Thanks, I had a Janspeed conversion in the early eighties and it had the same problem (pulling in oil, I guess from the centre turbo bearing when shutting off fully after running on full boost). That car did not have a pressure/vacuum gauge but this one does. When I saw it was pulling nearly 30" of mercury (that's not far off total vacuum) I thought I'd experiment with a vacuum relief valve. Where I've fitted the valve is right in the centre of the plenum chamber so I might have altered the vorticies and made a difference to the air flow. Also it may be more responsive as I don't have as much vacuum to fill before the engine can breath again and not having all that oil to get rid of must be a good thing and add to the engine's reponse. As I said though, I'll monitor things over the next few weeks.