TheNick

Yeah I'm with Matt. And I'm going to have to stick to my guns on twin tubes needing gas pressure to have compression force. Its just common engineering sense. If there is no pressure on the other side of the foot valve, then there is no pressure drop across the valve and therefore no force against the piston/shaft. Sure there is a "little" bit because of the atmospheric pressure - but the way Koni valves the Yellows - gas pressure isn't needed.


In my experience - rebound is the devil - run the minimum amount necessary to keep the car from bouncing. I have almost as much low speed compression as Matt and I've never experienced any skipping or loss of grip from too being too stiff. I have on the other hand experienced a lack of grip from too much rebound as the car skips over the surface because it can't move.

I wanted Stimola to do a digressive/linear piston but he wouldn't do it.

TheNick

I can tell you this much that if you think Matt is bucking the trend then you might be a little mis-informed. He's not the only one running all the low speed compression - there are quite a few National Champion autox'ers on similar valving and have been for awhile.


All that being said - 2 of the top 5 cars in ST last year were on blown/5yr old Koni Yellows...

PilotSH

How is there no pressure drop? When the shaft enters the inner tube, it pressurizes it. The pressure drop comes from the fluid in the pressurized inner tube flowing into the outer tube thru the foot valve. In terms of common engineering sense, I'll just stick to common sense (I'm not an engineer): Koni engineers who specialize in shocks have said that it's ok, and my experience with a degassed shock showed that running degassed was ok.

Where am I mis-informed? I think you mis-read. I didn't say that increasing compression is bucking the the trend, using really low low-speed rebound was.

James Yom

TheNick

Then yes I misread - I thought you were saying that low speed compression is bucking the trend.


It doesn't pressurize it if there is a pocket of air on the other side of the oil. I'm not saying its bad - I'm saying its not optimal. Clearly it works, could it be better? IMO yes, and the founder of JRZ happens to agree.

Perhaps this thread should be locked until everyone reads this book and becomes more well informed:

http://www.amazon.com/gp/product/144...ef=oss_product

robinson

That will add nicely to my other book I just got today, Tune To Win.

Forcednduckshn

I assume you were joking about locking this thread.

Everyone that has been contributing to this thread: James, Matt, Nick, Marc, Corey and the rest I really appreciate it. Differing views on the subject are perfectly acceptable and it's a good exercise to go through. A pat on your backs for keeping ego out of the equation and participating in a meaningful discussion (as these threads can go down the tube quickly.) I knew this type of discussion would create some debate and it's why I started it. I've learned a bit from the conversation and it's verified some of my thoughts while questioning others. Above all it's made me think critically about how our shocks perform at the limit, which is what I find particularly valuable.

Would anyone be curious for me to create a thread that goes through my tuning process this year? It will be entirely at Devens Air Force base in Massachusetts where a bunch of National Tours were held. For those that don't know the track, it's pretty smooth, fast and pretty high grip. My hunch is that stiffer compression and fresh tires are going to work very well there-

Forcednduckshn

Thanks in particular for this post James. This was a similar conversation that I had with Andrew at Performance Shock which was identical to what you just described.

I'll check out your link to Lee-

Forcednduckshn

Posted from Lee 10-14-08: (This post puts to rest every concern and the debate over the effectiveness or any issues that may occur with zero gas pressure twin tube Konis My confidence has been fully restored regarding the capability and reliability of his Konis:

"Wow, 50 posts in about two hours. And unfortunately more effort has been made in the discussion (and a minor pissing match) possibly than in the value of degassing the shocks themselves.

The degassing thing can be of some but limited value and seems to have best benefit in a stock class autocross situation where a softly sprung, light weight car with geometry allowing much camber change in a short distance.

Pretty much most everyone had bits of info correct but I'll go through it. When a shock moves through the oil, the low pressure side of the piston will often see some amount of oil cavitation that can have from a minimal to a high effect of performance based on the shock design and the oil's characteristics with heat and pressure. Having some head pressure in the system can raise the boiling point slightly and raise the pressure at which cavitation occurs, same basic theory of the tea kettle havng pressure and raising the boiling point of your hot water for tea. A mono-tube shock must have a high pressure gas charge or it has failed and will not work. A twin tube shock can work with or without a gas pressure charge inside. The better the oil's pressure and heat characteristics are along with some possible differences inside the shock, the higher the pressure or temp threshold for cavitation or effect that cavitation will have. Many of us were taught long ago that "gas shocks are always better than non-gas shocks" by the marketing depts. of some shock companies but the reality is that shocks with lower oil characteristics will benefit more from some head pressure behind oil. At KONI, we use the same oil of our own design of oil in all of our street car and racing shocks so the heat and pressure characteristics are very high. In that case for normal use like street, autocross and many forms of racing (older F1 cars down through Improved Jalopy), in a twin-tube shock we can leave the gas pressure charge out with no negative effects. On a low pressure gas shock, we rarely use more than about 100 psi of gas charge anyway and often well less than that.

A side effect of the presence of some gas pressure is that is can give a very small boosting effect to your ride height based on the gas charge, piston rod size, weight of the car and spring rates. Some people seem to like to blow things totally out of proportion and say that that will use gas charge to have a big effect on the spring rate of the car but that is not as realistic as one might think. It is more like a static lifting effect of about 8 lbs of rate per 100 psi in the shock (numbers I have heard for years) but it doesn't really affect the spring rate when the car is in motion. So since the KONI oil doesn't have to have the gas charge behind it to work at a high performance level, sometimes primarily in autocross we will leave it out when revalving simply to eliminate the very minor boosting effect on the car. Small, light, soft sprung cars will be effected the most (because 8 or whatever lbs. is a more impactful percentage on this car than one stiffer sprung or heavier). Although we have done it for years, it was a first gen Miata that made the most notable differences to me. Since that Miata has a fair amount of camber change during ride height change, by simply leaving out the gas that wasn't really needed in the first place, the car sat a tad lower and the camber got a bit more negative. Very simple, very easy gain and no loss in performance because the oil and shock characteristics were not affected. The amount of change in height can be zero to normally about 1/2 inch max. I have seen one car claim much more than that about which I am still skeptical but have yet to find another reason.

So why do we put gas in a large percentage of our street and some racing twin-tubes at the time of manufacturing? Two reasons mostly:
1) many cars come OE with gas charged shocks and we'd rather not introduce ride height changes for most of the public that we'd have to explain
B) So many people for so many years have heard that gas shocks were better from various marketing depts. that it is easier to simply include the gas change than it is to try to reeducate the vast majority of the motoring masses.

In autocross, like so many things the values or reasons for degassing a shock can get blown out of proportion or build a life of their own that far outshadows the reality of the benefits. So if your car can benefit from it, why not leave it out? But I have had people chew me out because I wouldn't degas their mono-tube. Or have people with Mustang's or Camaros that are heavy and have no rear camber change wonder why the car didn't sit much lower or get negative camber. It is what it is, it isn't what it isn't. If you can benefit, why not try it.

In our Shop for the longest time we didn't regas the twin tubes that we were revalving for many IT cars, etc. unless someone asked. Often now we will tend to leave it out of shocks that we know are specifically going to be used on stock autocross cars. I would revalve my own shocks for my ITA CRX but not bother to regas them. The height change didn't matter because I set my heights by coil-overs. During long enduros, the tires, brakes, and driver would fade but the shocks didn't. Pablo the Wonder IT enduro car has no gas in the twin-tube front struts and one set of rears might while anotyher set does nt. No function or handling changes there either from fade. It simply removed one step of the process and the function didn't change. When we made the Honda and Miata RACE units, we discussed adding or deleting the gas charge. Ultimately, we included it because in mass production it is an easy step and we wouldn't have to go into a long discussion as to why it wasn't there if anyone cared enough to ask. We could send you out on track or to do autocross runs with gas charged twin-tubes and with non-gas and you would never, ever know ther edifference. The gas change alone in quality shocks is basically imperceptable.

If you have KONI twin-tubes and are interested, it there is the number 4 in the part number prefix (aka 8741-, 8041-,8641- etc.) then it has low pressure gas. If there is no 4 (8710-, 8010, 8611- etc.) then there is no gas from the factory. I think every one of our coil-over dampers are non-gas simply becasue in a product made for changing ride height, why include (if not for a specific need) a component that would give a boosting effect only to need you to adjust down to compensate for it?

The most important part of the gas or no gas question on a twin-tube so long as the oil is capable of doing it's proper job, is to not blow it out of proportion."
__________________

TheNick

My post wasn't meant to alarm anyone or degrade the Koni Yellow shock - they are designed to have very low compression damping and no gas pressure. My posts were meant to be informative on the design of the shock - nothing more.

Forcednduckshn

Understood Nick, I appreciate your feedback especially as a guy with a lot of autocross experience running Koni's.

I'm going to try and source the dyno plots from Andrew to see if he did tests at settings other than full soft and full stiff. I want to see a) how non-linear the adjustments are and b)how significant or minor the cross talk is between rebound and compression adjustments.

Pretty pysched about this season!