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Today (after replacing the motor mounts in my better half's Miata), I got some time to put the car in the air and do some research... It turns out that whatever brand top hats these are on the front fit without an issue! HUZZAH!
I don't have my ball joint separator here so I didn't get a chance to get the rears all apart. I can't wait to have the shorter Penske's in and not have to disassemble half the suspension just to get a strut assembly out. I'll tackle that later this week and see what all will have to be modified back there.
On that note, would anyone be willing to throw out their ride height measurements so I can figure out what spring lengths to get (and figure out if the RX8 or NC rear top hat will be a better solution)? Preferably wheel arch to hub, or something similar.
After a conversation with Mazda Motorsports and some emailing back and forth it appears the front top hats I have are in fact the ones that were standard on the NC chassis MX5 Cup Cars. Still waiting on word if the bearings are available from anyone (they are a weird shouldered setup that appears to have a machined and pressed in sleeve to interface with the spring perch). The bearings are not completely shot yet so worst case I can run them for the time being.
Second up, I got the rear in the car as well, so I have been playing with one whole side of the car with the Penskes to see what I'm working with. I did plenty of test fitting, measuring, what-if'ing and so far I haven't found a case where things don't work. The aluminum Miata rear top hats fit correctly with the shock length I have, so the decision of modifying the RX8 steel ones with the extra bracket vs. just running the Miata ones is still bouncing around in my head. If I modify the RX8 ones then I can switch to a spherical bearing for the shock shaft, but after spending an evening under the car I am convinced the odd spring perch location and the VERY non-coaxial nature caused by it is a bigger issue than side loading the shaft due to a pillow ball setup. Has anyone thought about making an upper mount that will allow proper spring/shock location?
From my measuring, I determined some limits as well as what I think the static numbers are going to be for suspension travel. I'd love to get some feedback on what others have seen to make sure I'm in the ballpark before ordering piles of parts.
Front Rear
Full Droop: 17" 16.75"
Full Comp: 11" 11.75"
Ride Height: 14" 14.5"
Spring Length: 8" 7"
Bump Stop: 2" 2.5"
This was measured with the 285/30R18 R1S's on 18x10 +38 RPF1s, full compression was where it started to scrub something important (the fronts could not be turned at that much compression though). I'm just trying to make sure I'm in the ballpark on spring lengths and all, as far as perch interference and adjustability goes on the front.
Here's some photos of the process. It feels good to finally get these shocks off the shelf!
We chatted a bit on facebook, but I would recommend a little lower static ride height, a little stiffer springs (up front at least), stiffer front bar (not stock at least), and adding tenders to the rear so you can get the ride height you want and they don't dangle free at droop. Oh, and some magic shock valving to top it off
Also, not sure you can change the top hat in a way that would fix the weird geometry, at least not legally. I don't think we are allowed to change the motion ratio in SP.
Also, we don't run bump stops, but our Penskes can bottom safely according to Anze (not sure if that's all Penskes so maybe double check). We also don't bottom them based on our spring rates though.
The only real way to get around the dumb spring perch issue on the rear is to run the dampers inverted, but you'd probably have to modify your dampers quite a bit to get that to work. I think some people had shock bodies rubbing on stuff in that configuration too, but it looks like your spring perch adapters cup the spring on the outside, so that helps.
We chatted a bit on facebook, but I would recommend a little lower static ride height, a little stiffer springs (up front at least), stiffer front bar (not stock at least), and adding tenders to the rear so you can get the ride height you want and they don't dangle free at droop. Oh, and some magic shock valving to top it off
Also, not sure you can change the top hat in a way that would fix the weird geometry, at least not legally. I don't think we are allowed to change the motion ratio in SP.
Also, we don't run bump stops, but our Penskes can bottom safely according to Anze (not sure if that's all Penskes so maybe double check). We also don't bottom them based on our spring rates though.
How much stiffer on the spring rates are you talking? 50lbs? 200lbs?
With these shocks the tire contacts things before the shock is bottoming out, so I think bumpstops would be a good idea (although I doubt I'd ever touch them with the higher spring rates).
Originally Posted by Kennetht638
The only real way to get around the dumb spring perch issue on the rear is to run the dampers inverted, but you'd probably have to modify your dampers quite a bit to get that to work. I think some people had shock bodies rubbing on stuff in that configuration too, but it looks like your spring perch adapters cup the spring on the outside, so that helps.
I didn't even think about flipping them. I think I'll just run the Miata tophats for now and see what happens. If I run out of other things to mess with I may come up with a plan to improve that part.
Just realized I forgot to ever post video from the Finger Lakes Tour! It was an awesome race. The car was great, and I ended up less than 2 tenths back from Strano running JV's car, which put us both 1-2 overall on index for the entire weekend. It was pretty funny seeing so many black RX8's lined up in grid!
Got the correct springs in, went for a test drive to check for rubbing and such... and this happens! Never seen that happen with a shock before.
Since that one literally fell apart on me I went ahead and disassembled it completely to try and figure out what the deal was, seems it was assembled incorrectly in the past by someone. With that knowledge I don't feel comfortable running any of these shocks as is, parts and tools are en route to rebuild the full set!
In the image above, if you've ever been inside a Penske before, you should notice one part that is VERY incorrect. The ring nut has been replaced with a few more clamp shims and a nylon lock nut from Home Depot Racing Dept. The one that came apart actually had the correct ring nut, this is out of the other rear shock which makes me feel even better in my decision to rebuild the full set before trying to autocross on any of it. Another fun finding was that both rear shocks had vastly different valving in them, so I guess I'm going to grab shims to run a middle of the road setup in it as a baseline for the time being until a shock dyno happens and I can start playing with it for real.
I'm really not sure what the point of this post is other than an update, and a warning, about buying used shocks. Hopefully doubling down on the tools and setup to rebuild/revalve will pay dividends down the road. If anyone else is interested in some experimenting, I'm sure we can work something out. *wink wink*
Plan is still to go do a shake down event on the 22nd in the car, have a stack of A7s ready to go on but holding off until I find the bottom of the money pit on the suspension side of things. Fingers crossed.
Yep! It was set up with linear/linear valving, and not even close to matching left-to-right. I’m guessing the set was pieced together off of multiple cars. The nylon lock but takes the cake though. Hopefully the fronts aren’t as hacked together.
EDIT: I just got offered a set of VDPs for these shocks for free. Is anyone running them and have any feedback? I'm having trouble finding any relevant data on why you would want a progressive curve at very-high speeds.
Last edited by roflcopter; 07-10-2018 at 11:02 AM.
So I'm looking to change out my diff bushings. Mine are feeling pretty worn - not broken yet, but I already have replacements.
Anyone figure out, know, or have a good idea of a way to remove the diff bracket without removing axles or the drive shaft?
I don't think so... maybe do them at the same time as you change gearing so you're dropping the diff anyway?
Also, if you're trying to fix wheel hop, we noticed the biggest change from going to solid subframe bushings (we've had solid diff mounts all season). It's not THAT worse of a job when you're already dropping the diff and everything. Basically no additional NVH either.
I guess this is a perfect example of the danger of "well, while we're at it..." LOL
EDIT: I just got offered a set of VDPs for these shocks for free. Is anyone running them and have any feedback? I'm having trouble finding any relevant data on why you would want a progressive curve at very-high speeds.
Interesting. Looks like a pretty good piston. My guess is that Penske couldn't make it perfectly digressive out to infinity and meet the other design goals, so they specify that piston for "smooth, flat surfaces".
For autocross, it's probably not a big deal. I've heard most (nearly all) shock velocities in autocross is below 7 in/s, but I don't have data to back that up.
Another thought is that the progressive ramp helps to keep the car from blowing through suspension travel when a big bump or dip comes along.
Given that the double digressive pistons are just not that expensive, I'd skip the VDPs and go with the double digressive. I don't have shock pot data but the sharp pavement transitions at Lincoln don't seem like they would agree with a lot of high speed compression damping.
Interesting. Looks like a pretty good piston. My guess is that Penske couldn't make it perfectly digressive out to infinity and meet the other design goals, so they specify that piston for "smooth, flat surfaces".
For autocross, it's probably not a big deal. I've heard most (nearly all) shock velocities in autocross is below 7 in/s, but I don't have data to back that up.
Another thought is that the progressive ramp helps to keep the car from blowing through suspension travel when a big bump or dip comes along.
I've been talking to a Penske guy off and on over the last day and he said that the VDPs are great because you can really valve them for whatever you want them to do, either having a bleed-prone very stiff linear stack with a more usual digressive stack on top to simulate a purely digressive piston, or basically the opposite to make it linear. We went back and forth a bit and came up with a plan to run a pre-loaded digressive stack on the linear piston with some bleed shims (not brave enough to drill the pistons until I know it'll work) that should give me a decently digressive curve on compression side and a purely linear rebound setup. This is based off of an NC Miata that is set up similarly to what I am.
His opinion was that the VDPs are too hard to get dialed in without dyno data and suspension data and that I should use the linear pistons as a baseline for the time being. You're correct about blowing through the travel though, it seems like a lot of rally cars use highly progressive damping in the range that would be a jump landing to be able to run softer spring rates without nailing the stops too hard.
Originally Posted by John V
Given that the double digressive pistons are just not that expensive, I'd skip the VDPs and go with the double digressive. I don't have shock pot data but the sharp pavement transitions at Lincoln don't seem like they would agree with a lot of high speed compression damping.
What's your definition of not that expensive? The VDPs are free, which is cool. But for the time being I will play with the linear stuff and figure out my ballpark damping rates before diving into any fancy curves. Most places I run locally are quite smooth so I don't think it will be a problem... yet.
As an aside, I think it is interesting that there is very little talk around the internet of sports car shock tuning by end users. In the offroad and motorcycle world it is commonplace for people to do their own valving and modification, while it seems to have a voodoo magic stigma for sports cars. Like I've said before I am more than willing to share any findings I have in the open as things develop, hopefully lots of learning can take place.
What's your definition of not that expensive? The VDPs are free, which is cool. But for the time being I will play with the linear stuff and figure out my ballpark damping rates before diving into any fancy curves. Most places I run locally are quite smooth so I don't think it will be a problem... yet.
As an aside, I think it is interesting that there is very little talk around the internet of sports car shock tuning by end users. In the offroad and motorcycle world it is commonplace for people to do their own valving and modification, while it seems to have a voodoo magic stigma for sports cars. Like I've said before I am more than willing to share any findings I have in the open as things develop, hopefully lots of learning can take place.
Penske lists the double digressive pistons for $140/ea. I'm sure you can get them cheaper if you work with one of the usual damper rebuild companies...?
There are people in the SCCA Autocross community who do their own valving / rebuild, particularly with Penskes since the parts are common, available and not that expensive. There are a few folks who bring their equipment to Nats to make changes. I think that's a little nuts but I guess it's a hobby for them. I think in general people are hesitant to share their secrets.
I would never want a linear (and certainly not a progressive) valved damper for autocross. And I also tend to think that a lot of the cars I drive with aftermarket shocks have way too much compression damping dialed into them. But I am far from a damper or setup expert.
I think most of us are hesitant to let someone without much experience play with our dampers because they're so critical to how the car performs, but I can can only speak for myself. Good luck and let us know what you learn. Sounds like a fun endeavor.
I also think part of the hesitation is that seat time on a motorcycle/off road application is much easier to come by since you don't really have to wait for a race day with ~60 seconds to run.
You sort of have a bit more freedom to test and tune your setup and really feel it out. Also, cheap.
First event on the Penskes was yesterday, a friend of mine co-drove to put more time on the car and get more feedback on suspension things. The site we were using is one that an autocross has never been run at before, the course was a relatively fast and simple one as far as elements go, but had multiple pavement changes, crests, off camber corner exits, bumps, etc. It was quite fun and a good shake down for the car, definitely harder than it has been beat on anywhere else recently.
The car was very neutral and well behaved, slightly pushy when over-driven but nothing impossible to deal with. The plan is to drop back to the softer setting on the front bar for the next event and see if we can sort that out. I am surprised at how consistent and resilient the suspension is now. As I said before, the course was a lot more challenging on that front than typical, there was actually one crest at the middle of a right hander we were hitting flat out and managing to get the car nearly completely airborne... but it would land on rails and we never had to back off. I pushed too hard through a left hand tightening sweeper and managed to get the car loose once, but it maintained composure and held the slide perfectly. I'm pretty stoked on it for now.
My friend ran faster than me, but he has been consistently competing and I have not. The other DSP car from our area (Romesh and Mark Canekeratne with a BMW 330Ci) was well within reach, I was a few hundredths behind, with my friend a few tenths ahead, of them. I'll try to get some video at the next event, we were quite busy trying to get as much tire data as we could and keeping the car cool (I had a radiator fan fail Friday morning...).
Last edited by roflcopter; 07-23-2018 at 03:02 PM.
I figured I'd introduce myself here instead of the main forum as an Autocrosser. My name is Tj from Las Vegas. I recently bought an 04 RX-8 from a fellow racer. The car is currently setup for STX but me and my co-driver will be slowly building it up for DSP. It will be a slow build during the 2019 season as we continue to campaign our STX FR-S.
The RX-8 is on a freshly revalved AST 5200 DAs with 800/650 springs
Agency Power Front bar
RB Header, BHR midpipe and HKS exhaust
Madzamaniacs 91octane tune via cobb and many parts to max out in STX except for the stock diff.
Pic of RX-8
PIc of FR-S
Regards,
Tj
P.S. If I find time can I bug some of you about setup at Lincoln?
Welcome TJ! Sounds like you have a great starting point to jump into DSP with. Just add some wider wheels and tires, tweak the set up a little for any handling differences from the added grip (you're pretty stiff already), and maybe add some aero and the diff you already mentioned. You'll be at a pretty competitive point if you do those few things. Looking forward to meeting you at nationals!
New look for "Riley" before we head out to nationals. Tested a few more changes today and the car felt the best she ever has, so we are getting excited! Fingers crossed that all goes well at the most important event of the season. DSP runs last heat Thurs/Fri, so we will be closing down the week long party
Congrats on a good Solo Nats day 1. Hope day 2 will be just as good for you all.
Hello and greetings, I'm really excited to start my own DSP journey. I've picked up a Renesis from a pick-a-part to tear down and rebuild and I'm ever on the lookout for an RX-8 of my own. I race in the Utah region but hopefully can pull some national events as well as some Vegas concrete next season. I'm looking forward to getting more hands on over the winter.
06-17-2018, 08:06 PM
