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Old 03-29-2006, 07:40 PM   #6736
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I think the 2.9mm chassis and the 2.4mm topdeck would be pretty good. Perhaps try cutting it out like I mentioned as well.

got any pics of your ride?

chris i rum ny topdeck the same way if you can make it by socal on saturday ill be racing come by and check it out later jason
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Old 03-29-2006, 07:45 PM   #6737
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Quote:
Originally Posted by ERTRACHTER
I think the 2.9mm chassis and the 2.4mm topdeck would be pretty good. Perhaps try cutting it out like I mentioned as well.

got any pics of your ride?

chris i rum ny topdeck the same way if you can make it by socal on saturday ill be racing come by and check it out later jason
How about a pic for one of your Nor-Cal Homies....or am I the ENEMY! LMAO!

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Old 03-29-2006, 08:54 PM   #6738
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I know when testing out the Jaco proto 2 stages that my shock would be bottomed before the chassis would. I believe that the piston is up against the shock bladder before it bottoms out also. I ran my car like this for along time. I cut my shaft and eyelet before the Novak race and felt like my car reacted quicker with them cut.
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Old 03-29-2006, 10:52 PM   #6739
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I'm not sure how it applies to smaller shocks, but shock theory relating to their larger counterparts seems to support McFormula's math homework from earlier today.

"Damping is sensitive to shaft velocity, not position in the stroke. Yes, position sensitive shocks are there, but those are simply bypass bleed systems. Their damping resistance is still speed sensitive."

I've found several sources that say basically the same thing. It would appear to be true that the piston's position doesn't matter as long as it doesn't get into the reservoir. There's a LOT of theory on shock absorber design, and it's a fascinating read if you've got time.

There's still incentive to trim the shock shaft, as others have stated, but speaking strictly about the action of the piston and shaft moving through the oil, shock theory seems to indicate that the amount of oil on top of the piston doesn't matter. That makes sense, since if it did matter, as you compressed a shock its rate would change as the piston's position moves closer to the top of the shock, and has less oil on top of it. In a proper shock design though, you're not compressing the oil with the piston, you're displacing it (into the reservoir) with the shaft, and altering its compression rate with the viscosity of the oil and the size of the holes in the piston.
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Old 03-30-2006, 02:57 AM   #6740
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guys i got me a rdx and just put it together its great car. Got some Questions its the carpet spec and the front diff has a little wobble to it? anyone had that problem back is fine its just the front diff. Also should i put 64 pitch gears on this car or will it not really help much of anything? Last but not least what oil should i put in the shocks what came with it or something new and diffrent it looks like they supplied me with 35 or 40wt oil not sure?
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Old 03-30-2006, 05:32 AM   #6741
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hey Ultra, both gears should have some wobble to them. This is fine, as it is the gear floating on the diff balls. Both of mine do it in both my RDX's and I haven't had any issues. I believe the oil that comes in the kit is 40 weight, but I'll have to check on that. I run 64 pitch because it is more efficent and I can get more gear ratio's. If you are going to buy gears, I would buy 64 pitch. I hope this helps. If you have any more questions don't be afraid to ask.
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Old 03-30-2006, 06:00 AM   #6742
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Quote:
Originally Posted by McSmooth
OK, genius:

For internal incompressible flow, the flow rate of a fluid is defined as:

Q = (pi*delta p*diameter^4) / (128 *mu*length)

and the average velocity is:

V = Q / A

Nowhere, in either equation, is the "amount of fluid on top of the piston" even a factor. Flow through a hole is a product of cross-sectional area only, and not volume. All of the other variables are contant (viscosity, diameter, length, pressure, etc)
Well, I have a suggestion. Since our shocks are not of the constant volume type, the pressure in the shock rises when you push the piston, which induces the effect of shock rebound. IF you change the shock shaft's length whilst keeping the same rebound setting (i.e. 3mm less rebound when using 3mm shorter shafts) then you will change "delta p" and thus Q will vary.

Also, what makes you think the internal diameter of the shock body is really constant ? Maybe it has a small conicity which will also change the damping properties depending on the position of the piston. Maybe there has been a batch of them with a slight conicity and you have a batch that is cylindrical and that's why some people see a difference and some don't.

Maybe you all need to do what works for you... cut or not and see what you prefer, me I don't care I run a tamiya and if i'd be running a corally i'd still use tamiya shocks...
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Old 03-30-2006, 06:26 AM   #6743
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All of our racing shocks are constant volume. You put oil in, screw on the cap, and that's all the oil that's in there. There isn't an external reservoir like on those aftermarket Integy shocks.

Sure, the pressure will increase on one side of the piston as it moves, however, it also decreases on the backside. So the change in pressure remains constant. If the shocks were gas-filled, then there would be a change in delta-p since gases are compressible.

As for 'how round' the inside of the shock body is, that's a manufacturing issue. Any leakage around the sides of the piston is then represented by a fluid flowing between 2 plates, and not through a hole. I'm willing to bet the runout tolerance on the inside of the shock bodies is less than 5 thousandths of an inch.

As for the shaft/piston hitting the bladder issue...guess what? I checked a BRAND NEW shock yesterday, and the top of the shock shaft hits the bladder, and quite a bit at that. Further, the plastic cap/eyelet on the top sits down inside the bladder, providing a hard stop when it's tightened down. So it doesn't matter what you do....the shaft and piston is going to stop at the same position anyways.

I believe that's enough for this weeks lesson.
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Old 03-30-2006, 07:07 AM   #6744
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Quote:
Originally Posted by McSmooth
All of our racing shocks are constant volume. You put oil in, screw on the cap, and that's all the oil that's in there. There isn't an external reservoir like on those aftermarket Integy shocks.

Sure, the pressure will increase on one side of the piston as it moves, however, it also decreases on the backside. So the change in pressure remains constant. If the shocks were gas-filled, then there would be a change in delta-p since gases are compressible.

As for 'how round' the inside of the shock body is, that's a manufacturing issue. Any leakage around the sides of the piston is then represented by a fluid flowing between 2 plates, and not through a hole. I'm willing to bet the runout tolerance on the inside of the shock bodies is less than 5 thousandths of an inch.

As for the shaft/piston hitting the bladder issue...guess what? I checked a BRAND NEW shock yesterday, and the top of the shock shaft hits the bladder, and quite a bit at that. Further, the plastic cap/eyelet on the top sits down inside the bladder, providing a hard stop when it's tightened down. So it doesn't matter what you do....the shaft and piston is going to stop at the same position anyways.

I believe that's enough for this weeks lesson.
Well you're quite wrong... First off, they aren't constant volume and that's a fact, it's like the CVDs that we use that aren't real CVDs. Reason is, when you push the piston a part of the volume of the shaft goes from being outside the body to being inside. A constant volume shock has the shaft extending to the other end of the shock and out again so there always is a constant volume of the shaft in the body. Also, no matter what, in static the pressure is the same over and under the piston. In dynamic, the amount of rebound changes your delta p for a given pistion position.

Second is, your theory is all nice, but have you had a look at the gap between the piston and the body ? Yeah that's right, most of the flow goes around the piston and not though the piston's holes. The holes are just a way of fine tuning, any Off Roader bloke will tell you that.

How's that for a lesson
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Old 03-30-2006, 07:07 AM   #6745
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But when the shaft is pushed in the oil compresses because the shaft also takes up some space. So the shock is harder with "more" shaft within it and lighter with less shaft within it thus it should make a difference with different piston positions?
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Old 03-30-2006, 07:15 AM   #6746
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Quote:
Originally Posted by McSmooth
I'm willing to bet the runout tolerance on the inside of the shock bodies is less than 5 thousandths of an inch.

As for the shaft/piston hitting the bladder issue...guess what? I checked a BRAND NEW shock yesterday, and the top of the shock shaft hits the bladder, and quite a bit at that. Further, the plastic cap/eyelet on the top sits down inside the bladder, providing a hard stop when it's tightened down. So it doesn't matter what you do....the shaft and piston is going to stop at the same position anyways.

I believe that's enough for this weeks lesson.
I'm willing to bet those shocks are a bit crap and might not have that good a tolerance...

Also, you've just explained to everyone that they should shorten their shaft since they do hit the bladder (which wouldn't exist in a constant volume shock by the way).

You know an easy solution to all your problems is use the best shocks in the industry, you're already using the pistons why not go for the full monthy
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Old 03-30-2006, 07:22 AM   #6747
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Quote:
Originally Posted by TRF415boy

Also, you've just explained to everyone that they should shorten their shaft since they do hit the bladder (which wouldn't exist in a constant volume shock by the way).
They're cutting off some of the threaded portion on the bottom of the shaft, not the top section above the piston.
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Old 03-30-2006, 07:35 AM   #6748
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Wow, I do not think I have come across such a lot of mis-quoted physics in a long time........

You cannot take one formula and apply it because SOME of the factors apply.

There are a significant number of variables missing, such as temperature and the properties of the fluid.

Shock oil in this application is an emulsion, not a fluid.There are air bubbles suspended in it.

It compresses, therefore the initial equation is not solely attributable in isolation.
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Old 03-30-2006, 07:42 AM   #6749
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You know what, I have an idea. How about just putting oil in the dam shock and try running whats best for you instead of trying to put the big bang thery in place. Who gives a S#@* about volume and displacement. Fill the thing up and run it!
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Old 03-30-2006, 07:43 AM   #6750
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Yes, I understand that in real world applications, 1 single formula cannot take into account every minute factor that may come along. (Such as manufacturing tolerances in the piston/shock body as mentioned above).

What if someone puts too much oil in? What if there's not enough? What if you lean the shock over more? What if the oil is dirty?

These are the kinds of things that would be barely noticable.

Many have already agreed that cutting .118" off the bottom of the shaft is unnecessary...that was the point of this whole thing. It was then "reasoned" that it was the volume of the oil and the issue of the shaft hitting the bladder. I showed that those 2 were non-issues. I didn't want this to turn into an engineering lesson since it opens up another whole can of worms.

So with that said...I'll repeat. If you want to cut them for the sake of just doing it, go right ahead. It's just not going to make any difference.

That's the end of it.
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