i wanted to pull the wastegate actuator hose just to see what kind of psi i could get from my 15g i recently installed.

With the 13c i had on there before it would bang on 25 psi with easy with no wastegate hose attached. The 15g however will only go to around 12 psi and hold there even under WOT till red line with teh occasional spike to 15 psi.

my question is what would enable my smaller 13c to hit 25 and the larger 15g to stop at 12? the CBV maybe getin weak? im kind of at a loss to why it wont just spool like a madman like the 13c would.

thanks again

Bryan

I tried replacing the CBV valve this weekend with a good one from a 13C and there was no difference at all. I am now starting to wonder if some cracks in the snail housing near the wastegate in the hot side are starting to leak significantly under boost allowing the exhaust to bypass the turbine wheel. Would this make any sense?

I have a 15g on my 1992 740 and I have to admit that I am also not very impressed. I can also make max 12 psi. I thought that my problem had to do with the flimsy wastegate actuator bracket that I have along with a weak actuator which is not uncommon with the 15g's. I had not considered the CBV before, but that would also certainly cause lower maximum boost so I have something else to mull over. EDIT: I found a possible answer at IPD. They say that the stock CBV is only good to 12 psi:

http://www.ipdusa.com/product.asp?strParents=&CAT_ID=0&P_ID=5223&strPageHistory=search&numSearchStartRecord=1

In general, I have not been overwhelmed with the 15g and stop light to stop light and I liked the 13c because it spooled up faster in comparison. Also, if all sorts of boost is leaking into the exhaust then that would also explain why my car has been running leaner than usual since I made the switch. It looks like I also have a project for the weekend and an excuse to upgrade the CBV.


Mike

hmm there is a group buy on VS now for the upgraded CBV that should be wrapping up by the end of the month if you are interested in that.

meanwhile back on the ranch i think im going to try to put in the cbv from the 13c and see what happens since as i said before it would spool 25 psi easily with no wastegate.

trial and error yeah? =P