Speed density

[93_tsi_fwd]

I going to run speed density and have 1 concern on where to put the vacuum line.

I dont want to take out my intake manifold and drill and tap on the suggested location but can i just hook it up to the PCV valve location on the IM and just run the PCV valve to a catch can?

Has anyone done it like this? If so, how did it go?

 

[DSM_munky_man]

No help on my part, but I was wondering the same thing.

 

[BrokenTsi]

You can do that. Just use a short vacuum line.

Right now, I have it bolted directly to my intake manifold. (Jmfab) I didn't have to take the manifold off to do it. Im going to switch to a 12" -4an line and mount it on the firewall.

Magnus told me that they prefer to run a shorter line and not run it directly on the intake manifold because vibrations can kill the sensor. Makes sense.

I dont see a problem mounting it remotely with a short line.

 

[DSM_munky_man]

ecmlink recomends 6-8" max for map signal. the longer it is the more delay from when it gets signal thus making your throttle response slower. Not saying that 12" may make that much of a difference, but just something to think about.

 

[93_tsi_fwd]

cool. thanks for the quick reply.

 

[BrokenTsi]

ecmlink recomends 6-8" max for map signal. the longer it is the more delay from when it gets signal thus making your throttle response slower. Not saying that 12" may make that much of a difference, but just something to think about.

Ya, shorter would be better. Only one way to find out really. Its tough to only use 6" of line unless you mount the map sensor way down low on the firewall...that is...if you have a SMIM with the ports on the bottom. Either way, it should work fine.

 

[Calan]

The problem with using a line is that besides the flex in the hose, air is compressible. It varies a lot, but you may see a choppy MAP signal due to the flex in the hose and the air inside it compressing and expanding as the pressure changes.

Going as short as possible with the line minimizes these effects, but they are still there to some degree.

 

[BrokenTsi]

The problem with using a line is that besides the flex in the hose, air is compressible. It varies a lot, but you may see a choppy MAP signal due to the flex in the hose and the air inside it compressing and expanding as the pressure changes.

Going as short as possible with the line minimizes these effects, but they are still there to some degree.

Yeah, thats why I have a SS -4an line to prevent that. Good info. I haven't used it yet, but then I remembered how expensive my AEM 5 bar map sensor is. I've never really heard of them going bad due to engine vibration, but you never know.

 

[snowborder714]

I've had my AEM 5 bar threaded directly into the intake manifold for a while now and it still works just fine. Granted, I have solid front/rear roll stops and Prothane side mounts, so there really isn't much engine movement, but it's still in there directly.

 

[Calan]

I've never really heard of them going bad due to engine vibration, but you never know.

Me either.

IIRC, the 2G MAP sensors are mounted directly to the IM from the factory. And I don't know about you, but most of the high HP cars that I've seen where it would be an issue have pretty solid motor mounts; the firewall vibrates as much as the motor.

Here's where mine is mounted now, right next to the -4AN line for the BOV. The fitting just to the left (originally the brake booster port) is to the meth injection controller:

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[turboglenn]

YOu can tee it into the fuel pressure reg line. two places you NEVER want to "t" into are the BOV and wastegate lines though. the fluctuations in them from their diaphrams and the boost controller will cause erratic running. I've been on SD for about 10-11 years on my DSM. Also, mount it above the intake mani on firewall so condensation cant build and settle down into it.

 

[DSM_munky_man]

I have mine mounted on the bov port. With a short like 3" hose and have the omni 4 bar with a little bolt holding it into one of the holes for that little plastic loom cover.

 

[9!'clipseDOHC]

I'm, sure you guys have probably read this but I'm going to post it here just in case: sdhose [ECMTuning - wiki]. It says that you want to avoid "T's" at all costs, that is the "worst case" scenario.

Here is my Omni 4-bar mounted on the firewall, the vacuum line is 2-3". I know you said you didn't want to drill and tap the manifold, but it is the best option.

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[Calan]

Here is my Omni 4-bar mounted on the firewall

Well technically, it's mounted to the clutch reservoir.

 

[9!'clipseDOHC]

Well technically, it's mounted to the clutch reservoir.

You never let me get away with anything.

 

[DSM_munky_man]

I'll take a picture of mine when I get home, mine has been fine where it is, but only have few hundred miles on it.

 

[Calan]

This got my curiosity up, and I decided to compare logs from before and after I changed to the direct MAP sensor mounting a few weeks ago. (I knew the boost curve was smoother, but I never really compared it in detail). I found a couple of logs with similar boost curves from before and after I changed things around on April 23/24, and they show the results pretty clearly.

Here is the boost curve with the sensor mounted on the firewall with a 6" piece of rigid fuel hose connecting it to the IM:

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And here is a similar pull after mounting the MAP sensor as shown above in post #10:

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Both of these plots have identical display parameters, with the MAP item scaled to show 0 to 40 psi in both.

Notice how the direct-mounted boost curve is much smoother and shows a more accurate representation of what's going on during spool up.

 

[snowborder714]

The other issue (that I was experiencing) is during tip in. My AirflowPerRev and SDAirflowPerRev would not line up, with the SDAirflowPerRev being behind. Tom noticed this and this is the reason that I relocated it. I originally had it in the cabin with about 3-5' of vacuum hose running to it and the lag was very big. I moved it to within 6-8" of the intake manifold and it got much better. But it finally was the closest once I put it directly into the intake manifold.

 

[DSM_munky_man]

Here is how mine is set up.

 

[9!'clipseDOHC]

Here is how mine is set up.

So where do you run your BOV line from?

 

[1990AWD]

I'm, sure you guys have probably read this but I'm going to post it here just in case: sdhose [ECMTuning - wiki]. It says that you want to avoid "T's" at all costs, that is the "worst case" scenario.

Here is my Omni 4-bar mounted on the firewall, the vacuum line is 2-3". I know you said you didn't want to drill and tap the manifold, but it is the best option.

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I plan on doing mine just like yours. It looks clean and should work very well. Good job again!

 

[9!'clipseDOHC]

I plan on doing mine just like yours. It looks clean and should work very well. Good job again!

Thanks!

 

[DSM_munky_man]

So where do you run your BOV line from?

The P-port for now, But I am going to drill and tap another fitting where yours is actually since my car is apart now.

 

[-red97rum-]

Hmm I have mine mounted next to the fuse box under the hood (close to the air filter). I'd say my vacuum line is at least 15-16 inches long. I used to have slight tip in issues but I was able to tune it out and get the car to run pretty decent. But after checking out your log Craig I'm seriously thinking about relocating it closer to the intake manifold.

 

[snowborder714]

There should be no serious thinking about that, or even casual thinking. Do it!