Saturday, March 19, 2011

Front & Rear Struts, Springs, and Shocks

Even though 323 sports are NO LONGER AVAILABLE, Bilstein does have the dimensions. Ask them to compare the e21 323 size with the e30 6cyl/m3 size, SSDD



Product Name: Bilstein B6 Sport shocks VA BMW 323i E21 51mm Strut

Axis: 2 shocks for the front

Design: B6 Sport

Model: P36-0223

The early/late model e21 320i 4cyl model share the same front strut inserts, only the gland nut is different. The e21 323i uses a different setup altogether. Since Bilstein no longer makes Front Sport Strut inserts for the E21 323i, and if you want to use the E21 320i Bilstein Sport inserts on the 323i strut housing, then you would need the following gland nut from Bilstein--Bilstein P/N: B4-B30-U232A1.



The 323i front strut housing has a 36mm piston diameter. The 320i strut insert has a 30mm piston diameter. So, you need a male gland nut that has an inner diameter of 30 mm and a outer diameter of 36mm.

320i 45mm strut od, uses a 38mm insert (shock) which has a piston size 30mm

323 51mm strut, uses a 45mm insert, and has piston size of 36mm.



This is what Metric Motorsport said about building coil overs: "We use revalved VW Rabbit gti sport fronts, they are shorter, to maintain travel after lowering.The rabbit struts are from 1983 VW gti. As for spring rates, 350/275 is usually what we ship our coil overs with for street applications. I have 450/325 in my E21, But I have a S52.. I would say 375/300 should be a good place to start. the fronts should be around 100 LBS stiffer then the rears."
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Gland nuts M45 x 1.5 (Secures the sturt insert inside the strut housing). 


Early (77-79)
31321115398 (BOGE)
31321130068 (BILSTEIN) <--- Has a different Bilstein part #

Late (80-83)
31321123901 (BOGE)
31321126275 (BILSTEIN) <--- Has a different Bilstein part #
Part # for a post-80s bilstein gland nut is B30-629 F1











Bilstein Sport Dampners
Front: P30-0125-H1
Rear: B46-0617-H0

Bilstein Heavy Duty Dampners
Front: P30-0121-H1
Rear: B46-0612-H0

323i Specific (any year)

Bilstein Heavy Duty Dampners
Front: P36-0223-H0
Rear B46-0612-H0

Gland Nuts M48 x 1.5
31321117376 (BOGE)
31321130069 (BILSTEIN) <--- Has a different Bilstein part #



AFTERMARKET & MOTORSPORTS
HEADQUARTERS - WEST

14102 Stowe Drive
Poway, CA. 92064
1-858-386-5900



http://www.bilsteinus.com/

Source: http://www.autosportgallery.com/305-%209-09applicationguide.pdf


When considering which shock to buy for an E21..consider the following between Sport/HD shocks...suspension works both ways (up and down), static sag is an important consideration.

if a billie sport has 115mm of travel then i would try to get 25-30% of static sag, or 32mm. then you still need to check the compression and make sure there is enough travel for bump.

the best way to do this is with a zip tie around the shock's shaft. with the car lifted tie a zip tie and slide it down onto the top of the shock, put the car down on it's wheels and then lift the car back up and measure the distance between the shock and the zip, that's the static sag.

take the car for a spin putting it hard into a corner or two. lift the car and measure the distance from the shock to the zip, this is the total shock travel. deduct the sag measurement and you have the amount of 'used' bump travel.

if the total used travel is as much or close to the length of the shock travel (115mm for billie sport) then you need stiffer springs. if the static sag is too little then softer springs are required.

the above is just a basic outline, but it gives you a good idea of what the suspension is doing. this is how we setup motorcycles where the results are much more critical than a car.

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