First up I have to say that I have the same love hate relationship with koni's that a lot of other people have, great shocks but it REALLY
pisses me off that I can't buy spares and service koni's myself.
Koni make 3 different main types of Shocks.
Twin tube Hydraulic
Twin tube hydraulic low pressure
Mono tube high pressure
Each type has it's pro's and con's, Mono tubes have good heat transfer properties and with high internal pressure are good for raising
static ride heights, however most can't be adjusted easily unless they have external oil reservoirs, Rally guys tend to use Mono tubes
because the Nitrogen charge stops the oil from cavitating, Bilsteins are a rally favourite.
Monotubes can also be mounted at any angle so can be used on inboard suspension designs unlike twin tube Hydraulic which require
gravity to keep the oil near the foot valve.
Twin tube hydraulic designs can easily have external adjustment, the pressurised versions have a small amount of Nitrogen to control
cavitation, generally adds about 8lb/in to your spring rate, sometimes you will hear the term 'degassed' that just means they have taken
the gas out of a low pressure shock, usually done on control or OEM dampers to lower the car slightly, not the best idea really.
Most Koni dampers are twin tube hydraulic with or without low pressure gas, they are what we are mostly concerned with, construction
is pretty similar regardless of how they are packaged, main flavours are,
Sealed strut ie, Mk2/3 Rear Koni sport
Cut a Strut ie, Mk2/3 Front Koni sport
Dry Cartridge/insert , ie 8611-1257RACE
Wet kit- the same internals from dry cartridge built directly into your old strut housings.
Photo shows left to right, sealed strut, some models will come with the spring seat welded to the body.
Next is the 'cut a strut' easily spotted by the retaining post on the bottom, cut and gut your OEM strut and install the insert in.
3rd photo is the dry insert, many older cars have struts that have inserts from the factory, vw golfs, corollas etc, this insert shown is the
double adjustable race one with the bump(compression) adjuster at the bottom.
The 'Wet' inserts are exactly the same internals as the others but are installed directly into the strut, essentially a collection of parts adapted
to fit into a strut housing, pretty much any existing strut can be modifed to be a Koni double adjustable.
Should probably clairify rebound and compression damping before I go too much further.
To plagiarise the koni website :D
"Compression or bump damping controls the unsprung weight of the vehicle (wheels, axles, etc.). It controls the upward
movement of the suspension such as hitting a bump in the track. It should not be used to control the downward movement
of the vehicle when it encounters dips, also, it should not be used to control roll or bottoming."
Basically it affects the interaction of the tyre with the track, getting it right maximises the grip.
"The rebound damping controls the sprung mass of the car, it controls transitional roll (lean) as when entering a turn.
It does not limit the total amount of roll; it does limit how fast this total roll angle is achieved.
How much the vehicle actually leans is determined by other things such as spring rate, sway bars, roll center heights, etc.
The reality is rebound is the most important part of the damping, not enough and the weight transfer will play havoc, too
much at one end and you'll lose response and cause undue loss of car balance and too much in total can cause 'jacking down'
where the shock gets compressed under bumps and never extends back up, hit enough bumps in a short time and the shock
will be compressed onto the bump stops.
"Contact with the bump stops causes a drastic increase in roll stiffness. If this condition occurs on the front, the car will understeer;
if it occurs on the rear, the car will oversteer."
On a road car the bump settings are optimised for the road which has all sorts of bumps, potholes, manhole covers, different types
of surfaces etc, the race track however is generally very smooth so you can run much more compression damping.
Here's a quick photo of the internals of a twin tube shock.
On the end of the inner tube is the foot/compression valve and on the end of the piston rod is the piston, imagine the shock is fully
extended, the inner tube is full of oil, when the piston rod is pushed in, some oil flows without resistance from below the piston to above
and the rest thru the non return bump valve at the end of the inner tube and into the outer tube which is effectively just a reservoir, this
valve controls the oil flow and therefore compression damping.
On the rebound stroke, the piston rod is pulled out and the oil above the piston which is pressurized is forced to flow through the piston
this generates the rebound damping, at the same time some oil flows back, without resistance, from the outer tube through the footvalve
to the lower part of the inner tube to compensate for the volume of the piston rod emerging from the cylinder, basically under vacuum.
So looking at the two piston rods the most obvious thing is the rebound stop (black arrows) is in a different place, this stop determines
how much of the piston rod is left inside the shock when fully extended, so shock travel is basically the length of the inner tube/shock body
minus how much piston rod is left inside.
So if you ask your koni agent to shorten the shock they will usually add some nylon rebound rings (yellow arrow) which prevents the piston
rod from extending out of the shock as far.
So why does the subaru piston rod extend so far out of the shock at full travel? well the shock has a very long stroke ratio to the over all length
of the shock and the problem is at full extension the shock is very weak, ie not much piston rod left inside, since it's a macpherson strut it's
subjected to side loading, the top bronze bush and the piston are what stops the shock from bending in half, the further the shock is compressed
the stronger it is in terms of side loading as there is a greater distance between the top bush and the piston.
OK, back to the suby shock, droop is the answer, they use progressive rate springs and huge droop, the actual ride height will put the piston back
in the middle of the stroke where it's stronger but the advantage is over bumpy stuff the shock has extra travel to control the wheels, with 190+mm
of travel they probably run about 90mms of droop, pretty hard to lift one wheel off the ground when there is so much travel in reserve.
For a race car the higher spring rates mean for a linear spring you won't get much droop, on my car with 280lb front springs I get 33mms of droop
and for the rear I get 27mms of droop, a rough guide is to run at least 1/4 travel for droop, so 33 x 4 gives me 132mm of travel, not much point
having any more travel than that, standard swift strut has 155mm of travel, basically I would have 23mm extra travel which adds to the ride height,
only way to add droop to lower that ride height is to use keeper, tender or progressive rate springs.
So what are our options???
We'll start with the obvious choice, the swift Koni sports front and rear, part numbers 86-2588sport and 87-2429sport respectively, great value for money and excellent for a road car.
The issues with them are
Same length as standard shocks.
Improved valving over OEM shocks but is struggling to control 270-300lb spring/wheel rates.
No external rebound adjustment.
I'll discuss the rear shocks first as there is only two options, off the shelf 87-2429 and custom made.
The problem is Suzuki came up with a bizarre rear hub clamp which no one else uses hence no interchangible shocks from other cars, fit though is straight forward as it's a complete
shock, again no external adjustment, to get around the length issue you can either make a new strut top with a bearing really high up or mount the shock lower in the clamp, no idea
about waranty issues so modify at your own risk.
First you need to knock the retaining lug off, a cold chisel and a hammer usually does the trick, it's not actually needed but makes lining up the groove in the shock much easier when
trying to install the clamp bolt in the rear hubs.
Secondly you'll need to make a new groove, 25-30 mm further up is about the right amount, the wall thickness of the shock is 2mm so you can press and or file a groove relatively easily,
below is a photo of a 15 yr old Grp N short double adjustable rear koni with 2 extra grooves added lower down, the owner must of needed more ride height at some stage...
Remember though that lowering the shock 25mm will not lower the car by the same amount unless you shorten your springs, it will increase preload making them slightly stiffer though,
a 25mm reduction in shock length might result in a 15mm car height reduction, all depends on the length, spring rate and weight.
Don't forget the suzuki oem rear spring location has a 2-1 ratio, so a 600lb spring is actually the same as a 300lb coil over spring, really important to point it out to your koni agent if
you ever get the rear shocks revalved because he will ask what rates you are running and the valving for a 600lb spring is quite different from a 300lb spring!
Plenty of threads around on installing the 'cut a strut' sport insert into the oem suzuki struts, again the same issues of length, no external rebound adjustment and bump
adjustment only suited to mid 200lb spring rates exist, there are several things you can do to make them shorter, a decent set of fixed alloy strut tops with the bearing mounted
high actually lowers the car in respect to the shock.
You can shorten the over all length of the shock but if you have standard springs then you are only adding preload so you will be lowering the car slightly by reducing droop.
However if you have super low springs which are stiffer and shorter then you will see a bigger result, if you have adjustable spring seats then you can really benefit from shortening
Easiest way to shorten these inserts is to actually seat them lower into your old strut housings, you can drill out the bottom and weld a new bottom on, you can trim down the retaining
post as well and seat the insert at least 30mm lower.
Remember if you trim down the retaining post then you will need a press to push the insert in all the way, I have shown a pan head philips bolt in the end on the insert and would only be
used to ensure insert retention not for actually pulling insert into strut housing, also you don't actually need to weld the washer or plate onto the end of the strut, the large domed
washer would be fine once it's all torqued up.
The main limitation in lowering the insert is the retaining bolt rubbing on the CV boot, you could also tack weld the shortened retaining post into position instead of using a bolt, you
could also cut a groove in the retaining post and use a circlip over the outside, or machine up alloy cups to fit into the bottom of the struts.
Here is an example I turned up very rapidly as a demo, excuse the finish, blunt tools and no bench grinder... anyhow you get the idea, I pressed it into the bottom of the strut and it fits
nicely, again the limiting factor is the retaining bolt rubbing on the CV but this one has plenty of clearance so you could make them deeper if you wanted to.
Before I get to other cut a strut inserts I should mention that if you are stuck in a racing class that prohibits adjustable spring seats/perchs then using a mk1 swift housing is a good
option as 65mm id racing springs actually fit really well, I used them on my old mk1 years ago and the ability to buy springs of all different rates makes fine tuning your car much faster,
easier and cheaper, I can buy and sell a set of race springs and usually get 90-100% of my money back if I don't need them.
Below is a comparison between mk1 and mk2 struts, body diameter is the same at 40mm ID and 44mm OD, if you are a mk1 owner then installing the mk2 koni sport into your housing
will result in a decent length reduction, you'll lose 20-30mm off the body length and 10mm stroke reduction, you'll need to drill out your strut tops as the mk2 shock shaft doesn't have
the flat part and you'll need a spacer tube to accomodate the extra shoulder length sticking out.
I've seated a spring to show the length and a suspected stoke range, haven't done the mod yet so can only guesstimate, depends in part as to how low you can get the insert.
The spring is 250mm long, 300mm gives far to much preload so you will need to play around with thicker top spring seats to get the preload right.
The example below was on a standard mk1 kyb, I think it was either standard height or 20mm taken off the shock shoulder, with the shorter koni insert I think that a 250mm long spring
will be getting close to being captive.
Other Cut a Strut inserts
I have mentioned before about people using EP82 Toyota Starlet inserts, GtiJedi bought a set and measured them up for me, same 40mm OD means it will fit into a swift housing, in fact
a lot of small cars appear to have 44mmOD / 40mm ID struts so there is a large range of small cars with similar front struts, the lengths are similar but the main difference is the top of
the shock shaft and therefore the type of strut top being used.
If you are converting to a pillowball/camber plate with spherical bearing then the end of the shock shaft is not much of an issue, personally you must be crazy if you are still using the
rubber oem strut tops, not only do they flex badly robbing you of your negative camber when cornering they also don't allow enough articulation through the suspension stroke and the
forces try to bend the piston rod/shock shaft resulting in less smooth travel and more wear on the brass bush at the top of the shock body.
Whats so great about the EP82 Starlet cut a strut insert? well it does have external rebound adjustment and it's also one of the few that is low pressure gas charged, because of this
they are slightly more expensive than the swift koni cut a strut inserts but well worth the extra money.
My Koni agent gave me the open and closed measurements of EP82 insert as 524mm and 369mm respectively and that compares to the swift at 523mm and 384mm, I also found the
BG Mazda 323 as having 501mm and 349mm, potentially a shorter insert, not sure if they still make them though.
EP 82 Starlet 8641-1214 Sport Ext adj + gas
BG Mazda 323 86-2447
Diahatsu Charade (G200 I think) 86-2400
I also think the Nissan March 86-1319 would be worth looking at as it also has external rebound adjustment, not sure what the difference with the EP91 Starlet is over the EP82 but the
front shocks have a different part number, the part number for the EP91 is 8641-1353, again cut a strut, Ext Adj and gas.
A lot of the other cars I have looked at have dry cartridge inserts, mk1,2,3 golfs and fwd corollas for example, most of them are too long as they are much bigger cars but the housings
can be adapted to run other shorter inserts including the Koni twin tube 'Race series' cartridge's.
Dry Cartridge Inserts
To quote Koni again
"The 8611 series double adjustable strut insert is a universal strut insert that can be used in many different applications. Originally designed for European touring car classes utilizing
strut suspensions, the 8611 has become an affordable double adjustable option for club racers and auto crossers in North America"
Here is the Koni NA website, the inserts that apply to us are the ones I've arrowed
Dry Cartridge Inserts
Ok, now the interesting part, these inserts need a 44mm ID shock body, I know alot of the Corolla fwd models had front suspension with cartridge shocks, here is a photo of some AE101 (edited for accuracy)strut housings that have been shortened, not pretty but will do the business, http://www.locostusa.com/forums/viewtop ... 1&start=15
Here is a pic of the bump valves, on the right is the standard foot valve, oil flow is controlled by the stack of shims and washers.
The adjustable foot valve has a small hole in the top and oil flows through and around the shims, the tension on the shims is applied through the adjuster which is on a ramp type arrangement.
I should probably mention that the 8610 rebound only race cartridge has crazy hard bump damping in it, really designed for Hondas and the like running really stiff springs and would be
way over damped out of the box if used on our cars.
Here's an ad for Truechoice, Koni agents in the states, circa 2005
Here is a photo of a double adjustable rear shock showing you the length difference to the stock shock, notice the collar, your koni agent has access to blank collars, it's internal diameter
suits their small top rod guide, you machine it to fit what ever strut housing you want, also at the bottom is a machined up 'double adjuster housing end plug', both are fitted and welded in place.
The OD of the collar is the perfect size to slide a threaded sleeve over the top, a small sleeve is required at the base of the threaded sleeve.
Last photo is of my front double adjustable, have included a rule for length reference.