05/06/2026
One of the most common upgrades for CIS-equipped Porsche 911s is the installation of an airbox pop-off valve (often affectionately known as the "toilet seat").
In this video, I fit a pop-off valve to a classic CIS fuel-injected Porsche 911. These simple devices can save you from an expensive airbox replacement by relieving pressure during an intake backfire.
If you own a 2.7, SC 3.0, or any CIS-equipped 911, this is a worthwhile modification that could save you hundreds of pounds and a lot of frustration.
🔧 In this video:
• What a pop-off valve does
• Why CIS airboxes crack
• Step-by-step installation
• Tips and common mistakes to avoid
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