In general: S size is suitable for engines with a displacement of 1.0-1.6 liters, with exhaust pipe diameters ranging from 32-43 mm.Approximately 69g M size suitable for 1.6-2.0 liters of displacement, exhaust pipe diameter 37-48 mmApproximately 87g L size suitable for 2.0-2.4 liters of displacement, exhaust pipe diameter 44-55 mmApproximately 106g XL size suitable for engines with a displacement over 2.4 liters, exhaust pipe diameter 56-85 mmProduct Name: Car Modification Turbine Whistle Exhaust Mimic Sound Generator Specifications: Small, Medium, Large, and Extra Large, 4 models The above price is for the small size. For other sizes, please contact customer service! Easy installation, beautiful and stylish, low cost, is a decoration for your car. This product is divided into small, medium, large, and extra large, 4 models. The product length is just the length of the whistle, not including the length of the fixed frame. About size selection: /Please measure the inner diameter of your car's tailpipe first, Then compare it with the size in the picture, which one fits your car; Under the premise of the appropriate installation size, try to choose a larger size. Sound similarity: The sound of a real turbine relief valve is usually "sizzle, sizzle". This whistle makes a "hoo, hoo" sound, more similar to the kind of whistle we usually play with our mouth. After all, this is a mock sound generator for a few dollars, and technically, it cannot be imitated to the same extent as the real one, only so. Non-product quality issues do not accept returns.