reccakun08

The old thread.
http://zilvia.net/f/tech-talk/203812...l-redline.html
The new.
So yesturday i went ahead and used my boost leak tester that i made years ago. I was able to track down a vacuum leak from the bov nipple. The vacuum line was an extended line using those plastic hose connectors.(they suck ass) Upon trying to fix the leak my friend broke the blitz bov elbow. (its the piece that connects to the bov to a vacuum line) therefore i am using his brand new hotpipe w/ forge bov. We hooked it up and kinda ghetto rigged it.

Here is the diagram of the old setup:


(the connector where the lower tb vacuum port to the bov connected was leaking)

New setup



Ok so with the new setup the car pulls harder than before but now my car has a wrx sound and a weird lag. The sound is only apparent in vacuum but only from 736mmHg to ~250mmHg. However going from 0 to 250mmHg does not. The lag is right after the next gear engaged but if i shift a bit faster with a bit more gas its normal.

Any ideas? I think i might have a slight exhaust leak at the cat. Possibly the crappy ass turboXS manual boost controller?

!Zar!

Uncap that vac line above the throttle body and run the bov to that.

I'm not a fan of T-ing off of wastegates.

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reccakun08

So have the bov run to the capped port. Then have the bottom port run to the mbc that is connected to the actuator?



After driving today it seems like a misfire/bogging during crusing vacuum pressure but as soon as u give it some throttle or full throttle it goes away.... Any ideas on what could cause this? its weird cause this only happened after fixing the leak and with a different vacuum routing along with a different hotpipe/bov? (exhaust leak? another boost leak? coilpacks? sparkplugs?) Also my idle is slightly higher than before(~6-700rpm to ~800-900rpm)

g6civcx

There are some major problems with your setup.

1) The BOV/VTA valve needs to see 2 things: a) intake manifold pressure after the TB, and b) charged pipe pressure before the TB.

When the TB is opened, a = b. When the TB is closed, a = vacuum, and b = whatever the turbo is boosting at.

When the TB is closed suddenly, b >> a. The pressure differential b - a = c makes the BOV/VTA compress the spring. The stiffer you set the spring, the higher c has to be to make the valve go off = less boost leak, but also less response.


You need to make the vacuum line going to the BOV/VTA as short as possible. This gives you maximum response since it takes a shorter time to pressurize a shorter vacuum line. The newer SRs have the CBV on the cold pipe.

You should aso not T this vacuum line anywhere because the extra line decreases the BOV/VTA response.


I recommend shortening the vacuum line as much as possible, and to recirculate pre-turbo and post-MAF. BOV placement is a matter of taste, but I recommend the coldpipe if possible.


2) The wastegate needs to see boost before the TB. If the boost gets above a certain amount, spring tension releases and exhaust gas is diverted away from the turbine.

When you put the wastegate signal after the TB, when the TB slams shut, b > a above, but the turbo is still making boost against a closed throttle plate for a little bit. This can make all kinds of problems for you, including making your idle go to hell.


I recommend putting the wastegate signal on the coldpipe as close to the TB as possible, and to make the vacuum line as short as possible.


The idea is to make boost pressure as linear with the gas pedal as much as possible, but I don't know much so anyone else is free to correct me.

burnsauto

FTG-QuickTap-CompHSG: atpturbo.com




Get a quick tap, $10 bucks.

The BOV should have a direct line, nothing tee'd off it.

Wastegate signal should be between the turbo and bov. Putting the nipple closer to the TB will just make the turbo work harder and could cause initial boost spikes.

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g6civcx

There are different opinions on this so choose the one that makes the most sense to you.

I really don't know.

S13 SRs has the signal on the coldpipe.

reccakun08

Alright so it would be fine if i un-T the BOV and have the current hose running to it run directly to bov instead of bov&mbc. I guess your Quicktap solution is because i do not have a nipple on the new hotpipe? So what should I do with the boost controller if i run the bottom port directly to the bov? (i was just going to run it to the other capped port but hearing from what people are saying its whats causing my car to lag)



Im guessing this is what you mean? The pink being ideal and the blue being the only way i can run it with 1 vacuum port directly to bov.

reccakun08

I think this may be happening where it kinda feels like it builds a bit of boost against a closed throttle plate. Where am i suppose to get signal on the coldpipe? get a fitting tapped in?

g6civcx

First, please let me say that this topic is highly debateable, and we can be here all day.

Second, there are typically 3 places that people use for the wastegate:

1) hot pipe;
2) cold pipe;
3) intake manifold after TB.

There are pros and cons associated with each individual choice.

I personally prefer choice #2 because it provides you more consistent boost because you take the IC out of the equation. Yes, if you have a boost leak the turbo will work extra hard to push everything to the coldpipe; however, boost will be more consistent compared with the hotpipe.

#3, which is probably where you have right now, is great for aggressive acceleration, but during off-throttle when the throttle plate slams shut, that port sees vacuum and the wastegate has no idea what boost is going on.

Great for all out racing, not so great for driveability, which is the problem you're having.


So instead of debating, I say #1 or #2 would be equally good choices, and I prefer #2.

Save #3 for RACE Wars when SR20s are at a premium