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ghoffman Shock dyno comparo
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Ok, here are 5 force-velocity and Force-displacement plots we ran on our dyno. These are all Corvette C5/C6 rear shocks, 5 different brands, which do you think is the best, and which one actually works the best on the street and/or track? What curve do you think is the worst? What do you think causes the hysteresis in some of these curves?

Without a dyno, you are only guessing, and real world (road race and steet) has lots of greater than 3 in/sec velocities. Body roll, squat, dive, etc is the less than 3 in/sec stuff, but bumps, curbs, ripples are much greater than that and 8-10 in/sec is very common. An interesting thing is when I was at Penske last summer, it was mentioned to me that a tolerance variation of .0005 inch (yes, 1/2 a thousand) could cause 20-30 pounds (depending on the valving) on the dyno, and that is why each shock has to be tested and if not within spec, it is made to be correct. If the super quality CNC parts in a Penske can cause that kind variation, what do you think you get in a mass produced cheap imported shock? The first plot is Force-Velocity, the second is Force-displacement. There were many details that we have not discussed, but I will later (things like not holding gas pressure, leaky seals etc)

We have seen new GM T1 shocks that flat were not working (shown here):

[IMG width=640]http://i67.photobucket.com/albums/h287/gshoffman/Corvette%20shocks/shockT1bad.jpg[/IMG]
[IMG width=640]http://i67.photobucket.com/albums/h287/gshoffman/Corvette%20shocks/shockT1badFD.jpg[/IMG]

The rest are shown here, brand names deleted.

Brand A
[IMG width=640]http://i67.photobucket.com/albums/h287/gshoffman/Corvette%20shocks/shockbad.jpg[/IMG]
[IMG width=640]http://i67.photobucket.com/albums/h287/gshoffman/Corvette%20shocks/shockbadFD.jpg[/IMG]

Brand B
[IMG width=640]http://i67.photobucket.com/albums/h287/gshoffman/Corvette%20shocks/shocksoso.jpg[/IMG]
[IMG width=640]http://i67.photobucket.com/albums/h287/gshoffman/Corvette%20shocks/shocksosoFD.jpg[/IMG]

Brand C
[IMG width=640]http://i67.photobucket.com/albums/h287/gshoffman/Corvette%20shocks/shockgood.jpg[/IMG]
[IMG width=640]http://i67.photobucket.com/albums/h287/gshoffman/Corvette%20shocks/shockgoodFD.jpg[/IMG]

Brand D
[IMG width=640]http://i67.photobucket.com/albums/h287/gshoffman/Corvette%20shocks/shockMfullhard.jpg[/IMG]
[IMG width=640]http://i67.photobucket.com/albums/h287/gshoffman/Corvette%20shocks/shockMfullhardFD.jpg[/IMG]
Posted on: 2008/7/6 15:06
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CentralCoaster Re: Shock dyno comparo
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I'll go with brand C.
Posted on: 2008/7/6 23:43
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ghoffman Re: Shock dyno comparo
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Can you believe that ZO6vette.com denied this post? No names, no brands, identical to this and they denied it!
Posted on: 2008/7/7 0:50
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CentralCoaster Re: Shock dyno comparo
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Why? Do they have a dog in the fight? I presume the OEM shocks are always a compromise, to reduce costs. Nothing to be offended over.
Posted on: 2008/7/7 1:28
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BrianCunningham Re: Shock dyno comparo
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This forum is a little more relaxed.

I'm sure you could post the name brands here if you wanted to.
Posted on: 2008/7/7 3:26
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CentralCoaster Re: Shock dyno comparo
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Until some big name manufacturer of crappy shocks bribes me to edit out the names...... post away.
Posted on: 2008/7/7 3:48
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ghoffman Re: Shock dyno comparo
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The first is a new GM T1 C6 shock as labeled.

The ones labeled are

A=Renamed brand made in Asia (Japan or China) coil-over on full soft. The adjuster only effects rebound, but there is some bleeding over. It only added a little to full hard to 225 pounds.

B- Bilstein aluminum body after re-pressurizing it. It would leak down in an hour to 75 PSI. We kept it up at 150+ for the test. The fronts leaked too, and they were about a year old. At least it had a Schrader valve so it could be recharged, otherwise you would only know when it is on the dyno because you can hear the cavitations. It sounds like a kid sucking at the bottom of a soda with a straw.

C- My old Penske 8100’s (that I bought used and rebuilt like 2 years ago, now sold) with the bump on full soft, rebound on ½ hard, after 6000 miles or so and 20+ track days. I did these plots when I sold them as a QA check before I shipped them to him.

D- Moton T1 shock on moderate bump, max rebound.

Dyno's don't tell the whole story but clearly they can find issues like the T1 shock that was broken and I really don't know what was going on with sample "A". Sample A made audible clunking when cycled as did the fronts from the same manufacturer. I presume it had some kind of a floater gizmo inside it, which we have seen (or heard) on KYB's.
Posted on: 2008/7/7 11:13
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CentralCoaster Re: Shock dyno comparo
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Looks like the damping on the C6 shock was the same as the Penske until the higher speeds where it stayed soft. Wouldn't that make for a smoother ride, aside from the wheel maybe coming off the ground on small road upsets?

The Moton shock is stiff!

Sample A looks like a mess. It seems to let loose momentarily. Bad seal?
Posted on: 2008/7/7 14:51
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ghoffman Re: Shock dyno comparo
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The C6 shock was broken, it was cavatating very bad, that is why it has so much hysteresis (not coming back along the same path it went out). With that much hysteresis, it is sloppy and not really controlling the wheel very well and would chatter over bumps. The C and D shocks can be adjusted so that either could do the rebound values of the other. Note that they both have alot more compression (top half of the curve) than the other 2, and is velocity sensitive, which is what you want. The sample A shock is fairly new, had no outward signs of leaks, but has such stiff urethane upper mounts that is prematurely wears it out internally.
Posted on: 2008/7/7 15:07
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BillH Re: Shock dyno comparo
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Shows ya one of the reasons that street shocks don't do well on the racetrack.

Gary, Someone should lend you a pair of the Bilstein street shocks with a couple of miles on them to do a plot.
Posted on: 2008/7/8 23:46
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ghoffman Re: Shock dyno comparo
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Quote:

BillH wrote:
Shows ya one of the reasons that street shocks don't do well on the racetrack.

Gary, Someone should lend you a pair of the Bilstein street shocks with a couple of miles on them to do a plot.


OK, I will do it, but we publish it, OK?
Posted on: 2008/7/9 2:10
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BillH Re: Shock dyno comparo
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Quote:

ghoffman wrote:
Quote:

BillH wrote:
Shows ya one of the reasons that street shocks don't do well on the racetrack.

Gary, Someone should lend you a pair of the Bilstein street shocks with a couple of miles on them to do a plot.


OK, I will do it, but we publish it, OK?


Sure, and maybe post the plots of those "other" shocks you sent me.
Posted on: 2008/7/9 13:18
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BrianCunningham Re: Shock dyno comparo
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Here's another pretty good read on shocks
http://farnorthracing.com/autocross_secrets6.html
Posted on: 2008/7/30 21:45
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Steve40th Re: Shock dyno comparo
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What does it cost to get shocks dyno'd?
Posted on: 2008/8/1 0:36
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BillH Re: Shock dyno comparo
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I've had them done for $25 each. I think Gary at Hardbar is somewhere near that price.
Posted on: 2008/8/1 14:10
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Steve40th Re: Shock dyno comparo
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I wonder what a company like Ferraris shocks would do?
Posted on: 2008/8/1 15:45
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BrianCunningham Re: Shock dyno comparo
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The same, they don't manufacture their own. They buy from the same suppliers we do.

You can call a supplier and get them if you want.

http://www.penskeshocks.com/penskeracing/sportscar.html

http://www.penskeshocks.co.uk/penske/racingshocks.htm
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Posted on: 2008/8/1 17:31
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