One of the perks of a turbocharged engine is the blow-off valve sound every time the throttle closes. Blow-off valves are not something you can use on a non-Turbo engine and while some companies may sell speakers that reproduce this sound, they are noticeably fake and pointless. Simply put, to get a blow-off valve sound, you need a turbocharged engine. Even then, most factory-installed blow-off valves tend to be as quiet as possible, allowing forced induction without any unusual noises that may prompt warranty or service concerns. Fortunately, this is an easy problem to remedy.
Most factory equipped blow-off and bypass valves are quiet because they recirculate vented air back into the intake tract, which in turn is muffled by the factory air box. The easiest way to obtain a more noticeable sound is by installing a blow-off valve designed to vent directly to the atmosphere. Airflow is vented directly to the engine bay with no intake tubing or air boxes to muffle the sound, resulting in a far louder discharge. It should be noted that venting blow-off discharge to the atmosphere is a highly inadvisable course of action should you own a car that uses a mass air flow system. Because of the way these systems measure air, venting to the atmosphere will cause sudden overly rich fuel mixtures which will cause stumbling and stalling.
Short ram intakes and cold air intakes do away with factory air boxes in favor of a shorter more direct route for airflow to enter the engine. A side effect of this more direct airflow route, is a substantial increase in blow-off valve discharge noise, even on units fitted for factory style recirculation.
Any blow-off valve vented to the atmosphere will give you a louder, more noticeable sound, but it is not without its tradeoffs. For the best compromise between sound and drivability, consider installing an intake system. More power and more noise can be yours in one affordable upgrade.
Proper blow-off valve tuning is essential to the proper operation of your turbocharger system. Incorrect blow-off valve tuning can cause serious damage to your engine on the more serious side or rob your engine of large amounts of usable horsepower and torque when you need it most because the turbo hasn’t spooled up to speed yet.
A hybrid blow-off valve vents the pressured air both to the atmosphere to obtain the characteristic sound they make and into the intake pre-turbo in order to keep the air fuel mixture correct. On certain cars, venting only to atmosphere will cause a rich condition to occur which can cause stumbling or dying.
Using a sequential pull-type of valve like the HKS SSQV, or Super Sequential Valve, improves throttle response because the valve responds faster to changing engine conditions than the larger push-type of valves. This type of valve has the advantage of being less prone to pressure leaks because of its design.
For the most optimum results you can obtain, you will need to have your car on a dynamometer, a device that measures horsepower and torque output. You will need to very carefully and slowly adjust the blow-off valve until the most optimum readings are obtained.