Tech Tips: Tech Tips: Decoding the Vintage Porsche Strut Jungle (1965-1989)
If you’ve ever stared at the front suspension of a classic 911, 912, or 914 and wondered exactly what you were looking at, you aren’t alone. Between Boge, Koni, and Bilstein—not to mention the "great ball joint transition" and varying caliper spacings—things get confusing fast.
Whether you’re looking to refresh your daily driver or prep a 911S for the track, knowing your hardware is the first step to better braking and handling. Let’s break down the "Big Three" of Porsche strut housings.
• Boge (The Workhorse): Found on the vast majority of Porsches. Typically black or gray, these are the most versatile housings. Because they are so common, most manufacturers (including Bilstein and Koni) make inserts designed specifically to fit inside Boge housings.
• Koni (The Performance Classic): Standard on 911E and 911S models through 1977. Recognizable by their iconic red/orange paint and a distinct taper in the housing just above the knuckle. Almost all Koni struts feature the wider 3.5” brake spacing. Pro Tip: Modern Koni inserts are a breeze to adjust—the knob is right on top!
• Bilstein (The Inverted Innovator): Introduced in 1971, these use a "silver body" insert mounted upside-down to reduce unsprung weight. You can spot these by the roll pin at the bottom of the housing. This pin holds the shaft in place; don't mistake it for the ball joint bolt!
How your strut attaches to the control arm is crucial for safety. This also matters when you’re doing a 5-Lug conversion because you’ll want the best strut available to utilize the latest technology in ball joints.
• 1965–1968 (Bolt On): The early short-wheelbase cars had a bolt on ball joint that attached to a union at the end of the front control arms. While these are great for authenticity, they’re expensive and not ideal for suspension conversions (914 guys).
• 1969–1972 (Pinch Bolt): These housings have a slot that clamps down on the ball joint pin. Over time, if not torqued and tightened properly, these can "ovalize," leading to dangerous slop.
• Post-1972 (Wedge Pin): Porsche solved the slop issue with a threaded wedge pin that pulls across a groove in the ball joint shaft. It’s a much more secure, "solid" connection.
Before buying those shiny new calipers, you must measure your bolt spacing.
• 3.0” (76mm) Spacing: Found on early 911s (through '75), 914s, and early 912Es. These use "M" Calipers. Or our AM Caliper reproductions that offer S-Caliper and 911SC performance with a 3” mount.
• 3.5” (89mm) Spacing: The gold standard for performance. Found on 911S and 911E models, and eventually all 911s from 1975–1989. These accommodate "S," "A," and "Carrera" calipers.
The names have changed over the years (you might know them as "HD" and "Sport"), but the choice is simple:
• B6 (Formerly "HD"): Best for stock ride height. It provides a sporty, firm feel without sacrificing comfort.
• B8 (Formerly "Sport"): The go-to for lowered cars. It features a shorter internal shaft to prevent "bottoming out" and keeps your control arms properly seated even when the suspension is fully extended.
Wait, what about the 914?
Good news: Any 911 front suspension will bolt directly into a 914! However, keep in mind that 911 inserts are valved for a heavier car. If you put 911 struts on your 914 you’ll enjoy options like vented rotors and multiple caliper choices. In the past this could potentially throw your brake bias a little heavier toward the front of the car (there are worse places to have that bias). Now with the advent of PMB Performance’s 914-6 and 914-6/GT rear calipers… the world is your oyster.
Ready to refresh your front end? Whether you need a set of Koni Sport Adjustables or a pair of restored "AM" Calipers, we’ve got you covered.