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997 Turbo / GT2 20062012 Turbo discussion on the 997 model Porsche 911 Twin Turbo.

Shocks, why you should care.

 
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Old 03-19-2019, 12:28 PM
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Shocks, why you should care.

I want to share a recent experience of mine, and in some way attempt to get others interested in what a good suspension can do to your perception about how a car rides / handles.
Some of you may have heard of FatCat Motorsports, a lot of you may not have. I had a chance to meet with Owner/Operator Shaikh Jalal Ahmad and get hands on involvement in the build/ optimization of a set of shocks for my 997TT. Rennlist's own Christopher Hurst had a recent sit down with Shaikh here:
https://rennlist.com/how-tos/slideshows/shaik-it-up-part-1-the-ultimate-guide-to-shocks-557133#tale-of-the-shaikh
Here FCM's YT channel: https://www.youtube.com/user/SuspensionTruth


I've been a car enthusiast all my life, posters, models, RC cars, etc. I got my start with Volvo's and then later Mustangs and BMW's. I've had just about every type of aftermarket suspension on my cars over the years in a never ending search both to know what each option was good/bad for and if I could find something "better". I've always tried to find information online and in books as to how or why changes in suspension are done. Mainly to understand if I am doing the "right thing" and is my money being spent well? Every forum I have found to be similar, if you ask about suspension each online corner has their preferred brands, vendors, "copy this", and "go custom" suggestions. Then... that's it the trail goes cold, it's literally take someone at face value or you're SoL. Even in the custom space there is not much involvement between customer and vendor, if you ask for recommended spring rates you are given a number with no explanation as to why (beyond "it's what the pros use" or "because we use them" etc). If you ask about damping forces/ curves again you are given some general information. You might even hear keywords like "Digressive", "Linear" or "Dual flow technology". You might even see a very generic shock dyno as a sample or what could be, but again there is no real explanation as to why any particular vendor has decided on their damper curve values for their final product. I found FCM's youtube channel by pure chance one day, I believe it was his "Why flat ride matters" video. Being the skeptic I am I immediately thought it was snake oil and decided to look into what it was and why I knew it was wrong. Turns out its not... Flat ride allows you to setup a car so that it settles evenly front and rear over a bump before the chassis goes into bounce. So you get a single up-down motion instead of a see-saw. Major auto manufacturers use flat ride, including Porsche as such flat ride is a completely valid suspension strategy. Which promotes comfort and an increase in performance both due to a predictable setup and the inspiration of driver confidence.

Ok cool, my car has flat ride... now what?

Well beyond the spring there is crucially the shocks, they exert a spring like force which contributes to the total spring rate at the wheel. And serve to "dampen" the oscillations the car experiences as it drives over the road. I have had Bilsteins, KW, Koni's of all different flavors, Ohlins, etc All have had their issues and all have been way too harsh, and whats worse is in addition to being harsh most of the coilovers would maintain a non flatride spring rate, or make it worse! Even going with custom setups it was always a choice of stages and no real customization was performed. It didn't matter how many *****, adjusters, spring swaps I did everything was always too harsh. It took an incredibly long time for me to understand the difference in transmissibility, in that springs transmit stiffness, and shocks transmit harshness. Something FCM does on their YT channel is delve into what it means to have a properly functioning shock which can provide awesome performance while at the same time not beat you up, no matter the application. Properties of shocks I didn't even know existed, or did not draw the "how is this relevant to me parallel" are covered in good detail. For instance in a monotube shock the gas force has a real impact on the initial behavior of the shock as the piston begins to flow the oil contained inside. In fact Roehrig did a technical analysis to show this (https://cdndata.co/cdn/1da5d52075cbbe77d356d4a71cd20d43c1d45dd3/Force_at_Zero_Velocity_Explained.pdf).

In all of my googling and researching I have only found corroborating information to FCM with regards to valid suspension tuning, there is no good refutation to utilizing flat ride and being conscientious of shock gas forces, damping ratios, etc. So I decided to give FCM a shot, Shaikh prefers to work with Bilstein shocks and with his help I sourced a set of H&R street performance coilovers. Which are basically Bilsteins made to spec and H&R slaps their sticker on them, they are inverted struts and are serviceable.

Here is a front strut going on the dyno:


This is the result of the dyno, I will have to re-edit the image as something went wrong and some of the rebound stroke got cutoff:


You can see that there is a clear imbalance in the rebound (bottom right) vs the compression (top left) as the shock moves through 1-10 inches per second. This causes a behavior known as jacking down, it is pretty much used in all automotive vehicles as it promotes bump stop engagement This is what manufacturers usually use to give you the impression of a sporty "tight" ride. In many cases it is detrimental to the actual capability of the vehicle. Take my 997 for instance, the previous owner put lowering springs on but kept the OEM shocks. That lowered the car over 1 inch and as such I have lost that in total suspension travel. When I take a sweeping turn the car just bounces around on the bump stops or if I hit a rumbly section of road... you can almost head bob like its the Night at the Roxbury! I cannot for the life of me find an honest to goodness answer as to why this is so common on vehicles, aside from safety and to avoid legal ramifications of operator error!

Next came careful disassembly:










Until finally we have the factory H&-Bilstein-R piston and shim stack laid bare. This is the meat and potatoes right here, the changes made to these components are what makes it so you can drive over speed bumps without abandon, or put in a personal best lap time. The piston is digressive and made by Bilstein, the shim stacks are rather simplistic and use thick shims. The less used and more thick they are the more sharply generated shock forces are. Vs using many shims and with smaller thickness which provides a more progressive build up. Until piston blow off occurs.


Next is introducing improvements to the piston, in my case H&R sports do not have any bleed holes for filtering frequent bumps like a rumble strip, Shaikh calls his application of road filtering "Ripple Reducer". Some aftermarket suspension makers do include bleed holes for road surface filtering such as Penske and Ohlins in some of their products:


Afterwards we sat down and discussed damping ratios and where practical experience dictated what percentage of critical damping one should aim for. We looked at another 997 Shaikh has done for an AutoX customer and taking things into consideration such as the turbo is heavier, awd, and I DD mine we came up with a damping curve. The final data for my setup specifically will be available in the coming days/ weeks. In the mean time I was able to mock up my own test setup to get an idea of the assembly process:









Dyno of the test shock:



My hands on experience was very informative and really removed a lot of the mystery that goes into shock construction / development. To call Shaikh a mad scientist is an understatement. His shop was rife with boxes full cataloged parts from test after meticulous test, tangible evidence that sometimes good old trial and error has no equal. A bonus was I got to go for a ride in Shaikh's bmw which he both DD's and AutoX's. His car is equipped with his ripple reducer and very a interesting compression blow off configuration. We drove over every road imperfection you can imagine, plain jane crappy California roads, railroad tracks, pot holes, expansion joints, and smooth road as well. The best way to describe how the ride felt was "not normal" I did not know non purpose build track cars could grip so well, the car felt like it wanted to do whatever it was told. Its balance on/off/ steady state throttle was highly predictable and confidence inspiring. It's always a good thing when you can try before you buy and that trial informs you in all of the good ways that yes... you need more than you have.


In the end, suspension is one of the most subjective experiences in car and makes for highly unique preferences between drivers of the very same car. Why not have your cake and eat it too? Why not demand more information from the industry? We should be able to do better than simply Option A, B, or C. Whether you try FCM like me or whom your preferred confidant is in the car modding world, why not strive for the very best
 

Last edited by GT3 Chuck; 03-19-2019 at 03:34 PM.
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Old 03-19-2019, 10:07 PM
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Awesome write up. Thanks for the info.
 
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Old 03-23-2019, 06:06 PM
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Thanks for sharing. Keep us posted in your experience.

I've seen the FCM videos online and read writeups of other suspensions he's done.

I'd love to know if he can revalve Damtronics as I love my DSC. Maybe that combo is unnecessary, but it seems like there's some intersection of the two that would be magic.
 
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Old 03-23-2019, 07:44 PM
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Originally Posted by Brainz View Post
Thanks for sharing. Keep us posted in your experience.

I've seen the FCM videos online and read writeups of other suspensions he's done.

I'd love to know if he can revalve Damtronics as I love my DSC. Maybe that combo is unnecessary, but it seems like there's some intersection of the two that would be magic.
He could revalve damptronics. If you had a custom revalve done you wouldn't necessarily require the dsc. Also the electronic suspension tends to have smaller shaft and pistons which means you're leaving some performance on the table. If you co e down to tx I'll give you a ride.
 
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Old 03-23-2019, 08:59 PM
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Where in TX? I'm in Houston.
 
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Old 03-23-2019, 09:02 PM
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Originally Posted by Brainz View Post
Where in TX? I'm in Houston.
Austin, hah small world.
 
 
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