Pistons 6 hole, 4 hole, 3 hole etc?

[chet]

Hey

I just wanted to put this out there since Durango really plays with this more then other cars.

I have only run 4 hole pistons in my 210 so far, because I looked up most of the set ups on durango web set and thats pretty much all Jorn uses. 90% of the time he runs 1.3 4 holes in the front and 1.2 4 holes in the rears.

Has any one played with this a lot to see the highs and lows for carpet?

Theres more pack with less holes right? I've used 4 hole pistons in my dex408 on a blown out 1/8 track and it was really bad compared to 6 hole.

[chet]

Someone must have some info on this since the run 3 pistons no?

[Jason A]

Hi mate I am running this on carpet on my 210 seems work for me

Front
3x 1.5mm
40wt
Red springs

Rear
4x 1.5mm
30wt
Black springs

[chet]

1.5mm thats big, how does it jump? What size of batteries do you run with this set up, shorty or full size?

I would think it would dive into corners well and not tip over?

[maineyak]

Hi Chet, I believe more holes gives more pack. Read this section from the Team Associated handling bible. Applies to any car though:

The 3 hole pistons generate more "Pack" than a two hole piston. As oil passes through the piston holes the resistance that you feel is actually the oil shearing across the edges of the hole. With more hole surface area (three hole piston) there is more "Shearing" as the oil passes through the holes.

This gives the shock more pack. Don't confuse Pack with Damping though. Damping is the consistent resistance the shock provides when it is slowly compresses and decompressed. Pack is the instant resistance a shock provides when it is quickly compressed or decompressed. Here is a good example of the two. Damping is how fast the Chassis leans in a corner or when you change directions. Pack is how much the shock compresses when you hit the face of a jump or land after the jump.

It all comes down to how much pack you need for the track you are racing on. If you are running on a track that has a bunch on big air time jumps, you will need to use a setup with a lot of pack. If you are running on a track that is rough, rutty and has small jumps you will need a setup with little pack.

[Timee80]

I thought more holes meant less pack

[av4625]

so did i lol craig put up a good shock setup in another thread about carpet setup, 1.6*3 35 dark blue front and 1.6*4 30 light green rear i kust used light blue spring it was really good i think thats it take a look at it!

[chet]

Originally Posted by maineyak

Hi Chet, I believe more holes gives more pack. Read this section from the Team Associated handling bible. Applies to any car though:

The 3 hole pistons generate more "Pack" than a two hole piston. As oil passes through the piston holes the resistance that you feel is actually the oil shearing across the edges of the hole. With more hole surface area (three hole piston) there is more "Shearing" as the oil passes through the holes.

This gives the shock more pack. Don't confuse Pack with Damping though. Damping is the consistent resistance the shock provides when it is slowly compresses and decompressed. Pack is the instant resistance a shock provides when it is quickly compressed or decompressed. Here is a good example of the two. Damping is how fast the Chassis leans in a corner or when you change directions. Pack is how much the shock compresses when you hit the face of a jump or land after the jump.

It all comes down to how much pack you need for the track you are racing on. If you are running on a track that has a bunch on big air time jumps, you will need to use a setup with a lot of pack. If you are running on a track that is rough, rutty and has small jumps you will need a setup with little pack.

Good info thanks man

[bigred5765]

Originally Posted by maineyak

Hi Chet, I believe more holes gives more pack. Read this section from the Team Associated handling bible. Applies to any car though:

The 3 hole pistons generate more "Pack" than a two hole piston. As oil passes through the piston holes the resistance that you feel is actually the oil shearing across the edges of the hole. With more hole surface area (three hole piston) there is more "Shearing" as the oil passes through the holes.

This gives the shock more pack. Don't confuse Pack with Damping though. Damping is the consistent resistance the shock provides when it is slowly compresses and decompressed. Pack is the instant resistance a shock provides when it is quickly compressed or decompressed. Here is a good example of the two. Damping is how fast the Chassis leans in a corner or when you change directions. Pack is how much the shock compresses when you hit the face of a jump or land after the jump.

It all comes down to how much pack you need for the track you are racing on. If you are running on a track that has a bunch on big air time jumps, you will need to use a setup with a lot of pack. If you are running on a track that is rough, rutty and has small jumps you will need a setup with little pack.

nope, more hole or bigger holes equals less pack my friend
but i agree with most of the rest set ur damping/pistons to suit the track, not just the car

[discostu]

you beat me to it agree more hole bigger holes les pack

[Gonzo]

The "shearing" explanation is not 100% correct.

The big difference between slow compression and fast compression (pack) is the "inertia" of the oil. At every hole, most of the oil needs to go 2 times around a corner to get through the hole. Physics do not allow something that moves in one direction suddenly to move 90 degrees differently: also oil is influenced by it's inertia. The higher the speed of the oil around the corner, the bigger the 2 useless "pockets" that are created at the corner. So you could say that the higher the oil speed, the smaller the usable hole diameter gets.

With this in mind:

For infinite slow compression, less big holes and lots of small holes are almost the same, as long as the total hole surface is the same. (The extra friction because of having more hole side-surface when having more holes will be very small)

For fast compression, with the same total hole surface, lots of small holes will have more pack than less big holes, because of oil inertia at the hole corners. With small holes the inertia could completely "close" the hole >> lots of pack. With big holes, there is always a "usable" hole remaining.

That's also the reason that in theory, when you move a shock from inner position of your arm to an outer position, you should go to slightly bigger piston holes to keep pack constant. Outer position means more piston travel, so higher oil speed, so with the same holes that would give more pack.

[bigred5765]

sounds good till you realize that pack is what happens when the piston first starts to move,before oil has a Chance to speed up,

[maineyak]

Yeah let me confirm - when I said this:

Hi Chet, I believe more holes gives more pack.

I meant for an "equivalent surface area" more little holes will give more pack than fewer larger holes.

[jo90]

You also get more 'Pack' if you use something like lard in your shocks. Unless it's warm, then it's useless. Damn you lard and not being heat resistant !

PS...the above is meant to just break up the very serious content of the thread and not meant to disway from the fact the less holes you have the more pack you have but also slower the shock responds, so, being incredibly basic

Less holes = more pack/slower shock = ideal for flatter tracks with large air jumps/ramps

More holes = less pack/faster shock = ideal for bumpy tracks with little air jumps

Lots of small holes (area) = less large holes (area)

Large chest pillows > small chest pillows

[/tobys]

surely,

more small holes has more pack than fewer large holes

??

[Gonzo]

Originally Posted by bigred5765

sounds good till you realize that pack is what happens when the piston first starts to move,before oil has a Chance to speed up,

I don't agree. That inertia-effect acts on such a small scale that the oil in that small area around the hole speeds up very fast and has almost immediate effect. I'm sure that if you would measure the force the damper resists to a sudden fast compression like a landing, the piston will always need to move a small distance before the maximum pack-force is achieved. On a 1/10 shock I would estimate between 1 and 5 mm, depending on hole size and aggressiveness of compression.

[Chris Doughty]

Originally Posted by bigred5765

sounds good till you realize that pack is what happens when the piston first starts to move,before oil has a Chance to speed up,

I 100% disagree.

I always considered pack to be the oil flow going from linear (slow flowing motion) to turbulent flow (when the oil is forced through holes that are too small for it to flow nicely).

so I believe that pack is something that 'ramps up' as piston speed increases, more so with smaller holes

[bigred5765]

i was alway told pack is the Resistance of the oil to move through the hole IE the piston is trying to compress the oil,

[RogerM]

Originally Posted by Chris Doughty

I 100% disagree.

I always considered pack to be the oil flow going from linear (slow flowing motion) to turbulent flow (when the oil is forced through holes that are too small for it to flow nicely).

so I believe that pack is something that 'ramps up' as piston speed increases, more so with smaller holes

Chris is, not unusually, 100% correct.

Also, assuming the hole area is the same between a few hole and many hole piston (say a 2 hole and 6 hole piston with different hole sizes but giving the same total hole area of, lets say 7mm^2), the many hole piston will have the higher 'pack'.

To this end with the Kyosho stuff I set about developing my setups around a hole count that I have proven works well 90% of the time (5 in the case of the Kyosho BB shocks) and then match the static flows to get the same static damping with both more hole and (higher pack) and less hole (lower pack) pistons to tune for different surfaces / layouts leaving the oil ranges basically the same (again in the case of the Kyosho big bores my low pack setups use 4 hole pistons, high pack 6 hole pistons).

I hope that explaination makes sense

[Chris Doughty]

Originally Posted by bigred5765

i was alway told pack is the Resistance of the oil to move through the hole IE the piston is trying to compress the oil,

Yes, the first part is correct, the second part I don't agree with.

also one thing I don't agree with is that the smaller holes make the oil flow faster if compared with the same overall hole area but less holes.
If the overall area of the holes are the same, the speed which the oil flows must be the same...?

I think the pack comes because with the smaller holes, there isn't any oil that ISN'T affected by turbulence from the edge of the hole.

for example, if turbulence happens within 0.5mm of the edge of the hole edge(when at piston speed X), in 1mm holes, ALL the flowing oil will be affected by turbulance from the edge of the hole.

If you had 2mm holes that had the same overall area, there would be a part in the middle of the hole where the oil isn't affected by turbulance meaning this part oil still flows efficiently, which means you get less 'pack'

because as speed increases turbulence happens further and further away from the edge of the hole, the 2mm holes will eventually 'fully pack up' just at a much faster piston speed than the 1mm holes.

All of this is how I understand the physics to work, however, its never as perfectly uniform as the theory. there are so many factors involved but that's how I think it works.

throw in hole shapes, rounded edges, taper pistons, angled holes multi-size holes etc etc and you can spend YEARS testing this stuff out.

... and probably end up where you started!