Guys, hoping for a bit of advice here.

I will try and describe the problem as clearly as possible….

Car is a series 6 FD, stock sequential turbos (with 40k miles) running 13psi (with fuel/tuning to suit)

At WOT from low down in the revs the car pulls very cleanly, dip in boost for change over, and then as the boost increases from the 2nd turbo at approx 4.1k - 4.2k rpm a whistle starts. I don’t think it’s the turbo on the way out (I could be wrong), it sounds to me like an air leak. Car is still pulling 13psi on the 2nd turbo

Here is some more info that should help diagnose the issue – after a WOT run past 4.1k rpm, if I change gear and the revs drop below 4.1k rpm and accelerate hard again Ill get the whistle (even though its below 4.1k), if I lift off and accelerate again (and im still below 4.1k) the whistle will not happen until I accelerate past 4.1k rpm.

The above instance is the only time I get the whistle below 4.1k rpm.

All the vacuum hosing looks good, I checked them very carefully. Also I replaced the hoses 4k miles ago
I swapped the air bypass valve with no change

I would appreciate any suggestions at all?! This problem really has me scratching my head!!


Thanks
John

 

Couplers can develop splits in them that will only leak boost under the right amount of pressure, so inspect those very carefully.

If you still can't find anything, you can try a tester like this one at the bottom of the page:
http://www.fighters-garage.com/rx7.html

That tool helped me find my leaking BOV that was driving me crazy.

 

Thanks AHarada, Ill take a look at all the couplers.
Im just after remembering there is an o-ring sealed joint that connects both turbo's to the crossover pipe. That might have split.....