Flutter like that of a VL turbo is not achieved with a blowoff valve kids, nor is it with the turbo intake open directly to the atmosphere... On my VL I have moved the AFM into the cooler pipes, and on the front of the turbo have fitted a 15cm long piece of 2.5" intercoolre piping with filter and mesh held over the end with a hose clamp. That is what makes the distinctive fluttering surge sound you hear VL's dropping here and there. Enjoy.