Boost variance on the new setup.
 

Hey guys,
Once again, I know all of this has probably already been covered somewhere on here and I wish I had the time to search, but you know how it goes...
So, I put the GReddy on last week and ran it stock for a couple of days after break-in before installing the 'fancy stuff'. I added Jim's pipes with a Starion, a recirculated brass Bosch BOV, and a MBC.
My problem is that, with the current setting, my boost will initially spike to just under 8psi at about 3800 and maintain that until just over 5K where it will quickly pedal back to 6psi until redline. It does this in every gear similarly. I know this boost level is well within the 15G's operating range, but the effect is quite pronounced and consistent at 5K with no accompanying sounds or aberrant vibes. Though I didn't have a boost gauge while running the stock kit, I am almost certain the problem only started when I installed the IC and other associated hardware... and it was definitely present even before I installed the MBC. I am running the pressure line to the BOV from the port on the very front of the manifold next to the TB that was apparently plugged from the factory and all of my IC fittings are reassuringly tight and solid. My boost gauge is tee'd off of the same line as the FMU and I had adjusted my wastegate prior to installing the turbo to be sure it moved freely (my kit was new).
I have several ideas of what might be causing this, but I'd really appreciate a nudge in the right direction to save some time. A friend suggested that my BOV might be leaking... Does that sound plausible? Any help you guys could give me would be fantastic. Oh, and could someone possibly link me to a good procedure for adjusting the timing? I'm fairly sure on that as well, but better safe than sorry and I'm almost out of race gas...:crx:
Thanks,
-Jake

I amy be wrong, but the boost spike is real short duration, you probably have the controller set to 8psig, and the wastegate is staying shut until it finally gets overwhelmed and starts opening to bypass some of the flow around the turbo adn causing the boost to drop off. Seems like a lot of people are having this trouble at higher boosts with the greddy, and they use a helper spring to help keep the wastegate shut. That is just my guess. Throwing it out there.

its pretty notorous for the greddy wastegate to do as described....research "helper spring".

Yeah... thanks for that helper spring idea. I searched and found the exact problem and discussion started by Samnavy last week. See what I could've done with a little more time?:bigtu: I guess I just thought the spike seemed too long to be wastegate overshoot, but the problem the other guys are describing sounds just like mine, so that must be it. Any easy link for the timing that you know of?

Yeah, go to the diagnostic connector, jumper ten to the grnd, Hook up the timing light to #1 cylinder, start the car, check the timing now, loosen the cas bolt, turn the cas real slowly to acheive the desired timing, tighten the cas bolt, and remove everything. You will probably have to adjust, then drive, then adjust again. Listen for knock, pretty clear when it is knocking, so you will know. Good,luck and take it real slow with the timing adjustments.

Here's tom's:

https://www.miataturbo.net/forums/at...8&d=1158612378

And the old one of the GreddyFAQ page:

http://www.greddyturbofaqs.com/sheild.jpg

any part number for the helper spring?

Part Number?!?! Welcome to DIY country.....ACE Hardware carries plently of various sized tension springs...in the nuts & bolts section.

yeah, but is there a certain length or tension guys find works best?

I don't think there's a whole lot of science to it, as not that many people utilize a helper spring.

buy the length specific to how you'll mount it....then try one or two different tensions to see what works best...It might preload the wastegate too much and never open.

First off, thanks to everyone for all of the help. You guys have definitely made this whole turbo transition thing much easier.
Now, had I pulled the timing back to 6 a couple days ago and have since run all of the good gas out of it, so now I'm stuck with MO's crappy 91 :td: . I'm still getting a bit of ping right at 5K just before the overboost backs off, but I'd really rather not pull any more timing if at all possible. When the pressure settles down over 5K, it goes to right at 6psi and the ping goes away. I'm going to try first backing the MBC off at much as possible for now and If that doesn't work, I suppose I'll just have to pull more timing since I can't get back home to fab the helper spring for a while. Does this seem like a decent course of action? It already runs subpar down low on 6 degrees, so I hope it doesn't get too much worse when backed off more. Anyone know if it will? Thanks again...