Koni Racing strut conversion...

Suspension and other discussion

Re: Koni Racing strut conversion...

Postby MWP » Thu Jun 02, 2016 5:33 pm

Normally i would write longer replies, but im a bit short of time at the moment :(
BTW, sorry if i do come across as being argumentative... i know i do have a bad habit of replying that way, i don't do it on purpose. I enjoy discussions like this.

diceman wrote:I did read your original posts and even watched the videos :-).
Your roads appear far better than ours! I would say those roads have undulations and the odd bit of surface break up. Ours seem to have major grooves from traffic, roads that have dropped in short parts due to partial subsidence of the road sub-layer and large amounts of camber to assist rain run-off (centre whiteline as high point). I've never had the opportunity to drive hard in a firmly sprung GT4 over these roads but much firmer than I am aiming for I would expect would result in large vehicle body movement and wheels leaving contact with the road too much. It would probably be fine on 60mph plus roads. Again I hope to be educated/experience this soon in a friends car.


Our roads are terrible! They truly are.
Before your comments, i had considered 8kg to be fairly soft. Most guys here buying Tein, BC, etc coilovers go for above 10kg. The ride must be terrible!
Watch some more of that Corsican rally footage too, you can see that the ~8kg springs they are running aren't really that stiff.

Sorry for any confusion; I said "drop" not "droop". By this I mean the suspension lowered the static ride height by xx mm over standard springs.


Oh! Oops, my mistake.

Our state government has legislated minimum ride heights for all cars. They measure it by "eyebrow" height which is the distance from the center of the wheel, to the lip of the guard arch.
After thinking about it for a while is actually a great way to measure suspension height as wheel size doesn't effect the measurement.
The minimum ride height they state for a ST185 is a front eyebrow height of 345mm, and a rear of 330mm.

I have figures for standard and calculated droop somewhere but I seem to remember that my current (BAD and not my choosing) AVO springs provide around 115mm of droop! this leaves around 40mm of suspension travel until the wheel/tyre has come into contact with the wheel arch and the shortened bump stop is solid and compressed. Given that we only start off with around 140-150mm of suspension travel we need around 50mm of droop according to the 1/3 and 2/3 guide suggested (which I have also read before) and aligns with a circa 8kg/mm spring at the front (without any helper or preload) and would give around 100mm of bump travel but only if you run at standard ride height otherwise you will be reducing the available bump travel. At this point you have 2 options as far as I can ascertain: -
1) run the stiffer springs at circa 8-10KG/mm and lower the vehicle a fair bit (say 40-50mm) in the knowledge that the stiffer spring will require less suspension travel.
2) run the softer spring at circa 5kg/mm and don't lower the vehicle as much (say 15-25). Also don't suffer as much from bump steer in this region.
I'd guess there is merit in both approaches depending on application.


Yeah, it really comes down to personal choice.
Though if you intend to run light springs and a decent level of compression damping, that overheating/cavitation problem might come into play.

From your writings it sounds like you have read similar sources as myself when endeavouring to select/fine tune spring/damping rates. These seem to be loose guides and far from precise. My concerns have been that all full suspension kits (spring & shock) I have reviewed so far have been way off the numbers from the guides I have read, why I have yet to establish. In particular the commonly reported "Rebound damping needs to match the spring. Ideal compression damping is determined by vehicle weight" seems massively simplistic and bears little resemblence to the shock dynos I have reviewed.
Hence - I keep saying damping rates = compression & rebound as I am not convinced as yet to the accuracy of the sweeping statements that are banded about.
Please don't take my posts as argumentative, far from it. I am merely trying to ascertain the truthes. If we can calculate that Tein/BC/Bilstein/KYB/TRD are all doing differently to the ideal damping calculation (some are miles out) then to me it suggests that the calculation is flawed or there are different requirements.


The ideal damping rates can only be achieved by trial and error from feel and lap times.
You can do the math and theorise all day, but they will never be correct.
It's one of the reasons why i do like the Koni Racing inserts over Bilstein. They have easy adjustment, a wide adjust range and decent accuracy and repeatability. Where as Bilstein's would need to come off for a re-shimming every time.

I'm very interested in to why you feel the Koni 8611 will not be upto the job with respect to the heat and cavitation, again this isn't argumentative but hopefully your experience or findings may save me from making the wrong choice.


The more a damper restricts oil flow, and the more they move, the more heat they generate.
So hence why i do worry a bit about running a soft spring (=lots of movement), and lots of compression damping (=lots of restriction).

The 8611's have to be housed in another tube, which means they dont get the best cooling effect from air passing over the housing tubing.
Rally dampers are built to dissipate a lot of heat via special strut tubes and the external canisters.

The 8611's also aren't pressurised (i dont think so anyway, you have any info on this?), which means they cavitate easier than pressurised dampers.
Also when they start getting hot they will be prone to more cavitation.

It may not be a problem at all... its just all this adds up to something which could be a problem.
I guess the only real way to tell is to put a temp sensor on the inside of the strut tube somehow and monitor temperature.
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Re: Koni Racing strut conversion...

Postby diceman » Thu Jun 02, 2016 7:07 pm

MWP wrote:Normally i would write longer replies, but im a bit short of time at the moment :(
BTW, sorry if i do come across as being argumentative... i know i do have a bad habit of replying that way, i don't do it on purpose. I enjoy discussions like this.

No problem - I had feared the same for myself.

diceman wrote:I did read your original posts and even watched the videos :-).
Your roads appear far better than ours! I would say those roads have undulations and the odd bit of surface break up. Ours seem to have major grooves from traffic, roads that have dropped in short parts due to partial subsidence of the road sub-layer and large amounts of camber to assist rain run-off (centre whiteline as high point). I've never had the opportunity to drive hard in a firmly sprung GT4 over these roads but much firmer than I am aiming for I would expect would result in large vehicle body movement and wheels leaving contact with the road too much. It would probably be fine on 60mph plus roads. Again I hope to be educated/experience this soon in a friends car.


Our roads are terrible! They truly are.
Before your comments, i had considered 8kg to be fairly soft. Most guys here buying Tein, BC, etc coilovers go for above 10kg. The ride must be terrible!
Watch some more of that Corsican rally footage too, you can see that the ~8kg springs they are running aren't really that stiff.

I'll have a look.

Sorry for any confusion; I said "drop" not "droop". By this I mean the suspension lowered the static ride height by xx mm over standard springs.


Oh! Oops, my mistake.

Our state government has legislated minimum ride heights for all cars. They measure it by "eyebrow" height which is the distance from the center of the wheel, to the lip of the guard arch.
After thinking about it for a while is actually a great way to measure suspension height as wheel size doesn't effect the measurement.
The minimum ride height they state for a ST185 is a front eyebrow height of 345mm, and a rear of 330mm.

I've just measured mine at 320mm and 305mm respectively. I will be aiming for pretty much the minimum ride height legislated in Oz. Mine is too low.

I have figures for standard and calculated droop somewhere but I seem to remember that my current (BAD and not my choosing) AVO springs provide around 115mm of droop! this leaves around 40mm of suspension travel until the wheel/tyre has come into contact with the wheel arch and the shortened bump stop is solid and compressed. Given that we only start off with around 140-150mm of suspension travel we need around 50mm of droop according to the 1/3 and 2/3 guide suggested (which I have also read before) and aligns with a circa 8kg/mm spring at the front (without any helper or preload) and would give around 100mm of bump travel but only if you run at standard ride height otherwise you will be reducing the available bump travel. At this point you have 2 options as far as I can ascertain: -
1) run the stiffer springs at circa 8-10KG/mm and lower the vehicle a fair bit (say 40-50mm) in the knowledge that the stiffer spring will require less suspension travel.
2) run the softer spring at circa 5kg/mm and don't lower the vehicle as much (say 15-25). Also don't suffer as much from bump steer in this region.
I'd guess there is merit in both approaches depending on application.


Yeah, it really comes down to personal choice.
Though if you intend to run light springs and a decent level of compression damping, that overheating/cavitation problem might come into play.


From your writings it sounds like you have read similar sources as myself when endeavouring to select/fine tune spring/damping rates. These seem to be loose guides and far from precise. My concerns have been that all full suspension kits (spring & shock) I have reviewed so far have been way off the numbers from the guides I have read, why I have yet to establish. In particular the commonly reported "Rebound damping needs to match the spring. Ideal compression damping is determined by vehicle weight" seems massively simplistic and bears little resemblence to the shock dynos I have reviewed.
Hence - I keep saying damping rates = compression & rebound as I am not convinced as yet to the accuracy of the sweeping statements that are banded about.
Please don't take my posts as argumentative, far from it. I am merely trying to ascertain the truthes. If we can calculate that Tein/BC/Bilstein/KYB/TRD are all doing differently to the ideal damping calculation (some are miles out) then to me it suggests that the calculation is flawed or there are different requirements.


The ideal damping rates can only be achieved by trial and error from feel and lap times.
You can do the math and theorise all day, but they will never be correct.
It's one of the reasons why i do like the Koni Racing inserts over Bilstein. They have easy adjustment, a wide adjust range and decent accuracy and repeatability. Where as Bilstein's would need to come off for a re-shimming every time.

True but it is rare to find a shock with adjustment that shifts the damping curve evenly like the Konis, The Bilstein will probably be closer than most so called adjustable shocks over more of the velocity range.

I'm very interested in to why you feel the Koni 8611 will not be upto the job with respect to the heat and cavitation, again this isn't argumentative but hopefully your experience or findings may save me from making the wrong choice.


The more a damper restricts oil flow, and the more they move, the more heat they generate.
So hence why i do worry a bit about running a soft spring (=lots of movement), and lots of compression damping (=lots of restriction).

The 8611's have to be housed in another tube, which means they dont get the best cooling effect from air passing over the housing tubing.
Rally dampers are built to dissipate a lot of heat via special strut tubes and the external canisters.

The 8611's also aren't pressurised (i dont think so anyway, you have any info on this?), which means they cavitate easier than pressurised dampers.
Also when they start getting hot they will be prone to more cavitation.


Wow, on checking the Koni 8611 is there hydraulic type; you have brought to my attention something that I had totally missed. see : - http://www.motorspot.com/konimotosportcatalog.pdf
They also list the more common road car 8640/8641 as low pressure gas and others as high pressure gas. The race series is therefore not pressurised at all it seems! Totally the opposite of the mono-tube Bilstein which is high pressure (enough to actually jack the static ride height up a little as it contributes to the spring rate in this direction)

I would however question your thinking on this (I'm not saying you are wrong), running a bit more bump/rebound damping than calculated ideal (but the same as theoretically ideal damping rate according to the wilhelm calc for say a 8KG spring) will provide more displacement of the shock piston but the rebound velocity will be less with a lower rate spring acting on it and the bump velocity is presumably dictated by the contour of the bump you travel over? I can see the weight transition phase exerting a higher force but that should be minimal compared to a big bump I would think. People often seem to suggest shocks can "control high rate springs" or "will blow with a high rate spring" so maybe my thinking has been skewed toward thinking that higher rate springs make the shock's life harder.

It may not be a problem at all... its just all this adds up to something which could be a problem.
I guess the only real way to tell is to put a temp sensor on the inside of the strut tube somehow and monitor temperature.
[/quote]

Indeed it could be a problem. My old Koni inserts were fitted with oil between the insert and the strut case to transfer heat as reccomended by the supplier, this clearly isn't an option with the double adjustable where you have drill a hole in the bottom!
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Re: Koni Racing strut conversion...

Postby diceman » Thu Jun 02, 2016 7:24 pm

Another factor that we have both not mentioned is tyre wall stiffness and relative grip levels. Most stuff I have read indicated that you will only really get the benefit of stiff springs with race spec rubber grip levels and the stiffer side walls it brings.

And I should say that thank you for your thread, I've wanted to see a guinea pig do this first so any pics and info would be great :-) It's also nice to see I'm not as mad as friends on the GT4DC seem to think I am when discussing the use of Koni and running through calculations to select suspension components for my purpose :-) If I am then at least there are 2 of us!
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Re: Koni Racing strut conversion...

Postby MWP » Mon Jun 06, 2016 2:36 am

So its all finished and installed in the car :D
It was a super huge rush to get it all done and installed for the 5pm Friday deadline, so i didnt take as many progress photos as i would have liked.
I'll still try to do more write up's in the next few days, but it just wont have as many pretty pictures as i would have liked.

More rebound & compression damping tuning is needed, but it handles awesomely now (front: 1-click of compression damping, 1 turn rebound. rear: 0-click of compression damping, 0.75 turn of rebound).
It wasn't bad before with the 1259's up the font and KYBs in rear, but now with the 1275's in the front and 1259's in the rear the back of the car is much more stable, doesnt bounce, and the turn in is amazing.
On the first drive i almost hit a couple of inside curbs from turning in too early :twisted:
I haven't quite gone there yet, but on the limit of steady-state cornering i think the back of the car may come around first which isnt ideal. Im going to dial back the rear whiteline sway bar to the softest setting which should help. Some driving on a circuit is really needed to test it properly though.
Trail-braking the back will come around quite easily which is a good thing.
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Re: Koni Racing strut conversion...

Postby Aaron » Mon Jun 13, 2016 12:29 am

Come on, dude. It's been a whole week. What did you do to it this weekend? 8)
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Re: Koni Racing strut conversion...

Postby flyingdutchman » Tue Aug 23, 2016 4:18 am

Any progress on this build?
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Re: Koni Racing strut conversion...

Postby CMS-GT4 » Mon Aug 29, 2016 3:09 pm

A fwd guy had some threaded tubes made for his 8611s on his 5th gen.
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Re: Koni Racing strut conversion...

Postby MWP » Thu Sep 01, 2016 3:53 pm

flyingdutchman wrote:Any progress on this build?


Yeah, it's all in and done.
I do need to spend some time fine tuning it though. I'll wait until ive done so to finish the write up.
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Re: Koni Racing strut conversion...

Postby MWP » Thu Sep 01, 2016 3:55 pm

CMS-GT4 wrote:A fwd guy had some threaded tubes made for his 8611s on his 5th gen.


Nice... if not a rather expensive way to do it.
I wonder what he used for the lower housing, hopefully its not alloy.
T3 strut tops is a bad idea too... the bearings are undersized and flog out really quickly with our heavy front-ends.
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Re: Koni Racing strut conversion...

Postby PDoane » Fri Sep 02, 2016 12:46 pm

I modified MR2 OEM struts for Koni 8611s

http://www.mr2oc.com/47-road-racing/312 ... ild-5.html
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Re: Koni Racing strut conversion...

Postby MWP » Tue Aug 22, 2017 7:14 pm

Sooo this didnt end up working out so well :(

The 8611's worked great up the front until they didnt.
They lasted about 12 months before the developed some shaft play and started leaking oil.

My guess is that they simply aren't made to take the side loadings that the heavy car and mcpherson strut setup is putting on them.

So... next up will probably be Bilstein 46mm universal struts, and possibly the Prius upright conversion at the same time.
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Re: Koni Racing strut conversion...

Postby flyingdutchman » Wed Aug 23, 2017 5:57 am

Sorry to hear that! I was really looking forward to hearing how this build rode.
Have you reached out to Koni at all? Their site says the 8611s are for strut suspensions
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Re: Koni Racing strut conversion...

Postby MWP » Wed Aug 23, 2017 12:52 pm

The car handled really nicely until they failed.
Quite a shame really.

I have talked to the Australian Distributor, and they said they can rebuild them and help prevent it happening in the future.
I rather doubt thats really the case though. Even if they last twice as long, it'll only be 2yrs, and i dont want to be paying for rebuilds that often.

Where those inverted bilsteins should be bullet proof in comparison, and I can service them myself.
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Re: Koni Racing strut conversion...

Postby diceman » Thu Aug 24, 2017 2:08 pm

That sucks - sorry to hear that. I have seen similar issues on the Koni yellows and they ed sonner than I would expect for a road based product.
I kept coming back to the Bilstein universal motorsport strut myself but the costs started rapidly increasing (partly as they are not sold in the UK and shipping from USA was proving difficult/expensive - already had one set of struts returned to seller as the freight company had pressurised cansiters on the prohibited items list). Once you add up the machining, re-valving and welding of lower ears costs it's a bloody expensive project for a non-adjustable but bulletproof construction. I then figured I'd be better just buying DMS coilovers but still they are a chunk more money.

I suspect for your use only an inverted tube will deal with the sideloading so sensible options are few and all costly.

I know we chatted earlier in this thread and I've ended up specifying my own spring rates & digressive valving for some BC 46mm piston struts. These are however non-inverted so I suspect would fail very quickly under your use but for my road tyre/road use hopefully will be OK. Part of the attraction for me was being able to rebuild them myself with Bilstein 46mm digressive valving at a later date but it really isn't in the same league. I assume you have looked at the BC inverted but I've recently pulled a used set partially apart to inspect and they use a smaller valve that is not replaceable by any Bilstein parts.

Please keep us posted on your future journey and hopefully it will be better news next time.
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Re: Koni Racing strut conversion...

Postby MWP » Thu Aug 24, 2017 3:12 pm

Normal OEM replacement Koni yellows/reds last a decent amount of time if they are not abused.
Given the size of the 8611's, i think they were mainly aimed at small'ish club/track racers.

Today pulled down a front corner to start measuring everything up again to work out what length Bilstein 46's i'll be after, and to also work out exactly what will be involved in doing the Prius upright conversion (if i go ahead with it, i need to have the car back on the road in 2-3 months).
Doing it all should vastly improve front suspension performance, but it's a decent amount of work and $$s.

DMS's actually have a rather average reputation here in Aus.
Out of the Aussie damper/strut manufacturers, the order of preference seems to be: MCA Golds, Supashock and MCA last.
MCA had a bad run a few years back of having weak lower legs on the struts, and havent really been too popular here since.
Both MCA Golds and Supashock are about $10k AUD for a full setup. Very expensive.
https://mcasuspension.com/suspension#golds
http://supashock.com/aftermarket-suspension/

That's interesting about the BC's, i hadn't heard that about the piston sizes before.
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