Thucydides

I agree, Hustler, a properly valved shock is a thing of beauty.

Bernie, what kind of shock oil do you use and why? What are the options?

Thucydides

But check this **** out.....

Bernie was telling me that a street shock get's assembled two or three times before it meet's his standards. He assembles the shocks, dyno tests them (at a consistent temperature), and disassembles them to correct any inconsistencies or mismatch between shocks. Then they're reassembled and tested again; and disassembled and redone again, if needed.

A race shock he does fifteen to twenty times before it's perfect.

So I asked him if he could use better, more consistent parts, like from Penske or Ohlins.

Sure he can he says, if you don't mind paying $75 for the piston plus the costs to machine the parts. It turns out, and I'm quoting Bernie here:

"They (Bilstein) use powdered metal pistons, and stamped shims.

Penske uses 6066-T6, hard anodized, pistons. EDM shims."

This is why Dennis Grant of Farnorthracing says:

"It was INSANE just how much blatant, evil-wrong stuff I found running shocks on the dyno. Stuff that I had always considered decent based on reputation and referral turned out to be crap once tested.

With that track record, any given shock is more likely to be crap than not - especially if the shock supplier can not or will not provide an individual dyno trace for each shock he sells you. If he can not (because he doesn't have a dyno) then HE has no idea what the shock is doing either, and if he will not (he dynoed it but won't give you the data) then he is hiding something and should not be delt with. My experience with shock builders who have Secret Squirrel valvings is that they DO have something to hide - the fact that they do crappy work. Insist on dyno plots!"

I always though this was a somewhat militant position, but now that I know a bit more I understand the reasoning completely. Even if you make no mistakes assembling the shock, the internal components of even a highly regarded shock such as Bilstein are sufficiently variable to give you a very wide range of performance, and significant inconsistency between a pair of shock assembled with "identical" components.

JustinHoMi

Awesome. I know for a fact that certain other shops do NOT do this. It's pretty common to have left/right shocks that don't match. I have the dyno charts to prove it :/

greeenteeee

I thought the low speed damping is for steady state cornering and body roll (suspension loads slowly) and that the high speed compression and rebound settings are what has affects for a comfortable DD'd Miata as it goes over rough roads (shock speeds are high during potholes and bad roads)?

That's what I got from the STANCE dynos, reviewed by Emilio, who said they'd be great for smooth tracks but use too much high speed bump and rebound that would make them too rough and harsh on rough roads, inevitably causing them to have bad grip on rough roads (I think this is typical of japanese low-budget shocks?).

JustinHoMi

Low speed is more corner entry and exit. The shocks don't do as much mid corner, unless you hit a bump.

Yeah, this is why I asked the question. I've always had the impression that most of the things that affect performance on track/autocross are low speed (assuming a smooth lot), while the things that annoy us on the street are mostly high speed. I think that pot holes are sort of on the low end of the high speed spectrum. I don't know that I like to generalize it like that, but it does seem like that's where the shocks spend most of their time.

Koni RACE, in particular, have a lot of high speed compression. And I question whether that's necessary.

Here's a plot from a few autocross courses. The dotted line separates high and low speed velocity. This is from DG's site. I've never been to Forbe's field, but I understand that the concrete is in very bad shape.

Bernie S.

The movement of the shock has to always go through the low speed first.

Also, a car is traveling a little slower on the street than the track. Slower car, slower shock movement.

Read the earlier posts, maybe 2 weeks ago.

Bernie S.

This is false. The majority of what the shock sees comes from the little movements generated by the pavement surface.

JustinHoMi

How significant is the fact that a shock goes through low speed prior to seeing high speed? I assumed that the acceleration was fast enough that the low speed valving would not be a significant factor in such a situation.

Bernie S.

The low speed is more important than the high speed. You can keep the shock from seeing the high speed with the low speed.

Seriously, read through the earlier posts first.

JustinHoMi

I have actually read this entire thread. But it was late at night... so I'll do it again

Bernie S.

Start around post #26.

Not trying to sound like an *******, but I want people to keep coming back here for fresh information.

wannafbody

iTrader: (1)

IMO I wouldn't be too concerned about powdered metal parts. The rods in LS1,2,3 engines are powdered metal-so it's pretty tuff stuff.

Bernie, what about Afco monotubes that use the airbags-I know they are fairly popular in dirt tracking-is that really an advantage over the sliding piston in the Bilstein?

Does too much low speed rebound cause jacking down as some people claim?

Generally what percentage of springrate variance can be run on one of your revalved shocks?

Bernie S.

It's not the strength of the part, but the surface finish.

Bilstein does not machine the face, or any surface, of their pistons.

I was not aware that Afco made a monotube with a gas bag. Where are they putting it?

Yes, too much low speed rebound can make a suspension jack down.

wannafbody

iTrader: (1)

Here's a link with a photo-the bag is in the bottom of the shock or the top depending on which way you mount them.

http://www.afabcorp.com/AFCO_Dynatec...e=ct_M2_single

Bernie S.

The only advantage I see with this shock is having less friction during the moment the shock changes direction. You would still need the same amount of pressure on the fluid to control cavitation, so you wouldn't be gaining the benefit of low gas pressure like the twin tube design.

I'm a little surprised by Afco coming out with this "technology" instead of using a low friction o-ring. Then again, Afco has never really been the "standard".

Thucydides

Penske shims are cut using EDM (Electrical Discharge Machining) while others are punched. They both work just fine, but more careful assembly and testing will likely be required with a punched part vs an EDM cut part.

My understanding is that Bernie de-burrs all of his shims, both new and used. It's another step, but the upside is more consistency between parts and fewer test/reassembly cycles.

Speaking of cavitation, I was told used shims are often coated with a black film of oxidized oil. I'd guess the oil oxidizes from heat caused by cavitation as the oil passes through the piston or shim orifices.

greeenteeee

Quoted from your third link:
"Unfortunately, the new shock curve is still not ideal- it will cause harshness over small amplitude,
high frequency road disturbances. It is desirable to reduce the damping ratio at high shock speed
(above the Low/High speed split velocity) to reduce this effect."

I have been under the impression that a quality shock, whether or not it is a single adjustable, will still ride better over rough surfaces than a sub-par shock.

That has been my experience with two different brands of shocks from lower-end shock manufacturers, I've never had KONIs as they posed problems on my other car, but I'd imagine the KONI RACE shocks would be comfortable on the street if it were a "good" shock. That seems to be the consensus for Miata-specific owners who have jumped between KONI RACE vs TEIN FLEX/MONOFLEX.

I found this thread late one night as I was falling asleep... it eventually woke me up as I kept reading.

Nagase

iTrader: (6)

Just want to point out here:

Good on the street doesn't mean good on the track.

A good shock is not good at everything, it's good because it's good for one specific purpose. A good shock is one tuned for a very specific issue.

A bad shock is not designed well for one thing...

You could get a perfect street valving that will be ok on track, and be terrible off road. A great off road that's terrible on track and bad on the street. A great shock for a two ton car that's bad for a one ton car. All of the variables matter. Everything is a compromise.

greeenteeee

NAGASE: Yes I am aware of the "compromise" dilemma, but I've a friend who went to Racing Gear shocks from Mugen shocks (on a Honda, yes, a little off topic), but their experience was exactly as I said... the RGs handled rough roads better, keeping the car composed.

Just because it is a race track (or autox), does not mean it is smooth (as Justin's autox plot shows)... and not to mention the KONI RACE vs MONO FLEX point, was not something I made up, but direct input from a Miata owner who has tracked their turbo miata on both suspension setups.

Thucydides

Assuming the bag pressure is the same as the gas charge in a conventional piston, the difference in friction at the damping piston would likely be insignificant. I would worry about the gas bag durability on a shock that doesn't see periodic rebuilds, however, as that flexible bladder expands and contracts constantly whenever the vehicle is in motion.