A turbo still requires back pressure from the exhaust and something i been doing some light reading on
its also something that is spoken about even less when it comes to us normal car owners and tuning the mini.
the complete lack of any true back pressure from the exhaust except the exhaust pipe itself can be a problem.
overboost is one in a way because the turbo is just spooling too damn fast and the rest of the car isnt able to keep up in certain situations.

but your little blow by there would simulate the waste gate dumping boost straight out the exhaust i guess??

 

Yeah, I guess it sort of works like a second wastegate, lol.
according to Arric at JMTC “back pressure kills turbos” so I’ve tried to eliminate as much as possible.

 

That is correct, too much back pressure
but when you look at big turbos with hundreds of horse power its different
overall back pressure can be bad if its really heavy, but more outward flow (exhaust) is good but when its super free flowing there was serious talk about it causing the turbo to spool too fast this was something i had come across in a few threads that mention the complete lack of the CAT is causing the spooling of the turbo to be too quick and quite possibly overboost as the engine isnt ready for that much boost which to me implies low rpm

 

Interesting

 

Well I got the downpipe gasket swapped out. Haven’t been driving it very much, because I a have a leaking tire that can’t be fixed.
But, so far so good. It quieted some things down and seems to have fixed my hooting whistle. Fingers crossed.... I have thought I fixed it in the past as well, so I’ll give it a while to be sure before I proclaim success. Lolz
Now onto the next step.... first thing tomorrow morning Duncan is getting a new HPFP, and 4 new kicks in the afternoon. Tomorrow should be be a pretty good day.

 

Hi, could you please confirm whether the cause was an exhaust manifold gasket leak?

I am having the same symptom as in your case, namely a strange high pitched whistling/burbling sound only at partial load. And what is more confusing, that the car does the sound inconsistently. Actually I have discovered some kind of correlation: it usually does it after longer engine brakings, then after I have accelerated a few times it disappears for a while.

I've had the impression that this is some kind of a vacuum hose/accumulator problem. So I checked vacuum hoses (replaced actually) and diverter valve, but they are ok. Then I thought maybe the pressure control valve or the vacuum pump could be the culprit, but after reading this thread I am really not convinced. Any help would be appreciated.