port Fuel Injection System
94106211
Multi-Port Fuel Injection System 575-670 HP with 42lb/hr Injectors and Wideband Oxygen Sensor

Had I known that this existed and that it was what it was a few months ago, I would have opted for it, instead of the mass air conversion that I put together. They have other kits as well that are broken down into more basic systems. So if you didn't need the manifolds (or whatever) then you could purchase the kit with just those parts you needed. It's roughly $1300 (you figure a good meter is $400+ and a custom chip is $500+) for the ECU and all wiring, etc. With something like this, you can run whatever cam you like on SD.

Mass Air vs Speed Density

RacerXGT

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