Re-valve my Bilstein shocks!

[Nutzy]

Hey all!

This is kind of a long post, but I wonder if anyone can shed some light on this for me?

The current parts of my suspension are:
F - 8KG (447lb) linear coil-over springs with 325ix with Bilstein P36-0251 shocks
R - 12KG (670lb)linear springs with B36-2027 Bilstein shocks

The result is hopelessly under damped! I read that the 325ix shocks have even less damping than the regular e30 Billy shock.

The problem is that although Bilstein Sydney in Aus can re-valve these things, it has been pretty much "yeah sure, we can valve them". But what specs? No other info was sought from me about the setup so I am not inclined to think that the settings are anything more than a wet finger stuck out in the breeze! I am also not impressed that the price has doubled in less than 12 months....$1250AUD ($916USD) to valve 4 shocks seems a tad over the top to me. In any case, I guess the most important aspect here is to get the damping specs right!

After much reading, I think that my initial impression of the front shocks having too much compression damping is actually that they are under damped and are crashing into the bump stops, thus giving the impression of being harsh. This seems to be a fairly common thread among Bilstein users (and FatCat MS).

Some values I found are as follows:

(at 20 inch per second as per Bilstein testing, or 52cm per second in metric)

BMW 325i HD FRONT
Rebound: 2320 N
Compression: 800 N
P36-0136

BMW 325i SPORT FRONT
Rebound: 2330 N
Compression: 755 N
P36-0335

BMW 325iX 4WD FRONT
Rebound: 1365 N
Compression: 465 N
P36-0251

BMW 3-SERIES E30 SPORT REAR
Rebound: 1650 N
Compression: 565 N
B36-2027

BMW 3 SERIES E30 HD REAR
Rebound: 1650 N
Compression: 565 N
B36-2028

BMW 3 SERIES E30 CLUBSPORT REAR
Rebound: 2600 N
Compression: 1200 N
B36-0604

BMW 3 SERIES E30 CLUBSPORT FRONT
Rebound: 3000 N
Compression: 1200 N
P36-0135

BMW 3 SERIES E30 GROUP N REAR
Rebound: 2000 N
Compression: 2000 N
BE3-04630

BMW 3 SERIES E30 GROUP N FRONT
Rebound: 3000 N
Compression: 3000 N
PE3-04629

NON-BMW SHOCKS:

MERCEDES BENZ W124 (FOR SHORTER REAR LENGTH 18" V 20" - EXTENDED)
Rebound: 2870 N (potentially way too stiff, but 670lb spring, so.......?)
Compression: 900 N
B36-1470
https://www.youtube.com/watch?v=UXgY...ture=endscreen

MUSTANG REAR KONI TOP ADJUSTABLE
Rebound: ? N
Compression: ? N
8041-1186

So there are some off-the-shelf options, and then there is Linear and Digressive valving options when customising as well as many other possibilities when customising. One could also talk with Bilstein USA and get a valve kit from them, then get crafty and mod the shocks myself! FatCat specialise in this stuff and have many winning cars and customer testimonials.

http://www.fatcatmotorsports.com/FCM_Elite_FAQ.htm

Here is some talk on off-the-shelf items, Lee @ Massivebrakes has a fair bit of comment up in this thread:

https://s14net.vbulletin.net/forum/s...-rebound-specs

I guess I'm just really unsure of which direction to go in, take a chance on customised valving from Sydney Shocks, or just get 'OTS' items. I think that for the rear, either the W124 Bilstein or the Mustang Koni would probably make sense, but the front is more of a problem (because 325ix shorty shock).

Does anyone have some practical advice regarding the damping rates for my springs?

TIA


Pete

[Nutzy]

I'm guessing that this in an area that there is very little knowledge in...

I guess I will have to jump into the deep end and hope for the best, although I'd really like to be informed and not take a cookie cutter approach to it.

[jakermac]

You should probably post in the Track, Autocross and Drag racing part of the forum.

[Nutzy]

You should probably post in the Track, Autocross and Drag racing part of the forum.

Cheers, I'll give it a try.
Pete

[E36M3LX]

Just FYI, Odi Bakchis at Feal Suspension can rebuild almost any shock to almost any specification. you may want to try to get in contact with him.

[ajsalida]

I'd tend to ditch Bilstein entirely here and go with Koni sports (yellows). Adjustable rebound. For 325ix front they are inserts into stock housings and require some work. I run that set up on both my 95 M3 (front inserts into stock housings) and my 09 335xi (replacement strut), with Eibach pro kit sway bars and various springs (Eibach and OEM). Have run Bilstiens on both cars and wasn't really that impressed.

Hard to beat this relatively inexpensive set up for street plus track days or autocross, some even run it in SCCA IT. Next level up is very expensive. Have been out of the game for a while so there may be other options now.

[wazzu70]

Pete, the numbers listed in the S14 thread match what I remember. They are a pretty good general spec for a street car IMO. All out race cars tend to look for something more aggressive as is commented in the thread.

I would send a note to Lee and see what he has to say for valving rates. He has enough experience he should know what will be a good target with your spring rates. Since he does not sell dampers I think he would be willing to help out.

Rama at RHD engineering (racehead.com.au) would be another person I would hit up. Since hes based in Oz he probably knows your tracks/roads and if he does not know a good rate probably knows who would.

I assume ketting some revalved Konis from a US supplier is expensive with the import fees so its not a reasonable option. I prefer the konis because you at least get some adjustment range for different tracks and spring rates.

For others reading, there are tons of places who can valve to what you want. The secret sauce is knowing what to valve to. If a shop can’t say they know what spec they want to revalve to for your application they are just parts swappers and not the kind of shop you want to do this work IMO.

[Nutzy]

Rama and Digger! Why didn't I think of two local guys who are right into track and handling? Duh!

Thank you for the replies, all. Much appreciated.

Pete