A friend is having this problem on his R33, he has a Batmbl dump pipe and a GCG high flow.. We haven't tried any other actuators. There is a separator that extends between the dump and exhaust gasses on his Batmbl dump. I thought the wastegate flapper might be fowling on it.. Do you have the separator on yours PaulR33 (or others)?
Perhaps GCG replaced the wastegate flap with a larger one and it is fowling? We have a compressor and will drop the dump off and check things next weekend. I'll keep you updated..
