T-leg Piggyback ECU R&D

[BAC5.2]

Well, I will be running something functionally similar to the UTEC. A piggyback capable of timing, boost, and fuel control.

[vrg3]

I dunno... you might have a hard time using a piggyback without modifying the ECU as well. It all depends on how the piggyback works, I guess.

[jake15]

so what car would i look at to get a MAF that flows 235-245 grams per second? and what kind of wiring stuff would have to be done to make it work?

[vrg3]

Wait, why would 235-245 grams per second be a good peak measurement?

[-K-]

Did I do my math wrong?

[vrg3]

What math did you do?

[-K-]

Well here goes.

Stock 370cc/200g min =1.85 cc per g min
440cc/237g min =1.856 cc per g min

Got any other ideas of how to scale the MAF to injectors?
If you could map MAF voltage and injector duty cycle you would be able to make a better guess. Thats what mine is, a good guess. I could maybe bore out the MAF housing to get X amount more air at the same voltage.

I'm not even sure if I'll even run out my stock injectors before I get the power I want out of my car.

[vrg3]

Oh, I see. So it in principle give you better fuel mixtures at full scale.

Note that you'd still run rich at lower airflows. A MAF that tops out at 200 g/s and a MAF that tops out at 237 g/s would behave almost identically at most airflows.

I think your idea of boring the MAF sensor housing out a little is probably the most straightforward way for you to get a little more range from the sensor.

[-K-]

I think it would put it close enough that the ECU could trim during normal driving.

Range is the big thing to me. About how much HP is 200g sec of air?
So what % increase of airflow do you think would run 440cc's well?

[vrg3]

One gram per second is very roughly one horsepower's worth of air.

It seems to me that you'd want to increase the airflow by the same fraction you're increasing fuel flow. Something like a 20% increase, then, right?

A 20% increase in cross sectional area translates to something like a 10% increase in radius. Hmm. I don't know if there's enough material to remove from the housing. Maybe you could make your own larger housing, though, and just install the element. The Hitachi sensors have removable elements.

[boostjunkie]

While we're on the topic of larger housings... does it REALLY make that much difference to locate the sensor dead-center within the housing? I've been told yes, but I'm having trouble figuring out how the reading would be altered from locating it slightly off the center.

[vrg3]

You got me. Without knowing anything about the fluid dynamics of the air going through the sensor I couldn't say.

[evolutionmovement]

Doesn't the ECU use the MAF size to calculate air flow? If you bore it out how is the ECU going to know or are you talking about aftermarket ECU and then how do you accurately measure the new airflow capacity?

Steve

[vrg3]

He's talking about tricking the ECU "on both ends," so to speak. Skew the airflow signal on the input side (by boring out the sensor), and skew the fueling on the output side (by using bigger injectors), and try to make them match up.

[IronMonkeyL255]

Trying to make two wrongs make a right, so to speak.

[vrg3]

Yesh.

[Matt Monson]

I've got a '94 WRX MAF (VRG, that is what you sold me, right?) Does anyone know if it's voltage is any different?

And one comment on something said earlier in this thread. Not only does lean run cause detonation, but a super rich car can also detonate. This could be a problem you run into with these injectors.

BTW,
Are these the yellow tops?

[All_talk]

You may be on to something here… A hot wire anemometer output is actually relative to velocity (fixing temp and pressure), which for a given flow area is directly proportional to mass flow. The velocity profile in a round duct is not even across its diameter, the flow moves faster in the center, it looks something like this.




If the hotwire ventury is center mounted in the EJ22T MAF (its all the way to one side in the older MAF for the EA82T), then moving it to the side would present it with a lower average velocity for the same overall mass flow and would output a lower voltage. If this translation were properly matched with the larger injectors you might be able to preserve stock (or near) fuel output over the stock flow range with more headroom. In fact you could build an adjustable MAF if you created a mechanism to move the hotwire element.

The spoiler here may be the range of the duty cycle that the ECU can output, at idle the MAF would be outputting a lower voltage and you could reach minimum duty cycle at some point above idle, with the larger injectors you would still be rich. But the velocity differential from center to edge is less at lower flows, which will help move the lower end output closer to stock. And remember, injector flow has a nearly linear relationship with fuel pressure, lower fuel pressure might be a fix.

A combination of fuel pressure and MAF adjustment should make it possible to use the stock ECU.

Just thinking out loud
Gary

[vrg3]

Gary - Neat. So maybe you could do this by just fabricating a spacer to go between the MAF sensor element and the housing!

Matt - Well, I don't know what car in particular that sensor came off of, but it is the one used on EJ20Gs. It's also the same one used on many non-turbo US-spec Subarus, including 95-98 Imprezas and Legacies, as well as post-facelift non-turbo BC/BF/BJs. It's funny. A non-turbo 92-94 Legacy has a larger MAF signal range than a turbo from the same year.

I'd like to try hacking the stock EJ22T ECU to correctly use the JECS sensor. I will, one day.

[NICO]

how about just getting some one to reflash your ECU with bigger injectors installed that way its much easyer then messing with your maf sensor and breaking it.

[-K-]

Because you can not reflash it. You can add a chip that has custom lookup maps for the ECU, letting you adjust what you want.

[georryan]

I though MileHi had a way to reflash the ecu. At least he talks about raising the ecu's limit on the psi for the car.

Not trying to hijack the thread, this is way too interesting of a read to do that. So if anyone responds to this keep it short.

[NICO]

sorry K i ment rechip it, my mistake. so if i drop my sti injectors in and get a rechiped chip in, do you think the car will run fine?

would any one want me to start making chips for the turbo legacy and i can send them out to you just for the reason of everyone doing bigger injector up grades?

[Myxalplyx]

sorry K i ment rechip it, my mistake. so if i drop my sti injectors in and get a rechiped chip in, do you think the car will run fine?

would any one want me to start making chips for the turbo legacy and i can send them out to you just for the reason of everyone doing bigger injector up grades?

Why just stop with Legacy's? Do the EA81T and EA82T equipped cars as well. Sorry, I'm getting desperate reading this thread as I'm in the same situation with an RX turbo. I'll shaddup and keep reading. Great thread! Someone from USMB pointed me here.

[jake15]

hopefully i can get the pics of the injectors off of the camera tomorrow. i pulled the 92-94 N/A rails off the intake manifold, cleaned them up a little then dropped the STi injectors into them, but i havent had time to install them in the car. and it looks like thursday of this week or possibly tomorrow may be the install day, but of course, its subject to change. the injectors just dropped right into the rails like they were meant to go there. i also got the STi fuel pressure regulator, which mounts up in the same place but it has a nipple thing coming out of it thats in a different place, but thats only a matter of some longer hose.