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AST 4150 Monotube Coilover Struts and Shocks for Porsche 993

Regular price $3,000.00 USD
Regular price Sale price $3,000.00 USD


The 4000 Series damper stands as AST's entry level, adjustable damper. Using the same internal technology found in the 5000 Series competition sets, the 4000 Series creates near-budget level single adjustable and double adjustable dampers for the track and amateur road racing market.

Key Features

  • Monotube dampers that use 22mm shafts for struts and 14mm shafts for shocks
  • Nitrogen charged to 175 psi for 22mm shaft shocks and 265 psi for 14mm shaft shocks
  • Utilizes AST's Load Bearing Piston (LBP) for all strut designs (AST is the only coilover in this price range to use this feature)
  • Steel bodied struts and shocks all use European KTL coating which is stronger and more weather resistant than powder coat or wet paint found on most shocks
  • Utilizes design principles required for grueling TUV testing including withstanding 1 million cycles with 1100 pounds of side load on the strut
  • Available as Rebound-only adjustable (4150) or Rebound and Compression adjustable (4250)
  • Fully rebuildable and revalvable
  • Shortened appropriately for lowered performance cars
  • The 4000 series have been tested at events including SCCA Nationals, NASA Nationals, 25 Hours of Thunderhill and Grand Am races
  • Valved for a comfortable, aggressive street ride that performs great at the track

Parts Included:

  • 2 Front AST 4100 Single Adjustable (12 adj, Rebound only) Monotube Struts
  • 2 Rear AST 4100 Single Adjustable (12 adj, Rebound only) Monotube Shocks
  • Does not include shock mounts or springs
  • AST Tool Kit

The Design

AST coilovers are monotube, high pressure nitrogen shock absorbers. Most other products on the market are twin tube designs that are not pressurized, or only have 1-2 atmospheres of nitrogen inside a little bag. Monotube shocks offer the biggest pistons for more control and the high nitrogen gas pressurization in monotubes (8-12 atmospheres) means the oil will never cavitate around the piston. This is particularly important in environments where the vehicle makes rapid changes in direction like during an autocross or while road racing because a monotube shock will continue to provide consistent damping force and performance. Monotubes also allow for a wider damping range and can more easily provide a better ride with stiffer spring rates - we usually start with 3X the stock rates and often go to 6-7X the stock spring rates, even on street driven cars. This is the same technology used on $7,000-10,000 shocks packaged here in a competitively priced kit.

Tuning Assistance and Installation

At Lang Racing Development we race all of our cars on AST suspension, that includes our BMW race cars, our Porsche rally cars, and our daily driven/weekend track vehicles. That means we know how to install your suspension right and how to suggest any other changes you might want to consider at the same time, get the most out of your AST suspension by having us professionally install it and get the initial settings configured.

We can also help you dial in your suspension with the easy to adjust AST dampers. We can also provide you with spring recommendations based on your car and particular application. As as Swift and Hyperoil spring distributor we can get your car set up with the perfect spring to match your AST dampers. Whether you are road racing, rally racing, or have a dual duty track day/daily driver, we can help you get the perfect setup. To get started tuning your AST suspension we suggest reading through the AST Tuning Guide.

Custom Valving

AST-USA is setup to offer custom valving services to its customers, including dyno services on their Roehrig 2VS shock dyno; they can even rate your old springs if you are curious (fees apply). There's no need to find a third party company to get your custom valving applied - Just send them back to us and we will work with AST to get your shocks revalved to your exact specifications.