Turbo Boost Leak Query

I'm slightly confused about boost leak detection. If you remove the outlet from the Turbo and shove a bung in it with a shraeder valve fitted , them proceed to add some air , what is stopping that air travelling all the way to the heads via the manifolds and just leak into cylinders as one of the inlet valves will be open? I mean , what is stopping that from happening? Throttle bodies aren't a complete seal when closed are they? :?:

I guess if both inlet and exhaust valves are closed, the piston rings ought to make a good seal, so while air pressure in the cylinder may rise, it shouldn't leak out quickly if all's well. But surely an exhaust valve somewhere will always be open, so yes I'd have thought it would leak into the exhaust. Do you have to plug the tailpipes too? I'd have thought it would be worth using a bung at the throttle body as well.

I haven't worked it out but 100% that some inlet and exhaust valves are open when you shut the engine down Some people are talking of their throttle body O ring leaking as well No mention anywhere of blocking off at the Y pipe exit (to throttle body) All these check valves and things are all over the place , how are they stopping leak down via the engine itself?? I haven't done it yet but boost is down, at the PCGB Anglesey track day last week my Turbo was struggling to keep up with my mates 3.2 Carrera!! He's a better track driver admittedly but even on the straights I should have flown past I was touching 0.8 before I went down and now 0.5 , it's still fast but doesn't have that insane punch after 4k revs now. I've checked the big hoses from Turbo's to IC's and they seem fine and I would think the IC's are good, it's a very low mileage car that's been in a collection for many years so it's in very good nick but I'm aware things deteriorate as well.

Best of getting it down to 9e, RPM JZM etc and they can probably do a quick boost leak check whilst you wait. Can be so many things on a 996 turbo better to let the experts check. Most turbos of this vintage running with boost leaks and owners not aware as they still feel quick.

I live in Scotland so not really an option for those but met a chap at Anglesey with a fully rebuilt insane GT2 that owns a garage up here, I think I'll give it to them...Ecosse Automotive at Bo'ness Like you say it's still fast but I know it doesn't have the same punch as I 'm able to look down at the boost gauge now and I dare not before , you had to keep your eyes in front.

Matt at Ecosse can do it, or Stuart at SP Autobahn in Stirling, who did mine recently as I had a boost leak and was getting similar boost to you Stuart did it from the air intake hose - it was one of the little pipes off the left hand divertor valve - the point isn't so much that it will hold 100% of the air pressure fed it, the point is that when it's pressurised you can hear the air escape and then track down where it's coming from! There are two divertor valves. If it's one of those they are relatively cheap to replace as well - it's probably nothing serious!

Ok thanks I'll maybe get one on order just in case. It's booked in with Matt in a couple of weeks so looking forward to that and seeing his set up. Hopefully it's nothing too bad and I can get my full boost back

Don't buy anything, let Matt sort it - if it IS a divertor valve it's a VW part and easily available from motor factors!

Perfect thanks. I'll take photos and do an update when we've found out the cause

Boost leak detection Here you go https://www.markskituning.com/pressure-test-101-how-to-find-boost-leaks/ The way my tuner does it 👍real easy, he remotely tuned my turbo to circa 650bhp with me on the spanners, I also changed virtually all the valves and plastic bits on the boost circuit, my bad leak was the throttle body O ring seal leaking. Good luck with it, it's really not complicated just terrible for access 🙄😂😂