Subaru Impreza GC8 & RS Forum & Community banner
1 - 20 of 21 Posts

·
Premium Member
Drag 00 Impreza 2.5 RSTI
Joined
·
1,525 Posts
Discussion Starter · #1 ·
Hey...
I have finally found someone who knows how to tune in my area. He even has ecperience with tuning Electromotive Tec3.
On Saturday, we went on a street tune and began leaning out my maps.
Anyways...had it tuned well for about 10psi of boost when i wanted to raise it to about 14-15lbs (sti shortblock). Since the wastegate had a small spring in it, I decided to replace it with a bigger one. I opened my wastegate and found a small blue wastegate spring (good for 8.702psi/0.600bars). My question is how exactly did I have 10psi of boost running through the turbo while the wastegate only had a 8psi spring in it... Replaced the small spring with a large blue one (14.5psi/1 bar).
What do these psi rating corespond to? The wastegate opens at 8 psi then? so now since I have this 14.5psi spring in there, is it too high? Should I set it lower to 12 if i want 14-15psi of boost going though my turbo...

Sorry I am a newby when it comes to subarus...

Thanks
Ben
 

·
Premium Member
Drag 00 Impreza 2.5 RSTI
Joined
·
1,525 Posts
Discussion Starter · #3 · (Edited)
I used to be running 10psi of boost with the small blue wastegate spring (8psi). This worked perfectly. Now.. I am going to run 15psi of boost. What spring should I put in my Tial wastegate? I was planning on puting a big blue spring which is 14.5psi in the wastegate. Should I use that or should i use something rated for less...I have a small red (5.8psi), small yellow (3.6psi) and small blue (8.7psi). I can run combinations of one or two springs also...

What is the rule of thumb when it comes to wastegate springs and boost...? What wastegate spring should I use for my 15lbs of boost goal?

Ben
 

·
Registered
1998 Forester on Orange 57F
Joined
·
4,129 Posts
Either your spring is not rated well or your setup does not flow properly through the wastegate. A 8psi spring should run 8psi. like wise 14.5psi should be 14.5psi. Of course it's mechanical so there will be some variation in springs and over time. I've run all kinds of springs and never had an issue unless you are trying to run much more boost than the spring is rated for. IE using a boost controller to run 30psi with a 12psi spring or something crazy.
 

·
Registered
2015 STI Crystal White Pearl
Joined
·
1,861 Posts
if you plan on going higher with your 8lb spring, your turbo will fall flat in the upper range because it will no longer be in its efficiency range. go for a stronger spring if you plan on upping the boost in the future, at the same time, suiting your needs for the time being.
 

·
Registered
2015 STI Crystal White Pearl
Joined
·
1,861 Posts
yup. your problem will be 'boost spike'. it's when there isn't enough exhaust gases to overcome the spring and open the wastegate valve. so the turbine overboosts and now you have a hot motor that is pretty much a running time bomb.

basically, it's not possible to go lower than your wastegate spring pressure.
 

·
Registered
2000 2.5 RS-T srp sedan
Joined
·
2,732 Posts
I thought that you can't go lower than what the spring is set for but you can raise psi above the set spring.....so it shouldn't matter what spring?
 

·
Registered
2001 Subaru 2.5 RS-T BRP
Joined
·
359 Posts
I mean...if I run lower boost than 15 again ever, will I have a problem with the wastegate not opening at all.... Wouldnt that effect my performance...?
Once you put that 15 psi spring in there, I dont see why you would actually want to run lower boost. 15 psi is pretty fun.
Now, if you are thinking of going back, just get a MBC and keep the 8psi spring in there... should be the same. I run a 6 psi spring and 11psi off of the MBC since I didnt feel like opening the wastegate to change the spring. The car runs great. No drawbacks in doing this.
 

·
Registered
GF OBS-T, GM RS EJ20, SF EJ20
Joined
·
4,973 Posts
+1 get a boost controller MBC or EBC this is the +'s of a turbo set-up you can up boost on the fly without having to swap spings or any other pieces (pulleys for changing boost on S/C cars).
 

·
Registered
GF8
Joined
·
938 Posts
Whats happening is like Brydon said,
Basically something is wrong with the way your configuration is flowing. What this means is that your turbine is outflowing your wastegate. Path of least resistance equals more boost since the exhaust gases aren't being alowwed to bypass the turbine.
What turbo are you running?
What size wastegate are you running?

This is most likely going to mean that you need a bigger wastegate because your turbo and wastegate aren't quite compatible or efficient together.

-Kurt
 

·
Registered
2015 STI Crystal White Pearl
Joined
·
1,861 Posts
i did a quick search on this guy. he's using a garrett T04E with a tial 38mm wastegate (he said 30mm on his post, tial doesn't make 30mm). i didn't see any type of boost controller on his list, just the Tec3 EM, which controls fuel and direct ignition and such. so it looks like he's just running wastegate boost off of his tial. however, 10psi on a spring rated for 8psi with no boost controller looks to me like it's got some creeping issues. makes sense where a larger wastegate is needed because the 38mm is too small of a hole to bypass exhaust gases from the T04E. a tial 44mm will probably be a better candidate for his setup. an ebcs can help with the current setup by adjusting duty cycle and gain, but will be limited due to his wastgate size.
 

·
Premium Member
Drag 00 Impreza 2.5 RSTI
Joined
·
1,525 Posts
Discussion Starter · #15 ·
The reason i dont have a Boost controller is becasue I heard that Tec3 EM controls boost somehow in the software....Haven't been able to find where in the software I can do that but I think it might be a feature in the newer Tec3R and TecGT. Think im going to do it the old fashion way and get a manual boost controller. About the wastegate.....yeah spring rated for ~8.5psi and my boost guage reads 10-11psi at max boost. In the future I plan on running a 35r. Would a 40mm be enough for me now and then?

Btw...yeah...it was a typo...I do have a 38mm....lol
 

·
Registered
2015 STI Crystal White Pearl
Joined
·
1,861 Posts
yep, you got creeping issues. a 44mm will most likely eliminate the creeping and since you're upping the size of your turbo in the future, you might as well get it.

if you get an mbc, get the hallman pro. it has more of an analog feel than most mbc's out there. it also has an optional 'in-dash' dial attachment so you can adjust boost in your cabin instead of getting out and popping your hood.
 

·
Premium Member
Drag 00 Impreza 2.5 RSTI
Joined
·
1,525 Posts
Discussion Starter · #17 · (Edited)
It is weird....
I was running a PTE 6152sp (basically 35r) with a 38mm wastegate without any problem at about 25psi with a boost controller on my old 96 eclipse gst...
Why am I having this problem on the suby with a smaller turbo but the same wastegate with less boost....?
 

·
Registered
2000 2.5 RS-T srp sedan
Joined
·
2,732 Posts
internal ones such as on the td04 uses the vacum/preset spring inside. Min boost is I think 10psi on the td04.

Just like the external ones...spring dictates the min target boost and the boost controller allows you to add more boost but never let you decrease boost below that preset spring pressure.
 
1 - 20 of 21 Posts
Top