KONI Sports for Classic Z's

[gundee]

Sent you a PM Lee.

[KONI Lee]

On ‎2‎/‎15‎/‎2019 at 7:13 PM, Carl Beck said:

We measured the load it took to compress the Tokico Gas Pressure Shocks (non adjustable) at 80 psi. at a local machine shop.  So it was easy to see that a 240Z with a spring constant of 83 lbs/in wound up sitting about 1” higher after installation. As for taking accurate and comparable measurements - a lot of the people involved are Engineers and pretty picky about accuracy. So lets hope your new offering are closer to the 3 Bar than the 5 Bar. At any rate better to know in advance of installation, so any necessary adjustments to spring rates or installed length can be made ahead of time.

The 80 psi gas charge that you saw in the damper does not equate to an 80 psi increase in the spring rate, it doesn't work that way.  It does add some quite limited preload boosting effect in conjunction with the preloaded spring rate when the weight of the car is loaded onto it and the damper gets closer to full compression.  In the past I have heard engineering generalizations that internal Low Pressure Gas charge effect might have some similarities to a 7-8 psi spring rate increase but even that is not exact because it doesn't really work that way between gas charge and spring rate. 

I definitely disagree that one should try to change your spring rate or installed length to compensate for internal gas charge, especially when there are so many ways throw off ride height measurements.  The most common that we see is taking measurements before the car has had an opportunity to move enough to settle from being raised in a droop situation, or from tightening control arm and similar bushings when in droop then putting the car on the ground with some lifting effect og bushing wind up in it.  There are certainly others but those alone can cause measurements to be unintentionally off by greater amounts than the gas charge itself alone.

I do not have any records to see if the factory Z-car dampers were originally LPG or non-gas charged so we don't know if there gas any gas effect or not in the factory info. That doesn't really matter though.  If the limited effect of the LPG charge is still bothering you so much  and you feel that you absolutely must must must have a non-gas charged, one could pretty easily degas the dampers oneself.  This is a trick that has been used for years (only in a T-T LPG, not M-T HPG!) in Stock/Street class autocrossing and can be beneficial mostly on slight weight, light sprung independent suspension cars that get some camber change with ride height change.  I am not going to explain how one would degas them on a public forum for a host of reasons but it can be done with no ill effects.  Technically this could put your warranty at risk but the damper's actual function or longevity will not be altered if done properly. 

[LeonV]

On 2/15/2019 at 4:13 PM, Carl Beck said:

Hi Lee: Great to have you here for this discussion. A further comment about our experience with gas pressure shocks several years ago.  Front corner weights on the 240Z’s were 562 lbs and 604 lbs for 1972 as an example. (and varied a little 70/71).

 

We measured the load it took to compress the Tokico Gas Pressure Shocks (non adjustable) at 80 psi. at a local machine shop.  So it was easy to see that a 240Z with a spring constant of 83 lbs/in wound up sitting about 1” higher after installation. As for taking accurate and comparable measurements - a lot of the people involved are Engineers and pretty picky about accuracy. So lets hope your new offering are closer to the 3 Bar than the 5 Bar. At any rate better to know in advance of installation, so any necessary adjustments to spring rates or installed length can be made ahead of time.

PSI is a unit of pressure, not load. Load would be the pressure multiplied by the area that the pressure pushes on.

Along similar lines, the gas charge is a pressure inside the damper, not a spring rate. The force exerted by the gas charge, and thus spring rate, depends on the piston damper rod size and pressure. This can be measured but you need to do some math if it's done using a hydraulic press, which I imagine is how that machine shop did it.

For example:

F=P/A (pressure measured in press / area of press piston)

k=F/x (the above force is calculated at two positions around center of damper travel, difference in force / difference in damper travel = effective spring rate)

Edited February 19, 2019 by LeonV

[jfa.series1]

I know that @Carl Beck is quite competent to defend his posts but nothing in his last statement suggests equating the compression force on a Tokico to spring rate.  Simply put - where the OE hydraulic shocks were passive in the suspension setup, the Tokico shocks are an active suspension ingredient by creating downforce with 80 pounds of pressure.  With the springs as a constant, ride height is affected.  I have these shocks with Eibach Progressive springs and can attest to a degraded ride quality.  His statement to Lee says nothing more than a hope that the pressurization does not approach the Tokico level of 5+ bars and a request that the pressurization be a disclosed specification.

My unsolicited $0.05 worth!

[Captain Obvious]

6 hours ago, LeonV said:

The force exerted by the gas charge, and thus spring rate, depends on the piston size and pressure.

I'm no suspension expert and I'm going to go out a little too far on my limb here, but I don't think that's quite right.

I believe the force exerted by the gas is proportional to the diameter of the strut shaft where it exits the cartridge, not the diameter of the internal piston. I don't think the diameter of the internal piston has any effect in this case.

My understanding goes like this:

The more the strut is compressed, the more of the shaft is INSIDE the strut.
The additional volume of the shaft (A*L) inside the strut assy will displace oil inside the body.
That volume of oil displaced will compress the gas inside the strut, but only by the amount of VOLUME of the strut rod which has entered the strut.

The internal gas pressure is static across the internal piston. At least that's how it appears to me way out on my limb here. 

[w3wilkes]

13 minutes ago, Captain Obvious said:

I believe the force exerted by the gas is proportional to the diameter of the strut shaft where it exits the cartridge, not the diameter of the internal piston. I don't think the diameter of the internal piston has any effect in this case.

So in you diagram the plate (red arrows) inside the strut that the shaft is attached to has holes so the oil flows through the plate and it's the additional shaft volume inside the strut that compresses the gas. This plate is to keep the shaft centered in the strut. This does make sense to me.

[Captain Obvious]

The plate you pointed to is the main hydraulic piston where the damper valve(s) are located. There is a seal around the outside of that plate and valves built into it. It does keep the bottom of the shaft centered, but that's not the only thing it does. That's where the primary "function" of the damper is located.

Here's what I'm talking about with the gas compression. When fully extended, there will be some preload factory set pressure in the gas.

And then when the strut is compressed, the gas does get compressed some, but it does not see compression proportional to the diameter of the main internal piston. It only sees compression proportional to the diameter of the shaft that enters the strut assembly:

[w3wilkes]

Thanks for the clarity, I thought that's pretty much what I said about the shaft volume increasing in the strut is what compresses the gas. Since these new Koni's are adjustable, I'd guess that the adjustment is to what you refer to as the "damper valve(s)" which changes how easily the oil can move through the plate attached to the shaft. The more open the Damper valve(s), the softer the ride.

Edited February 19, 2019 by w3wilkes

[KONI Lee]

2 hours ago, w3wilkes said:

Since these new Koni's are adjustable, I'd guess that the adjustment is to what you refer to as the "damper valve(s)" which changes how easily the oil can move through the plate attached to the shaft. The more open the Damper valve(s), the softer the ride.

With the adjustable KONIs, you are adjusting the rebound (the upward stroke) damping forces generated when oil flows through the piston (the "plate" you reference) valving.  By turning the knob higher or lower, you are closing or opening piston rod orifices and increasing or decreasing spring preload holding valves closed against the piston blocking other piston orifices. This provides changes in damping force from the slightest piston motion through very high pistons speed and lets the KONI Engineers finely contour the damping curve for optimizing both control and comfort.  The lower the adjustment setting is, the more open or less restrictive the damper valving is and the softer the damping force is.  That means you have less motion control but that doesn't necessarily mean that you have a softer or more comfortable ride quality because sometimes insufficient control can provide an uncomfortable ride quality.

[w3wilkes]

Thanks to both of you @Captain Obvious and @KONI Lee

[Captain Obvious]

My pleasure. I'm just glad I didn't fall off my limb.

One last thing while I'm here... I forgot to emphasize above that the gas in these struts is not intended to be a "lifting" device. It's simply in there to help inhibit foaming of the oil, not to provide any springiness. The fact that the shaft self extends due to the internal pressure is probably considered an unwanted side effect of the gas pressurization. I'm assuming (and KONI Lee would be the perfect expert to provide real insight) if they could get oil that never ever foamed ever, they wouldn't need to gas pressurize at all. Cheaper to manufacture and there wouldn't be all these people talking about how gas shocks raised their car's level.

But the point is these aren't the old "air shocks" that you put on the back of your dad's station wagon back in the 70's and pumped up to get that really cool body rake. Everyone did that, didn't they?   

[NVZEE]

This is great access, Koni — thanks for the info. So based on all this, what would define “Sport” ride and performance characteristics at their softest setting? What I’m getting at is how would the Sport Koni distinguish itself from a Brand X non-adjustable gas shock in a stockish suspension (other than by its range of adjustment)? Lots of owners these days are opting for preserving the original flavor of these cars.