AST Releases The New 4150 Suspension Upgrade

All New AST 4150 Damper

AST is now releasing its update to the 4100 series damper; the AST 4150 Series Damper. The 4150 design builds on the basic architecture and market success of the AST 4100 series monotube single adjustable damper, and brings experience learned in the recent wins in GRAND-AM Continental Tire Sports Car Challenge, including new technology developed specifically for GRAND-AM racing teams. There is also some technology sharing from proven Moton Suspension dampers that have made their way into this strut, which is detailed below.

You can read about this new 4150 damper in the Official AST-USA Press Release. Here is an exploded view of the new 4150 damper highlighting some of the design changes:

This is a 3D rendering AST made recently showing a cut-away view of the production 4150 version. All of these upgrades and new parts have been tested on various race and street cars, including the DDP pistons, low drag seals, and top guide. Let’s look at some of the new components and explain what has been changed.

DDP Technology Piston

AST’s latest digressive piston was developed for GRAND-AM and gives drivers and race engineers the best of both worlds. Drivers love the low speed damping response and body control, while race engineers love the “blow off” (the knee point digression, shown in the dyno plot below), with a tapering off of the rebound forces at high shaft velocities.


When the rebound adjustment is set to soft, the damper curve looks similar to an OEM street shock profile. When the rebound adjustment is set to firmer settings, the damper curve looks like a race shock. The most critical portion of the dyno plot area is affected the most – the portion at low shaft speeds. So much in racing happens at 0-3 inches per second shaft velocities, and that’s where these pistons really step up the damping forces, when adjusted firmer.


Those two documents above list more details, and you can click them for larger images. The graphed rebound curve shown on the right shows the large amount of adjustment from full soft to full firm, and the super-digressive curve shape that these new DDP pistons can achieve. This “Jekyll and Hyde” personality is exactly what AST 4000 Series customers want: soft street ride and firm race car track performance in ONE shock – all with the turn of a knob.

Adjusting the knobs on the prototype ASTs with the DDP pistons makes a night and day difference – with more adjustment potential and valving change than we’ve seen in any other shock. We were driving it at one of the bumpiest tracks around and were able to get the track set-up dialed in quickly, still soaking up the bumps but with sharp turn-in and controlled braking. When turned down to full soft for the drive home from the track, and it rode like stock.

Lower Drag Seals & Stronger Top Guide

High performance seals are a challenge for any damper. They must balance friction and sealing ability while not impacting shock performance and not leaking; All of this makes for a difficult balancing act. While the seal was originally developed for GRAND-AM road racing, AST is taking their knowledge from the track to the street once again.

These newly redesigned shaft seals have a low-friction polymer inner liner and an outer jacket with the appropriate amount of stiffness and flexibility needed in a street strut. This gives the low seal drag characteristics usually only seen in a race shock, with a street-worthy seal. These new seals reduce hysteresis in the damper plots by decreasing seal drag over 50%.


One of the benefits of AST and Moton being owned by the same parent company is technology sharing – when there is one design element obviously superior, it can and should make its way into another model across brand lines. There isn’t much of this cross-pollination going on between AST and Moton, but one improvement to the 4150 strut design is the addition of the longer and stronger top guide from the Moton Motorsport strut. This Moton top guide is extremely strong, and will help minimize shaft deflection under extreme racing loads, and is a welcome addition to the 4150 AST strut. This is another reason why the 4150 will work well on the street and on the race track.

Discontinuing Steel Shocks

In 2012, most AST 4150s will come with aluminum shock bodies. Strut bodies will continue to be built from steel, but all shocks will switch to aircraft grade aluminum. Economies of scale have allowed the factory to switch to aluminum without a large increase in cost of manufacture. For some models, this represents a 50% reduction in the weight of the damper (unsprung weight).


All 4150 aluminum shock bodies will also be fully threaded, unlike the smooth steel bodies on the previous 4100 shock. This allows for a potential to convert almost all 4150 shock models to a “coilover shock”, with the appropriate threaded collar, coilover spring and upper spring perch. This is beneficial on cars that normally do not have a coilover shock set-up (there are other issues that must be discussed with your shock dealer, of course), when that is desired for altering the spring motion ratio or reducing suspension mass. There is no longer a need to make an aluminum (5100) and steel (4100) version of every shock, so some former 5100 models for shock-only car set-ups will come under the new 4150 product envelope.

Structural Improvements

Several new designs proven in GRAND-AM racing will be added to various products on an “as needed” basis. All strut models will receive a new two piece top guide assembly that separates the dust seal assembly from the oil seal/bearing assembly (see the cut-away picture at top of this post). This two piece design is stronger in compression loading (bottoming out) and side loading (in the turn). Some models will receive weld-on stabilizer brackets which take the guesswork out of setting the stabilizer height and torque setting of the clamping ring.

Upgradeability to Doubles!

Finally, the upgrade path of the 5000 series has made it to the 4X50 series shock! Yes, AST 4150s will be upgradeable to 4250 internal double adjustable monotubes. Using a modular build system, customers can send their shocks to AST at a later date and upgrade from a 1 Way shock to a 2 Way internal reservoir or remote reservoir system. Some models may only upgrade to remote reservoirs. An upgrade matrix will be published in early 2012, and I will show the details of the 4250 in this thread as they become available. The upcoming 4250 will replace the 4200 models starting in March, and we will get our hands on them as soon as possible.


The 4150 dampers have a screw-in bottom assembly that can be removed and the “guts” of the 4250 internal double can go inside most strut and shock models. Any 4150, and especially short bodied struts and shocks that have limited stroke, will also have the option for a remote reservoir assembly to be added there as well, to make them into remote doubles. I think they will be called 4250RR, but that might change. AST-USA did this before on some 4200RR models, as shown above, and it worked great when the additional stroke or added fluid capacity from reservoirs was necessary. The 5200 inverted strut (and the 5200GA) with remote reservoirs is still going to be in the AST line-up, of course.

Cost & Availability?

The parts have been tested, the design is finalized and production begins at AST Holland on several 4150 models in early January, so we should see 4150 models coming to our shores by late January.

The 4150 pricing is fairly close to the outgoing 4100 model, and in most cases within $100-150 of the old part numbers. That’s not much of a cost increase considering the number and breadth of updates these 4150 dampers have. The upgradeability feature (to 4250 doubles) alone is huge, and will be a big selling point for racers that want to ease their way into double adjustables, with less pain up front.