Maybe it was my criteria but I searched and only came up with TN overboosting threads.

Maybe my situation is unique in a way.

I try to give details but if you wanna get straight to the question, its at the bottom.

2003 G35
Greddy TT
UTEC /w turboxs boost controller

The car was tuned to about 9.5PSI maybe...2 years ago when I built it. Even on the coldest nights I never saw above 10PSI.

Over the winter I cleaned up the spaghetti of vacuum lines and "T's" with a BLOX vacuum manifold. Previously I used the AAM throttle body spacer but didnt like how it pushed the charge piping out 1/2" or whatever it is.

1 key change I made was screwing the MAP sensor directly into the vacuum manifold as a direct source.

I changed sparkplugs, I changed K&N filters (I bought new ones but they are the same I've used for a few years now), powdercoated my plenum and re-installed it torquing everything accordingly which I am going to double check ones the car cools down. I also installed a CCA Oil catchcan.

Anyways, I took the car out today since its nice, first time out since I've installed my OS Giken Twin Disc.

I rolled into 3rd, the car felt SOOO strong, like almost too strong, pulled real hard, so I looked at my Zeitronix display, checked the peak and see I hit, 9.7lbs. Which I found odd.

So I do another pull in 4th, and now the max is 11.7lbs.

Dont get me wrong, car feels awesome and runs like a champ but it isnt right and Im scared of bending a rod or dropping a valve on my stock motor.

Could relocating vaccum sources cause the 2PSI increase I am seeing? It seems to never peak above 11.7, but on a cold night Im sure it would hit 12.

Thoughts?

 

I am going through the same stuff. I dropped my car for retune. I usually stay at 15-16psi but I saw 18psi after new clutch install.

 

oh **** really? We have that in common? I just wanted to check with the gods before a re-tune.

 

Yep I checked all the lines wasted hours spraying for vacuum leak and wasted 2 sets of plugs. I just think I need a retune. Oh well I'll find out more this wk I'll be tuned by Uprev. I'll post Dyno too. Btw I checked the under carriage foe kink of leaks too! Nothing. I tracked the line all the way! So before I dropped it off I did all I could. I even bothered Sharif about 10 times

 

A vacumn source will stay the same vacumn anyplace it comes from and should not change your boost in anyway.A larger vac hose and a small one connected to a guage will show the same result.

 

This is what I am thinking... you had a very small vac leak for your WG reference or solenoid reference, which you did not know about. Then you boost controller was tuned. Now that you cleaned up and did a few changes to your vac lines, you probably got rid of that small leak it had and now your getting a different pressure at your solenoid or wg.... just an idea. possible

 

Yeah that makes complete sense, and I agree the vacuum/boost should be the same no matter where the source is located.

 

Not really true.

Your boost will always be slightly higher right at the compressor. There will always be a slight drop across all the piping and intercooler.

Also, wastegate reference boost should be taken at the compressor discharge. This is the "true" boost pressure. BOV vacuum should be from the intake manifold, after the TB.

 

Gotcha.

Just for reference this is my current vacuum setup.



So this year like I said, I moved to a vacuum manifold, I just realized a major difference from the past is I "T'd" into the EVAP vacuum hose (3), where as last year I was using the AAM throttle body spacer for UTEC MAP Sensor, ZT-2 MAP Sensor, and EBC IIRC.

It seemed like an appropriate vacuum source, am I wrong?

Car still runs fine, just more boost.

 

Although what you have works, like buddy mentioned above. its always good to get the WG reference straight from the turbos compressor housing, and let the boost controller adjust to the proper pressure. You basically have more control when you have the reference straight from the turbo.

If your worried about too much boost, just make some adjustment to the boost controller, If it were me i wouldnt worry at all, just gotta readjust your boost.

 

Sorry Im not sure I understand where the compressor housing reference would be?

Would I have to tap it?

 

Well some turbos have a fitting on the housing towards the outlet of it, but in your case you can tap the charge pipe itself, like right after the coupler that joins the turbo to the charge pipe. That way you dont have to drill the actual housing.

 

^^what he said.


Just make sure to clean up the pipe from any metal shavings afterwards. It is also a good idea to de-burr the inside of the pipe after drilling. You don't want any metal shavings that are just barely hanging there to come loose down the road. Unlikely that they would make it through the IC, but why take a chance.

 

I see more boost in higher gears as well. Ambient temperature also makes a huge difference. Are you sure that you just never noticed it before?

Can you see what you boost control settings are in the UTEC and adjust accordingly?

This is why I use a GReddy Profec B instead of the UTEC boost control...adjusting boost pressure on the fly is easy - just turn the ****!

 

Wastegate actuators are not supposed to see vacuum, only boost, according to Garrett. So referencing some point BEFORE the throttle body and after the turbo compressor would be called for. That's all besides the point though, the fact is that changing the reference point for boost going to the boost controller or solenoid will change your boost set points using open loop control (open loop is fixed vs. closed loop, which should adjust automatically).

 

Ok so there is nothing "wrong" with my vacuum references but they could be better is what everyone is saying.

As well shortening the vacuum line to my boost controller and T'ing a different reference point may have caused this increase.

Safe to say?

I'll do some logging and tuning.

 

Eesh so maybe I caused my own issue, according to this and as everyone else has said, my WG reference should be before throttle plate (it was before the throttle plate last year with the AAM Spacer before I moved it this year).

I suppose I should move it back.

http://www.tialsport.com/documents/w..._wginstall.pdf

Where do other Greddy TT get their W/G reference from? Anything before the throttle body?

 

Random Hero........

You really should use a better vacuum source than the line connected to the evap stuff!!!

your best bet is to drill an tap your manifold for a -4 or -6AN fitting and run a dedicated line to your vacuum manifold. The evap line has fuel vapor in it......not ideal for feeding your vacuum manifold.

 

Thanks. Will do.

As well I should re-locate my WG reference before the TB?

 

yes, wastegate/boost controller needs reference before the TB