Running a Greddy kit with BOV, EMU, car is otherwise stock. Still using a manual boost controller. I'm just wondering if someone can take a look at this boost curve and tell me if it's typical, or if something needs attention. The boost always spikes up to just over 6 psi, but then the system can't maintain more than about 4.5 to 5 psi for the rest of the rev range to redline. If I turn up the boost, then the spike gets higher, but the nominal level of 4.5 to 5 psi stays the same. Is this normal for this kit, or do I have some kind of problem somewhere? Is this something an electronic boost controller could help out with?

Also if one of you experts could look at the rest of the curves and make sure something doesn't look out of whack, that would be appreciated.

Thanks,
Ken

 

Wastegate can't hold the boost would be my guess. I know the Greddy's have a problem with that.

I mean the spring on the door. Either the total exhaust gases are overwhelming it, or your Manual Boost controller (if it is a check valve) is opening and hitting the Wastegate all at once causing it to open. If it is one of those slow bleed off kind (can't think of the name) then that may not be it...

 

Indeed it's one of the dual-valve types, with a ball valve and also a bleed valve. But before I even added the controller, I was seeing the same basic problem. Boost high, then falling off to 4.5 to 5 psi across most of the upper rev range. In fact no matter what I do, it seems to max out at 5 psi except for that high spike initially. Is that all this turbocharger can produce without further mods? I thought some people were getting a lot more boost than that. And I'd really like to see a flatter boost curve.

Thanks.

 

Try tightening the WG spring. That would be my recommended step one.

The boost will drop off as the engine requires more air flow. I haven't gotten to the point of actually mapping a logfile to the compressor map, so I can't say exactly what those numbers are. Wanna be a guinea pig?

 

PS. You would have seen the same thing W/O the controller, as the boost is running straight to the WG, causing it to open. THe controller just delays the onset of that.

With a check valve, once it opens, that WG is going to fly open with the full boost signal.

 

Sorry, I don't even know what that means. Can you elaborate?

 

Doesn't look normal to me, but my setup isn't the same as yours. If you watch this old video of mine (0:45 in till the end), you'll see I can hold 8-10 psi at 8,000 rpm just fine.

http://youtube.com/watch?v=vTFWJiHOGv0

That's with a electronic boost controller, before it was properly tuned.

It looks like your wastegate is opening, preventing you from building boost.

 

Could it be "normal" considering the stock cat and exhaust? If the exhaust is restrictive enough and the WG spring is soft enough, could the WG be actuating early, limiting boost?

 

Look up my tuning thread. I also want to do the same kind of mapping for a turbo compressor map. So you can see where your engine / turbo combo fall in the overall efficiency of the turbo.

On topic, pls update us on the WG spring. Down stream of the turbo (cat, exhaust) shouldn't matter much. It is the total volume of exhaust gases passing the WG are what could be pushing it open.