Powell YYZ/Bilstein Strut/Spring Combo


This product is currently out of stock.


  • (2) Custom Bilstein struts (assembled with YYZ springs and Powell top plates)
  • (2) Rear YYZ Springs

This kit is intended to go with a pair of the Bilstein B6 Rear Shocks. 



We set out to improve on the front Cobalt strut with the very best monotube damping.


The FE5 struts are twin tube linear valved pretty decent inexpensive struts, that are no longer easily available. And the FE5 do wear out pretty fast, as do any twin tube shock.


Koni replacement inserts are available but these are linear valved inserts like the FeE5 , and require cutting and installing correctly into the OEM strut housing. Frequently , as the Koni instructions for installation are incorrect, the Koni inserts break out of the strut housing. Even if the insert is installed correctly, the Koni is not a stellar performer.

For the Powell YYZ Bilstein program we chose Bilstein, and we spent some years searching and then working with Robby Bilbrey in Alabama to come up with the right stuff.

Bilsteins are the original  monotube gas pressure shock.  The Bilstein patent ran out a long time ago, but the “digressive valved” Bilstein patent remains. All Powell Bilsteins are digressive valved for us to custom specifications produced for us,  by shock expert Robby Bilbrey  in Alabama. We produce the new strut housings here in Canada, with DOM tubing and recycled attachments, built in a jog, tig welded and powdercoated, then assembled with YYZ springs for sale.


 Monotube shocks offer better damping than twin-tube shocks because of several aspects. ... The oil capacity in a  monotube is much higher than that in dual tube shocks and also plays a fundamental role in quickly dissipating heat. The free-floating piston valve never allows oil and gas to mix thus minimizes foaming.

To find the best shock it is vital to look at  both ride quality and damping performance ; both in on-track conditions as well as street driving,  Shocks ( and struts ) are designed to dampen spring movement when driving the car. Un-damped  springs would behave like a pogo stick.  The twin-tube feature two chambers (an outer and an inner chamber). When under pressure, the fluid flows from the working or inner chamber to the outer chamber via valves which also provides damping. Unfortunately, when under intense pressure or moving fast, the fluid starts foaming leading to poor performance. The car will bottom out on rough roads, and at high speed, both   braking and cornering is negatively affected. The car can be dangerously unstable.

Monotube shocks feature a single chamber with a top section containing the hydraulic fluid and the bottom section filled with gas. The gas and fluid never mix courtesy of a free-floating piston hence don’t suffer from foaming and provide a much better ride quality than twin-tube.


This is not an easy task to produce Cobalt struts.. Rear shocks are , however, easy as Bilstein  produce a direct fit rear Bilstein for the Delta platform. This was an  Opel Astra (also sold as a Saturn Astra) produced for two years before Saturn was discontinued by GM.


There are other suppliers who have tried to produce Bilstein struts for Cobalt. However, these efforts have basically failed. That’s because any rebuild able  Bilstein 36 mm monotube wont physically fit as an insert into a Cobalt housing and the rest of the required  OEM parts wont work.  Saturn upper strut mounts and different to Cobalt.


It took time to figure out what it would take to produce a custom Bilstein set up.  We had difficult sourcing correct parts, had several missteps in prototype testing, with incorrect metric thread source supply and  the need to accommodate the monotube housing. And  much fine tuning damping rates.  If it was easy, Bilstein would have done it themselves. I actually worked with Bilstein almost ten years ago, as they were interested in the Cobalt market for struts. That interest evaporated when Bilstein figured out they would have to build a whole new strut. Mix and match was their option. But that doesn’t  work for me. Serious drivers want the best  performing parts for their car.


You can go more cheaply with  a complete coil over set up. But these cheap coil overs are basically  generic junk for damping , internal seals and spring rates. Decent professional coil overs like the Ohlins I produced for the GM time attack and grand am race cars, ran about $7,000 in 2004 and required custom parts machined to use along with an upper camber plate which required modification to the strut housing.


We will only sell Cobalt front Bilstein struts as a complete bolt on package. That is because it requires a new, different specification, strut mount, bearing , spring plate and strut housing , along with a revalved Bilstein  insert.


The inserts come from Germany  and  are shipped to the USA , then revalved to specifications I have developed through considerable on road and track testing. Then the inserts are shipped to us in Canada, were we  make  new strut housings mounts and plates , These parts are then powdercoated and assembled as complete bolt in assemblies with Powell YYZ springs  for easy installation.


We guarantee the YYZ sprIngs  and the  Bilstein assemblies for the lifetime you own the car,  on which   you have installed them . You cannot transfer the warranty, and the warranty does not include replacement if the car is damaged in a crash. Other than that, you are good, and so are we. We believe the assemblies will last as long as the car, assuming reasonable care and anti corrosion steps are taken during ownership. .

Note: Powell  YYZ Bilstein package requires a strut core; I(f you already own YYZ springs the front YYZ springs can be returned with the core struts for a credit.


  • Front Strut assemblies with monotube Bilstein assembled powdercoated yellow housings
  • POWELL  front and rear rising rate  Hyperco  blue colored custom springs  
  • Revised strut mounts with bearing
  • Revised spring plates and upper and lower isolators
  • Rear Custom monobal shocks are alloy silver color. OEM Bilstein rubber mount shocks are yellow in color.
  • Front strut housings are powdercoated yellow. Standard powdercoat alternative colors optional at no extra cost.

These kits are built to order and may require 4-6 weeks depending on parts availability.