Oddball of a setup.
Forge Lq9 /317 heads, cam/dual valve spring
Quad turbo-on3 t3 gt35 (2 cylinder per turbo) and each turbo has its own tial style 38mm Wastegate.
Spring in the wastegate is suppose to be 22 psi(bench test shows it cracks open around 20 psi)
Boost leak tested good.

Heres my issues- Im trying to up the boost to 30 psi but even with my turbosmart electronic boost controller that utilize the top port of the wastegate it just wont make the boost. (ive tried to reference the boost source via turbo housing and manifold.)
Last resort I added an inline MBC to the WG with the rest of the system hooked up to the top port of the WG using the turbosmart and mange to up the boost to only 25psi(jumps to 28 but quickly drop).

Really odd- the only thing I can think of is that maybe I have too much backpressure that is causing the wastegate to open? Has anyone else encounter a setup that is struggling to bring the boost up?
Im considering adding a shim as I cant seem to locate a 30+ wastegate spring BUT I wanted to see if there is something that I may have missed or should check first.
Ive never had a setup that wont go up in boost with EBC lol

 

I'm sure the initial responses will be have you verified you don't have a leak in your plumbing? I had just two GT35's on my setup in 2020 and it shot past 30 psi the first time I took it out, so I'm sure with 4 turbos it's not the turbines. Sounds you'll have to go thru the process of elimination.
1. pull off each waste gate and bench test the opening, maybe pull the cap off and check the diaphragm for leaks.
2. Smoke test the plumbing by getting the car into a dark garage, etc, plumb some smoke generation into the cold side while shining a flashlight around to look for exiting smoke.

With that many turbos, I imagine you have several connectors that might have come apart somewhere. Best of luck to you.

 

Thanks, Yea I checked those out.
1. Boost leak tested the whole system as a whole - 35psi and no leak
2. smoke tested the whole system also good
3. removed the wastegate again and tested the diaphragm for leaks. Bench tested and it all checks out.

Honestly dont know what else to do at this point.
Just looking for ideas of anything else I can check.

 

Post up a few pics of the setup. Let’s see if anything stands out.

 

Two cylinders feeding a GT35, I'd think your drive pressure is fairly low. Rev it higher to get more airflow across the turbine and see if boost rises.

 

Agreed. Spin the turbos harder

 

I rev all the way to 6500 I dont think its that as I was able to build boost to 30psi but as soon as it reach that it falls back down to 25- wastegate not closing?
Im thinking it maybe the turbosmart street boost controller. Setting? or limitation

I switch the WG springs to 25 psi and it seems to do that. I can get it to build 30 psi by adjusting the set point to 80 (ive gone as far as 95 and not much changed.
Gate pressure at 25
sensitivity at 20(though tried up to 80.

Anyone use the Turbosmart eboost street?
theres only 3 setting and I could not get it to boost higher than 30 even with 9x duty cycle.

 

You have turbos that most use as twins and ur running them as quads. Your not spinning the turbos hard enough to get your desired boost. U need smaller turbos or less of them. Your 38mm WG will only be a problem controlling lower boost pressures and there is no way you have too much BP with 4 of them. If you had 1 turbo and a single 38mm and tried to run low boost like 4psi you might have an issue bleeding enough exhaust to get the boost low enough as your leak isn’t big enough. Big WG means easier to provide a lower boost threshold and smaller WGs mean better for higher boost thresholds as u bleed off less exhaust.

you prob need to step the turbos down to GT30 or GT25 territory to get them to spin up and create the boost that you want. I have a feeling your max boost is all you can get with the turbos u have.

FYI I have a single T4 and a 60mm WG and bend test showed 12psi crack pressure but on the car I got 6psi due to exhaust pressure and the surface area of the valve. I doubt ur exhaust pressure is high enough to provide enough pressure on those 38mm to open them up. Most people run 4 cylinders on one of those so you would have 1/2 the exhaust feeding each turbo.

 

on the BP Yea that makes sense, I just couldnt wrap my head around why its opening before boost set point. I just slap on a 25psi springs and on the bench test the crack pressure was about 32ish.
I originally had 52mm set on the car and that spooled great but couldn't push it anymore on power. Downsizing at this point is out of the option, i was hoping to break 1000 awhp with this bc after that ill be going to a single setup for more power - but that still 1-2 years from now when I upgrade to a stroker.

The setup just seems like its capable of pushing 30psi, I mean it builds it then drops down.

Something odd that happened last night and I didnt think much of it until today. I floored it at 4rth gear and it struggled to build 20psi, then it returned to normal.
My bov is pre IC, since im running ebay IC it probably has 3-5 psi drop? what are the chances of that bov getting cracked open under boost? as there is bound to be some delay for the boost pressure to balance out between pre IC pipes vs intake manifold. When I test for boost leak its a slower build of pressure so maybe during a test its unaffected?
I normally run my bov near the TB but I might run methanol injection so I decided to vent before the IC so im not dumping methanol in the engine bay later on. but maybe that was a mistake.

Thoughts?

 

my BOV is also pre intercooler as well. You have to measure the pressure drop to verify the IC. I measured mine eBay12x30x3 and I have basically no pressure drop at 10-15psi…. Like .1psi or something. But mine looks like extruded channels
and not a typical tube/fin so higher flow but less cooling. I always reference off the compressor
housing for my WG (EBC) and since my BOV is 6” from the compressor outlet they are tied in together. I vented pre IC as I’ve heard it helps with surge to vent closer to the turbo.

you could easily swap in a pipe to delete the IC if you wanted depending on how it’s setup to see how much your actually loosing from the IC flow. I tried A2W and my IAT temps were higher than and A2A overall but I saw less of a spike during boost so I went back to A2A which cooled faster after a pull and didn’t head soak as much. I would see 130*F cruising with A2W and with A2A I will see 100-110*F cruising and 90s spraying wiper fluid 3ft before the TB. You could just inject after the BOV and not
worry about it going in the engine bay as well.

the BOV has spring pressure and it should be closed at idle. So figure if boost is referenced off of the compressor it will have boost plus spring pressure and shouldn’t have an issue being closed. So I doubt that is your issue if u reference off the compressor.

 

Have you tried adding spring pressure in the gates? Have you disconnected the reference lines altogether to see if it'll make more boost if the wastegates dont open at all?

 

Your rev limit is too low to me no matter what boost level. Rod/piston 6.0's shine at 7000+, heck even stock ones rev well over 7000.

I've used the eboost street for over 30PSI so that shouldn't be an issue if all else is plumbed well and settings are correct. If you set your gate setting higher than your actual spring rate you usually get a spike with a controller like you are seeing. Make sure you have overboost setting correct as it will revert to gate if its not. What have you set your boost group 1 and 2 settings to?

 

Instead of guessing what is going on and throwing parts at it. May try to get the actual data? Check back pressure at one of the turbos. Its a $16 sensor. Great info to have and you can repurpose it after. I moved mine over to coolant pressure after.

I also agree you aren't revving it hard enough. Very easy thing to test. Bump redline up to 7200 and go run it out to 7k see if the boost curve follows.

It could be blowing the WG open if you still have a pressure source to the bottom port. I'd try it briefly with no boost control lines to the gates at all. Then try it with the BC to the top ports only if you need more boost.

How does that setup run on 25lbs? How lazy is it building boost? I'd like to see it if you have pics. I always wanted to run 3 of them since 2 seem to support around 900ish without pushing too hard.

 

I finally had some time today and tried that out. very consistent boost- i kept letting off at about 25psi as i felt like it would shoot up past 30+.
Well i think I need to look into my boost controller set up- or setting.


I'm surprised to hear that. A few years back when i was doing my research I though that people concluded that it was risky to rev in the 7000+? I suppose with my dual valve springs/forge bottom its much safer.
Whats the general consensus for the rev limit?

Just confirmed that its my boost controller(well likely how I set it up). Since it boost fine with the WG fully disconnected.
Maybe the turbo housing itself sees a that much higher pressure vs manifold, But it still doesn't make sense since the Solenoid should not have opened until the manifold sees the set boost.
Overboost is set at 40. And I have tried multiple settings- BG =10-30, SP = 20-99, SN 20-50.
Only thing left is I have the solenoid being fed by 1 turbo then it goes into a hardline splitter. I think this may be causing it to not be controlled correctly? even with Tial 25psi springs the car will only read 20psi boost with the EBC being set at lower setting.
I ordered a 2nd solenoid to test if its that- So I will have 1 solenoid on each side.

Whats your setting look like? I was not use to how this controller controls the boost. If I understood correct, You set your BG to 5 psi below target,(so say 25 if I wanted 30), then crank up your SP till your boost hits target. This about right?

unfortunately the way the IC is setup i cant just replace it with a straight pipe. I ended up just moving the bov anyways since I wanted to redo a reducer and remove a coupler.
Right now all im spraying is water for temp anyways.


what kind of sensor did you use? link? I'd love to log what the 4 turbos are doing.
video below, this was an attempt at 30psi but only spike to 27 not much more. Kept bumping into the rev limiter as i wanted to capture as much of my VE table to make sure im good for runs. In hindsight i should have probably raised it so it populated better but it is what it is lol
Not lazy by any means but it feels like it should come on harder. only 14* timing btw since its street tuned atm.

 

Stock bottom ends have seen 8100-8400 and lived a long while, playing it a little safe for a street car I have been revving stock stuff to ~7800 or so for years on end without issue.

On my car I never had to mess with sensitivity. I set over boost to 37 or so, gate pressure at 20, then SP1 at 50% and SP2 at 75% but creep up on it and see what works for you.

 

You can find these cheaper on ebay usually but I’m an amazon junkie. You can also get smaller ranges. But I use 0-100 for back pressure.

Would also be great to plumb one before the IC. I’ve seen as much as 11psi lost through the commonly used Ebay 3” cheapie IC. Get a decent IC on there if you don’t have one already. Treadstone is great for the price. Garrets cores can’t really be beat IMO. (but out of my price range). If your on E85 with lots of turbo… you probably don’t need the best of the best IC. Just be sure you get one large enough to flow the air you are pushing so you don’t have a massive pressure drop across the core.


As mentioned above RPM is your friend. Set her to 7500 at least. Should be fine. Even though it sounds like you found your issue, shifting the power up in the RPM range is going to help the motor stay alive. You don’t want to make gobs of power until WELL after PK TQ. Limiting the RPM to 6500 doesn’t allow for much of a power band. IMO you shouldn’t really be dumping power in (timing and big boost) until 5800+ anyway.

As far as the controller goes… Unless you want less than 25lbs, leave the bottom ports open. Slowly apply manifold pressure to the top of the gates to get more boost out of it. You have A LOT of gate area with 4 38mm valves. Even cracking them a hair is going to bleed off a lot of drive pressure. They will be very sensitive.

 

Thanks I will check that out.
Im holding off on the IC upgrade as Im on the fence if I want to try a A2W IC.

yea I think my WG is definitely extra sensitive. I added a 2nd solenoid, while it feels like it controls things much better it still maxing out at about 25psi.

I will try bumping the rpm once I get this boost controller dialed in.

Thanks ill give that raised rev limit a try once I get my boost control corrected.
I have maxed out my boost control setting and it just cannot ramp it up. I think forcefed may be on to something about the wastegate cracking just slightly being enough to bleed off the boost.
I think Ill order a Hallman MBC and use that inline just to drop the boost signal lower so that the Eboost can control it.
I have dual usage for the car so I want to keep the low boost and high boost switch capability that Eboost provide(plus its triggers my water injection and 2nd pump).

 

This might sound dumb but, can you put some restrictors in the wastegate dump tubes to limit the flow through the gates. That way when they crack they aren't dumping all the drive pressure.

 

Or tie the inlets of the two gates into one on each side, drop the flow by half.

 

I dont know about adding the restrictor after the wastegate- that sounds like it would force exhaust into the wastegate valve seals. But I suppose it will be under boost so maybe not?

due to the placement of the wastegate wouldnt that be problematic in controlling the boost? it would add about 1 foot of wastegate pipe between the manifold and wastegate.
Im thinking I might just have to bite the bullet and just remove my setup and cut down the pipe area before the wastegate by about 30%.
Hopefully that would be enough. 50% since a bit high since thats equivalent to dual 38mm on a 1k whp setup?