[Former_Boosted_IS]

I have to admit I have focused on the performance aspect of the N54 for most of my journey thus far, but the need for suspension mods has always been unavoidable. I have read a lot of stories about the installation being difficult and maybe that is what has kept me away from this modification... until now. My car started on ZSP suspension for reference, but not anymore!

Once, I decided I was going to focus on suspension then I had to decide between a spring/shock combo or a coilover setup. In the past, I have gone the coilover route more often and felt that was the obvious choice here. The flexibility with coilovers for height adjustment was just too important to me. There are so many people have clunking/chirping issues with KWs that I just felt I couldn't go that route, plus I really wanted a monotube strut design if at all possible. I want a daily driver that does not ride harsh, but lowers the car and can give me the street response I need with maybe a rare track event. After sorting through the limitless options, I ended up going with the AST 4100 shock absorbers with Hypercoil linear rate springs. AST interested me for a lot of reasons:

1. AST hand builds every coilover at a very reasonable price
2. AST struts are well known for their performance
3. AST is known to be very street friendly and race tuned easily with simply adjustments
3. AST uses high pressure monotube struts which has a whole lot of benefits
4. AST coilovers can be completely re-built and re-valved making this a worth while investment
5. AST coilovers have fully threaded strut bodies so we can get a big tire in there without rolling fenders or using spacers

Now, I mentioned I went with Hypercoil (sometimes called Hyperco) springs. They are linear rate springs which tend to be much more predictable then progressive rate springs and that was appealing to me. AST provides thrust sheets to use with the Hypercoil springs protecting you from irregular spring rates during the unwinding process. The spring rate and length was custom selected by STETT Performance based on my need for a great street car that may see the track on rare occasions. You can custom select the springs yourself or simply share your performance goals with STETT and have them custom the application for your needs.

Performance is great, but I do want these to hold up through the seasons. AST uses a KTL process to coat all of the struts and I found the read very interesting from AST’s website:

Originally Posted by AST

We're often asked if the struts bodies can last in harsh environments such as salt. First of all, all struts are produced using high grade steel as opposed to aluminum, stainless steel and other materials. Steel is by far the strongest, most durable material for this application. AST then coats each body in a process called "KTL" in Europe. This process is not common in North America but is often referred to as cataphoretic dip painting. Dipping the part into a bath all but guarantees complete, even coverage. This provides the best protection against corrosion. This process far exceeds OEM standards on corrosion and is extremely tough.

Each cylinder is dipped into a bath and baked to dry the chemical onto the body. This differs from powder coating where the product is essentially spray painted then baked. Most factory applications use "wet paint", simply sprayed on paint. We've removed struts off cars and noticed no scratches on the body from the installation. Even factory pieces would have nicks in the paint. KTL is expensive and time consuming, two things not condusive to a factory part, but well worth the price to produce the highest quality aftermarket struts.

I avoided camber plates simply because I do not want the clunky sound that can come with them. For me, the risk just wasn’t worth the gains.

The bottom line is AST is proven on the street and on the track as a superb setup. Some of the most reliable people I have spoken to refer to them “ unmatched” and I think I have to agree.

Vendor Interaction

After I decided on an AST setup, I had to decide who to buy the kit from. My dealings with STETT Performance have all been very pleasant, so it was an easy choice for me there. I made the order from STETT around SEMA time, so I knew a small delay was likely. The week after SEMA ended, I received a notice of shipment from STETT which I always appreciate. I tracked the product to my door and was very excited for that work day to end! LOL!

The products were extremely well packaged and protected.



All the items are bagged, wrapped, or cardboard enclosed to protect them from damage.



Taking the kit out of the box, I was very excited to see everything laid out. The kit is just awesome looking! Notice how the rear springs are protected against damaging anything in the kit by adhering them to the cardboard tubes holding the rear shocks.



Here is everything unwrapped. You see the rear shocks, rear springs, rear orange adjustable spring perch (with attached thrust sheets), rear rubber lower spring seat, front spring on strut design, front strut tube used to seat the coilover in the knuckle pinch clamp.



The AST coilovers are your traditional coil on strut assembly in the front.



When you see the monotube shocks for the first time you will be blown away with how big the pistons are. Those things are beasts!



The shocks are steel bodied and they are well built. AST uses brand new, custom housing on every single shock you order from them.



Each AST 4100 is rebound adjustable. The adjuster knob on the top of each shock is easy to view and easy to set. Each turn of the knob is accompanied by a clear "click" so there is no question on where it is set. The adjustment knob is also clearly labeled.





The AST rear suspension is a spring setup with an adjustable perch and separate shock.



Here is a look at the rear hyper coil spring.



After my initial testing, a slightly different orientation of the springs was selected and immediately shipped to me:



Installation

I must admit that I was a bit intimidated on the installation because some people really have made the installation sound very difficult. After completing the installation, I honestly felt it was completely straight forward with no real hooks. The install is really not hard, but just takes a little time. If you are patient when you remove the stock front strut from steering knuckle then this is an easy project. I combined a few different DIYs to help on the installation:

Spring DIY:

http://www.e90post.com/forums/showth...6R+springs+DIY

Front Strut DIY

http://www.e90post.com/forums/showthread.php?t=65204

Rear Strut DIY

http://www.e90post.com/forums/showthread.php?t=27474

Torque Spec

http://www.e90post.com/forums/showth...r+torque+specs

Front Torque Specs At A Glance:

-- Strut top bearing to chassis: 25 ft-lb
-- Strut brace to strut tower: 30 ft-lb
-- Stabilizer bar to strut: 43 ft-lb
-- Strut assembly to steering knuckle: 60 ft-lb

Rear Torque Specs At A Glance:

-- Swing arm to rear subframe (camber bolt): 122 ft-lb
-- Shock to swing arm: 28 ft-lb
-- Shock to body: 27 ft-lb
-- Stabilizer link to sway bar: 43 ft-lb


Since these DIYs cover the installation well, I will defer to them. I do want to touch on a few items though. I would really suggest two jacks to make life easier. Some of the bolt/nut sizes were wrong in the DIYs, but if you have 17-22 mm box wrenches and deep sockets, then you should be covered on everything. Some cars also have the headlight level on the driver’s side and other’s on the passenger side, but you cannot miss them. Probably the hardest part of the install was breaking the front strut loose from the steering knuckle. Just soak your shock with liquid wrench or WD-40 and gently use a pry bar to open the front knuckle pinch clamp so you can slide the front strut out. Two sets of hands here really are invaluable. Also, get a Bentley Service manual to verify all torque specs! That thing is worth its weight in gold!

I also removed the speed or ABS sensors during the install because I know how finicky they can be. They are held on by a torx bolt and look like this in the rear:





The front ABS sensors are just as easy to locate.

In the rear of the car, use this diagram to help guide you on how to assemble your new shocks:



You will re-use items #3 - #7 on the shocks, but remove the bump stop on item 3 and just the top cups on the rear springs. Since the springs are flat on the top and bottom, you don’t need the stock spring bump stops on the top or bottom. I placed the adjustable perch for the springs on the top of the rear spring.



For the front, use this diagram to help:



I re-used the top-hat to mount the coilover. That is item #1, #2, #5, #6, and #7.

Here is the final product in the rear:







Up front things should look like this:











Adjusting height is easy using the adjustment tool that comes in the kit.



You can adjust both the front and the rear if the car is jacked up without removing the tires.

One thing to note… the strut bodies are fully threaded so you can keep the stock orientation of the sway bar links on the front. This is really a fantastic feature because basically you can adjust where the upper sway link attaches to the strut potentially avoiding future problems. We are starting to hear stories of clunking/popping when the wheel is fully turned with some coilover kits and some are speculation the cause is improper orientation of the sway links caused by lowering.

Lower Range

The first goal was to lower my car, so that was nicely accomplished with the kit. At full dump in the rear, you are probably down 2". At the top of the adjustable perch you are near stock height. Here is a look at the rear drop.

REAR



On the front of the car at its lowest you will be down around 2.5" - 3". At its highest settings up front you will be near stock. Here is a look at the front drop.

FRONT



This fits my needs perfectly with 19s.

Performance

The adjustment process was quite simple. AST has the adjustment knobs mounted on the top of each strut and that makes them easy to access. The front is obviously very easy to get to because it sits in the strut tower in the engine bay, but you need to get behind the carpet liner in the rear to adjust them. I just dropped the back seats and that makes accessing the adjustment knobs simple. I started 2 “clicks” from the softest setting to get a feel for the AST setup. The car seemed too bouncy and floated a little. It really floated when pushing through corners and if you got some bounce during a corner it became a little unbalanced for my preference. I dialed one more click toward firm and found exactly what I was looking for. So I settled on 3 “clicks” from soft on the front and back.

I do want emphasize having a “streetable” car with substantial improvements in handling was something that was critically important to me in this process. After I took the car out for the first time, I was really blown away that coilovers can make this big of a difference on the car. In the past, I have needed sways, strut braces, etc. to accomplish my suspension goals, but I think the AST coilovers may have accomplished almost all of my goals! The linear rate Hypercoil springs gave me exactly what I was looking for and that is predictability. I really feel like I know how the car will react and for me that is very good. The AST dampers have completely eliminated the body roll that made very hard cornering “soft” and a bit on the edge. The car is extremely predictable and controlled through the entire corner now. Light or hard bumps through the corner no longer bounce my car to the edge of “out of control”. Bumps in corners really made me very skittish with the stock ZSP setup, and that feeling that the car is skipping is completely gone. This is something I really want to emphacize, with the AST coilovers I can push the corners to the limits of the tires with high confidence. I am no longer concerned that I will go from totally in control to losing control due to a bump or unexpected body roll and this has absolutely changed my driving style. I can now enter corners faster, take the corners faster, and exit corners faster. It really has allowed me to completely use the power my car makes and enjoy that full driving experience.

Finally, I mentioned I didn’t want any of the chirps or clunks that have plagued some of the other coilovers on the market. The AST are simply noise free. I specifically tested this area with all types of speed bumps and some rough roads. Whether it is small bumps, large bumps, or speed bumps the suspension is absolutely quiet. Since that was an area I would not compromise, I am very pleased.

The overall comfort of the ride is kind of a tricky thing. We want sporty, but not bouncy. The ride is a little bit bumpier on rough surfaces, but I still feel it retains the sporty feel you have with the ZSP suspension. I think the best description would be a little bit more sporty then the stock ZSP suspension.

Conclusion

STETT Performance hit another out of the park for me. Their communication with me has always been top notch. I love that the send tracking information once the shipment is initialized so I know when to expect the product. They have always been available to answer my emails within 3-6 hours and take my phone calls when I need support. Simply put they dialed in an absolutely phenomenal suspension setup for me.

AST coilovers with Hypercoil springs offered me the lowered stance I wanted and the increase in performance I needed without the infamous “bouncy” ride quality. I personally have never owned a better quality set of coilovers and I have owned quite a few. The monotube struts are everything they are made out to be plus some and the damper adjustment is simple. The cornering improvement is just phenomenal! The flexibility in lowering your stance is perfect for the front and rear. The linear rate Hypercoil springs AST selected give you predictability and they are very streetable. Again, I cannot say enough about the quality of the AST coilovers. Now, I have a fast car that I can use in the corners.

If given the ability top make this choice again knowing everything I know now, I would end up AST coilovers again. This was a good choice.

If you want to watch a short video on the AST coilovers, check this site: http://www.ast-usa.com/.

[GreenPlease]

Great review! I've been procrastinating on coilovers for nearly a year now and I've been of a similar mindset: I simply can't justify going KW considering all of the horror stories I've heard. I was considering Bilstein but now AST is on my radar. Thanks!

[Donald-335i]

nice review!

can't wait to purchase my coilover system once on done with the meth!

[stressdoc]

Superb review and DIY, great product. Spring thrust sheets and flat spring tops and bottoms are the way to go. My only minor concern would be weight; I think the Swift springs are lighter, as are some dampers.

Thanks for posting all this; excellent photos.

What spring rates are you using?

[kenneth]

Wondering why you didn't go with the swift springs! not much difference in price....

[Former_Boosted_IS]

Originally Posted by GreenPlease

Great review! I've been procrastinating on coilovers for nearly a year now and I've been of a similar mindset: I simply can't justify going KW considering all of the horror stories I've heard. I was considering Bilstein but now AST is on my radar. Thanks!

GreenPlease, thanks for the kind words. It sounds like we are in the same boat. LOL! If you needs are similar to min, then give the AST a try. They are absolutely a superb performing system.

Originally Posted by Donald-335i

nice review!

can't wait to purchase my coilover system once on done with the meth!

Any idea which coilover setup you are going to choose?

Originally Posted by stressdoc

Superb review and DIY, great product. Spring thrust sheets and flat spring tops and bottoms are the way to go. My only minor concern would be weight; I think the Swift springs are lighter, as are some dampers.

Thanks for posting all this; excellent photos.

What spring rates are you using?

stressdoc, thanks for the compliments! I totally about the flat springs with thrust sheets. I know the Swift springs were a little lighter, but I chose Hyperco simply because they have such a good, long standing reputation in racing.

The spring rates and length were selected by STETT but I can check if you want.

Originally Posted by kenneth

Wondering why you didn't go with the swift springs! not much difference in price....

Again, I chose the Hyperco because of their long standing reputation. If you wanted Swift, it is a simple change that can be made when purchasing the coilovers.

[TT3 iN NyC]

Wow. GREAT review. I'm in the market for some coilovers and I was going to go with the KW V2's. However, after seeing your review I may change my mind. I have consulted with a friend of mine that's a suspension guru and he advised AST is definitely the way to go.

Can you please PM me how much you paid and where I can get a set from?

Is your car an e90 or e92? I have an e92, do they have an application for it?

Thanks!

[E92-Lighting]

great review

[CPI]

Great Review as always!!

[kenneth]

Thanks for your post, I will be getting ASTs too in the new year. They don't come cheap, but still cheaper than Motons

[ianbiz]

Good read and info!

[GreenPlease]

Can you please PM me how much you paid and where I can get a set from?

+1

[Sea2Ski]

Originally Posted by TT3 iN NyC

Can you please PM me how much you paid and where I can get a set from?

+1 here too!

[Former_Boosted_IS]

Originally Posted by TT3 iN NyC

Wow. GREAT review. I'm in the market for some coilovers and I was going to go with the KW V2's. However, after seeing your review I may change my mind. I have consulted with a friend of mine that's a suspension guru and he advised AST is definitely the way to go.

Can you please PM me how much you paid and where I can get a set from?

Is your car an e90 or e92? I have an e92, do they have an application for it?

Thanks!

iN NyC, thanks for the compliments on the review.

I have never driven a set of KWs so it is hard for me to compare, but I can tell you these perform superb. Everything people have said about AST is true in my opinion.

You can get these from STETT Performance as I did. I am E92, so they definitely have our application.

Originally Posted by E92-Lighting

great review

Thanks E92-Lighting.

Originally Posted by CPI

Great Review as always!!

CPI, thank you for the kind words and taking the time to read it.

Originally Posted by kenneth

Thanks for your post, I will be getting ASTs too in the new year. They don't come cheap, but still cheaper than Motons

Bingo! The AST give you an extraordinary value for what you are getting! Monotubes are simply incredible.

Originally Posted by ianbiz

Good read and info!

ianbiz, thanks for taking the time to read. I am glad the info was useful.

Originally Posted by GreenPlease

+1

Originally Posted by Sea2Ski

+1 here too!

Green and Sea, I will send you guys a PM.

[ar design]

GREAT writeup! I will definitively be eying an AST coilover setup in the near future here.

[Hedges]

How much are these coil-overs and what are the direct competition of this product? KW's? GC's?

[Mike@F1 Autohaüs]

Nice and thorough review

[Alpina_B3_Lux]

Great review! Thanks for taking the time to write it all up so well and post those splendid photos.

Alpina_B3_Lux

[Craig@SupremePower]

nice write up...

[Former_Boosted_IS]

Originally Posted by ar design

GREAT writeup! I will definitively be eying an AST coilover setup in the near future here.

AR, thanks for the kind words on the review. I know you love to drive and I think you wouldn't find a coilover that fit your driving ability better for the price then AST.

[Former_Boosted_IS]

Originally Posted by Hedges

How much are these coil-overs and what are the direct competition of this product? KW's? GC's?

Hedges, I think you would have to step well above the KWs and Ground Control to get a comparison. I believe both are twin tube designs with progressive springs. The AST are monotube struts, linear rate flat top/bottom springs with thrust sheets. I think most would agree that AST is a much more affordable version of the Motons.

[Former_Boosted_IS]

Originally Posted by Mike@F1 Autohaüs

Nice and thorough review

Mike, thanks for taking the time to read the review and I am glad you enjoyed it.

Originally Posted by Alpina_B3_Lux

Great review! Thanks for taking the time to write it all up so well and post those splendid photos.

Alpina_B3_Lux

Alpina, I have enjoyed some of your reviews thoroughy, so it does mean a lot to hear your compliments.

Originally Posted by Craig@SupremePower

nice write up...

Craig, thanks for kind words.