Boost Drop Off - falls at higher RPM

[KFoster]

I was going to order a 1 bar spring for my car, but now the boost only reaches .6 bar. It has been hitting .8 bar and holding OK. Now, it hits only .6 bar and falls to .4 bar at high RPM (5500 and above). Car still pulls good to redline, but you can feel that it is down on power. 330rwhp at .8 bar. B&B intercooler and exh with a K27. I looked on a couple sites I deal with and could not find a rebuild kit for the wastegate. Any ideas? Rebuild time? I'd appreciate any and all help.

[lucittm]

K,
You can rebuild the WG yourself. There are some tricks. First, the spring (any WG spring) is under considerable tension. You will want to contain the top and bottom of the WG before you remove the 10mm nuts and washers. I put mine between the centers of my lathe and use the tailstock to let the spring expand slowly.

Next, you need to inspect the diaphragm, I suspect you have a pinhole leak. I have a spare diaphragm that I can send you if you need it.

Then you can remove the cast iron cylinder from the aluminum housing. There is a NLA asbestos (if original) washer-type gasket between these pieces and if it tears, you will have a leak. It is possible to replace the gasket with some pieces of header gasket, but you will likely need to double the thickness, it will be about a 1/8" - 3/16" gap. Use the old gasket as a template.

Inspect the valve, valve guide, and valve seat and clean all the parts before reassembly. Mine had about 50K miles and were still all in good shape. Replace the two aluminum washers, 900-123-043-30 under the middle banjo bolt, the top banjo bolt just vents to the atmosphere and you can re-use the washers. Replace the square exhaust gasket, 930-123-194-06.

Finally, replace the three valve body nuts with 8mm copper nuts if you can get them, 900-076-025-02 (or plain ones, 900-910-097-02). Get someone to help you reassemble the WG top housing, being careful not to pinch the diaphragm and you will be back in business.

Mark

[lucittm]

They say a picture is worth 1000 words:

[mooney265]

Originally Posted by lucittm

K,
You can rebuild the WG yourself. There are some tricks. First, the spring (any WG spring) is under considerable tension.

Or, you could not take that advice and almost end up with the wastegate in your face I watched the spring fly right by my face... #'s If I had to guess, it's under about 75#'s of pressure...

I have a stock spring in mine and just re-assembled it yesterday with new diaphram. Because I'm now aware of the "considerable tension" I could hold it back [while in vice] with my hand/arm. I was able to re-assemble by pushing with my left hand [really leaning into it...] and screwing the nuts with my right [of course the WG was in a vice...].

Good luck...

[lucittm]

Mooney,
There is nothing quite like the education provided by the experience gained when actually doing the work yourself.

Mark

[KFoster]

I will try what you suggest and change the spring at the same time. Should be no problem. I would prefer factory gaskets though. I appreciate all the help and suggestions.

[mark houghton]

Originally Posted by lucittm

You will want to contain the top and bottom of the WG before you remove the 10mm nuts and washers. I put mine between the centers of my lathe and use the tailstock to let the spring expand slowly.Mark

I don't have a lathe, but instead used my drill press (inappropriately) to hold the wastegate together, removed the nuts, then slowly raised the chuck to decompress the spring.
Do this piece wrong - no matter what your method - and you will have a missle flying across the shop. Not cool....

[lucittm]

KFoster,
The white composition wastegate gasket is NLA (No Longer Available). There was a post in another thread about a guy purchasing the last one from Andial a few weeks ago, although I would wager that gasket was aftermarket.

Good Luck,

Mark