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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 Wed, Sep-19-2018, 08:15:06 PM   #31
ethan
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Default Re: FCM E46 M3 Ride Harmonizer suspension spreadsheet (bounce freqs, FRC, roll stiffn

Thanks Shaikh - super helpful.

Quote:
Originally Posted by ShaikhA View Post
Would be interesting to see your feedback from those tests added here!
Once the car's together, I'll give it a shot. It is on MCS 1WNRs though (in reference to your gas pressure note).

--

When playing with the spreadsheet, I noticed that if I set the rear bar OD to 0 (trying to see what would happen to FRC with no rear bar), varying the bar thickness still makes changes to FRC. If I set both of those values to 0, am I getting an accurate FRC for no rear bar?

If so, then using a vehicle weight of 2850, a 30mm OD front sway with 4mm thickness (Hotchkis), no rear bar, a 1.05 rear spring motion ratio for coils, and a 55% front weight distribution (estimate), then I'm looking at something like 450F/325R for 2.28F/2.45R frequencies and 78.7% FRC. So that's about 150lb less front spring and maybe 25lb less rear spring than I've been recommended by race shops (but the same sway setup and roughly the same FRC as 600F/350R).
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Old Wed, Sep-19-2018, 08:18:30 PM   #32
ShaikhA
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Default Re: FCM E46 M3 Ride Harmonizer suspension spreadsheet (bounce freqs, FRC, roll stiffn

Quote:
Originally Posted by Obioban View Post
Shaikh,

Any thoughts on how to get useful data on the stiffness of the inconsistent OD (possibly also ID) CSL front sway?



Known:
-CSL sway weight (4.12 kg)
-M3 sway weight (6.26 kg)
-CSL OD at the thick and thin points (30.8mm at the thick points, will measure the thin)
-M3 sway OD (it's a solid bar) (26mm)
-M3 and CSL sways are the same length/dimensions/angles other than OD
Hey Obioban,

I know there are direct bench methods to calculate sway bar rates, although I honestly don't use them. To estimate the change in stiffness when switching bars I take the basic bar parameters, as you've measured, as a good starting point and apply common sway bar formulas. It's accurate enough to gauge the before/after changes.

EDITs below!

I think it's more likely that the OD would vary, but not the ID as that would involve some pretty sophisticated machining practices. Someone else may know differently, or perhaps there's some custom extrusion process being used. Goggle suggests that powdercoating could add from 6 to 12 mils, so up to 0.3 mm max. From your measurements of 30.8 mm at the thick points, this suggests the bar is a base 30 mm OD. Now to find the ID / wall thickness...

For comparison, I just measured the approximate 'straightened' length of the Turner E46 M3 front bar at ~59" (~1.49 m). Obviously it's an estimate due to bends but close enough.

30 mm OD, 5.0 mm wall thickness raw steel tubing weighs 3.08 kg/m, which multipled by ~1.49 m equals ~4.59kg. Since your CSL bar weighs 4.12 kg with powercoating, we're in the ballpark. Looking more closely at your photo, it seems perhaps 1 lb of material may have been shaved off (prior to bending!). This is my guess - it could be more, but I don't think more than 2 lb. Removing 1 lb would be 0.45 kg. If we subtract 0.45 kg from 4.59 kg, we get 4.14 kg. That's right near what you measured (remember the errors in my 'linear length' measurement). So, compared to the total bar weight and stiffness, I don't see the removed material dramatically affecting the bar's overall stiffness.

Unless someone wants to cut one open or has specific build info, I'd enter the CSL bar in the spreadsheet as 30 mm OD with 5.0 mm wall thickness.

For reference: http://metric-steel.spahrmetric.com/...-round-tubing?

Quote:
30 mm 3.5 mm 23 mm 2.29 kg/m
30 mm 4 mm 22 mm 2.57 kg/m
30 mm 4.5 mm 21 mm 2.83 kg/m
30 mm 5 mm 20 mm 3.08 kg/m
30 mm 5.5 mm 19 mm 3.32 kg/m
30 mm 6 mm 18 mm 3.55 kg/m
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Last edited by ShaikhA; Wed, Sep-19-2018 at 08:33:58 PM.
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Old Wed, Sep-19-2018, 08:22:44 PM   #33
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Default Re: FCM E46 M3 Ride Harmonizer suspension spreadsheet (bounce freqs, FRC, roll stiffn

Quote:
Originally Posted by ShaikhA View Post
Hey Obioban,

I know there are direct bench methods to calculate sway bar rates, although I honestly don't use them. To estimate the change in stiffness when switching bars I take the basic bar parameters, as you've measured, as a good starting point and apply common sway bar formulas. It's accurate enough to gauge the before/after changes.

I think it's more likely that the OD would vary, but not the ID as that would involve some pretty sophisticated machining practices. Goggle suggests that powdercoating could add from 6 to 12 mils, so up to 0.3 mm max. From your measurements of 30.2 mm, this suggests the bar is a base 30 mm OD. Now to find the ID / wall thickness...

For comparison, I just measured the approximate 'straightened' length of the Turner E46 M3 front bar at ~59" (~1.49 m). Obviously it's an estimate due to bends but close enough.

30 mm OD, 4.5 mm wall thickness raw steel tubing weighs 2.83 kg/m, which multipled by ~1.49 m equals ~4.21 kg. Since your CSL bar weighs 4.16 kg with powercoating, we're in the ballpark. It's seems very likely the material that shaved amounted to less than 0.1 kg and was for clearance purposes. I don't see it dramatically affecting the bar's stiffness.

I'd enter it in the spreadsheet as 30 mm OD with 4.5 mm wall thickness.

For reference: http://metric-steel.spahrmetric.com/...-round-tubing?
30.8 was the base measurement-- not 30.2. That was BMW's listed thickness, though (not my measurement)-- so my guess would be that 30.8 is the thickness without powder (can verify if you want).
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Old Wed, Sep-19-2018, 08:42:22 PM   #34
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Default Re: FCM E46 M3 Ride Harmonizer suspension spreadsheet (bounce freqs, FRC, roll stiffn

Yes - I must have edited my post after you'd already replied! If you can also measure the thinner regions (and see if they're the same at bar center and near the arms) I can see how that may affect my assumption for the bar's thickness. Right now I'm thinking it could be either 5.0 mm or 5.5 mm.
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Old Wed, Sep-19-2018, 08:52:42 PM   #35
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Default Re: FCM E46 M3 Ride Harmonizer suspension spreadsheet (bounce freqs, FRC, roll stiffn

Quote:
Originally Posted by ethan View Post
Thanks Shaikh - super helpful.



Once the car's together, I'll give it a shot. It is on MCS 1WNRs though (in reference to your gas pressure note).

--

When playing with the spreadsheet, I noticed that if I set the rear bar OD to 0 (trying to see what would happen to FRC with no rear bar), varying the bar thickness still makes changes to FRC. If I set both of those values to 0, am I getting an accurate FRC for no rear bar?
Heh, that's a funny feature of funky inputs but the spreadsheet provided accurate results with correct inputs. The sway bar stiffness calculations as I've set them up use a delta between bar OD and bar ID. The calculations and resulting FRC / roll stiffness are accurate when you (correctly & intelligently!) set the wall thickness to zero when you have a diameter of zero (meaning, no bar!). If you notice, the roll stiffness values DECREASE when entering non-zero wall thickness with zero bar diameter. This tells you that something is amiss in your inputs...!

Quote:
If so, then using a vehicle weight of 2850, a 30mm OD front sway with 4mm thickness (Hotchkis), no rear bar, a 1.05 rear spring motion ratio for coils, and a 55% front weight distribution (estimate), then I'm looking at something like 450F/325R for 2.28F/2.45R frequencies and 78.7% FRC. So that's about 150lb less front spring and maybe 25lb less rear spring than I've been recommended by race shops (but the same sway setup and roughly the same FRC as 600F/350R).
Sounds like reasonable calculations and correct assessment to me. I've been using ~2.3 / 2.4 Hz on my E46 330i with a GC Race front bar and de-sized 15 mm (E46 323i) rear bar. About 78% FRC by my estimates of the GC front bar setting. Works quite well street, track, and autocross.

You can make screen shots of your current and 'next to test' setup and see how your driving experiences reflect what the spreadsheet suggests. We do need to consider alignment settings since they're crucial to the overall behavior, but I've been making use of these kinds of analysis for over 15 years and it definitely helps guide me toward more and more optimized setups that I can track from change to change.
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Last edited by ShaikhA; Wed, Sep-19-2018 at 08:56:00 PM.
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Old Wed, Sep-19-2018, 09:03:10 PM   #36
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Default Re: FCM E46 M3 Ride Harmonizer suspension spreadsheet (bounce freqs, FRC, roll stiffn

Quote:
Originally Posted by Obioban View Post
Shaikh,

Any thoughts on how to get useful data on the stiffness of the inconsistent OD (possibly also ID) CSL front sway?



Known:
-CSL sway weight (4.12 kg)
-M3 sway weight (6.26 kg)
-CSL OD at the thick and thin points (30.8mm at the thick points, will measure the thin)
-M3 sway OD (it's a solid bar) (26mm)
-M3 and CSL sways are the same length/dimensions/angles other than OD
For people looking to apply Flat Ride and not wanting an excessively stiff or heavy front bar, it's looking like this CSL front bar is a really good choice.

I did calcs for 300/550 (1.77 / 1.84 Hz front/rear, 4% Flat Ride) and 350/650 (1.91 / 2.00 Hz front/rear, 5% Flat Ride) as previously suggested and get FRC of 78.0% and 76.5%, respectively. Recall that stock FRC is about 75% (when not hard on the bump stops).

For a more hardcore track setup, the CSL front bar, no rear bar and 450/850 spring rates would give 2.17 / 2.29 Hz front/rear (6% Flat Ride) and 77.6% FRC. With no rear bar you'd have really good on-throttle capability and also better compliance when applying power on rougher surfaces. Downside would be a bit more understeer in very tight / low-speed corners.

John in Socal, if you're reading, this could be a nice setup for you (along the lines of our consult call yesterday)!
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Old Wed, Sep-19-2018, 09:12:10 PM   #37
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Default Re: FCM E46 M3 Ride Harmonizer suspension spreadsheet (bounce freqs, FRC, roll stiffn

So I am curious as to how you assess, relative to Flat Ride guidelines, the setup that most of the NASA GTS3/4 and ST3 drivers use with E46 M3s, viz.:

900 lb front springs
450 lb rear springs (true coilover), usually with light helper springs
GC front roll bar
GC rear roll bar set on full soft
MCS triples with typical pressure settings in the 175-190 psi range

--Peter
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Old Wed, Sep-19-2018, 11:59:48 PM   #38
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Default Re: FCM E46 M3 Ride Harmonizer suspension spreadsheet (bounce freqs, FRC, roll stiffn

thanks for the explanation!
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Old Thu, Sep-20-2018, 12:40:47 AM   #39
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Default Re: FCM E46 M3 Ride Harmonizer suspension spreadsheet (bounce freqs, FRC, roll stiffn

Greetings Peter,

That setup doesn't have Flat Ride. Based on 3100# race weight and 51% fr.wt.dist (close enough I trust) with 900 front / 450 rear (c/o) springs, I estimate 3.3 Hz front and 2.7 Hz rear. I can't estimate FRC or roll stiffness without more info on GC front / rear bar arm length (front infinitely variable) and bar OD / thickness.

By the way, you may say 'most' but FCM-equipped BMWs had a very strong showing throughout this year including NASA Nationals last weekend at COTA, in your neck of the woods. All the cars at Team Edge Motorworks (from out here in Northern California) are using FCM Elite Stage 3 suspension. Prior to working with me on FCM-optimized Bilsteins, they used AST, TC Kline, Moton, GC/Koni, etc.

Anthony Zwain, co-owner of Edge Motorworks Mtn View, is VERY happy with how our setups are working for them and their racers! I love working with them and they care excellent care of my E46 330i on all areas that I don't specialize in.

Their Team Edge car #38 (E46 M3) finished 2nd in ST3 and 3rd in TT3 (fastest BMW) behind two Corvettes. They were the top-finishing BMW in TT3 class by over 3.4 seconds to the next BMW.

Team Edge E36 M3s finished 2,3 and 5 in ST3 and WON TT4, plus a 2nd and 4th in class. The top finishing TT4 Edge E36 M3 would have beaten the top-finishing TT3 non-Edge BMW.



NASA 2018 National - TT3/TT4

NASA 2018 Nationals results - GTS3, GTS4, ST3, ST4

All these setups are using a softer front spring than what you posted. I kind of had to convince them to test softer springs than what they were previously using and they've found it to work better for them.

I don't currently have GTS3 and GTS4 BMW customers but would love to work with some! There's a sea change happening in the world of "what's fastest"

===

When aero is an important consideration, you need to make sure front height changes are well-controlled and fairly small - I understand this. However, from cars I've built, raced, and designed for my customers along with the analysis of where the majority of our roll stiffness comes from, there are benefits to aiming for Flat Ride first, THEN going away from it to the extend that your specific situation absolutely demands it. I think with BMWs (unlike race Porsche, from what I've seen) there's a strong bias toward much higher front springs than are truly necessary. Some BMW racers I've worked with in the past few years were oriented toward very high front spring rates for track setups but have experimented and found benefits with less spring and more sway. Variations in track conditions, horsepower levels, very high aero downforce, etc. may warrant adjustments that prevent Flat Ride from occurring. As long as one has tested and has data, you won't wonder if you're leaving grip (and time) on the table.

For strong over-sprung front dampers, I observed oscillations in my suspension position traces when I had a suspension with >3 Hz front ride frequencies. I was using Hoosier R7 tires capable of producing ~1.3-1.4g. The data acquisition system was our AiM EVO3 from Veracity Racing with individual Penny & Giles shock pots at all four corners of my '95 track Miata. At Laguna Seca, in particular at higher speed going down the main straight, I could feel AND see oscillations on the damper traces. When I looked closely the frequency closely matched that of the front bounce frequency! That's no bueno for grip!

At the time I was also experimenting with no sway bars which I liked for wetter conditions but not for dry racing. When I dropped the front frequency to 2.3 Hz, added a reasonable front sway bar, and set the rear frequency to about 2.4 Hz, that oscillation in the shock data (and from behind the wheel) went away. The car was more consistent and easier to drive fast. I firmly believe that the pitch-induced oscillations (with a higher front frequency than rear, and a high-enough front frequency to cause the tire sidewall to flex) were factors compromising tire grip and driveability/confidence. I talk about this in a more recent video exploring the idea of minimizing vibrations at all levels of the suspension's response.


I'm going back and thinking deeper into the idea of more front spring / less front sway vs. less front spring / more front sway... IF there's significant front sway bar bind occurring and since we are so dependent upon front bar stiffness as % of total roll stiffness, then I can see where keeping front bar softer could help grip. Some aftermarket sway bar manufacturers have designed 3-piece sway bars with spherical bearing to reduce binding / friction. I'm not sure if such options exist in the BMW marketplace? I can definitely feel quite a lot of cross-coupling on the front of my E46 330i with the GC Race bar in place. Other than tire pressures, I don't change any settings between autocross and track so I effectively have my 'track side' grip available all the time when I'm driving on the street.

I'm motivated to look more closely at sources of bind in the suspension and how the front sway bar may be contributing. From what I've found running 285 BFG R1S at autocross with my E46 330i, I need to be mindful of properly loading the front tires (good braking technique) before aggressively turning in, but that's true in general. Once the front end bites, the grip is enormous. I will be gathering data soon (hopefully this weekend) with a new Aim Solo2DL and have it overlay on the SmartyCam video. At some point, I need to get the EVO3 + shock pots on Christina to get more detailed data on velocities, etc. I learned quite a lot from my data analysis with the Miata and that data gathering / analysis helped convince me that multiple damper adjustments could often mask a poor baseline damper setting.

===

This is a VERY important video to watch and understand for anyone who believe that 'Playing with Knobs' is required to have a true race car:


BTW, non of the dampers on the winning Team Edge E36 and E46 M3s (or Christina) have knobs. 99% of the setups I build don't, and for good reason(s). And several of the Edge drivers and other BMW track-focused customers have commented, when driving on the street such as to get gas, etc. that the cars are rather comfortable. Hmmm... I'm VERY surprised to hear that Igor, who I quote below, has a Z4M coupe with Flat Ride and track-focused frequencies of about 2.3 / 2.4 Hz with 200 treadwear high-perf. street tires.



===

So for aero in racing situations, the suspension tuning does necessarily need to focus on maximizing the aero effectiveness and that can often mean using a fairly high front spring rate. But - as I've pointed out with examples - there can be a cost to going TOO STIFF on spring rate (or damper forces, or gas pressure, etc.). Too much of any component in the suspension WILL hurt grip and predictability which means higher-than-necessary lap times and often a more 'punishing' driving experience. People can get away with very stiff setups ('make it like a gokart, man!') but that doesn't mean you're making optimal use of the tires. For anyone curious, watch this video where I analyze the Spec Miata suepsnion, which is notoriously stiff (and designed to jack down into the bump stops). Most of the lap times gains my customers found was through me REDUCING rebound damping and adding compression to help make the damper more balanced.


How does a racer or setup engineer know when a suspension is too stiff? How often is that even a question that gets asked? I utilize lap times, data acquisition (when available), and tire temperature testing along with video and driver feedback to make changes which drop lap times while keeping driver confidence high.

===

I'd also be curious how many BMW race / competition cars have left vs. right corner weight different-enough to warrant a change in spring rate. Corner weights do vary and I'm currently using a 25 lb/in heavier LF spring than RF spring. My LR is 50 lb/in stiffer than RR. I've done this on numerous builds and that's what the Racer's Edge section of the spreadsheet helps visualize. Enter the corner weights, see what the per-corner bounce frequency is and, if you're curious, simulate a different rate per corner. I bet most people never even imagined this, but I KNOW certain OEMs do this to achieve very smooth settling response.

The orientation toward selecting spring rates to provide Flat Ride isn't even limited to ride quality considerations. Flat Ride actually QUICKENS the suspension's settling response when cornering! When I describe Flat Ride as relevant to racers, I like to say 'Fast Settling' because it sounds more relatable. But it's the same concept just focused on what a racer cares about.

By the way, the MCS with 22mm front strut shaft with 175 psi-g fill pressure gives 79 lb front gas force. 190 psi gives [b]120 lb[/]b gas force. Ouch and ouch. With the smaller shaft, the rear isn't so bad but is still over-pressurized vs. what could be used with some simple/effective design changes that allow a lower gas pressure. That's one of the benefits of our Ripple Reducer modification.


{{{

EDIT: Another consideration of why certain setups seem to work better with softer main springs it that the GAS FORCE from the nitrogen gas pressure is contributing to the total spring rate! This is often forgotten / neglected when looking at the car's real-world suspension behavior, but you can't 'zero out' the damper gas force as 'spring preload.' Every time the damper moves into compression you have to overcome that force and with large shafts / high gas pressures (even sub 200 psi) you get VERY high initial 'cracking forces' which feel like quite stiff springs. Gas pressure inside a damper operates through a different mechanism and is not the same as adding a turn or two the spring perches. The damper (and gas spring) are in parallel with the main spring and the damper gas pressure affect the initial stiffness and 'rise time' of the suspension.

Misunderstanding or neglecting the impact of high damper gas pressure is definitely a reason for inconsistent results and skittery driving behavior. You often see people with these kinds of setups hacking and sawing at the wheels - a lot of that is from gas pressure, along with fighting extra oscillations from spring rates that product pitch. You want the absolute lowest possible gas pressure possible to prevent adding a 'gas spring' inside your damper (which his supposed to DISSIPATE energy from suspension oscillations, not ADD MORE OSCILLATIONS!). I can't emphasize enough how crucial it is to understand both theoretically and practically what the gas pressure is doing to the damper and to your tire's grip.

With this in mind, it's easier to see why higher rear rates won't work well on a highly-pressurized damper, 'cause your damper is giving you 'gas spring rate' but not in a way that maximizes grip! Until you experience a well-tuned, lower-pressurized monotube, you won't know what you're missing. EricSMG got a sense of this in his review of our FCM Elite Stage 2 setup for his E46 m3 street car. Ripple Reducer is a wonder for attentuating the high-frequency vibrations. Ripple Reducer also allows us to run lower gas pressure since the drilled holes on the piston reduce the pressure build-up as the shock piston moves in compression that would cause the oil to deflect the nitrogen chamber (which is a main cause of hysteresis). KBO takes it up a notch with big-bump compliance.

}}}

===

An observation re: nitrogen fill pressures. Even with using the same spring rates as your example, reduced gas pressure will improve grip and driving stability at the limit. I'd only adjust canister / damper fill pressures via shock dyno testing to ensure no hysteresis or cavitation occurs. I made these changes to some AST dampers that Team Edge previously used (prior to me building them some optimized FCM dampers) and where they felt the car was 'skittery' before was less-so with the lower gas pressure. With the MCS 22mm front shaft it's hard to get the pressures (and rod force) low enough to maximize traction. They were really frustrated with how poorly their car was hooking up and aside from damper valving that could use improve, the gas force was a big factor.


Also depends on if the damper profile has a strong low speed bump ramp or not. Too much low speed, while giving 'good feedback' will also compromise grip due to excessive 'jerk' as the suspension transitions rapidly back and forth between compression and rebound.

As a last comment, these are the comments of our NASA customer Percy on his ST4 setup from us, previously with TC Kline doubles.


I've heard from other BMW owners who were not happy with information or lack thereof from when getting information about 'high end' dampers including the one you mentioned (it may have been a distributor). There are a LOT of variable to consider and many parts that need to work together. I hope over time the rest of the aftermarket can see there's room for improvement.
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Last edited by ShaikhA; Thu, Sep-20-2018 at 01:00:57 AM.
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Old Thu, Sep-20-2018, 01:18:23 AM   #40
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Default Re: FCM E46 M3 Ride Harmonizer suspension spreadsheet (bounce freqs, FRC, roll stiffn

interesting. this seems like a bold new direction for suspension tuning for this chassis.
the concepts and logic are sound, and like someone else said: some people are fast in spite of their set ups, not because of.
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Discussing FCM E46 M3 Ride Harmonizer suspension spreadsheet (bounce freqs, FRC, roll stiffness) 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)