KONI Sports for Classic Z's

[Diseazd]

On 4/21/2019 at 4:41 AM, Nils said:

 

Thanks for the replies gentlemen! For clarity, I've collected all info on my setup in this post.

Car: 05/71 HLS30-30267 US model. Two previous owners before me (1971-1979 / 1979-2013). To my knowledge, it's an unmodified/stock car. It came with original open-type struts, springs and strut housings. The struts were leaking so I replaced them with KYB Excel-G's and supplied gland nuts.

Strut housing part numbers: 54303-E4151 and 54302-E4151. I can't find any production date/number stamped on them.

Strut housing dimensions: Inside: Between 15" 1/16 and 15" 1/8. Outside: 16" (slightly difficult to measure precisely atm as they're assembled). It's difficult to see the inside bottom of the housing, but I did take a photo and it looks fairly clean. Can't see any sign of inside spacers being used.

Koni front shock part numbers: 8641 1031SPORT (1-2019)

Gland nut: I first tried with the supplied Koni nuts. I also tried with the original nuts and the two variants of KYB nuts (front / rear). As someone mentioned, the front KYB struts are shorter and therefore user a spacer inside the gland nut.

Strut lengths: The (yellow) housing part of the Konis are 387mm (15 1/4"). The KYBs are 377mm (14,84"). It's also worth noting that the two brands of struts have different bottom shapes - the Koni is convex while the KYB has a concave "cup" welded to the bottom. Depending on the shape of the bottom of the strut housing, ths might affect the fit.

Gap: I curently have a gap of around 8mm between the rim of the gland nut and the top of the strut housing. According to the Koni supplied instructions it should be between 1-4mm. On one side, the threads won't catch at all. On the other side, the threads enter but I only have a quarter turn before it's full stop.

 

FWIW, I bought a pair of new 240Z front Konis to replace a blown Tokico in my rear Ground Control sectioned coilovers. I had the same gap as shown above and had to return the pair. The Konis are taller than the Tokicos and the struts were sectioned to fit Tokicos. Many thanks to my friend  Jim Karst for selling me some nice used Tokicos, or I would have had to add a section to my strut (PITA). In the future, I would suggest shock tubes err on the side of too short, not too long (much easier to add a spacer to center the shock in the strut).

[KONI Lee]

On ‎12‎/‎1‎/‎2019 at 12:31 AM, bingo said:

Does anybody know if these are digressive or progressive?

As with pretty much all KONI dampers, these are digressive valvings on the Z cars. This means that as they initially begin to move, they build damping forces at a pretty steep rate to give very low piston speed, subtle body motion control but the rate of climb continues at a decreasing or digressing rate at target piston speeds across their working piston speed range so that they do not get too firm and causing handling, tire grip, and ride comfort issues once the suspension and body get into significant motion.

A progressive damping curve would normally be a bad thing as it would have very little damping force and control in subtle suspension motions but it would rapidly increase the rate of climb becoming overdamped and harsh over big motions and bumps.  A progressive damping curve on a car would be an extreme rarity and I can't say that I have ever seen such in my nearly 25 years in the business.  

Some cars and specific suspension designs (typically not struts) prefer a more linear damping curve meaning that that the rate of climb is relatively even across the piston speed range and typically have pretty limited initial low speed damping forces.  Some relatively linear damping examples are a number of BMW rear shocks that are mounted well behind the axle and trailing arm with an overdriving or more than 1:1 motion ratio. 

Progressive rates can very often be a very good thing for performance car springs but would be a bad thing for performance car damping. Progressive springs and digressive damper valvings can be very well matched, especially when adjustable.

[bingo]

Thanks Koni Lee for the great explanation. Since you know your stuff and I am clearly learning I am going to ask another newbie question. When looking for strut inserts for coil overs or looking at coil over kits digressive is often mentioned as the newer better technology for shocks, but even in the same manufacturer's line of products you will see digressive advertised as a higher end option, but they don't say what the more basic option is. Should the assumption be that the shocks are linear or just less digressive? 

Because of the basic research that I have done on this topic I was planning on going with the Koni Race struts, but these struts seem to bee a better option since they are already valved for the z and should support any reasonable spring rate and put me at the desired height in the middle of the stroke after camber plates. Does this sound reasonable?

[KONI Lee]

On ‎12‎/‎16‎/‎2019 at 9:50 AM, bingo said:

When looking for strut inserts for coil overs or looking at coil over kits digressive is often mentioned as the newer better technology for shocks, but even in the same manufacturer's line of products you will see digressive advertised as a higher end option, but they don't say what the more basic option is. Should the assumption be that the shocks are linear or just less digressive? 

Because of the basic research that I have done on this topic I was planning on going with the Koni Race struts, but these struts seem to bee a better option since they are already valved for the z and should support any reasonable spring rate and put me at the desired height in the middle of the stroke after camber plates. Does this sound reasonable?

Digressive valving is not exactly "new thing" for companies who have been making performance dampers for a long time (KONI has been doing it for at least 50-60+ years) but it might be newer to companies whose products were more replacement grade and not really within the performance realm.  It could be that their piston and valving component design might not have allowed the ability to really contour the damping curves very much but have moved in that direction.  Many shock companies may not have been around that long or possibly just their marketing companies have simply latched onto "digressive" as a buzzword that they are using heavily now. Some consumer marketing messages may make a big deal about mono-tube or twin-tube design suggesting that one is always better than the other but it is simply not true.  There are good and bad examples of both and different cars can have very different needs so it is more important that the damper function is tailored to the vehicle and it usage. Digressive and linear are general terms used to describe shapes of plotted dyno curves (however shocks on cars on roads never operate like dyno graphs look) but there are so many variables in car and damper design that you really can't just hang onto or use it as a "this is good" or "this is not good" gateway.  Don't make your purchase on the use or lack of the word "digressive".  You did not mention any specific shock brands but it is probably better that way anyway. 

As to your coil-over questions, it really depends on your usage and expectations of the car.  To be a coil-over, it really only means that the spring is mounted on the strut of shock and all 3 of the early Z-cars do that already. Modern usage suggests that you are also wanting to make the lower spring perch height adjustable so you can customize your ride heights, corner weight the car if you want to, and have the flexibility to interchange spring rates is pretty easily.  Beyond that, it is pretty wide open as to what your desired outcome will be and thus the path you should follow. With a coil-over, you can select a relatively soft spring rate for a compliant suspension and smooth ride, bump them up quite a bit for firmer ride and sporty control or run really big spring rates for a handling performance only/ don't care about ride quality set-up for mostly track use.  It really boils down to what your uses and expectations for the car are. 

I would let that be the deciding point of whether you choose these Z-car specific Sport dampers or the much more aggressive RACE dampers that are clearly intended for Racing performance track duty with no comfort, no warranty, etc. in mind.  Before these new Sports were introduced, there were few options for the car but now they offer more opportunities.  Having looked at the damping specs of them all, the RACE units are much, much more aggressive on rebound and compression damping and not specifically fitted as a drop-in for the Z-car strut housings so some level of machining and fabrication may be needed depending upon your intended outcome.  The Sport units are made to be a nice performance upgrade for the Z-car but still have a quite reasonable ride quality (so long as you don't overspring the car which will make it harsh), a standard lifetime KONI warranty against defects, be a drop-in solution to fit your housings, etc.. 

It all depends upon what you want,  e.g. "Whats for dinner?" What do you want?  Home cooked or eat out? Steak or chicken, Mexican or Italian, etc.  Pick what you want to satisfy your interests as there is no specific one right answer for everyone.

[jonbill]

@Joseph@TheZStore @KONI Lee
Guys I've just been attempting to install my new Konis, and the gland nut doesn't fit. Have I got the wrong ones?

It's a late '74 260z (I've always understood it to be 11/74) and they are marked 8641 1033sport.
They slide into the strut tube snugly but the gland nut is the same diameter as the tube at about 50mm. My old KYB gland nut is about 47mm.

Help!

[SteveJ]

Is the car from North America? Did the European 260Zs go through the same changes as the North American cars?

[jonbill]

It's a UK car. I did think that broadly the transitions for the 260 were the same in US and UK, but I could easily be wrong on that.

Edited March 17, 2020 by jonbill

[Zed Head]

There are a lot of gland nut sizes out there.  Sounds like they just put the wrong ones in the package.

The Motorsport Auto guys do much much better with phone calls.

 

[SteveJ]

1 hour ago, jonbill said:

It's a UK car. I did think that broadly the transitions for the 260 were the same in US and UK, but I could easily be wrong on that.

This thread describes some of the differences: https://forums.hybridz.org/topic/62919-260z-suspension-vs-240z-suspension/

Measure your rear strut tube diameter with a caliper. I can measure the ones on my 260Z for comparison.

Edited March 17, 2020 by SteveJ

[KONI Lee]

Hello Jonbill.  Sorry that you have had an issue but I was able to dig into some specs to sort it out.

If your car needs the M48 x 1.5 gland nut, then you have early ('70-'74.5) strut housings and thus need the 8641 1031Sport with the proper gland nut and a 42 mm OD insert diameter and 394 mm insert length.  Based on the late 1974 build date, you bought the 8641 1033Sport which use a M52 x 1.5 gland nut, have a 43.5 mm (1.5 mm larger) OD insert diameter and a 384 mm (note that it is 10 mm shorter) insert length.  Whether the cars is the UK were made with a later changeover date or maybe sometime in its life someone put earlier strut housings on your car, you have early struts and thus need the early strut inserts.  Remember that you said it was a tight fit but the insert went into the housing, the later car's slightly larger OD insert body fit but barely? If you'd had the M48 gland nut, upon installing it you would have found that the later, shorter insert was too short to engage properly.  Although you could stack some washers on the bottom of the tube to spacer it up to engage, there is also a difference in the reound damping force (a bit more on the later car) and compression damping forces (a bit less on the later car) that would also made a functional difference as well.  The top mounting pin dimensions are the same between the two models but the later car's inserts actually extend about 5 mm longer and compresses 10 mm shorter than the earlier cars too.

The rear struts are quite a bit different in length between the early cars and later cars but they have the same M48 and M52 differnces that you should check on your car as well.

[jonbill]

Thanks Lee, that sounds conclusive. My old KYB struts are about 42mm OD.  I have some other corroboration that my build date is earlier than I thought. 

It's interesting what you say about the insert lengths - the 1033 are the same length as my old KYBs, and actually the 1033's ended up sitting a coupe off mm higher than the KYBs. Maybe they're not bottomed out because they're tight. I'll have to check the length of my tube and check there's not a spacer at the bottom - as it stands, I don't think there's room for a 10mm longer insert!

 

[KONI Lee]

According to the drawings I am looking at that has most but not all of the measurements, the 8641 1033 Sport does step down from 43.5 mm OD to 42 mm OD a short distance from the bottom so there is an insternal restiction near the bottom.  The 8641 1033 Sport is a straight 42 mm OD all the way down.  The 1033 may have hung up on that diameter restriction before it reached all the way to the bottom and thus the length difference is not apparent when inside.  All the more reason for you to get the 1031s that are needed for the smaller diameter early struts.  It would be interesting to see if you car has the smaller diameter rear struts as well if you think they are original to the car.