New Product: 928 Competition Suspension Kit
03-13-2012, 01:30 PM
#16
Developer
Thread Starter
I'm no 928 guru but it appears that the shock an extremely short stroke relative to the body of the shock... can a 928 really only use that much suspension travel?
When I ran 800 pd front springs and our largest bar and raced it on a smooth track, we noted only 3/4" of suspension travel. Too little. As a target, we'd like to see about 1.5" of travel in a road racerer.... if the travel is too small the shocks do not move enough hydraulic fluid through their valves to work as designed.
So we went to 700 pound front springs, picked up a little suspension travel, and the car was both faster and easier to drive fast.
In contrast, I think the stock 928 in Highway Driving trim might see almost 3" of travel. That's just my guess.
03-13-2012, 02:38 PM
#17
Former Vendor
Wow. Carl. What can I say?
You've outdone yourself again!
Have you bolted this stuff onto a car and driven it 500 miles?
100 miles?
50?
Being the new, kinder, gentler Greg, I'm going to help you out here. Free engineering, to you.
That rear lower mount is going to pivot on the urethane. That's a given. That "C' shaped piece that you think is going to keep that mount from rotating is going to move....regardless of how tight it fits on that "inner" part of the rear control arm. In shock compression, it's going to move as far as it can one direction. In shock extention, it will get twisted, instantly, to the maximum travel in the other direction. Add in a bit of urethane distortion (which is a given) and that thing is going to sound like a train going down the tracks. Clickity-clack, clickity-clack, clickity-clack. As those "ears" on the "C" portion "pound" into the inner tube, they will wear huge grooves. That will increase the problem.
It's going to sound like people traded their 928 in, for a train.
So how do you fix that?
If you made the "C" portion out of thicker metal and you "increased" the "wrap" of the "C" piece, you could drill and tap the "ears" for set screws. Tightening the set screws into the inner tube would bring the movement to a minimum, until the urethane started to distort. One could go back and "tighten" the set screws each time they started to make noise, but that would be a full time job.
With your current design, you will need to weld your "rear adaptor' onto the inner portion of the control arm, to keep it from moving and them replace the urethane bushing frequently, to keep everything stable.
Hope that helps. Maybe you can "fix" it, before you start shipping pieces.
You've outdone yourself again!
Have you bolted this stuff onto a car and driven it 500 miles?
100 miles?
50?
Being the new, kinder, gentler Greg, I'm going to help you out here. Free engineering, to you.
That rear lower mount is going to pivot on the urethane. That's a given. That "C' shaped piece that you think is going to keep that mount from rotating is going to move....regardless of how tight it fits on that "inner" part of the rear control arm. In shock compression, it's going to move as far as it can one direction. In shock extention, it will get twisted, instantly, to the maximum travel in the other direction. Add in a bit of urethane distortion (which is a given) and that thing is going to sound like a train going down the tracks. Clickity-clack, clickity-clack, clickity-clack. As those "ears" on the "C" portion "pound" into the inner tube, they will wear huge grooves. That will increase the problem.
It's going to sound like people traded their 928 in, for a train.
So how do you fix that?
If you made the "C" portion out of thicker metal and you "increased" the "wrap" of the "C" piece, you could drill and tap the "ears" for set screws. Tightening the set screws into the inner tube would bring the movement to a minimum, until the urethane started to distort. One could go back and "tighten" the set screws each time they started to make noise, but that would be a full time job.
With your current design, you will need to weld your "rear adaptor' onto the inner portion of the control arm, to keep it from moving and them replace the urethane bushing frequently, to keep everything stable.
Hope that helps. Maybe you can "fix" it, before you start shipping pieces.
03-13-2012, 04:02 PM
#19
Rennlist Member
Greg: Dont the inner tube and the shock mount rotate around different centers?
If you welded to the inner tube, the shock bushing would be forced to deform itself in a..oval pattern as the shock mount point itself was not allowed to rotate inside the center dimention of the outter tube.
Right?
The inner rotates around the LCA mount point, the outter rotates around the spindle mount point.
If you welded to the inner tube, the shock bushing would be forced to deform itself in a..oval pattern as the shock mount point itself was not allowed to rotate inside the center dimention of the outter tube.
Right?
The inner rotates around the LCA mount point, the outter rotates around the spindle mount point.
03-13-2012, 04:29 PM
#20
Former Vendor
Greg: Dont the inner tube and the shock mount rotate around different centers?
If you welded to the inner tube, the shock bushing would be forced to deform itself in a..oval pattern as the shock mount point itself was not allowed to rotate inside the center dimention of the outter tube.
Right?
The inner rotates around the LCA mount point, the outter rotates around the spindle mount point.
If you welded to the inner tube, the shock bushing would be forced to deform itself in a..oval pattern as the shock mount point itself was not allowed to rotate inside the center dimention of the outter tube.
Right?
The inner rotates around the LCA mount point, the outter rotates around the spindle mount point.
Certainly, as the urethane deforms, really "strange" things are going to be happening, there. Actually, if the inner "C" piece got welded, the entire mount could be a solid "block" of material and eliminate the urethane completely?
I truthfully didn't study it. I saw the "problem" in the first 5 seconds (literally) of looking at his "mount" and moved on, as quickly as I could. I forwarded his "design" to one of my friends who is a suspension engineer, this morning, and we had a great laugh, over our first cup of coffee.
I'm not sure I have the time to really care....nor do I want to do all of his engineering work....it's just so obvious that it isn't going to work, like this.
03-13-2012, 04:35 PM
#22
Under the Lift
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Remember the problem with the original rear tiedown design, locking the pin to the control arm so the pin could not rotate independent of the arm, as it needs to do. The lower shock mount should move with the pin, not the control arm unless you completely divorce it from the pin area and mount it elsewhere (as Mark Anderson has done, welding a mount elsewhere on the LCA).
I think this design, attempting to lock the mount to the control arm, is going to lead to rapid wear or destruction of the urethane bushing. With the stock mount, there is no torque on or wear of the rubber lower mount bushing UNLESS you lock the pin to the control arm, as the original tiedown plate did. Using a bushing that is not bonded to the mount and having the mount move with the LCA instead of with the pin and shock is just going to be a wear item. What I have seen elsewhere with similar urethane suspension bushings that are not bonded like the stock rubber bushings is that they do not hold up well.
Carl successfully resolved the tiedown situation after receiving input from the List. Not having this supension in hand to examine, as Jeff and I did with the tiedown, nailing down the issue rather quickly, I could be wrong, but that's what I see only having these pictures as evidence.
I think this design, attempting to lock the mount to the control arm, is going to lead to rapid wear or destruction of the urethane bushing. With the stock mount, there is no torque on or wear of the rubber lower mount bushing UNLESS you lock the pin to the control arm, as the original tiedown plate did. Using a bushing that is not bonded to the mount and having the mount move with the LCA instead of with the pin and shock is just going to be a wear item. What I have seen elsewhere with similar urethane suspension bushings that are not bonded like the stock rubber bushings is that they do not hold up well.
Carl successfully resolved the tiedown situation after receiving input from the List. Not having this supension in hand to examine, as Jeff and I did with the tiedown, nailing down the issue rather quickly, I could be wrong, but that's what I see only having these pictures as evidence.
03-13-2012, 04:56 PM
#23
When NASCAR adopted the car of tomorrow it had front suspension designed with 3.5 inches of travel it caused all kinds of handling issues because the former design had TWICE that travel. Or about seven inches. That is using high sidewall 15 inch tires. How anyone could think that a street 928 uses only 3 inches or that a race car, any race car , would work with 1.5 inches is amazing to me.
But until there are some real race lap times on a known track, I guess it might be possible.
But until there are some real race lap times on a known track, I guess it might be possible.
03-13-2012, 05:08 PM
#24
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All fine and dandy, but for which audience is this aimed that? From reading this, I doubt this is for street use...
I guess the actual need that I see is the lack of options for a street setup, where track options are available, so while it looks nice, it wont apply to me.
So my question is, why the need to do this instead of a very good street setup? the 928 is a natural GT and while capable on the track and you guys prove, I just dont think that the majority of us are looking for a track biased setup.
I guess the actual need that I see is the lack of options for a street setup, where track options are available, so while it looks nice, it wont apply to me.
So my question is, why the need to do this instead of a very good street setup? the 928 is a natural GT and while capable on the track and you guys prove, I just dont think that the majority of us are looking for a track biased setup.
03-13-2012, 05:14 PM
#25
Developer
Thread Starter
I love armchair quarterbacks. Its so easy to sit in the seats and throw bricks.
No Greg, we have not had it on to a track just yet. The snow is still melting up here. Soon. Yes Greg, we did build a complete bench mock-up (with OEM parts from 928 Intl) and I believe that you are wrong, the lower rear shock mount will not turn. The load is very nearly straight up and down, and the twistiing moment is slight. The brace is 1/4" steel and is not going to move. The polyurethane is captured in steel inside and out and is not going to deform much. We tested for exactly this.
But, you cant see that from there - you just made your assumptions.
Anyway.... it a new product, its available now. If anyone would rather wait for a season to go by to know its been raced on, of course they may do that.
The subject line says "New Product" and that's just what it is.
No Greg, we have not had it on to a track just yet. The snow is still melting up here. Soon. Yes Greg, we did build a complete bench mock-up (with OEM parts from 928 Intl) and I believe that you are wrong, the lower rear shock mount will not turn. The load is very nearly straight up and down, and the twistiing moment is slight. The brace is 1/4" steel and is not going to move. The polyurethane is captured in steel inside and out and is not going to deform much. We tested for exactly this.
But, you cant see that from there - you just made your assumptions.
Anyway.... it a new product, its available now. If anyone would rather wait for a season to go by to know its been raced on, of course they may do that.
The subject line says "New Product" and that's just what it is.
03-13-2012, 05:17 PM
#26
Rennlist Member
you will see up to 5" of travel with a 928 sprung well and pulling some gs.
see my pic
Mk
see my pic
Mk
Suspension travel will be affected by the spring rate, the driver, the tire and inflation pressures, and the kind of surface it is on. Even the sway bar.
When I ran 800 pd front springs and our largest bar and raced it on a smooth track, we noted only 3/4" of suspension travel. Too little. As a target, we'd like to see about 1.5" of travel in a road racerer.... if the travel is too small the shocks do not move enough hydraulic fluid through their valves to work as designed.
So we went to 700 pound front springs, picked up a little suspension travel, and the car was both faster and easier to drive fast.
In contrast, I think the stock 928 in Highway Driving trim might see almost 3" of travel. That's just my guess.
When I ran 800 pd front springs and our largest bar and raced it on a smooth track, we noted only 3/4" of suspension travel. Too little. As a target, we'd like to see about 1.5" of travel in a road racerer.... if the travel is too small the shocks do not move enough hydraulic fluid through their valves to work as designed.
So we went to 700 pound front springs, picked up a little suspension travel, and the car was both faster and easier to drive fast.
In contrast, I think the stock 928 in Highway Driving trim might see almost 3" of travel. That's just my guess.
03-13-2012, 05:22 PM
#27
The Parts Whisperer
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03-13-2012, 05:26 PM
#29
Developer
Thread Starter
Bill,
Think about it for a second. Did the shock rotate on the pin in the OEM setup? Certainly not. The pin turned inside the lower shock mount. The shock stayed where it was.
This is no different. The shock will not move, the pin will turn inside the bushing we have put inside the lower shock mount - exactly as before.
Think about it for a second. Did the shock rotate on the pin in the OEM setup? Certainly not. The pin turned inside the lower shock mount. The shock stayed where it was.
This is no different. The shock will not move, the pin will turn inside the bushing we have put inside the lower shock mount - exactly as before.