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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 Thu, Jul-14-2016, 02:45:53 PM   #171
nrubenstein
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Default Re: Shock dynos, Fat Cat Motorsports and custom valved Bilstiens

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Originally Posted by TheM View Post
My cars feels pretty good to me but now you've got me thinking that it could be better. My M3 coupe has Eibach 500 lb fronts and 600 lb rears along with Koni yellows on full soft. I haven't done the frequency oscillation test yet but on the surface would you say it looks like my F/R spring ratio is biased too stiff in the front?
Roughly speaking, the wheel rate in the back is half. Ergo, 500F/1000R would be roughly equal at the wheels. Basically, it depends on what you want.
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Old Thu, Jul-28-2016, 01:10:50 AM   #172
ShaikhA
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Default Re: Shock dynos, Fat Cat Motorsports and custom valved Bilstiens

Quote:
Originally Posted by TheM View Post
My cars feels pretty good to me but now you've got me thinking that it could be better. My M3 coupe has Eibach 500 lb fronts and 600 lb rears along with Koni yellows on full soft. I haven't done the frequency oscillation test yet but on the surface would you say it looks like my F/R spring ratio is biased too stiff in the front?
Assuming an average driver weight of 180#, an E46 M3 coupe with 500/600 rates would have approximately 2.3 Hz front and 2.0 Hz rear. This which would not give Flat Ride and would tend to cause some pogo'ing/bucking/pitching on medium undulations, plus generally not give optimal grip. If you upped the rear spring rate, or reduced the front rate, you'd might need to compensate with some sway bar changes. I would consider 400 / 700 rates (2.10 / 2.19 Hz), or even 400 / 750. Depends how sticky your tires are and how firm a ride you want.

As you get to stiffer rates, the suspension is moving less and you don't always notice pitch as easily as when you have softer springs / lower frequencies. I still find that aiming for Flat Ride really does help ride, grip, and makes the car much less nervous. You can also use less damping which itself is better for grip and comfort. Sounds like you have the dampers at soft and don't feel a need to go stiffer. The Konis also have a strong amount of mid and high speed rebound and would always be jacking down anyway. By choosing to run a Flat Ride setup, you won't have the suspension experience additional jacking down from the oscillations that pitch would induce.

If you try the spring rate swap, I would use 6" springs up front and rear as well. I'm at 650 lb/in 6" rear and the car is quite low with GC weight jacks.

Last edited by ShaikhA; Fri, Jul-29-2016 at 11:08:35 PM.
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Old Thu, Jul-28-2016, 01:19:20 AM   #173
ShaikhA
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Default Re: Shock dynos, Fat Cat Motorsports and custom valved Bilstiens

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Originally Posted by nrubenstein View Post
Roughly speaking, the wheel rate in the back is half. Ergo, 500F/1000R would be roughly equal at the wheels. Basically, it depends on what you want.
Spring motion ratios I'm using on the E46 are 0.93 front (same for strut since coil-over) and 0.73 rear (OE spring location). Squared and divided, that gives a relative wheel rate of 62% rear vs. front. You wouldn't want equal wheel rates so some rear wheel rate bias would be ideal for Flat Ride conditions. For a 500 front (~2.33 Hz) an 850 rear (2.42 Hz) I feel would complement it well. I will be testing similar frequencies with the 18x10 275 BFG R1-S waiting for the fender mods to be complete. You wouldn't want to run those frequencies on a predominantly-street driven setup, though.

Last edited by ShaikhA; Thu, Jul-28-2016 at 01:23:49 AM.
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Old Thu, Jul-28-2016, 02:06:15 AM   #174
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Default Re: Shock dynos, Fat Cat Motorsports and custom valved Bilstiens

Thought I'd give an update. V2 has been fantastic. That said, I think for anyone considering my setup or similar, here's what I'd have FCM do:

1. V1 front bump stop lengths (a little longer = more progressive = better)
2. V2 front valving all around
3. V2 rear comp valving
4. V1 rear rebound valving (for V2 I had him take a pinch too much low speed out - V1 was better here over slow/medium rollers)

I will be contacting Shaikh soon to tweak my rears a bit Car is fabulous with stock springs and OE 18" PSS tires. Very, very good.
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Old Thu, Jul-28-2016, 08:01:27 PM   #175
The One
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Default Re: Shock dynos, Fat Cat Motorsports and custom valved Bilstiens

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Originally Posted by EricSMG View Post
Thought I'd give an update. V2 has been fantastic. That said, I think for anyone considering my setup or similar, here's what I'd have FCM do:

1. V1 front bump stop lengths (a little longer = more progressive = better)
2. V2 front valving all around
3. V2 rear comp valving
4. V1 rear rebound valving (for V2 I had him take a pinch too much low speed out - V1 was better here over slow/medium rollers)

I will be contacting Shaikh soon to tweak my rears a bit Car is fabulous with stock springs and OE 18" PSS tires. Very, very good.
It has been mentioned previously that new Bilstien HDs result in the car sitting slightly higher, and this has been attributed to the high gas pressures. After the FCM revalve, how is the ride height affected?
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Old Fri, Jul-29-2016, 07:21:40 PM   #176
EricSMG
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Default Re: Shock dynos, Fat Cat Motorsports and custom valved Bilstiens

The ride height after the FCM treatment is virtually identical to stock/Konis. The ride height issue is solved by lowering the gas pressure.
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Old Fri, Jul-29-2016, 07:28:56 PM   #177
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Default Re: Shock dynos, Fat Cat Motorsports and custom valved Bilstiens

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Originally Posted by EricSMG View Post
The ride height after the FCM treatment is virtually identical to stock/Konis. The ride height issue is solved by lowering the gas pressure.
Pretty crazy that the static pressure is so high it actually lifts the car! Says a lot about their out-of-the-box ride quality..
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Old Fri, Jul-29-2016, 11:16:21 PM   #178
ShaikhA
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Default Re: Shock dynos, Fat Cat Motorsports and custom valved Bilstiens

Quote:
Originally Posted by EricSMG View Post
Thought I'd give an update. V2 has been fantastic. That said, I think for anyone considering my setup or similar, here's what I'd have FCM do:

1. V1 front bump stop lengths (a little longer = more progressive = better)
2. V2 front valving all around
3. V2 rear comp valving
4. V1 rear rebound valving (for V2 I had him take a pinch too much low speed out - V1 was better here over slow/medium rollers)

I will be contacting Shaikh soon to tweak my rears a bit Car is fabulous with stock springs and OE 18" PSS tires. Very, very good.
Eric, this is music to my ears! Been lots of collaboration between us after you'd already run the gamut of options and weren't satisfied. I think this is a revolution to make our Ultimate Driving Machines exactly what they should be - solid, responsive, and comfortable.

I would venture that you saying 'fantastic and fabulous' and being as particular as you are means we really have a 95% dialed recipe! We can discuss the rear rebound changes you'd be looking for. I can see how a bit more low speed rebound would quicken settling on the slower / medium undulations but wouldn't want to increase the mid and high speed rebound too much - that would take us back into jacking down which we both want to avoid. There's certainly room to comfortably add LS reb, some mid speed, and a little HS if needed.

A slightly longer front bump stop also makes sense especially given the relatively soft OE front rate. You'd avoid the sudden spring rate ramp and harsher impact from a too-short stop.

Overall, it sounds like just a little tweak to rear low speed rebound and longer front stop then you'll be happy as a calf in clover! Then we can talk about your E36 M3 track car! Doing a couple E36s right now as street-driven track cars, with a handful already under our belt.
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Old Sat, Jul-30-2016, 12:06:01 AM   #179
ShaikhA
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Default Re: Shock dynos, Fat Cat Motorsports and custom valved Bilstiens

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Originally Posted by twentyseven View Post
Pretty crazy that the static pressure is so high it actually lifts the car! Says a lot about their out-of-the-box ride quality..
It's pretty wild how high the gas pressure can be on certain applications. I think the E46 M3 Bilstein HD is fairly reasonable (about 20 lb - the twin-tube Koni front strut he sent us had 25 lb). But the Bilstein rebound damping is really stiff and that's the major reason the ride quality suffers. Some Bilstein fitments can have 40-60 lb gas force and with a higher motion ratio like a BMW, Mercedes, Mitsubishi, Subaru, etc. that becomes a very stiff initial spring rate to have to overcome - each and every time the damper tries to move in compression. The suspension does NOT want to follow the road! Not to mention the Moton, AST, etc. setups that often have very high gas force and ride worse than necessary plus have reduced grip because of it.

The directly measurable gas force equals the nitrogen charge pressure times the area of the shaft. The equation is the familiar Force = Pressure * Area. The gas force is a crucial variable whose impact HAS to be considered in the suspension's *real world* operation. Otherwise, you have a 'beautiful' damping curve on paper, with the 'gas force subtracted' thinking "it's just a little static ride height change, no biggie!" but that ride height change is only a secondary effect. The tires aren't "subtracting the gas force" - they're being pounded by it! Which means you're being pounded by it, too.

Other than the requirement to prevent cavitation, the lower the gas pressure, the more smoothly the damper behaves - the higher the grip and the better your comfort. The effect of adding nitrogen charge is adding a preloaded spring internal to the damper. Either from a feature in the road or the driver's control inputs, the suspension has to overcome that static gas force before the damper begins to follow its designed curve. A description I've had from people dealing with high-pressurized dampers (usually monotubes) is "skittery."

Since the shaft extends out of the shock in our applications, the added nitrogen gas pressure will generate a force on the bottom of the shaft trying to move it outward while only atmospheric pressure is pushing the shaft back in. The higher internal gas pressure wins and the resulting "outward" force has to be overcome before the damper can begin to operate as a damper, i.e. begin responding to the input and dissipating energy.

This gas force internal to the damper is neither just a 'type of spring preload', while it may mimic the behavior or preloading the main suspension spring. Nor is the gas force 'stiction' since stiction is a BI-directional Coulomb friction which affects movement both into and out of the damper. The seals do create stiction, but this is usually under a pound. What some people think is stiction (including some manufacturers from what I can tell), is actually the gas force resulting from a large shaft (19+ mm say) charged to >200 psi. So efforts to reduce seal drag, while noble in principle, are sometimes red herrings because your real problem is excessive gas pressure (or thinking you absolutely NEED a PHAT shaft for your fancy strut suspension).

You could also pull vacuum inside the damper and in that case you'd have less effective compression force and more effective rebound force. The shaft would want to pull inward instead of push outwards. Check out this cool video of someone vacuum bleeding a motorcycle shock and watch how the shock shaft behaves based on whether he's putting in higher-than-atmospheric pressure or drawing vacuum in the nitrogen chamber.

FYI, I bought a custom setup from him and once I get it configured in the shop, will be bleeding our shock oil before final assembly.


Last edited by ShaikhA; Sat, Jul-30-2016 at 12:12:54 AM.
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Old Fri, Oct-28-2016, 07:58:03 PM   #180
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Default Re: Shock dynos, Fat Cat Motorsports and custom valved Bilstiens

Any updates on this? Drove my B6/OEM spring coupe today for the first time in ages and the ride is horrible on lumpy UK roads!
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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)