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2 stage pistons...Do they work?

2 stage pistons...Do they work?

Old 11-28-2011, 02:50 PM
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Scale has nothing to do with it. Physics is physics. All single hole pistons are going to have a slower rebound than compression for the simple reason that gravity pulls the car down. It's effect needs to be taken into account. It is very possible that you have a situation that a slower rebound works better than a faster one. It is very possible that the opposite is true. There are some pretty standard rules when it comes to how things work but there are no set rules on what works best at any track. This is why we go to so much trouble to tune. The bulk of tuning in regards to balance can be done on a bench but fine tuning is done on a track. At this point, results are the only thing that matter and it doesn't matter if those results in the real world agree with what you already know or not. Use what works.
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Old 11-28-2011, 03:48 PM
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Originally Posted by fredswain View Post
Scale has nothing to do with it. Physics is physics. All single hole pistons are going to have a slower rebound than compression for the simple reason that gravity pulls the car down. It's effect needs to be taken into account. It is very possible that you have a situation that a slower rebound works better than a faster one. It is very possible that the opposite is true. There are some pretty standard rules when it comes to how things work but there are no set rules on what works best at any track. This is why we go to so much trouble to tune. The bulk of tuning in regards to balance can be done on a bench but fine tuning is done on a track. At this point, results are the only thing that matter and it doesn't matter if those results in the real world agree with what you already know or not. Use what works.
Fred, I'm not sure I catch your drift, but it sounds like you are talking about rebound speeds/forces with the shocks installed on the car on the track. In other words actual rebound speeds on the track vs rebound forces of a bare shock. All the graphs being posted strictly of the shocks without even springs attached.

Mattnin, those charts (if I'm reading the blue "circle" correctly) re-enforce what I previously posted. The 600 SM (SuperMoto) build is for a 50/50 type track where you are on pavement street racing half the time and would have smaller jumps than an average supercross track. Most of the time is made or lost on the asphalt so they tune more like a street bike.

The Quad showed what I would definitely set a trail quad around as that is probably the market for that shock, but I didn't look awfully hard.

The mx blue circle graph you posted has compression on the bottom half of the graph because the crank was rotating counter-clockwise according to that write up. However, they leave out secondary pistons (high speed I assume). Something worth noting as I think I stated it backwards earlier: High speed damping removes damping force, not adds to it. That chart shows what I would expect for low speed damping, approaching a 2/1 compression/rebound ratio. High speed damping would definitely put the compression softer for the same velocity as the point of high speed damping is to avoid what we like to call the "pain zone". High initial damping at low to medium compression speeds provides the response most riders look for and prevent the bike from collapsing on itself too quickly. However, since damping is not a linear function (with flexible shims trying to make it linear not withstanding) the resulting force of a high speed impact with the face of a whoop would break wrists and ankles (the pain zone) and pop the bike up, so high speed damping for such instances produces the same effect that Baja trucks have right off the bat.

Because we don't have to worry about the "pain zone" with our RC cars (unless you are marshalling 8th scale ) the non linearity of static hole pistons provides that "pack", or high speed much increased damping that we love to mess with.

Maybe that's what we need next... variable speed damping. Marcus, get to it, but I call dibs on 25%.


Anyways, done any testing yet? I have 2 races every year I attend that have very few, if any jumps and are completely blown out all day everyday. They are very old school topsoil tracks that I could totally see lower compression damping to keep the chassis low and fast through the whoops with with the increased rebound damping preventing rollovers.
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Old 11-28-2011, 06:18 PM
  #873  
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Krio, I believe that bottom of that graph is still showing rebound, not compression. I don't think the bottom of the graph is BDC on the dyno crank which would indicate that the bottom is compression. I believe it is still only a plot of displacement vs force in the standard form and not a plot of force vs the cranks position.

I received the pistons on Saturday and I thank Marcus for the super fast shipping. The pistons looked really nice and fit together well. I really appreciate that someone actually spends the time to make dual stage pistons for the racing crowd and all our vehicles.

I spent almost the entire day working on these pistons. I was very excited and immediately started working on them Sunday morning. It is very fun to work on pistons and watch football at the same time

I took my front two shocks from my SCTE. I left one standard just so I could compare by feel. I put in my lowest weight oil, 17.5 and the shock felt just like there was no resistance and didn't really compare at all to the other shock. I worked my way up to 45wt oil and it still had little resistance; it still felt like a standard 20wt oil shock or less and I could barely feel a difference between bump and rebound and it definitely didn't compare in damping resistance to the standard 35wt shock.

I am already at the point where my truck could maybe even go up a little more in damping actually, so I felt like the way the shock pistons come wouldn't work for what I need. So with all respect to Marcus and everyone here, like I almost always do with any toy I get anyway, I began to modify.

My intent since the beginning is to run the pistons upside down so I could get more rebound damping vs compression as I have seen it in 1:1. Whether or not this will make my truck better, I don't know, but it is the premise I am starting with. So far, they seem like they are going to work fine upside, no problems. They fit nicely.

I ended up gluing shut some of the pistons on the fatter piston with 8 holes. I closed off 4 of the holes.



What this does when the two pistons close together during rebound is check off 4 of the holes from the flatter piston. So during the rebound stroke, only 2 holes are exposed. During the compression stroke, 6 holes are open giving me a 3:1 rebound:compression which is how I decided to model it after a Bilstein 1:1 offroad buggy shock. However, there is a problem. The fatter piston only has 4 holes, so I had to open the holes up to allow as much flow as possible for the 6 exposed on the thinner piston. So this piston maybe has less than a 3:1, maybe more like a 5:2 but definitely no worse than a 2:1.

I then began to test shock oils. I tried 30wt and even with just 2 holes open it still felt like 17wt or less on rebound. I went up to 45wt and it still felt very easy to rebound, much less than my standard shock with 35wt oil in it. So I made a run to the LHS and bought oils all the way up to 80wt.

I finally ended up with 60wt oil in it. During the rebound stroke, it feels slightly less than my 35wt standard shock on rebound. During compression, it definitely feels easier to push. As matter of fact, I walked away from my bench and when I came back, I forgot which shock I had changed pistons. So I cycled the compression/rebound and could easily tell which shock was modified.

I don't know if I am staying with 60wt. Maybe I should have tuned the shock so that the compression stroke should have felt more like the standard 35wt compression, I just don't know. I'll find out when I drive it on Wednesday. I was getting a bit of bounce last Saturday. Maybe that was due to the shock oil being to high and causing a high bump damping throwing my chassis up on bumps. Maybe low compression would help here. Or maybe it was due to the shock oil being to thin and rebound being to fast and allowing oscillations. I will be paying attention to this however and tune to the best of my ability which is very little actually, but I will do my best.

I am going to spend a considerable amount of time tuning everything, then I will have our best racer test it, I will probably make further changes to suit his style, then allow him to drive the hell out of this truck and I'm gonna tell him to push it hard while I videotape it. I hope to get some good video for everyone to view.

Like I said, it is just an experiment, and I am enjoying it. It may be wrong, it may be right, I don't know, all I can say is thanks to Marcus for even making this for us and giving us a new toy to play with.
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Old 11-28-2011, 06:47 PM
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mattnin I find it weird that you could not feel any difference in shock speed when you cycled the shock by hand. Before I put my 2 stage pistons in my car, not a scte I cycled them so I could get a feel for even compression/rebound. After I installed them , the normal way I could definitely feel the rebound stroke was faster.
Once you decide to run them the normal way look in this thread for oil weights that guys are running in your car and try it, and return the holes to stock as best as you can.
Even if you feel it is too light you need to keep an open mind.
Also you will most likely blow out the pistons running them upside down since there is not much material keeping them in place on that stroke. It is not an issue when installed properly since there is not much force on rebound when compared to compression.
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Old 11-29-2011, 12:57 PM
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Mantix,

I respectfully ask you to make your case that I would benefit from running your pistons on a 1/8 4WD dirt oval late model. I appreciate you doing this as I am very interested (I am ignoring all of the superfluous gas passing).

Mike
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Old 11-29-2011, 01:28 PM
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Originally Posted by kvrc View Post
mattnin I find it weird that you could not feel any difference in shock speed when you cycled the shock by hand. Before I put my 2 stage pistons in my car, not a scte I cycled them so I could get a feel for even compression/rebound. After I installed them , the normal way I could definitely feel the rebound stroke was faster.
Once you decide to run them the normal way look in this thread for oil weights that guys are running in your car and try it, and return the holes to stock as best as you can.
Even if you feel it is too light you need to keep an open mind.
Also you will most likely blow out the pistons running them upside down since there is not much material keeping them in place on that stroke. It is not an issue when installed properly since there is not much force on rebound when compared to compression.
WOW, very well put man! i am impressed


Gator, i am not an oval guy but have built some custom pistons for some oval guys and their 1/8 sc 4wd cars, wherever they race its outdoors and are close for the winter so i dont know what the results were as of yet. but i do know that we agreed that you would need to either run the inside pistons (left side of car) upside down to slow transfer but keep the outside with the quicker rebound, or you could even do opposite corners. really its just a trial and error thing but i do know that if you can find a setup that works, just like anything in oval you will notice a big difference good or bad QUICK!! the ones i made only used 4 holes and i sent them with .8mm holes so they could drill them out to where they need to be. So the answer to your question is yes i believe there is an advantage to them but i am in the dark about oval setups. there is a new dirt oval track opening soon near me so in the future i will have some answers!!
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Old 11-29-2011, 01:36 PM
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Mantix.

Thanks. Our cars are nitro (8 1/2 lbs). Since they use Losi 2.0 shocks would your stock 2.0 Losi 8 pistons be advisable or do you think the custom 4 holers would be better (after all, you made them for those guys for some reason...)?
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Old 11-29-2011, 02:47 PM
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Originally Posted by GatorNation View Post
Mantix.

Thanks. Our cars are nitro (8 1/2 lbs). Since they use Losi 2.0 shocks would your stock 2.0 Losi 8 pistons be advisable or do you think the custom 4 holers would be better (after all, you made them for those guys for some reason...)?
the std losi8 pistons will fit as they are 15mm but i think (remember i know nothing of oval) that you would end up having to run very thick oils. which is not necesarily a bad thing . if it were me i would buy a normal set and play with them for a while and then once you get a plan together i can make them however you want. custom pistons are 45.00 per set so keep that in mind.
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Old 11-30-2011, 08:14 PM
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I was able to play with the truck for 30 minutes yesterday, and 3 hours today. We didn't have enough racers today to have a race, so I have no access to lap times, so I can't see if I am any faster.

Yesterday, with 60 wt oil and my modded pistons, it seemed like there wasn't enough pack for landing, I would hit the chassis. Now granted, I didn't get a chance to check ride height either. After testing today, I think ride height may have solved this problem. I may have been running the truck low yesterday.

I went back home and decided to work on the shocks some more. As I cycled the stroke on both front shocks, they felt different. I decided to inspect the pistons and up the oil to 80wt. As I inspected the pistons, I found a major problem. Now, anyone that has tried to GLUE delrin knows what a headache it is!!! Delrin just does not like to be glued and your strongest CA glue will peel right off after curing and exposing a pristine looking piece of delrin underneath. One of my front shocks had a hole blow out. Now, on Sunday, I tried using liquid cement, regular tire CA glue, and I finally ended up using rubberized CA glue with an activator and I was still having problems gluing the hole shut. This is just a FYI to anyone wanting to try this mod, it is tough to do because gluing delrin isn't easy. I hope that by roughing up the inside holes helped the glue to hold better. I haven't inspected the pistons yet today but I am hoping it held up to 3 hrs of practice today. Marcus said he could make me a custom set if I needed it, thank you Marcus!

On to today's testing....

Today, I was using 80wt front, 70wt rear, black springs front, red rear, no swaybars, 27mm front and rear ride height. If I drop the truck any higher than 2 1/2', it will hit the chassis. However, that is pretty extreme if you need to land higher than 2 1/2'. My buddie next to me has a brand new and stock SCTE-Ten and his chassis hit the floor worse than mine dropping it from the same height. This gives me optimism that I can actually even reduce the shock weight now if I wanted to. When I was racing on the track I experienced no chassis slap as the setup is currently. My bump was more damped than his stock SCTE and rebound was certainly much more damped than stock.

Honestly, there wasn't much of a difference driving it like this than before. It felt fine, there were a few things I did notice. It seemed like braking was a little more stable, corner entry at high speed also seemed slightly more stable with a bit of push, I don't know if that is a good thing, there was no spinning out or other weirdness, it entered the turn with an appropriate speed of rotation and not too much. I could probably use a little more entry. The actual mid corner felt just about the same as before with no real increase or decrease, but I really enjoyed the controllable push and stable exit I would get coming out of a turn on power, this I especially felt there was some noticeable difference than before. Jumping was fine and seemed no different than before, it seemed to jump no less or no more than before. Our straightaway is pretty pockmarked and I honestly thought it was better now and more stable. I didn't notice any sort of sluggishness or lack of responsiveness, or glitching with anything, it just didn't feel like there was going to be much if any new learning curve and everything just seemed to feel ok to me.

I knew that if the rebound worked like it should, I should be able to remove or at least reduce the swaybars. Now, racing last Saturday, I was traction rolling with heavy swaybars. Today with fairly similar conditions, I was not traction rolling with similar speeds and cornering and I wasn't running any swaybar. In fact, I was getting just a bit of sliding. Todays conditions were even slightly more moist on the track than last Saturday as well. I think I should have traction rolled more today.

It is weird to see the slow rebound if you drop the truck and look at it, it does rise slower than before, but while driving, it feels ok and just nothing out of the ordinary. I see no reason to take these pistons out and I am going to continue running them!

-Matt
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Old 11-30-2011, 08:28 PM
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CA will not bond to delrin no matter what technique you try! need to try and plug the holes with a toothpick and then glue with some epoxy. by your explanation it sounds like your not getting much if any differences than before. i wish you would have tried them first the normal way with laptimes and then compare them to upside down. with the standard way you gain agility and jumping is increased pretty dramatically. if your able to run oil that thick then the holes are REALLY too big in my opinion. and that may be why the differences are only mildly better than normal pistons. think about how big your holes woudl need to be on single stage piston to run oil that thick.

not to pick on you but dropping your truck 2.5' doesnt really prove anything since you will never be in that situation on a track or even while moving its impossible to drop straight down, you will always be at some angle and either accelerating or decelerating, which makes a difference. just food for thought.
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Old 11-30-2011, 09:20 PM
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I have been using your shocks for a couple of mos. its on an RC8be, 25 oil in front, 30 rear.
Here is what I have noticed:
Wheels respond or move up & down faster.
I can go thru wash bds a lot faster than others without cart wheeling.
It turns faster.
My lap times are a good sec. faster.
I am glad I got them. Next I will try thinner oil in rear and see what happens.
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Old 12-02-2011, 06:00 AM
  #882  
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Originally Posted by mattnin View Post
I was able to play with the truck for 30 minutes yesterday, and 3 hours today. We didn't have enough racers today to have a race, so I have no access to lap times, so I can't see if I am any faster.

Yesterday, with 60 wt oil and my modded pistons, it seemed like there wasn't enough pack for landing, I would hit the chassis. Now granted, I didn't get a chance to check ride height either. After testing today, I think ride height may have solved this problem. I may have been running the truck low yesterday.

I went back home and decided to work on the shocks some more. As I cycled the stroke on both front shocks, they felt different. I decided to inspect the pistons and up the oil to 80wt. As I inspected the pistons, I found a major problem. Now, anyone that has tried to GLUE delrin knows what a headache it is!!! Delrin just does not like to be glued and your strongest CA glue will peel right off after curing and exposing a pristine looking piece of delrin underneath. One of my front shocks had a hole blow out. Now, on Sunday, I tried using liquid cement, regular tire CA glue, and I finally ended up using rubberized CA glue with an activator and I was still having problems gluing the hole shut. This is just a FYI to anyone wanting to try this mod, it is tough to do because gluing delrin isn't easy. I hope that by roughing up the inside holes helped the glue to hold better. I haven't inspected the pistons yet today but I am hoping it held up to 3 hrs of practice today. Marcus said he could make me a custom set if I needed it, thank you Marcus!

On to today's testing....

Today, I was using 80wt front, 70wt rear, black springs front, red rear, no swaybars, 27mm front and rear ride height. If I drop the truck any higher than 2 1/2', it will hit the chassis. However, that is pretty extreme if you need to land higher than 2 1/2'. My buddie next to me has a brand new and stock SCTE-Ten and his chassis hit the floor worse than mine dropping it from the same height. This gives me optimism that I can actually even reduce the shock weight now if I wanted to. When I was racing on the track I experienced no chassis slap as the setup is currently. My bump was more damped than his stock SCTE and rebound was certainly much more damped than stock.

Honestly, there wasn't much of a difference driving it like this than before. It felt fine, there were a few things I did notice. It seemed like braking was a little more stable, corner entry at high speed also seemed slightly more stable with a bit of push, I don't know if that is a good thing, there was no spinning out or other weirdness, it entered the turn with an appropriate speed of rotation and not too much. I could probably use a little more entry. The actual mid corner felt just about the same as before with no real increase or decrease, but I really enjoyed the controllable push and stable exit I would get coming out of a turn on power, this I especially felt there was some noticeable difference than before. Jumping was fine and seemed no different than before, it seemed to jump no less or no more than before. Our straightaway is pretty pockmarked and I honestly thought it was better now and more stable. I didn't notice any sort of sluggishness or lack of responsiveness, or glitching with anything, it just didn't feel like there was going to be much if any new learning curve and everything just seemed to feel ok to me.

I knew that if the rebound worked like it should, I should be able to remove or at least reduce the swaybars. Now, racing last Saturday, I was traction rolling with heavy swaybars. Today with fairly similar conditions, I was not traction rolling with similar speeds and cornering and I wasn't running any swaybar. In fact, I was getting just a bit of sliding. Todays conditions were even slightly more moist on the track than last Saturday as well. I think I should have traction rolled more today.

It is weird to see the slow rebound if you drop the truck and look at it, it does rise slower than before, but while driving, it feels ok and just nothing out of the ordinary. I see no reason to take these pistons out and I am going to continue running them!

-Matt
If you really wanted to run a thorough test you would have tried them in standard configuration first.

I hope you keep testing as I appreciate people who think outside the box. It's one of the reasons why I purchased these pistons in the first place.

A request: Could you please try to be a bit more methodical though? Saying you didn't check ride height before testing the first time is a red flag and makes me really question the soundness of your results.

Honestly, after reading your post, I'm not sure I see how your approach is any better than stock. Even if you managed a tiny bit of improvement is it worth it considering you can't seem t keep your pistons in one piece? It seems to me you wasted your money trying to recreate a stock experience.

You have no idea what you are missing with the recommended setup. Installed correctly the pistons make a huge change! My truck jumps dramatically better than before and feels more planted everywhere.

If you really want to be thorough, try the pistons in the recommended configuration as well. As curious a tinkerer as you obviously are, as am I, I would think you would have done that already to have a frame of reference. Instead all you're doing is comparing your invention to stock pistons.

I hope going forward you refrain from criticizing the standard approach as you've chosen to completely ignore it even though you bought the pistons.

Good Luck with your tests.

Last edited by Oso Negro; 12-02-2011 at 03:29 PM.
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Old 12-02-2011, 07:30 AM
  #883  
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.

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Old 12-04-2011, 02:24 PM
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We had some nice weather today and I was able to get out for some testing of the pistons in my Durango DESC410r short course truck. This is a large 1/8 track with whoop sections that I could never keep the truck stable before. I had driven losi's that did not have to let up on these sections and this was where they would make up ground on me. I started out at 25wt and the truck felt pretty good and I could go through the whoops with some better stability. So, next battery I bumped to 32 1/2 wt and I could fly through the whoops. Only problem it was too much pack for some of the other flat landers. So, next test day will be 27 1/2 and 30 to find the sweet spot. I plan on purchasing these for my DNX408 next.
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Old 12-04-2011, 03:46 PM
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Originally Posted by jmackani View Post
We had some nice weather today and I was able to get out for some testing of the pistons in my Durango DESC410r short course truck. This is a large 1/8 track with whoop sections that I could never keep the truck stable before. I had driven losi's that did not have to let up on these sections and this was where they would make up ground on me. I started out at 25wt and the truck felt pretty good and I could go through the whoops with some better stability. So, next battery I bumped to 32 1/2 wt and I could fly through the whoops. Only problem it was too much pack for some of the other flat landers. So, next test day will be 27 1/2 and 30 to find the sweet spot. I plan on purchasing these for my DNX408 next.
if you drill out your rebound pistons to the next size you will get quicker rebound and less pack. should put you riht where you need to be!
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