Speed Density Or Mas Air What's The Benifits?

Discussion in 'Fox 5.0 Mustang Tech' started by 1200gt, Sep 19, 2013.

  1. I am still speed density for the moment with my 86GT, but was thinking about some of the electrical issues some folks seem to have with wire continuity and such; I was wondering if its worth converting my car over to Mas Air?

    I think I can't do upgrades like heads etc.

    Also, I was reading a few threads about the MSD 6AL and distributor stuff. I have a new 6AL that I was going to install in the future and have a pending sale on a MSD Pro Billet Distributor.... just thinking what I should do on all these account...
  2. speed density can take mods.. they just cant reduce vacuum signal to far.. im at the limit.. i have trick flow track heat heads, comp cam XE264hr-14, and some 1.72 scorpion roller rockers..

    only pull about 13" of vacuum.. stock is 18-20ish.. i have surging issues a lil at idle. worse in gear than park..

    but you cant really do much more than i have on factory tune SD.. most aftermarket systems anymore are speed density, due to the simplicity and quick calculations the pcm can make based off vacuum..
  3. Installing the MSD stuff won't affect your speed density at all....but I have to ask, why do you want to? You don't need the MSD junk. Stick with the stock stuff. It's proven more reliable than any of the aftermarket stuff and quite frankly, you don't need it until you start making bigger power levels, forced induction, etc.

    FWIW...I have a Mass Air car, with a host of mods and my MAF system is having trouble keeping up. So don't think converting to MAF is going to necessarily be the cure to your woes. I say....start bolting things on and keep the money aside for the conversion. If you need it, you need it. If you don't, you don't. It's that simple.
  4. Don't fear the SD. I ran the following on a SD setup on my 87

    1.7 RR
    Vortech A trim
    and the other usual stuff
    crane cam 2031

    Unless you get way radical in a cam you'll be fine. I ended up swapping to MAF when I upgraded to an S trim and a larger cam, and got a tune.

    And you already know what to do with that POS MSD distributor.

  5. OK, the MSD distributor purchase is Dead!:dammit: I liked that shinny piece of Sh*#!

    Holly Canolabar! I have to admit, my mind is still stuck in the nineties on Mass Air Conversion Mod . Bear with me, I'm just trying to get back up to speed, and finally, after 15yrs. completing my build! Back when I was gathering up all my parts , like A9L and 75mm Mass Air Meter and the wiring kit and on and on. Everyone was converting over. Do you mean that was all hype too?

    These are some of the parts I already have:

    1. Stock 86 block with 45K - that I am pulling out to install a another motor that I plan to have built. IDK what I will do, 306, 331 or just put stock pistons in it...

    2. AFR 165 heads - new

    3. GT40 Tubular upper and lower intake

    4. Cam - I like something like a Bcam or Maybe the Ecam

    5. Roller Rockers - 1.6

    6. 75mm Pro-M Mass Air

    7. 75mm Throttle Body - Accufab

    8. Cold Air Kit - I think it was BBK

    9. Long Tube BBK Headers & OR X-Pipe

    10. Some model of Flow Master mufflers

    All of the above, I was planning on running thru my A9L / Mass Air Conversion.
  6. I'll assume you're going to jump up the injectors to something in the 24-30lb/hr range as well? Speaking from experience, I'll tell ya....It'll run and run ok, but it won't be perfect. A Mass Air conversion will give you a wider margin or error to work with over the stock SD, but don't expect it to be perfect.

    My car runs ok and for the most part drives fine, but It's pretty rich at idle. It surges erratically one moment and starts and idles fine the next, it's pretty rough running and really likes to buck until it warms up and is still jerky at anything under 1,500RPM when it does. The only codes I'm getting are a 94 and a 44 because of the smog pump delete. Otherwise, nothing is showing up.

    Quite frankly, I'm convinced it's the nature of the beast and the only way I'm going to fix these nuisance points will be to have the ECU reprogrammed to reset my base parameters up to match my new combo.
  7. Here's the technical description of the differences between Speed Density and Mass Air...

    Speed Density uses Manifold vacuum (MAP), Throttle position (TPS) and RPM, & Air Temperature (ACT) to guess how much air the engine is pulling in. Then it uses all of them plus the O2 and ECT sensors to calculate the air/fuel mixture. It is dependent on steady manifold vacuum and minimal changes in airflow from the stock engine configuration to maintain the proper air/fuel ratio. Change the airflow or vacuum too much and the computer can't compensate for the changes, and does not run well. Forget about putting a supercharger, turbocharger or monster stroker crank in a Speed Density engine, because the stock computer tune won’t handle it. Every time you seriously change the airflow through the engine, you need a new custom burned chip to make the engine run at peak performance.

    Mass Air uses a Mass Air Flow meter (MAF) to actually measure how much air is being pulled into the engine. The computer uses this information and inputs from the O2, TPS, ACT, ECT, RPM and Barometric Pressure (Baro) sensors to calculate the proper air/fuel ratio. It is very tolerant of changes in airflow and vacuum and tolerates wild cams, high flowing heads, and changes in displacement with minimal difficulties. Larger injectors can be used with an aftermarket calibrated MAF or a custom dyno tune. This makes it possible to use the stock computer with engine displacements from 302-408 cu in, and make many modifications without a custom dyno tune chip. Put a new intake manifold on your 331 stroker and the computer figures out how much more fuel to deliver without having to have a new chip burned to accommodate the extra airflow.
    Rammer12 likes this.
  8. I agree. Sounds like it's all in the tune to me. There are tables for all of the things you mentioned.
  9. How tolerant do you think the system is though jrichker. As I said, I'm having some pretty annoying drivability issues with my stroker set up and the only two codes I'm getting are related to the AIR injection system (44 & 94) that has since been removed. Otherwise, KOEO, KOER and cylinder balance test all came up passed. I'm running a highly regarded Pro-M 80mm MAF unit inside my fender well, calibrated to a set of 30lb/hr injectors. I've got brand new O2 sensors (NAPA brand....but still new, regardless). Doesn't seem to reveal any vacuum issues either.

    My TPS seems to operate smoothly (according to my DVM) and my IAC is clean too.

    I pulled the salt and pepper shakers apart, made sure the area was clean, worked the pins over to ensure good contact and have it back together.
    I replaced the Coolant Temperature Sensor with another unit I had laying around and I still have issues.

    Yet, it runs rich down low and has low speed drivability issues when cold....and even to some degree when warm.

    So....if it isn't a mater of ECU tuning, have you got any guesses?

    And this is where I'm at. I have not had the car in for a tune as of yet. I was hoping the stock ECU would be able to compensate for the changes made, but it doesn't seem so?
  10. Richker:
    I get it! J, base on your information, and the planned mods that I have lined up, I think its better to move forward with Mass Air conversation. I have all the parts anyway....

    I forgot to list the Injectors: I have a set of 24lb. units. But I plane to look at a chart that Jrichker put out a while back that kinda gives me a parameter for what injectors best fit my final combo - from what I have seen in the past - the not scientific method of choosing injectors, is that everyone running mild heads and cam bolt-ons just went with 24s.

    Gearbanger, why haven't you just gone Mass Air? Based on my understanding of Richker explanation of the workings of the two methods, it appears that you may benefit from a conversion.... You said you are at time down to 13" of vacuum. This appears to be were the speed density setup can't keep up.

    EDIT: Sorry Gearbanger that wasn't you with the low vacuum readings...

    I guess what I wrote above about gearbanger, him benefiting from a MAF conversion setup, would better be addressed to your setup.

    Can you talk more about most aftermarket systems that are speed density - maybe understanding one of the systems you speak of will give me an even deeper understanding of the differences.
    #10 1200gt, Sep 19, 2013
    Last edited by a moderator: Sep 19, 2013

  11. My car is Mass Air.
  12. A cheapo trick is to clock the MAF to see if it makes any improvement. Change the angle of rotation in 45 degree increments and see if that helps...
  13. That was going to be my next move. I assumed the airflow at idle would have been straight enough, as I'm using an Anderson Power Pipe, which comes with that generous, long sweeping elbow at the MAF meter, instead of the narrow, tight turn unit you see on kits like BBK.

    Looks like I'm pulling the front fender off tomorrow. Guess I'll give me an excuse to start my wire hiding project whil I'm at it. ;)

  14. Dwayne,
    If you get the SD tuned, then you'll be fine with your setup. The SD has limitations as everything is preprogrammed in the ECU and with no MAF, no availability to adjust itself if the variances get too much out of bounds. Hence, if you get a chip or a tune, your ECU will now know what parameters to expect for your setup. Many aftermarket stand alone setups are actually SD as believe it or not causes less problems once you have it dialed in. I had Chris Johnson burn me a "switch chip" back in the day that had two different programs- a street and a race setting- all I had to do was flip a switch on a circuit board in my glove box. I'm sure the new ones are far more advanced now. Hell I ran a HCI and a Vortech on SD and the car idled and ran without a hiccup. The only thing I would say is don't get too aggressive on the cam or you will run into problems. Crane used to make a SD specific cam that I ran, which if I remember was similar to the B or E cam in specs?

    If you want the flexibility and ability to grow , then it won't hurt to swap to mass air, but then you'll probably want tune anyway?
  15. @Gearbanger 101

    30# injectors are about at the limit of what the OEM tune can handle without too much difficulty. It's really hit or miss. Injector minimums and slope start to become an issue at 30# and higher.

    It sounds like that's exactly what you're seeing in symptoms. Even though your MAF is "calibrated" for an A9L and 30 lb injectors, the EEC doesn't know that you have 30# injectors. That results in the EEC commanding an injector minimum that is ABOVE what a 30# injector is capable of. This is why you're running rich down low and have driveability issues at low RPM.

    Once your engine combo starts ingesting enough air to match EEC's perceived injector minimum, then this isn't an issue anymore. The only way to REALLY fix this is a tune that modifies to EEC to operate the injectors at the new minimum pulse width of the 30# injectors. The other thing that you can try (yeah, it's a bandaid but often works) is to reduce your fuel pressure below stock values. Try this at 2 lb intervals with vac off. If this works, then it confirms what I think is your issue.
  16. I agree, the only way you get it to run the best is with a tune that includes street driving not just peak hp and tq numbers. Can prob be done just as easy with sd..

    Sent from my iPhone using Tapatalk
  17. I was throwing around the idea of knocking a couple of PSI out of the fuel pressure. Hopefully that'll work. Otherwise, it's tune time. Called the shop I had my last car done at and it's got me wondering if I should forgo the dyno and try tuning it myself with one of the methods out there (Anderson PMS, Megasquirt, Moats, etc)

    They want $500 for the dyno time and $400 for the chip. :eek:

    That's a heck of lot for a one time tune. Had me looking into one of the others described above...but that's whole other ball of wax.

    Anderson PMS....easiest to use, but most expensive
    Megasquirt....more features than the PMS and cheaper....but tougher to use and you have to build it yourself.
    Moats Quarterhorse.....cheapest out of the three, but I'm told you have to be an IT Tech to work the damn thing. :(

  18. Don't forget the AFR meter if you don't have one.
  19. Damn.... $900 for a tune? Like you said, for less than that you can get a MegaSquirt, an A/F bung for the exhaust and A/F gauge and have at it. The PMS is more expensive but more user friendly. I'd look for a used PMS ... Wish you were local. I could recommend a few places to bring the car for a tune.

    Have you considered a *gasp* mail order tune from Dirty Dog or JMS/SCT?

  20. dislike :notnice:
    FastDriver likes this.