Fred Brewer
03-19-2012, 06:03 AM
I had one of the older yellow shocks and one of the newer black shocks dynoed to see exactly what they do.
The yellow
http://lsspecialists.com/Shockdyno1.jpg
And the supporting data. The headings have me scratching my head a bit although it appears to be data from three runs on the dyno. Anyone have thoughts on this?
http://lsspecialists.com/Shockdyno2.jpg
http://lsspecialists.com/Shockdyno3.jpg
Now the black FSD shock
http://lsspecialists.com/Shockdyno4.jpg
and the supporting data
http://lsspecialists.com/Shockdyno5.jpg
Fred Brewer
03-19-2012, 08:35 AM
Here are a few numbers David Borden put together some time ago. I don't want to speak for him but to paraphrase him he was thinking these might be numbers to start with
The origional thread http://www.ffcars.com/forums/42-factory-five-gtm-forum/258924-spring-damper-rates-shocks.html
The pink and blue line represent approx range to target for the adjustment in rebound. The yellow is roughly where I would recommend starting around for the compression near max. If anything I would add more of a knee and slow speed damping if I could bleed it off. I would need to look at the 8300 compression plots to refine my suggestions. I have some and can do that. Just give me a couple days. I think the 8300 does a reasonable job at adjusting both slow and high speed compression. The bleed is much better on the canister compared to my 8100's.
This assumes that you subscribe to running a digressive shock. I feel this is more reasonable since the shock range that controls transient response are between 1-3 IPS(inch per second) Above that is generally considered high speed, such as hitting a pothole, or curbing.
Bleed controls the slower speed stuff and the shim stack controls the high speed mostly. When you use a digressive shock, you can keep your rebound and compression rates reasonable for high speed and then increase or reduce bleed to control the cars transition.
In general, rebound is primarily to control spring forces/rates, but is also a good way to control the chassis as well if you are not going with crazy expensive triples which have a dedicated slow speed bleed for compression. This is the prefered way to control the chassis, but you can get yourself in just as much trouble trying to comprehend and tune 3 settings on a single shock.... and finding a good range that works... and they can cost $4-8K a set . IMHO, you just dont need that unless you are building a dedicated track car and are willing to invest the time and understanding into learning to tune it. Its no small task... Regardless, a well tuned single or double will do better than a miss-tuned triple. Add to that getting the settings right.
A decent double(the Penske 8300 is superb) is plenty to tune the car.
Let me know if you have questions or comments.
David
Front with 450 spring
http://www.ffcars.com/photopost/data/592/critical-dampening-GTM-front.jpg
Rear with 750 spring
http://www.ffcars.com/photopost/data/592/critical-dampening-GTM-rear.jpg
kabacj
03-20-2012, 06:21 AM
This is great info Fred
I need to print the ohlins and koni graphs and see what conclusions we can draw from this info.
It looks like the yellow shocks are adjustable for compression damping. I did not realize that.
In theory with the yellows you could turn down the compression damping for a smooth street ride and firm them up for more aggressive track duty.
The other thing I noticed was the nice rising rate of the black shocks. I guess this is why koni claim it's self adjusting. (that claim always bothered me as its impossible without computers and magnetorheological damping oil) However the black shocks gets rapidly stiffer as the velocity increases then the rate evens out. It's soft on smooth roads and firm over a sharp bump.
Pretty cool. I can see why FFR made the switch. Its a great compromize for a street duty shock as long as they are mounted right side up of course.
John