Shock dyno comparo
08-23-2009, 05:20 PM
#81
Instructor
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Location: El Dorado CA
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I wanted to bring this thread back to the top.
Great deal of information in this thread, so thank you! What is the opinion on valving differences between road race and autocross valving with regards to running stock C5Z leafs?
From the research I have done, it appears that low speed dampening from 0-3 IPS is most critical for transient response control needed in autocross.
For example, the doc linked below talks about different types of valving and pistons along with types of adjustments and what part of the curve they affect. It also shows a histogram of average shaft speeds in an autocross run illustrating where you need control(speeds between 0-3 IPS)
http://www.neohio-scca.org/comp_clin...handout%20.pdf
My theory for an autocross shock, is if you cant afford a tripple Penske, Ohlin, JRZ, AST, or Koni, you are better off running a digressive curve with a sharp knee before 1 IPS on rebound and use the rebound bleed to control/reduce that knee and low speed control for chassis balance. If your shocks allow a knee on both rebound and compression and the bleed will adjust the lower part of the curve do that as well.
At least with Penske 8100s, the compression is high speed only, so controlling low speed rebound with bleed seems to be the only reasonable alternative for controlling corner exit and entry.
There is a fairly consistant thread of increasing the rebound above normal ratios to mimic higher spring rates, however, the question of how much comes into question. Too much will jack the car down.
When I spoke with the guys at Penske, they mentioned if running a linear piston and not going to the expense of upgrading to digressive pistons, they could flip the linear piston, preload the new rebound side(used to be compression before flip) to get a decent knee around 1 IPS and go linear on compression.
Valve them so that the softest setting in rebound was a bit below that of the 2004 C5Z with each adjustment adding both knee in the low shaft speeds and some high speed rebound.
Comments?
David
Great deal of information in this thread, so thank you! What is the opinion on valving differences between road race and autocross valving with regards to running stock C5Z leafs?
From the research I have done, it appears that low speed dampening from 0-3 IPS is most critical for transient response control needed in autocross.
For example, the doc linked below talks about different types of valving and pistons along with types of adjustments and what part of the curve they affect. It also shows a histogram of average shaft speeds in an autocross run illustrating where you need control(speeds between 0-3 IPS)
http://www.neohio-scca.org/comp_clin...handout%20.pdf
My theory for an autocross shock, is if you cant afford a tripple Penske, Ohlin, JRZ, AST, or Koni, you are better off running a digressive curve with a sharp knee before 1 IPS on rebound and use the rebound bleed to control/reduce that knee and low speed control for chassis balance. If your shocks allow a knee on both rebound and compression and the bleed will adjust the lower part of the curve do that as well.
At least with Penske 8100s, the compression is high speed only, so controlling low speed rebound with bleed seems to be the only reasonable alternative for controlling corner exit and entry.
There is a fairly consistant thread of increasing the rebound above normal ratios to mimic higher spring rates, however, the question of how much comes into question. Too much will jack the car down.
When I spoke with the guys at Penske, they mentioned if running a linear piston and not going to the expense of upgrading to digressive pistons, they could flip the linear piston, preload the new rebound side(used to be compression before flip) to get a decent knee around 1 IPS and go linear on compression.
Valve them so that the softest setting in rebound was a bit below that of the 2004 C5Z with each adjustment adding both knee in the low shaft speeds and some high speed rebound.
Comments?
David
07-04-2017, 06:30 AM
#82
You probably want the knee a little higher than 1 IPS. You might get away with 2, 3 is safer.
You don't want the shock force suddenly blowing off while still controlling the chassis movement. The knee is about getting the shock out of the way in response to bumps.
A linear piston works great on smooth surfaces, but the force keeps increasing in response to shaft speed. In effect, hit a big bump and the shock locks solid and now you are a go-kart. The digressive portion softens the shock rate so the shaft can still move when the wheel gets whacked.
The 8100 canister adjuster is not very useful.
You can get digressive-ish response by playing with preload, but you are better off with the correct piston.
ALWAYS get Penskes serviced by a Penske-approved dealer. If there is doubt, CALL PENSKE.
You don't want the shock force suddenly blowing off while still controlling the chassis movement. The knee is about getting the shock out of the way in response to bumps.
A linear piston works great on smooth surfaces, but the force keeps increasing in response to shaft speed. In effect, hit a big bump and the shock locks solid and now you are a go-kart. The digressive portion softens the shock rate so the shaft can still move when the wheel gets whacked.
The 8100 canister adjuster is not very useful.
You can get digressive-ish response by playing with preload, but you are better off with the correct piston.
ALWAYS get Penskes serviced by a Penske-approved dealer. If there is doubt, CALL PENSKE.
07-05-2017, 04:34 PM
#83
Team Owner
Member Since: Mar 2001
Location: Boston, Dallas, Detroit, SoCal, back to Boston MA
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Just jad my rears sevices by Penske
Kept loosing pressure
there was a hairline crack
older shocks, fortunately the service guy had a spare in his toolbox
Kept loosing pressure
there was a hairline crack
older shocks, fortunately the service guy had a spare in his toolbox
