Question on MAF vs Speed Density

[mcglsr2]

Okay, after all the turbo books I've read over the years, I came away with a general feeling of "there are two ways, SD and MAF. Both are good in their own ways, for turbos the best way seems to be SD." That was my general feeling, though if you asked me to be specific on why I felt that way I'd have a hard time without going back and re-reading everything - which I occasionally do. At any rate, the things you guys are saying are only making my "gut feel" for SD even stronger. I was considering building a kit car (and still am) with the goal of turbo'ing it - I had decided back in the conceptual stage that SD was my weapon of choice. I've loved the SD on the Shelby (and sometimes hated it, but that's probably more my fault than the setup). I need to do some serious lurking on the STI/Subie forums to see what's up with that. Regarding starting from scratch with an SD system, one would hope that some base maps for the engine already existing. I was looking at using AEM on a Ford 302, so I wasn't too worried about base maps... Regarding MAF, I can see a required re-tune if one were to go to a blow through setup or vice versa. Not sure I want to re-tune (or be forced to) from a lousy CAI. Although, it is what it is, and if that's what it is for Subie's, then I guess so be it.

I don't know if the STI's have a MAP as well. I've downloaded the FSM so I'll look for it as I read through it. And yes, people have put BOVs on there, and I guess momentary pig rich is fine for them. I have no such plans, the stock BPV will do, thank you

---------- Post added at 12:15 AM ---------- Previous post was at 12:14 AM ----------

I think one can get very wild with an 8v and get some terrific drivability in an afternoon with an understanding of how the ECU works.

I am very much inclined to agree

[mcglsr2]

Oh, and another thing I noticed - not really on topic with MAFs and whatnot, but the turbos on the Subie's look like they have the wastegate referenced directly off the cold-side outlet. Boo to that. Another thing I never really understood; I personally prefer to have the wastegate referenced off the intake manifold.

[risen]

Boosted MAF systems usually run a MAP too to get an actual measurement input of intake pressure.

I was actually picking my bro's brain about this since he's my most easily accessed compendium of knowledge outside this site. As far as the blue oval is concerned the cobra's (including the 2010's) are all MAF and only MAF, he couldn't think of one that wasn't going back to the early 2000s. He said the newer ecoboost engines all have both MAP and MAF sensors. He then started to describe WTF is going on with the new 6.7l diesels and lost me.

My parents have an 09 Sti. Perrin stage 1 tune and an intake. Runs real good for 2 mods. Don't know why it requires a re tune after just an intake. That's subi for ya lol. I beat my friends 03 350z 20-110mph with all bolt ons.

Likely because all the maps in the ECU that reference the MAP sensor are all off due to the increased flow from the new intake and/or to actually take adavantge of the intake. A tune can make all the difference. I know I saw huge differences when I set the boost in my CSX to 20PSI, messed with the timing and fuel ever so slightly. Nothing else done other than the cal and OBX and a clutch and that thing will hold a '05 'stang with a tune and an exhaust.

SD is easier to deal with. While it is true that the MAF reads the actual air volume rather than basing it off of an algorithm, they are much more difficult to deal with. The MAF still needs to be re-tuned per mods like intake size and such, since the sensor needs to be able to accommodate for the change in size. And getting this "re-tune" correct tends to be a pain in the butt. I know with the 3" GM MAF on the Talon, it was quite a trip trying to get it to read correctly EVEN with a laptop tunable ECU. The newer stuff is probably easier, of course.

Excuse my relative DSM noobishness (I've owned 2 but only ever had time to fix them, lol). But don't the GM MAFs all require a translator in between for the DSM ecu to read them? I'm under the impression that you can't just hook the GM MAF into the DSM ecu without that box, no?

I did help a friend with a quarterhorse on an EEC-IV upgrade his MAF. As far as I'm concerned changing the MAF couldn't have been more simple. The people who sold him the sensor gave him a table that related the grams (i believe) of air to a voltage reading. This is required for any MAF, think of it like a 2bar/3bar/4bar SD setup. For example you need to know that (for our cars and the most common MAP sensors) 2.5V is atmospheric pressure on a 2 bar, atmosphere is 1.6v for a 3 bar and 1.25 for a 4 bar. We plugged that table in and bang, away the thing went, like it was from the factory. No other changes needed. We did some small tweaks to his timing and WOT fueling AFR targets, but it took less than an afternoon and the thing was good.

I don't know if the STI's have a MAP as well. I've downloaded the FSM so I'll look for it as I read through it. And yes, people have put BOVs on there, and I guess momentary pig rich is fine for them. I have no such plans, the stock BPV will do, thank you [COLOR="Silver"]

But the thing was that the ECU detected the difference between what the MAP was telling it and what the MAF was telling it and didn't snap rich. I stood there and watched it. Now, if he was feeding me a line of BS about not having a tune or anything else done IDK, but both sensors were there and it looked factory-as-could-be and the car wasn't really that fast.



Anyways, my .02 is that it's a pain to tune anything that you don't have complete and total control over. If you're stuck intercepting something like the DSM and the maf translator or piggy-backing your ecu, you're going to have to put up with some level of kludginess and crappy drive-ability. But if you do have everything laid out in front of you say quarterhorse on a eec-iv or any of the ECU code from ShelGame then it's pretty easy to deal with. SD is a little less intimidating to fudge with, IMO since you only have to think about the overall VE number instead of considering the VE and the MAF reading and the total displacement.

PS - I greatly oversimplified that MAP-voltage thing. There's normally a transfer function provided by the manufacturer of the MAP sensor. But the explanation is still relevant.

[thedon809]

Also, if you have even a small vacuum leak with a car that uses a MAF sensor, it will run like crap. At least thats how my talon was.

[turbovanman²]

I just picked up the new Import Tuner, they did a CAI, cat back and cat delete on an EVO, no retune, made some good improvements.

Also, if you have even a small vacuum leak with a car that uses a MAF sensor, it will run like crap. At least thats how my talon was.

Ditto with SD,

[BadAssPerformance]

I was actually picking my bro's brain about this since he's my most easily accessed compendium of knowledge outside this site. As far as the blue oval is concerned the cobra's (including the 2010's) are all MAF and only MAF, he couldn't think of one that wasn't going back to the early 2000s. He said the newer ecoboost engines all have both MAP and MAF sensors. He then started to describe WTF is going on with the new 6.7l diesels and lost me..

Ford has been MAF on mustangs since 1989. It used to be the hot ticket if you had an 87 or 88 to convert it to MAF. Then Paxton, Vortech, ATI blowers came along. The MAF could be tuned to work ok up to 15psi but after that or with a turbo, most switched back to 88 SD systems. LOL!