Circle Track Sway Bar

[JMortensen]

After taking a step back, I started thinking about the revalved 3000GT struts. Called Bilstein, they are no longer doing revalves in house. They also don't make 46mm struts anymore, FYI.

They said they farm out rebuilds and revalves to Performance Shock Inc, who apparently is at the Sonoma race track. Called them 800-965-5664, they said $320 each for a revalved 3kgt shock, and if I sent them my graph, they could try to hit those numbers.

I asked about revalving the P30s too, and Bilstein did say that I'd be much better off with the 36mm, Performance Shock said the cost to revalve the P30 would be about the same as buying the 36s and revalving them. One issue is that I really need to get my hands on one to see how I will have to modify the strut housing. Would like to do that before I commit to 4 of them.

I'll reach out to MCA and see how their stuff compares and make a decision. 

[clarkspeed]

For what it worth, I happen to know some very very fast Z cars run the plain old 8611 Koni double adjustable. And they dont have any problems with premature failure. I think the lower settings fall right into the window you are looking for. The adjustment steps are kind of coarse, but at some point you are splitting hairs. 

[AydinZ71]

6 hours ago, clarkspeed said:

For what it worth, I happen to know some very very fast Z cars run the plain old 8611 Koni double adjustable. And they dont have any problems with premature failure. I think the lower settings fall right into the window you are looking for. The adjustment steps are kind of coarse, but at some point you are splitting hairs. 

 

How much of am improvement is the double vs. the single adjustable RACE Koni's? Its a big jump in price, and I was curious just how big of a difference it makes. For example, @gnosez described the huge leap in lap times going from a helical to a OS-Giken adjustable clutch LSD. I wonder if anyone has a similar experience between the single vs. double adjustment. 

[JMortensen]

I've heard of a few people have had issues with the upper bushings in the Konis, and I suspect that there are a lot more who have the issues but don't know it. Cameron aka Heavy85 is the one I can point to off the top of my head. 

Opinions on shocks are kind of like brakes IMO. You get people who put gigantic brakes on the front of their Z and couple them with rear drum or crappy tiny rear disc and then they report that the car stops so much better, etc. Most people, IMO, don't know what proper brake bias feels like, I say this because I was actually one of these people. I went to a driver's school with my Toy 4x4 setup in front and 280ZX disc and drove through a puddle and slammed on the brakes and the rears didn't lock in water. One of the driving instructors told me that, then I figured out the fronts were way too big, and ended up going back to stock front calipers and I was able to dial in the bias correctly and only then did I know what correct brake bias felt like. 

I think the same thing is true with shocks, and that there are people racing with worn out strut bushings who just don't know, and the vast majority don't know and couldn't tell you if their shocks were valved anywhere close to correctly. Doesn't mean they're not fast, but being fast doesn't mean that they're right either. Add in the fact that a good shock setup costs so much money, and a cheap ass Chinese coilover is cheap, and I think if you polled Z owners you'd probably find that Chinese coilovers are the best option, Konis are too expensive and they suck because you still have to buy the coilover parts, and the kind of stuff I'm looking at is just stupid because it's either hyper expensive or not adjustable.

Aydin, I think the rebound is more important generally, and single adjustables do actually adjust both a little bit. This page might help: https://wilhelmraceworks.com/koni-shock-dynos

[AydinZ71]

@JMortensen hey that’s a fascinating read! Thanks for the link! Have you or anyone else tuned in your shock resistance yourselves? I can definitely tell if a car is over dampened, but it’s hard for me to “feel” for the sweet spot. Wondering if shop tuning is a must on this item. I need to get my height, track, and finally camber adjusted before I worry too much about shock acceleration resistance. I’m assuming toe should be neutral, but il read up on that topic shortly. 

[JMortensen]

Koni has some rough guidelines on how to tune shocks but if you're doing it by feel that's subjective and what you like might not be what is best. I prefer to do it by the numbers, and what I'd really like to have is some dyno plots, so that if I changed the spring rate (which I've already done a couple times) I could move to the next closest adjustment. 

I have a feeling I'll end up with more Bilsteins and they won't be adjustable...

Side note - I did talk to a friend of mine who does Mustang stuff and he can get me inverted 36mm struts with a 2" OD tube. It's what they use on old Fox body Mustangs. The stock 240 tube is 2" OD or 51mm which is very close, so might be able to grind off the weld at the base of the knuckle, remove the original tubes, and weld these in their place. They'd probably need to be trimmed to the right length, but it sounds very doable. Problem is struts through them are more expensive and likely not valved right.

I have an email in with MCA. I think that's my preferred solution right now. If that doesn't work out I'll probably look at the 3kgt stuff since it's the cheapest. If I can figure out how to install them I'll go that route, and if that doesn't work I'll adapt the Mustang parts.

[JMortensen]

Koni's road course tuning instructions: https://www.koni-na.com/en-US/NorthAmerica/Racing/Road-Course-Tuning-Guide/

Autox tuning: https://www.koni-na.com/en-US/NorthAmerica/Racing/Autocross-Tuning-Guide/

[Gareth. J.]

9 hours ago, JMortensen said:

Koni has some rough guidelines on how to tune shocks but if you're doing it by feel that's subjective and what you like might not be what is best. I prefer to do it by the numbers, and what I'd really like to have is some dyno plots, so that if I changed the spring rate (which I've already done a couple times) I could move to the next closest adjustment. 

I have a feeling I'll end up with more Bilsteins and they won't be adjustable...

Side note - I did talk to a friend of mine who does Mustang stuff and he can get me inverted 36mm struts with a 2" OD tube. It's what they use on old Fox body Mustangs. The stock 240 tube is 2" OD or 51mm which is very close, so might be able to grind off the weld at the base of the knuckle, remove the original tubes, and weld these in their place. They'd probably need to be trimmed to the right length, but it sounds very doable. Problem is struts through them are more expensive and likely not valved right.

I have an email in with MCA. I think that's my preferred solution right now. If that doesn't work out I'll probably look at the 3kgt stuff since it's the cheapest. If I can figure out how to install them I'll go that route, and if that doesn't work I'll adapt the Mustang parts.

Just be aware MCA have had issues with shocks leaking gas, even on struts that sat unused! 

[JMortensen]

Looks like they also don't invert their struts... hmm.

[clarkspeed]

22 hours ago, JMortensen said:

I think the same thing is true with shocks, and that there are people racing with worn out strut bushings who just don't know, and the vast majority don't know and couldn't tell you if their shocks were valved anywhere close to correctly. Doesn't mean they're not fast, but being fast doesn't mean that they're right either.

Very true, but when I said very very fast I meant it. AutoX and Runoffs National Champions. I don't think Greg Ira will mind I dropped his name here. That is hard to argue against. And at roughly $400 each, they are a bargain. On the other hand, I know Greg's program well, and I don't think shocks are a big contributer to his many podiums. 

 

I don't know anyone racing the 8610 single adjustable. There were some posts on here a few years ago on the valving, but even that is probably outdated.

[tube80z]

On 2/20/2021 at 10:57 AM, JMortensen said:

I've heard of a few people have had issues with the upper bushings in the Konis, and I suspect that there are a lot more who have the issues but don't know it. Cameron aka Heavy85 is the one I can point to off the top of my head. 

 

Morgan Smith, who has the red Z with the large IMSA flares was running 550 lbs/in springs on his Z and using the 15 inch GY FA tires and the bushing died after a season.  He was complaining the car was inconsistent and when he took the strut off I shook it and it rattled.  The top busing was toast. 

[tube80z]

On 2/16/2021 at 9:22 PM, JMortensen said:

Possibly dumb/brilliant idea. Why not attach a shock to the sway bar and to a fabbed mount on the chassis, like welded to the front or back of the strut tower? 

 

The problem with this when you adjust your ARB or turn the car you also change the motion ratio.  I also don't know if the ARB would act as a filter for some of the frequencies the damper would normally see.  

[JMortensen]

I'm going to wait to hear from MCA. Looks like they do an upright monotube. Not my favorite. If that's the case, I'm thinking really hard about these 2" strut tubes for the Mustang. That really seems like it solves a lot of my problems. Should be easy to weld to the 240Z strut housing, fits the 36mm Bilstein, then I can get some revalved and it's been suggested to use Ohlins pistons in the Bilstein strut, as the piston machining is better and the struts are supposed be more consistent.

Then it's really down to how much the DA strut tubes and the rest of the parts add. Looks like they're $3K, which I might stretch for, or I might just go with a revalve and then try to resist the temptation to change spring rates, but man, I'd really love to have adjustables and know what the adjustments do, and put the valving I want now in the lower 3rd of the adjustment range. Then I could go a little softer or a lot stiffer. Decisions decisions...

[jhm]

To throw another monkey into the mix....I've heard nothing but positive feedback about Intrax, but really haven't seen any direct reports of first-hand use on an S30 in a race application.  Anyone able to weigh in on this, since we're exploring different options?  (I must admit, I'm very much enjoying this discussion and wide range of ideas and options.)

 

https://www.intraxracing.nl/en/products/shockabsorbers/nissan/432-fairlady+z%2c+s30%2c+datsun+240z%2c+260z%2c+280z%2c#partfinder

[AydinZ71]

I have yet to meet a shitty Dutch performance part vendor. Koni is Dutch as well. If they had a bigger country, maybe they would make cars too 🤷🏽‍♂️😂

[clarkspeed]

I still enjoy bench racing on this forum also. So many things have been covered but technology changes with time and there is a real hardcore group here. I have a bunch of FB pages I comment on but it is just not the same as this forum.

[clarkspeed]

I know we are getting off the original topic, but I have another crazy idea.  I was reading some old posts and saw one by JohnC that described converting a monotube shock to an inverted strut.  So I started thinking about this.  I don't see why you could not replace the strut tube with something of appropriate diameter and use some Delrin for the shock body to slide against.  Sounds easy but of course alignment and tolerances would be critical and possibly some polishing.  You could probably even add a seal to keep the bearings clean.  I googled around and could not find any references to doing this. But you can find plenty of cut-a-way drawings of inverted strut designs.

[JMortensen]

That's essentially what my Mustang engineer friend has done. They made a 2" OD tube that fits a 36mm Bilstein and has bushings in the tube and a seal on top. So gets around all the issues with the 240 strut tube. I need to look at the shock tech post again and verify, but I think they had a gland nut that fit the 280Z, but I don't think it fit the 36mm strut, just the 30mm. If they had a 36mm gland nut could probably use the 3KGT insert and save some money vs the Mustang parts.

The problems I see are that the Mustang strut has 7" travel where the Z has 6. He is telling me I can cut down the tubing a ways before I hit anything inside, but I need to make sure I can cut enough so that I get the right amount of bump travel. Also says you can limit droop from inside the tube. I need to have more droop than necessary because I use 2.5" tall spacers to lift the front so that I can get the car on my trailer. Bunch of little things to make sure of, but I think this is sounding like a really good solution.

[clarkspeed]

Yes, I was looking at this and not a lot of shocks fit into the required form factor.  Pretty much needs to fit inside 2" DOM tubing with 0.188 wall which has 1.624 ID.  Over 2" OD and you lose ability to run 2-1/2 springs.  Kind of rules out most adjustable shocks.   

Are the 36 Bilstein racer rebuildable? I know their 46 have an abundance of valves, shims. and tools available and plenty of instruction on how to do it yourself.

[JMortensen]

Yes, there are similar pistons, shims, etc for the 36mm stuff and he's telling me if I rebuild the Ohlins pistons are better, so apparently from more than one manufacturer. I don't think 36mm is as popular with racers as the 46 which is used on pretty much all circle track stuff, but it's still a lot more available than the 30 stuff, it seems.

I did come across one pretty big issue, the Mustang strut has about 4 or 5" of shaft sticking out the top where it goes through the camber plate. Definitely wouldn't clear the hood. Thinking I'm going to buy a tube for the Mustang and buy a strut for the Mitsu and see if I can put them together. If that works, then I might just go for it, buy 4 mitsu struts and revalve, then mod the housings.

Also I misunderstood and the tube can't be cut down, but as it works out it's almost exactly the right length. Looks like if I pull the stock tube out of a 240 strut and install his, the tube height from the base of the spindle to the top of the tube will be 14.5" or so. My sectioned P30 was cut to 14.75" so just about dead on. His tubes have 2 bushings inside, one at the top and another one right in line with the piston (which doesn't move up and down relative to the housing), plus a dust seal top and bottom.  

The one issue is that the rear strut tubes need to be longer so would need to cut the original strut tube and weld together with the new one maybe 2 or 2.5" up, not unlike sectioning the tube. Coffey suggested doing that at the bottom of the tube, but I always did it at the top and thought it was kinda weird to do at the bottom, seems like that's where all the bending load is. Not the biggest problem. If I felt like it wasn't strong enough would be super easy to get a 3 or 4" long section of 2" ID tube and slide it over the top and weld.

I'm just about ready to pull out my wallet and make some of this happen. Likely won't be with adjustable struts though. Just revalved. A big problem is the adjusters are on the bottom of the inverted struts, so you'd have to pull the steer knuckles off just to see them, let alone adjusting correctly. Maybe could cut a window in the strut tube, dunno. Sounds sketchy...