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E46 M3 (2001-2006) Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006.


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Old Sat, Feb-11-2017, 12:40:44 AM   #191
liam821
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Default Re: Shock dynos, Fat Cat Motorsports and custom valved Bilstiens

I also use a set of custom valved Bilstein mono-tube HD dampers in my Honda Civic eg race car. They're fantastic, especially when you consider the cost! I started with a brand new set for an Integra TypeR (I run a ITR style rear lower control arm) and sent them off to Bilstein. I told them what I wanted, the springs rates I run, and they did all the modifications for me. I'm an extremely happy customer.

Looking forward to seeing your results, OP, so far it looks awesome.
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Old Sun, Sep-16-2018, 03:26:32 AM   #192
ShaikhA
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Default Re: Shock dynos, Fat Cat Motorsports and custom valved Bilstiens

Shock dyno graphs illustrating the effect of nitrogen gas pressure. Why isn't gas pressure more talked-about??

Since Eric and I have previously shared shock dynos in this thread, I wanted to add a few more here. Although they're not specific to the E46 M3, the concept (especially the level of nitrogen charge pressure) applies to our BMWs and relates to observations people have made about ride quality and handling behaviors.

I've come to realize how critically important it is to measure and understand the effect of nitrogen gas pressure on a damper's real-world behavior. In this post I'll be more brief and link to two graphs showing damper force vs. velocity with a short discussion. In a subsequent post, I'll go into more detail about why we need nitrogen pressure inside the damper, and what happens if it's too high. In short, you need high-enough nitrogen pressure inside your damper to prevent any dissolved air from 'boiling' and 'foaming' (which reduces the damper's effectiveness) but also you need low-enough nitrogen pressure so you don't 'lock' the damper and prevent the damper from opening!

The graphs below were provided to me by a customer using Bilstein PSS10 on his F80 328 M Sport. He had someone near him perform dyno tests and he asked me to analyze the results and make suggestions on what damper settings and spring rates to use, etc. The first graph has the gas force subtracted, as is the common practice. The second includes the effect of the ~80 lb gas force, which raises the compression force and reduces the rebound force. This is an across-the-board change in the damper's real-world behavior. I've kept the scales the same for both graph so it's apple to apples comparison.



Same damper setting as above, but now gas force NOT subtracted (actual real-world behavior):



High nitrogen pressure and the resulting high gas force has an IMMEDIATE and CONTINUOUS impact on how the suspension tracks the ground. The gas force causes jerk, which is a sudden change in the acceleration of the vehicle. Jerk reduces grip as well as ride quality (grip and ride quality are really synonymous).

Keep in mind that gas pressure of 40 lb or more on our front strut suspensions will feel very stiff because of the high ~1:1 motion ratio of forces from the strut conducted to the wheel (and vice versa).



Bottom-line, if you find a monotube uncomfortable, high gas pressure and the resulting high gas force / rod force will often be the primary (hidden) cause. Make sure to find out the gas pressure in your front AND rear dampers, and notice if it's too high... You can use the 'bathroom scale' test as EricSMG did to get a sense of gas force!

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Old Sun, Sep-16-2018, 04:18:11 AM   #193
ShaikhA
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Default Re: Shock dynos, Fat Cat Motorsports and custom valved Bilstiens

This is the BMW E46 M3 'Ride Harmonizer' spreadsheet I've created with you folks in mind! Very proud to share it here for the first time!



FCM Elite E46 M3 Ride Harmonizer FRC and Ride Frequency spreadsheet




There are various inputs such vehicle weight, driver weight, weight distribution, tire / wheel weight, spring rates, sway bar dimensions, AND bump stop rates (you can approximate 200 lb/in for OE front, 100 lb/in for Bilstein black and OE rear, etc.).

I've created three sections which serve different purposes. This topic deserves its own thread but I figured to introduce here and then go into more detail later.

For those who want to understand the features in more depth, you can view this video and follow along. For a short summary, you can enter a few values for your car (such as car & driver weight) or leave those default. Then enter the spring rates and then examine ride frequencies that result. Our goal for better handling and better ride is to pursue 'Flat Ride', where the rear ride frequency is at least a few percent higher than the front. I recommend setting the resolution to at least 480p.


I've found that for our BMWs we NEED to pick a rear spring rate that creates Flat Ride, and that often means we need a larger front bar with a stock rear bar. Most 'matched' sway bar kits (where you add an aftermarket front AND rear bar) end up with TOO MUCH rear roll stiffness which forces you to use a TOO SOFT rear spring and that causes pitches (which messes up the ride, handling, grip, and your brain - literally!). Pitching is literally a cause for physical and psychological dis-ease and the US Navy studied it extensively back in the 1960s.



Bump stop behavior is essential to understand and account for, and damper behavior will contribute to overall stiffness, plus can bias the suspension toward jacking down (which makes the bump stops engage more often). I'll create another thread and cover more details, but feel free to make use of it, ask some questions here. It'll help you select spring rates so Flat Ride can work for you!

Shaikh
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Discussing Shock dynos, Fat Cat Motorsports and custom valved Bilstiens in the E46 M3 (2001-2006) Forum - Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006. at BMW M3 Forum.com (E30 M3 | E36 M3 | E46 M3 | E92 M3 | F80/X)