NC overboosting
 

Hello there. I know turbo NC's are rare on this forum, but this is more of a general mechanical question, I hope you guys can help me out..

I have an NC miata. Stock internals on the motor, upgraded clutch, and a Begi S3 kit with a GT2860RS. Their kit comes with a (and I am 90% sure of this) .86AR housing and a 7psi wastegate.

My engine is stock compression, I believe 11.5. I have a 3" midpipe and exhaust, with a high flow cat and a resonator (built by enthuza).

My problem is that I am reaching 14psi with this setup. I originally had boost creep past 10psi, so I removed the turbo and ported the hell out of the wastegate. Then I had too slow a boost build.. It would take me to around 6k to hit 10psi. So I decided to Install a Hallman manual boost controller to hold back the wastegate until the turbo could build enough boost. With the hallman fully unscrewed (what the MBC considers "completely stock" or straight pass-through) I am still hitting 14psi.

I should say, I also changed out the re-circulation valve. The original one was leaking past 3psi. I got a Forge stainless steel valve, and installed the softest spring in it. I was told this would cause some boost creep, though I do not understand how exactly.

All I am trying to do is get a leak-free, 10psi boost! Does anybody have any suggestions? I keep thinking to myself "Keep it simple, stupid" and think I am over-thinking and over-complicating this. Any suggestions or help or criticism would be greatly appreciated!

-Stueck9356

It seems the installation of the hallman was where you first had overboosting issues. Have you removed the hallman, keeping all else the same to see what happens? If you return to spooling at 6k, I would say that is your issue.

Hey! A fellow Charlottean!

I will try bypassing it tomorrow, and see what occurs. I kind of liked having that thing in, it spooled up a lot quicker. Though fixing that leak might have fixed the problem. Thanks!

Sure thing, Its what I do to fix issues, remove one piece at a time, see if problem fixed, or returned to a prior issue. rinse and repeat. If the spool returns to 6k, then I would assume that there is an issue with the hallman itself, I personally would be tempted to try a different boost controller and see if I have any issues with the different one.

As a side note, I know it sounds stupid, but are you sure you spun the controller the correct direction when you were adjusting it? Just a thought.

Edit: Lol, My charlotte senses were tingling??

your boost controller is installed incorrectly.
you can figure out how to install and adjust it correctly with a bicycle pump.

It is installed correctly. It goes turbo housing to the barb on the bottom, then barb on the side to the wastegate. and it is Basically a ball and spring, and even has arrows on the adjustment knob with "boost -" one way and "boost +" the other. Plus you can feel the spring tension as you increase it's resistance for more boost.. Pretty simple design, pretty sure I nailed the install :P

I just thought of this.. Originally there was a fuel line used for the waste gate, something along the lines of 1/8" ID. I went to advance auto parts to get a longer hose to reroute and the guy behind the counter said "fuel line? No no, you need vacuum hose so it doesn't collapse when vacuum is applied".. Ya.. Vacuum on a waste gate? Lol. Anyways he didn't have any fuel line so I took the vacuum hose. Unfortunately all he had was 3/16" vac Hose. Could the differences in diameter cause this?

It's really just whatever fits on the barbs properly.

And don't worry about the mBc, if it's spiking to 14psi without it, you can never lower it with a mBc. So fix the spike, then add the boost controller.

I bypassed the MBC, and reinstalled my old recirc valve, and I was still pushing 13-14psi. I talked to mike at moto-east, and he said the check valves I recently installed could have done that. The evap solenoid is weak, and could have been leaking that extra 3-4psi that I now have.

Basically, I was only pushing 10psi cuz I was leaking the rest :P

Now the question is, how to get that down to 10psi again. Perhaps a lower rated wastegate?

Update..

I have really dug into this issue. Contacted begi and they said that the -9 actuator is for 7-9psi, and the -6 actuator is for 13-15psi. They said I could check the side of the actuator to find out which I have, when I did...

Attachment 60837

lol. So I decided to take a picture of the dog tag and look around online...

Attachment 60838

I read "739548-5005S" for the model of the turbo. Looking around I found a site that lists the GT2 series by size and model no.

GT28 - Garrett - Catalog - TurboMaster

The one that makes the most sense is 739548-0005. Since, well, it is a GT2860RS and has a 5 in it... Yup. Clicking on my specific turbo I find it has the actuator "480009-0006" Which is listed as a 13-16psi actuator, depending on the website. I think I need to find a "480009-0009" which is a 7-10psi wastegate.

Does this seem accurate to you guys?

this doesnt make sense. you understand how a turbo works right? then it has to be a wastegate flapper that now doesnt seal.

I don't have as much knowledge as most of you guys on here, but I have a decent idea. What I was trying to say is that, the wg opens around 50% of its holding pressure (a 10psi wg starts to open around 5psi). The wg is sealed until it hits 5psi, then it starts to open and leak air past the turbine.

If that opening is bigger, it is going to leak more air, since it has a larger diameter. The wg is still going to open when it see's 5psi, and it is still going to open as much as it did before I ported the wg. Problem is now that the wg opening is so much larger, there is more exhaust escaping through it causing a slower spool.

If I had to guess it is probably 30% larger than originally. That is roughly 150% of the original flow, causing a slower rising boost.

I could be completely wrong, and just blowing smoke out of my ass. That is just how I came to understand this.

Do you have any pictures of where/how much you ported the wastegate area? Or if you could find pics online & put arrows to show where you removed material from?

If full boost didn't hit until 6k rpm you either need to increase the pre-load on the wastegate actuator, or you ported too much and the wastegate flapper is no longer sealing adequately to spool the turbo (or you ported the housing in such a way that the flapper is getting jammed open catching on the wider lip).

I routed it to about 0.7-1.0 mm from the outer edge of the flapper. The left side in the picture, towards the turbine, has a larger overlap because of where the wg is placed, the housing is thick right there. the red line is just a rough placement. I work in a dental lab, and so have access to all of the nice hand tools and burs. I rounded the edges, and polished the port to a shine. I checked it close, so it should not be catching. It is just as BIG as possible with the smallest amount of overlap for a seal.

I am going to check for clearance with the wg sometime in the next few days and might wire it open to see how much boost I pull with max bypass.

Attachment 60887

So your waste gate doesn't seal now...

I am 99% sure it seals. When I was grounding it, I taped shut the exhaust port, and attached suction to the exhaust manifold port. That way as I was grinding the shavings would get sucked out the exhaust manifold port, clear away from the turbine wheel. When I was finished I closed the wg flap and it sealed nice and tight against the suction.

There is a good 1mm overlap, where the wg port is smaller than the wg flapper.

you're supossed to make the hole bigger and leading edge into the hole wider to allow more exhaust gases to bypass the turbine...im unsure what making the flapper smaller would do, other than making it easier for gasses to push it open.

I.. I made the hole bigger.. as big as I could. The hole is as large as I can get it without compromising the seal with the flapper.

Lol, I think we are both confused. I think my question comes down to this:

Does my turbo (739548-5005S) Have the 7psi wastegate actuator or the 14psi wastegate actuator.

If it has the 14psi, then all is well and I just need to buy the 7psi one and crank my MBC up so I get 10psi. If it is in fact the 7psi one, then I need to find why I am pushing 14psi and how to get it down to 10.

What about the tension on the wga? With a mbc you're supposed to back off the rod a bit right? I keep just enough preload on the flapper to keep it shut.
I have a begi 7psi actuator and with my mbc I'm running 15psi no issue this way.