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2005 FXT
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174 Posts
Discussion Starter #1
Really surprised there are 0 threads here that discuss speed density tuning in lieu of a MAF sensor.

I just received a Perrin 4-bar MAP sensor as a prerequisite for upgrading to a larger turbo, so I figure it’s time to get the ball rolling on switching to a speed density setup.

For now, I’ll collect references and use the second post for storing them. Third post will be for my current progress.

Then I’ll attempt to document my progress as I learn and go through getting it working on a 2005 FXT 4EAT (USDM), hopefully evolving this first post into something of a quick & dirty guide for implementation that can be applied to other years.

If anyone has information or references to share, please do so. I’ll be using OS tools (EcuFlash & RomRaider) and not a Cobb AP.
 

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2005 FXT
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174 Posts
Discussion Starter #3 (Edited)
Progress
Perrin 4-bar MAP sensor (PSP-SEN-100) received.

Needed table changes...

Manifold Pressure Sensor Scaling:
Offset - 0.174 PSIa (.012 BAR)
Multiplier - 12.082 PSIa/V (.833 BAR/V)

Manifold Pressure Sensor Limits (CEL):
High Input CEL Above - 4.88V
Low Input CEL Below - 0.08V

Done and installed.
 

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2001 Forester STi 6spd with MapDCCD
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4,641 Posts
@Burkwerst Well worth it, but it is a more time consuming thing. It takes allot of the 'wiggle' room out that you get with MAF tuning certain setups. There is more time needed to hone in certain areas, but the inputs are quite direct and precise when your trying to achieve a target.
 

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2004 XT 5 MT
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13 Posts
@MikeDrives1 are you 100% SD or are you doing blended/hybrid MAF/SD? I like the idea of MAF for closed loop and SD for open. Did you relocate your AIT? I have read that moving it closer to the intake yields the best results. I am wondering if the massive seasonal weather changes in MI (-10 -> 100 degrees) would cause drive-ability issues at the extremes.
 

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Registered
2001 Forester STi 6spd with MapDCCD
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4,641 Posts
@MikeDrives1 are you 100% SD or are you doing blended/hybrid MAF/SD? I like the idea of MAF for closed loop and SD for open. Did you relocate your AIT? I have read that moving it closer to the intake yields the best results. I am wondering if the massive seasonal weather changes in MI (-10 -> 100 degrees) would cause drive-ability issues at the extremes.
Yep, 100%. I have done a blend for certain clients, but i prefer to go all SD. Yes, you basically HAVE to relocate the IAT close to the throttle for it to be tuned precisely, otherwise the thing will work funny when heat soaked because the MAF sensor location isnt a good representation of post-intercooler air temps. Pre-intercooler temps will almost always stick around ambient with a few degrees of heatsoak tacked in. Post intercooler temps are needed for accuracy. For top mounts you want the IAT in the base of the intercooler, usually to the left side of the throttle body, opposite your BPV flange, is the accepted area. For FMIC and piping, you want it a few inches back from the throttle in that last charge pipe. There are those who have dabbled in putting it into the intake manifold itself, but i have not tried myself, nor do i think its a good idea for getting an accurate representation of air temp.

Yes, weather changes DO affect it, but once you have dialed it in for each using just the temp compensation table, you are golden. Result is a perfect AF target that hits no matter the weather. Its not as drastic of an effect as you think, but its enough to need a few tweaks. Absolute best thing you can do besides moving the IAT to the proper place is to get your wideband's analog signal wired to a TGV voltage signal, allowing you to log it, and depending on model, convert it with COBBs custom file to convert itself already.
If not, the voltage equation is (TGV voltage signal X 2) + 10 which will take a 0-5 volt signal and translate it into the better known 10 to 20 AFR reading. This will make adjustments for WOT (and anything else) in the SD table SUPER accurate when you lay it all out in a log. Unlike MAF where it kind of just pegs on a few cells of voltage that you adjust, the VE changes as RPMs rise and AF will wander a bit, so having that ability to log and review it gives you the opportunity to perfect the AF output every few hundred RPM.
 

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2005 FXT
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174 Posts
Discussion Starter #8
@MikeDrives1

Never was able to find anyone willing to add SD functionality to the ‘05 FXT ECM, so I’m going to look for an STi ECM. Probably an ‘05 but open to suggestions.
 

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2007 Forester XT Manual
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287 Posts
I’m running speed density, but my tuner at theshopct did the tuning. Using a blouch 1.5xtr. It makes the engine run a lot smoother and I’m able to have more control of parameters. It’s on the pricey side, but well worth it. I’d find a tuner that knows about it and has installed a few to really benefit your setup. I still have the AFM but only for emissions. Basically what I do is swap the intake, plug in sensor, and change the map. After I pass emission/inspection switch it back to SD
 

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2005 FXT
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174 Posts
Discussion Starter #10
I’m self tuning using RR & flashing with EcuFlash; hence the need for a definition with SD. It looks like the easiest path would be an STi ECM, but since STis don’t use 4EATs, I might be out of luck there, too.

I’ve already tried AP and hated it, so no need to bring that up as an option. Guess I’ll try the RR forum again.
 

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2001 Forester STi 6spd with MapDCCD
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4,641 Posts
I’m self tuning using RR & flashing with EcuFlash; hence the need for a definition with SD. It looks like the easiest path would be an STi ECM, but since STis don’t use 4EATs, I might be out of luck there, too.

I’ve already tried AP and hated it, so no need to bring that up as an option. Guess I’ll try the RR forum again.
Im fairly certain the COBB accessport provides Speed Density for the FXT ECU's state-side in the US, but i know there is trouble getting support for this in the EDM, JDM and AUDM fields.
 
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