Bilstein - Coilover Conversion

[simpletool]

I've been looking into doing a coilover conversion for my Bilstein shocks. Currently I have King springs in the rear and some overly short sagged random coils at the front. I notice a few people have changed to the coilover kit that uses motorsport springs (with rear helpers) and they seem to get good results.

Essentially doing what is discussed in this thread:

Coilover thread

Anyway my question specifically relates to the upper spring mount. There are 2-ways to mount the spring. One way is against the body and separate from the shaft, the other is along the shaft with force against the shaft mount.

Pic 1 - this is the kind of thing I am talking about.

1.

To mount the spring similar to factory where the spring sit hard against the body mount (not the shaft mounted). In this configuration the shock can change angle slightly compared to the spring.

Pic 2

Advantages:

Spring load is transferred direct to the body as designed. Less load on rubber shaft mount (red arrow in pic 4). I would expect that the rubber bushings and the shaft thread is not designed to take the full force of springs and shocks.

Disadvantages:

The shock shaft can move at a different angle to the spring loading (I am not sure how extreme this angle would be on the Skyline).

2.

To mount the spring on the shaft with the force against the shaft mount (shown in pic 4).

Pic 3 Pic 4

Advantages:

The shock shaft can move at a different angle to the spring loading (I am not sure how extreme this angle would be on the Skyline). This means the spring does not bow under compression during angle changes.

Disadvantages:

A LOT of load on the rubber shaft mount (red arrow in pic 4). I would expect that the rubber bushings and the shaft thread is not designed to take the full force of springs and shocks. Also the force of the spring is damped by a rubber bush both up and down. I think these rubber bushes and shaft thread would only be designed for absorbing the loads of the damping action - not the spring load as well (a much higher force).

So...any comments?

Does the strut change angle significantly during it's stroke? If not I will install the spring hard up against the original spring mount and allow the shaft to move inside it as shown here:

I did see a pic of the Eibach upper perch but it sit below the large rubber bush from stock. This was from a member here "noone". Wouldn't this bush be compressed so much that the mount is hitting against the body? Or perhaps this is the best way, where the shaft mount is not subject to the forces as the big rubber bush transfers the load to the chassis?

Edited August 17, 2011 by simpletool

[djr81]

No gurus

To start sorry for the mixed units. Remember 1" = 25mm. 1kg/mm = 54lb/in.

Does the strut change angle significantly during its stroke?

No the damper shaft does not change is position enough to worry about it.

If you mount the spring against steel and exclude a rubber isolation bush you will get more road noise & vibration. This is not an uncommon way of doing it however.

See the photo below for a Bilstein setup using standard mounts but note that the shot is of the rear (The front is in the same order anyway). This is how the King springs setup is done aswell as a number of others. It can be regarded as "stock".

The damper shaft bolts to the black upper mount (irrespective of which of the two mountings you use) at the top. If you look you will see from the top down - nyloc nuts, cad plated plate, rubber bush, the black top plate that bolts to the strut tower. Underneath the black plate is another steel bush that locates the damper shaft to the plate - this is hidden by the bump rubber for the shock.

The point being that irrespective of the spring mount the location of the damper shaft is the same. It only changes when you get a "spherical" bearing mount. Which I wouldn't recommend anyway.

Going on to the spring mount.

Your King spring should have a rubber isolation bush between it and the top plate. It is a ring of about 110mm od and is 10mm thick.

The last photo you have shown is a setup that Gary has used (aka Sydney Kid). It uses a spring retainer from Eibach (The red plate) and insulates this from the black top plate by using the old damper bump stop. It is not ideal but appears to work. The downside is you lose otherwise available suspension travel (about 20 - 25mm) and have a damper bump stop isolating a spring. There is another bump stop for the damper itself below the red Eibach plate.

A third way

The best arrangement is like this.

http://www.skylinesaustralia.com/forums/topic/368458-racepace-tein-ra-coilovers-r32-gtr/page__p__5875110#entry5875110

What you can see is the spring has a rubber isolation mount.

The damper has its own bump stop.

The standard black top locating plate has been replaced by an aftermarket item

The problem with the arrangement shown is in the spring rates which are probably good for a drag car but not what you would want on the road/track. They are 9kg/mm front & 4kg/mm rear by the way. Note that the black Eibach springs are of a larger diameter that the red ones ie 70mm versus 2.5".

Ideally you would replicate this setup (and could) using a Bilstein shock, standard damper shaft location and better spring rates. To do so you need to get top plates to match the spring diameter. I don't know where such a thing can be found. If anyone knows then please post away.

Other random thoughts.

Spring rates.

I would use the following but you will find as many opinions as there are people. Some people like hard springs as it lets them talk it up how hard they are and also reduces the need to run much front end neg camber.

Front

5kg/mm (275lb/in) spring.

Rear:

4kg/mm (225 lb/in) or 4.5 (250 lb/in) spring depending on the application and setup of your attessa.

[simpletool]

OK thanks for the reply. You have confirmed my thoughts exactly. I didn't really like the idea of the old bump stop rubber being used to transfer spring load to the top mount. A simple solution might be to replace this thick rubber bush with a big poly bush.

I agree with the spring rates and I was going to order 5kg/4kg and I'm willing to bet the Bilsteins can handle that easily without revalving.

I didn't want this to cost a fortune but I wanted to do it the correct way. My only remaining issue was how to get the spring to mount properly at the top rather than against the shaft mount. There are a few companies that make a replacement mount for 2.5" springs but all use a spherical bearing (Tein, Cusco, etc). I think I could buy these mounts and change to a rubber shaft mount. The platform is also a few inches higher so I could use a 10" spring which means I will be a bit further from coil bind (where spring rates start to vary).

I plan on using the Bilstein coilover kit (actually made by Bilstein and has good reviews for fitment), but the spring mount at the top looks like it can't be used. See pic.

[djr81]

OK thanks for the reply. You have confirmed my thoughts exactly. I didn't really like the idea of the old bump stop rubber being used to transfer spring load to the top mount. A simple solution might be to replace this thick rubber bush with a big poly bush.

I agree with the spring rates and I was going to order 5kg/4kg and I'm willing to bet the Bilsteins can handle that easily without revalving.

I didn't want this to cost a fortune but I wanted to do it the correct way. My only remaining issue was how to get the spring to mount properly at the top rather than against the shaft mount. There are a few companies that make a replacement mount for 2.5" springs but all use a spherical bearing (Tein, Cusco, etc). I think I could buy these mounts and change to a rubber shaft mount. The platform is also a few inches higher so I could use a 10" spring which means I will be a bit further from coil bind (where spring rates start to vary).

I plan on using the Bilstein coilover kit (actually made by Bilstein and has good reviews for fitment), but the spring mount at the top looks like it can't be used. See pic.

What is it for a 32? I assumed so as the photos were from a 32R - actually mine in atleast one of them. If it is a 33 or a GTST the rates will be different.

If you want cheap springs try Summit racing in the US - about $80USD ea plus shipping.

Yes you can use poly bushes. I would use a shorter one than the old bump stop too. But the trick is to get the relationship between when the spring travel runs out and when the damper hits the bump stop. You need the damper to hit the stop only a little before the spring reaches its block height. If the damper stop is too long the car will pogo about all over the place.

[simpletool]

The below describes exactly what I want so I'm now contacting ISC...........

Ryan from ISC who is on these forums was very helpful and ended up purchasing a pair of upper mounts to suit the N1 coilover for R33. They have an aluminium mount with a rubber bush and steel insert which fit perfectly with the tein spring and obviously still mounted to the vehicle. They also have a rubber seat between the spring and upper mount which keeps things quieter. The ISC upper mounts suit 65mm spring ID and 12.5mm diameter piston rod - same as the tein. Possibly other makes may be interchangeable, just a matter of finding some dealers that can supply spare parts - most I contacted would only sell the entire set of coilovers.On the road is much better than pillow ball, much quiter and a little more compliance than before.

P.S - best thing is that the ISC upper mounts were much less than half price of replacement pillow ball mounts from Tein. Highly recommend dealing with ISC!

[simpletool]

What is it for a 32? I assumed so as the photos were from a 32R - actually mine in atleast one of them. If it is a 33 or a GTST the rates will be different.If you want cheap springs try Summit racing in the US - about $80USD ea plus shipping. Yes you can use poly bushes. I would use a shorter one than the old bump stop too. But the trick is to get the relationship between when the spring travel runs out and when the damper hits the bump stop. You need the damper to hit the stop only a little before the spring reaches its block height. If the damper stop is too long the car will pogo about all over the place.

It's for a R33 GTST. Tossing up between 275lb/225lb and 250lb/225lb spring rates and hopefully I can get a 10" on there. Hard to tell exactly what the static height of the spring will be without knowing the motion ratios but with a 8" spring and 250lb on the front it appears I will only have about 55mm travel until reaching the block height (my excel calcs are at home). However Hypercoil springs since 2008 have been introducing designs more like Swift springs so the block height has been reduced.

Well if I do it all myself then yep it'll be from USA and Hypercoil springs and they are significantly cheaper than $80 each + shipping.

I would like to support the local suspension guys but each part is double to triple the USA price and shipping isn't all that much for <20lb of stuff ($50!).

If it all works out I will post up what bits and pieces I used. It'll be under $1000 for all 4 corners (including helper springs in the rear) and will be using quality springs and parts.

I've got my bump stops pretty right at the moment and I'll put some effort into getting it right. I have a combo of poly and the SK bump stops (slightly shortened) at the moment. The only real issue I have now is the bad combination of sagged and seemingly too soft so it is riding at 340mm on the highest circlip (which gives only around 30mm until the bump stop starts getting compressed). Still it handles not too bad - no pogo action.

I noticed the aftermarket strut tops have the shaft join much higher than stock so I will have to use a longer poly bush than stock to ensure the shaft is near the right height - but still a touch shorter than equivalent height like you mentioned (this will slightly shorten the stroke of the shock). This also allows me to run a longer progressive bump stop (on the other side).

Alternatively if it is all too hard I am just going to slot some Tein s-tech springs in (medium rate ones have good reviews and are ~ 15% firmer than Kings/Whiteline)

Edited August 18, 2011 by simpletool

[simpletool]

You need the damper to hit the stop only a little before the spring reaches its block height. If the damper stop is too long the car will pogo about all over the place.

I know what you mean about the bump stop being the right height - you don't want to be on the bump stop and changing spring rates severely. The car should only be on the bump stop during extreme forces. Although the MX5, Nascar do use bump stops to effectively raise spring rates during hard cornering. But you have to use a comparatively soft and progressive bump stop and it takes some fine tuning.

In regards to the full travel being only a little before block height - I will have to disagree. From what I have seen from spring manufacturers you want to stay away entirely from near block height. You should use between 20 and 80% of effective stroke. which for an 8" spring 20% of effective stroke is 30mm, so stay 30mm from block height. I use the bump stops to start limiting travel near either full damper stroke or the wheel hitting body work (and use a progressive bump stop starting about 40mm before this).

but I'm no expert in this field - just been doing a lot of reading. Sorry if it sounds like I'm preaching here, I'm not.

Edited August 18, 2011 by simpletool

[djr81]

but I'm no expert in this field - just been doing a lot of reading. Sorry if it sounds like I'm preaching here, I'm not.

It doesnt.

I know what you mean about the bump stop being the right height - you don't want to be on the bump stop and changing spring rates severely. The car should only be on the bump stop during extreme forces.

The point being once you hit the bump stop with a bit of force the damper for all intents and purposes stops working The spring force relative to the damper force goes up quickly. So you have the situation where

1. Youve hit a big bump.

2. You have a high spring rate.

3. You have an ineffective damper.

Not a fun place to be. So you dont want an overly long damper bump stop.

In regards to the full travel being only a little before block height - I will have to disagree. From what I have seen from spring manufacturers you want to stay away entirely from near block height. You should use between 20 and 80% of effective stroke. which for an 8" spring 20% of effective stroke is 30mm, so stay 30mm from block height. I use the bump stops to start limiting travel near either full damper stroke or the wheel hitting body work (and use a progressive bump stop starting about 40mm before this).

Fair point - I wasnt being specific. Bear in mind that at the block height to use an example of a 200mm long 300# spring there is 6730N of force on it.

The otherway to look at is check the front weight of the car then halve it. Remove the unsprung weight. Then divide what is left by the spring rate. This will give you the amount of spring travel taken up by the car at rest. It is surprisingly high at times.

The different between this height and your total spring travel is your effective spring travel - minus a margin and accounting for motion ratios.

Anyway how much did the strut tops cost you?

Edited August 18, 2011 by djr81

[simpletool]

Bear in mind that at the block height to use an example of a 200mm long 300# spring there is 6730N of force on it.The otherway to look at is check the front weight of the car then halve it. Anyway how much did the strut tops cost you?

Yeah a lot of force which is why I want the springs mounted properly at the top. I sent a request to the ISC website - waiting for a reply. Not entirely sure they will have them as it appears the ISC N1 is only pillow ball now.

When all is said and done I will post costs and some pics - if it ever happens. All hinging on the top mounts.

[simpletool]

ISC upper mounts are $299 front and $199 rear. The fronts are spherical bearing, the rears are rubber mount.

The rest of the stuff 4 x coilover adapters/perch, 4 x springs and 2 x helpers/holders cost $700 shipped.

Total of $1200 is a bit more than I had hoped. Which is about the cost of cheap coilovers, although these should be better for 5/4kg.

The extra $500 for the upper mounts makes it hard to justify - perhaps I can find some 2nd hand crappy coilovers and steal the tops.

Edited August 18, 2011 by simpletool

[djr81]

Just to provide some info for anyone looking at this thread/issue.

I bought some rear strut tops from ISC (See first picture). The fronts are also available with a rubber mount (you don’t have to have a bearing)but are on back order for the moment.

Anyway they are very bling as you would hope. The only issue I had with them is the bush where the shock fits through the top. They are designed for a 12mm diameter shaft. (at that point - the rest of the shaft is typically a larger diameter - 16mm or thereabouts) The Bilstein shaft is 10mm at that point. Anyway I had a couple bushes machined up which makes the problem go away.

The mounting differences between the two shocks is shown in the second photo. Note that on the stock top the cad plated bump rubber cap is mounted upside - just for clarity - don’t ever install them like that.

The gain in shock travel is 34mm. Changing the small collar (see second photo) can change this dimension. You don’t lose any droop travel (Maybe a couple mm's?) as the standard top shock installation is still a little compressed at full droop anyway.

Lastly the spring types are different.

Stock spring is a 100mm ID at the top, reducing to 90mm at the bottom.

Spring for the ISC strut top is a 65mm ID item.

The back isnt so much of an issue as the front - just not got there yet.

[djr81]

Front pair turned up last week.

They are $199 for the type with the rubber bushes. Spherical ones are more.

The gain in shock travel is just under 30mm and the strut appears to match a 200mm long spring pretty well and hopefully a 250mm item.

They look to be a good improvement over the standard tops, even if you just do the front pair. Worth the money.

[dori34]

are you able to do this with the stock shocks? (tried searching and didnt find much info for 32/33/34 skyliens, aloy of ppl do this on DR30 or 240z etc)

might be a worth while (and cheap) upgrade to lower your car and still get a nice ride with comfort.

[djr81]

Maybe but not with those strut tops. The standard shockies have the seats on them for standard springs - the id of which is much larger than the 65mm the ISC tops work with. May work with other brands of tops but you wont be getting any height adjustment anyway.

[Mr. Untouchable]

love your work djr.

I think I'm gonna go that way too. what was the go, did the front need sleeves machined up too?

[djr81]

love your work djr.

I think I'm gonna go that way too. what was the go, did the front need sleeves machined up too?

Yeah 15mm OD, 10mm ID & 32mm long. Same front & rear. Going to send mine to get plated.

[Mr. Untouchable]

ahh no worries. I'll ask the local go fast guru if he can lathe some up for me.

[djr81]

Shown attached are the front & rear shocks with 8" and 10" springs and the ISC strut tops on them.

Not 100% sure which will fit best prior to actually putting them on the car, however it looks like the for the fronts an 8" spring is the go & a 10" for the rears. Obviously it depends a bit on the spring rate - the higher the rate the shorter the spring you will want and also on the ride height.

The 5kg/mm front is not brilliant for travel so I will try & get a 10" spring in there. Should fit (just) but any higher on the rate and you would go for an 8" anyway.

[NISSAN GTR]

This system is a great idea which i might have to change over to , as my rear stock bilstiens with tein springs keep making a metal clicking noise on rebound ?

[djr81]

Installed the 8" springs on the weekend.

Photo below is of the old damper rubbers - or what was left of them after taking the full weight of the car for a number of kms. So if you have this set up ie standard tops & a spring cap under the shock rubber dont be surprised if your ride height keeps disappearing. Unmangled rubber is next to the two stuffed ones.

Anyway as regards to spring selection the 8" fits fine. The 10" I wouldnt recommend if you want a low ride height. If you cut the extra grooves into the damper body then you will be fine with a 10". The threaded section is approx 120mm long.

Bump stops are dependent on ride height. I reused the stocker but it is probably a bit short to be honest. Made up a 55mm od 3mm plate to sit above the bump rubber and below the strut top which appears to work well. Koni make nice bump rubbers but not sure who else do.

Anyway I highly recommend all this - worth the effort.

As an aside to get the bump stop length correct you need to install everything then measure how much shock travel is left - compare it to the remaining spring travel and then trim the rubber to suit.

So the stuff I needed/used on the front:

Bilstein shock B46-1471 (or 1472 either or one is front one is rear from memory)

8" Eibach spring 0800-250-275 (8'/200mm long spring, 2.5"/65mm ID, 275lb in/5.1kg mm spring rate)

ISC rubber top mount.

120mm long threaded section.

Spring perch.

Spring lock nut.

Machined up parts were a new smaller id bush for the strut top to suit the 10mm section on the Bilstein shock and a plate to sit on top of the bump rubber as the washer supplied by ISC looked a little small for what I wanted.

Edited October 24, 2011 by djr81