Try the smaller pipe but from first hand experience I would recommend the Macs 1160. I used this on my OS VF .61 (OS 7D carb with factory fitted sleeve) with very good results. 14,400 - 14,500 static with the APC 11 x 7 prop, with a nice unload in the air, a good fuel draw and total reliability. If noise is a problem, consider the 1260 Macs.