These have been designed to improve the airflow by removing the butterfly mechanism in the factory tumblers. People will try to drill out the factory butterflies and often times, you will deal with a huge hassle such as metal shavings everywhere, tons of broken dremel bits, and lots of time.
Save yourself the pain and just go with a professional and proven product brought to you by one of the best in the industry.
CNC machined from aluminum
Anodized black finish
Installation required use of OEM hardware
Great upgrade for those looking to make big power as OEM tumblers can be a restriction
Sold as a pair