if mass air is so great then why.........
 

Im getting closer and closer to building my 78 351EFI Twin Turbo Fairmont. I keep reading that mass air is the way to go. The car has an 86 5.0 mustang body harness, so it would be super easy to use a Mass air engine harness. But the real question is if Mass air is so great then why do most of the aftermarket EFI companies utilize a speed density setup? SDS, Speed-Pro, DFI, they're all based on a speed density setup. Each of them seem realtively easy to tune and work with, so what gives? THANKS

It is not the same as speed density it is far better then speed density. And better than Mass air. because there in no mass air unit to hurt air flow

Hmmm.

Unless its Alpha N, or Mass air, its pretty much speed density?

Alpha N is the dumbed down version of fuel injection, Usually its just throttle position and RPM, with maybe manifold vaccum(?). Pretty simple stuff.

A notch up the scale is Speed Density, in the case of the Fel-pro unit, Electromotive, ect. whatever, you program in the fuel and spark tables which are optimized for each individual application. the draw back (if any), A/F ratio is trimmed after reading the O2 sensors.

Problem with most Mass-Air, they are pretty much factory based systems which means limited resolution.

If somebody would come out with an increased resolution Mass-air system it would probably rock since mass-air measures actual air entering the engine

MAF is setup very much detuned from the factory. It's also much more expensive than speed density. Speed density works great when it's programmed with the proper parameters.

The aftermarket systems like DFI use if/then situations. Like "if there is this much load on engine then it tells the injectors to perform a predetermined task. That's really oversimplifing. The factory systems can be reprogrammed with chips, but cannot be changed or tuned on-the-fly. DFI is supposed to only use the o2 sensor while tuning it(closed loop) and when done you are supposed to use the if/then tables, which are very detailed and quite hard to fine tune on your own unless you are an automotive engineer.

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65 fastback
347 DFI injected, TFS heads, T5, 4.11 9", tc subframe conns, torq thrust D's
A little history lesson using today's tech.

its cheaper and simplier, and serves the purpose at hand. Speed density has its place, as well as mass-air.



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1993 GT/AOD
'93 Mustang GT

Just as a side note, I recently read that Saleen's new super-car (the S7 I think?) uses a speed-density engine management system.

E

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1991 5.0 LX Coupe - 38,000 miles

13.17 @ 106.14 mph w/ 2.138 60'

Speed density is cheaper to set up and easier to tune if you can reprogram the computer. GM switched back to Speed density for a while on the TPI and LT-1 motors. For a stock car all the airflow parameters can be pre-calculated, thus no real need for the Mass air measurments.

Even a stock Mass air can compensate for a supercharger etc, much harder for a stock speed density.

Aftermarket systems that are speed denisty allow more adjustablitly, some custom setups have no space for a MAF meter etc...

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Frank W
90 5.0 LX coupe Daily driver. K&N filter. Flexalite fan, 3 core radiator. FMS flywheel and Clutch, FMS blue wires Energy Suspension end links, MAC 2.5" cat back FMS aluminum driveshaft, MSD blaster coil, MAC shifter
88 Notch 2.3L FOR SALE! My two Notchbacks

74 Chevy Laguna Type S-3 305 Finally fixed getting a 454 to put in garage
<A HREF="http://www.chevellepages.com/f

Your setup isn't going to run right unless you get a chip for you computer, I'm not even sure if people do that with a stock SD setup. The stock 86 computer is designed for a mild 302, hence it will run really bad with a tt351. I would go with MAF, A9L, EEC-Tuner if it is going to be a street car, if its a race car I would consider the EPEC, DFI, or the Speed Pro setup. Yeh at elevated hp levels the MAF becomes a restriction, but its benefits on a street car far outway the restriction.

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89'notch

331ci Scat Stroker, Stage II Holley heads, ported Holley Systemax Intake, 70mm Holley TB, 50lb Holley Fuel Injectors, 80mm Pro-m MAF, AFM B-3 cam, Vortech S-trim Supercharger, AFM Powerpipe, EEC-Tuner, TKO, Koni, Eibach, HPM, etc...

Beaten Daily..

http://lowkey.stangnet.com

MAF can compensate for forced induction, but then you need to add a bigger MAF which puts SD and MAF on more equal price ground when modding like that.

SD computers are routinely run on custom chips.

Also MAF won't run worth **** if at all with the wrong injectors. Say 24lbers on a 19lb MAF, but SD will work fine with 24s.

Like was pointed out, SD and MAF both have their positives and negatives, but for a really wigged out engine like you are talking about building, I would go with MAF.

[This message has been edited by Unit 5302 (edited 10-12-2001).]