Quote from: AJP turbo on February 14, 2019, 02:37:13 PM

Quote from: StealBlueSho on February 14, 2019, 02:18:32 PM
So I did this a couple years ago, and if you are dead set on getting the MBC dialed in (weather dependent I might add) here is what I ended up doing...


I used a spring setup that was almost right at desired, and then used the MBC to dial it in the rest of the way. If I used a spring that was too heavy, I was unable to get it to crack open at the correct the time, and the MBC is only there to keep the wastge gate closed longer than the spring allows.

So.. used a spring that will allow the WG to crack earlier than you want, and then dial it in with the MBC... I was able to keep fuel rail pressure almost perfect, but run much higher boost than I would normally since I didn't deal with boost spikes...

This log is pretty gnarly... holding 16.5psi and almost perfect rail pressure even with the spikes... AJPTurbo tuned throughout this process..

Using a lighter spring but using an mbc to keep it held shut is basically the same as using a heavier spring...but then as the weather changes you may not have the same consistancy which is what you had if I remember.....and I've thought a lot about this since then but you always believed that the mod made things run hotter and turbos harder because the wgdc was higher but in reality the turbos were not running harder...the increased wgdc was because the the reference was lost through the mbc and the ecu needed to increase wgdc to get the proper boost reference to the turbo wastegates to compensate for what was lost

1 psi springs are enough to give a beneficial difference...boost spikes don't have to be completely motivated to see a benefit you just need to take the edge off....you can see 4 psi spikes on the 2-3 shift...taking the edge off helps a lot without needing to complicate things with an mbc

2000 psi dead nuts even is not really critical ...people have been running 1000 psi on terrible tunes for years with very few failures...we all know who they are and have see them...id rather keep it simple and less components and if a spring makes it better I'd rather do that than continuously messing with an mbc

If the fuel pressure only drops to 1700 for a second without an mbc id do that  than to use an mbc and get the ecu upset because the boost reference is lost somewhere

Yup, you are 100% correct, the weather played hell with this MBC setup. I was looking for a particular load, and was having a hard time getting it where I wanted as the springs were either too light or too heavy.. I needed an inbetween but instead of ordering the correct springs.. I monkeyed around with a stupid MBC for awhile...

Maybe I am wrong... BUT the MBC was coming off the reference port on the wastegate mod.. not off the lines from the wastegates to the turbos... so the ECU shouldn't have even been aware of it? In any event.. my 2010 SHO ran freaking hot anyway.. not sure why that car got so hot... oh well.. its in the hands of another tinkerer at this point...

For the record, the only time the car wasn't happy was when fuel pressure dropped below 1000psi... otherwise you couldn't even tell pressure was dropping..

@sbs....but where were you getting the reference that went to the wastegates mod? I thought you were getting it from near the charge pipe at the boost solenoid

Electronic boost control is very sensitive to volume of airflow changes in the reference lines because of the nature of the solenoid...I remember the Subaru's had restrictor pills that were inside the vac lines and you could change a lot of you removed them

But yeah I suppose if you got your boost reference from the intake manifold then you are correct the ecu would not notice anything

But if you think things were running harder because of the mod and you were grabbing reference from the manifold(I don't remember)I would think it's because the gate was opening early which a heavier spring would remedy.....the gate should never open at or below boost target so there is just simply no way the mod would make it run harder

Ha, I'm not dead set on the MBC, I just happened to have one lying around and wanted to try it. It's clearly causing more trouble than helping. I already wrote that I would use the 14 PSI spring set. The MBC will remain on craigslist.

Regarding the boost reference issue,

Since the wastegate, when actuated, bleeds air through the valve guide for cooling, isn't that already affecting the boost reference significantly?
In my case, I had plugged the bleed port on the MBC and when bench testing the setup, the only notable bleed was from the valve guide (a tiny bit through the MBC cap as well) when it actuated.

Quote from: Brewineer on February 14, 2019, 03:25:18 PM
Ha, I'm not dead set on the MBC, I just happened to have one lying around and wanted to try it. It's clearly causing more trouble than helping. I already wrote that I would use the 14 PSI spring set. The MBC will remain on craigslist.

Regarding the boost reference issue,

Since the wastegate, when actuated, bleeds air through the valve guide for cooling, isn't that already affecting the boost reference significantly?
In my case, I had plugged the bleed port on the MBC and when bench testing the setup, the only notable bleed was from the valve guide (a tiny bit through the MBC cap as well) when it actuated.

I'm not sure what you mean by cooling?

If the diaphragm on the waste gate is not damaged then no air is lost from the reference

I read that the reason why wastegates leak around the valve stem in the valve guide was to cool the valve stem, and this was normal, even with high end wastegates.

I suspect it has more to do with the tolerances required to machine the valve guide & stem smooth & tight enough to make an air tight seal.

Do those of you with high end wastgates, e.g. Tial, not have any significant leaks around the valve guide?

https://www.youtube.com/watch?v=WjNbMTLzZck

Update!

I had put in the 14 PSI springset and removed the MBC, however the springs are a bit lower rate than expected, allowing the gate to open at full boost instead of just the spikes on shift.

I went ahead and ordered a Tial MV-S to replace this eBay experiment in preparation for the 3bar Meth tune.

Quote from: Brewineer on March 25, 2019, 06:44:08 PM
Update!

I had put in the 14 PSI springset and removed the MBC, however the springs are a bit lower rate than expected, allowing the gate to open at full boost instead of just the spikes on shift.

I went ahead and ordered a Tial MV-S to replace this eBay experiment in preparation for the 3bar Meth tune.

Assuming the MV-S you ordered comes with a full spring pack...

I put together the attached spring chart that shows all the possible combinations you can achieve using the springs in the kit. There are a couple of ways to get the same "advertised" opening pressure with different spring combos. Depending on the pressure you're shooting for, it might be worth trying a different combo to fine tune (due to manufacturing tolerances on the springs, you might get a slightly higher or lower opening pressure compared to nominal).

Brad can hook you up, just don't drive him nuts (like I did) by swapping out all your springs and inundating him with data files. LOL

I thought I had posted this chart once before, but I couldn't find it on the site. I would double check to make sure the base spring colors/values still match what's in your kit as I put this together a couple of years ago.

Thanks for the spring rate chart, MiWiAu!

The Tial came in Monday and got it set up with a 13.05 PSI spring combo which seems to be working quite well at the moment, though I've barely driven it and haven't logged yet. I also changed the boost reference to the brake vacuum assist line.

Sadly, I did notice that there is a LOT of oil in the piping, so I might be looking at a new set of Turbos soon.