Penske (or other option) shock for SLC ?

Howard Jones

Supporter
I am in the first stage of researching shock options for my SLC track car, The original QA-1s, while functional are not suitable at the spring rates I will ultimately want to run on the car. I called QA-1 and they said that they cannot re-valve them and the model number on my car is no longer available. So now the search for a viable alternative starts. Since the Penske shocks are an upgrade option for SLCs from RCR I am wondering what model number they offer. Are they a special custom model configuration for SLC's ? Has anyone ordered a custom valving and spring package for them (track appropriate) ?

I can of course call Fran but I think I would like to do a bit of research before that. Any info would be helpful. Also, a model number would be helpful as well as full-length and compressed-length eye-to-eye center measurements. Do they use 2.5 or 2.25-diameter springs? I would like to stay with 2.5 springs as I have several and they would suit slow bumpy tracks at their lower spring rates. Then run the stiffer springs at high speed/smooth tracks

I am thinking I need R1100 lbs and F850-900 springs for the highest settings.

Anyone got any ideas ?
 
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Joel K

Supporter
Howard, not sure if you are aware. RCR now offers an optional QA1 shock setup for the SLC. Here is the description off the web site…

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These are QA1's latest 4-way adjustable shock. They are adjustable for compression, rebound, slow-speed bleed and high-speed bleed. Mostly aluminum and anodized an attractive red and black, these shocks stand out as well as perform. Provided with remote canister configuration to allow mounting flexibility.

Similar in performance capability to the Penske optional shocks, these are noticeably less expensive, better looking and offer more adjustability than the 8300 series.

They offer the following features:


  • QuickTune™ Modular Valve Packs can be changed on the car without losing oil or gas pressure.
  • High force curve capability and exceptional tunability with available tuning kits.
  • High- and low-speed adjustability for both compression and rebound.
  • The first shock able to be revalved while still on the car.
  • Indexable base loop allows you to position the knobs and canister how you like.
  • Made in the USA.
  • Features QuickTune™ Modular Valve Packs that allow for completely revalving the shock without even having to remove it from the car!
  • 24 click independent compression and rebound adjustment with low-speed bleed
  • Large solid piston (with blow-off valve)—improved driver feel and control with up to 1,600 lb. force
  • High-speed valving adjustment (coarse adjustment)—relates to shock operation during impact events, like hitting a pothole or curb
  • Low-speed valving (fine-tune adjustments)—adjusts ride quality and weight transfer on corner entry/exit; more bleed for softer feel and less bleed for stiffer feel
  • Indexable base eyelet—multiple mounting position to optimize knob access and provide more mounting flexibility
  • Piggyback or remote canister options
  • Thrust bearings included
  • American-made
 

Ken Roberts

Supporter
How about this option…….custom made for the SLC bilstein shocks. Rumoured to be about $6000. Perhaps Stu could chime in.

 
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Scott

Lifetime Supporter
Mesa and pnut ran into TractTive (TracTive Suspension – The Art of Suspension) at PRI a few weeks ago. TracTive offers an electronic semi-active damping system which has a 6-10ms response time. They seem to be an engineering-focused company (a good thing), so there isn't a lot of detailed information on their website. To my understanding they've been successful on the track and street and are used by multiple OEMs and at least one halo-car OEM. They have a touch-panel-based ECU which enables you to configure 5 different tunes. This is particularly useful for a combination street/track car.

If they can provide a solution for the SL-C, I will upgrade my Penske shocks. Since some non-recurring engineering (NRE) will need to occur, it's likely important to have an initial volume to get their attention. Pnut spoke with Fran and he's conceptually interested. If anyone else is interested, let us know.

Having spent a lot of time to get my Penske shocks to fit properly, here are a few things that I learned along the way:

(1) You want a bump stop.

(2) You want at least one bump spring. Otherwise your spring rate at max compression will suddenly go exponential which will upset the driver if not the car. A bump spring acts like a really stiff main spring that's mounted on the shaft like a bump stop. This provides a more progressive and manageable experience before max compression is reached.

(3) You should not need to jack the lower control arm or modify the bottom of the wheel arch to get the wheels off. Many shocks support droop limiters which allows you maximize full droop without hitting the body. Penske sells them in 1/8" increments, but they're made of Delrin so it's trivial to make perfect length ones on the lathe.

(4) If you design a different upper bracket for the front shock, you can remove the shock by merely removing the pin in the lower eyelet and the bolt in the upper eyelet. I don't need to remove one of the bolts in the suspension bracket, loosen the other, rotate the bracket and then remove the associated bolt that goes through the rod end like the stock configuration requires. This all works even with the hydraulic lift puck installed. With services like SendCutSend, it's simple to make these types of brackets. If you go the Penske route, I'm happy to share my bracket design.

(5) If you have remote reservoirs carefully think through the orientation or the outlet and what type of fitting. I sent my RCR supplied shocks to Penske to have the body/outlet clocked 90 degrees and I changed the hard-90-degree fitting to a banjo and everything works great now.
 

Howard Jones

Supporter
Joel. Those QA-1s look like they might just work for me. I will call them and discuss lengths and some other things that occur to me. I'll report back on what find out. I also had a look at Summit. They can source them also. I can get a pretty good discount sometimes from Summitt. All I will need is a part number.

Denton, The builder's series of JRI shocks look good also. I am going to call them and see if they can offer a 12-inch extended length/3 inch travel version. I measured my QA1 shocks and they are approx 12 inch extended. Maybe a bit longer, I measured them eye to eye centers. If the JRI's are end to end then the 13-inch shock would be the one I think.

Scott. If you replace your Penskes then I would like to discuss purchasing them, should you want to sell them. I am also working on a simple fix for the "take the shock off the front issue" More on that if I make it work. What is the extended length of your Penske's? If you have a part number for them that would help if I want to call them for other info. I assume that the fronts and rears are the same part. correct?

Thanks guys.
 
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I am in the first stage of researching shock options for my SLC track car, The original QA-1s, while functional are not suitable at the spring rates I will ultimately want to run on the car. I called QA-1 and they said that they cannot re-valve them and the model number on my car is no longer available. So now the search for a viable alternative starts. Since the Penske shocks are an upgrade option for SLCs from RCR I am wondering what model number they offer. Are they a special custom model configuration for SLC's ? Has anyone ordered a custom valving and spring package for them (track appropriate) ?

I can of course call Fran but I think I would like to do a bit of research before that. Any info would be helpful. Also, a model number would be helpful as well as full-length and compressed-length eye-to-eye center measurements. Do they use 2.5 or 2.25-diameter springs? I would like to stay with 2.5 springs as I have several and they would suit slow bumpy tracks at their lower spring rates. Then run the stiffer springs at high speed/smooth tracks

I am thinking I need R1100 lbs and F850-900 springs for the highest settings.

Anyone got any ideas ?

I second this for sure! Would love to find out part numbers and upgrade options. I've been talking with Fortune Auto, who makes 3-way adjustables for many other model vehicles. Utilized them on an rx7 time attack car, amazing quality made in Virginia. They're interested in developing a set for the SLC but I just don't have enough data yet and they need a shock to measure. If I had part numbers I could order replacement qa1s and send a front and rear from slc to them

At what spring rate did you find the limit of the qa1? I'm setting up for 800 front, 900 rear but now beginning to wonder if that's beyond the capability of these shocks.
 

Howard Jones

Supporter
The original QA-1s were these (picture below) and are not available anymore. They are the same dimensions as the current QA-1 double adjustable shock.


I think mine are the 8.625 compressed and 11.375 extended. They may be the 8.75/11.125 however. I am running mine with 750F/900R springs and at about 90% fully dampened. (1-2 clicks left to full stiff) I am also currently leaning toward the new QA-1 MOD series and ordering them with the stiffest valving range. My best guess for high-speed/high downforce/ smooth tracks like COTA is 800-850F and 1000-1200R.

For much slower tracks that are bumpy like MSR Crescent, I think 550-700F and 650-800R would work as long as you can dampen the bumps. It's not going to be wing downforce rear compression that is the limiting factor with top speeds below 120mph or so. COTA back straight speeds can easily exceed 150 mph and at the same time the rest of the track is asking for high downforce levels being smooth enough to support stiff spring rates and tight damping settings. 800R simply will not work at 150mph.

I am not an experienced race car tuner. I do have a good amateur understanding of the basics and I think reasonable experience with my car to make the above statements. The advice is free.............

 

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Joel K

Supporter
Howard,

Not sure if this info is useful, but these are the shock numbers of the QA1 double adjustable that came with my car…The DD303 are for the rear…

13FEC85F-C83F-4CDC-B614-D8DF04FE5002.jpeg
 
Awesome info! Thank you!

My friend Bryan Leonard met you or saw your slc at Cota a few months back when he was out testing new gt3rs said it was super cool!
 
Interesting, I was not aware that QA1 had come out with this shock. I wonder which size would suit a GT40


mod_shock_canister_left-450x450.jpg


mod_shock_piggyback_left-1500x1500.jpg
 

Howard Jones

Supporter
Joel, So here's what I get from those two numbers:



Looks like different lengths to me with the one you have marked rear about an inch shorter. Mine were originally about 12 years ago so this is very good current information.
 

Howard Jones

Supporter
Ryan, I have my GT40 rear shocks off the car and they are also QA-1's. All four are the same on my GTD. I'll measure them and post the results.
 
No stress @Howard Jones, i have a long way to go with my build at present. I have seen the drawings in "GT40 Uncovered" from Porter Press that show what the original shock sizes. I just have not committed the open and closed lengths to memory yet. I know where the information is and that is all I need to know at this point.

I guess the other thing worth considering is how rebuildable and customizable are they. I have a friend that has some Penske shocks that are away getting modified by Penske at the moment for his particular requirements. I am also waiting on some shock bits for one of my bikes as I am trying to alter some of the suspension characteristics. I often see Penske and Ohlins parts, shims and shock eyes listed as spares for sale. Sometimes complete tackle boxes or rebuild bits as teams move from one shock platform to another.
 
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