Since I recently discovered the SCCA Club Spec MX-5 / CSX class, I have been looking pretty hard at picking up another NC2 / NC3 Miata and building it for the class.
After reading through one of the previous GRM threads on the required Penske shocks, I saw some speculation as to the maintenance / rebuild intervals on the shocks that gave me a bit of pause. I've seen recommendations from Penske on rebuilding some of their shocks, quoting anywhere from 25 to 100 hours of track use, which would get someone like me through several seasons without a problem (likely 7+ autoX events and a couple TT events a year). However I would still want to use the car on the street (where it would primarily be used) and I couldn't find a recommended street mileage rebuild interval (I would likely only put 1500-3000 miles on them a year).
In a previous thread, I saw numbers as low as 1000 miles, which would probably scare me away from the class. If that figure turned out to be accurate, it would leave me scratching my head, wondering why these shocks were prescribed for a cheaper-entry spec class?
I've consulted my all-knowing-robot-overlord (ChatGPT), which says general recommendations are anywhere from 15,000-25,000 street miles, depending on usage.
I sent the fine folks over at Penske a message, inquiring about what kind of intervals I'm likely to see before a rebuild is necessary. Hopefully I hear back from them soon.
In the meantime, what has been the hive's experience? How many street miles would a person expect to get out of these shocks before a rebuild is necessary?
We have tested the spec Miata versions on street cars and they make a racket. The mounts are not designed for isolation. It would have been a tough sell for our customer base. Just FYI.
The rebuild interval is probably due to oil degradation. You can go longer but not if you want to run at the pointy end of a spec class.
For reference, using the SCCA guide as a reference ( https://www.scca.com/pages/club-spec-csx ), I broke down what it could cost to build one of these cars:
Basic Setup for autocross:
-Total for all specified suspension parts: $4347 (not counting tax and shipping)
-17x8 RPF1 wheels (silver) with 225/45R17 Falken Azenis 660 tires on TR (with tax and shipping): $2185
-Alignment, well, it depends, doesn't it???
Total to get started for autoX: $6532
If you want to track/do time trials as well and want to give yourself some advantages while not breaking things as often:
Brakes:
-Goodridge G-Stop Brake Line Kit (Optional): $164
-Mazda Motorsports 2.5” Brake Duct Kit (Optional): $374
-Brake fluid of your choice: ~$20
-Hawk ER-1 Endurance Racing Brake Pads (used only for reference): $363
Total brake cost: $921
Hubs:
-Mazda Motorsports Competition Rear Hubs: $760
-Rear Hub Bearings: $202
-Mazda RX-8 OEM front hubs: ~$500 (depending on where you source them- aftermarket versions are cheaper)
Total hub cost: $1462
Misc:
-Mazda Motorsport Intake System: $336
-Mazda Motorsports Oil Cooler Adaptor with Lines: $549
-Upgraded radiator (several to choose from): ~$450
-Upgraded expansion tank: ~$300
-Blackbird Fabworx NC RZ Roll Bar (Hard Dog is half the price, but some debate on SCCA legality): $1365
-Muffler of choice- pick your poison: ~$550 (or less at your local exhaust shop I suppose)
I didn't break down the cost of racing seats, harnesses, hard tops, etc. The overall cost can go up dramatically if you start going down that rabbit hole.
Total for the misc. parts you might want to include on track: $3550
Total cost for what is essentially more of a "complete" build to run time trials: $12,465
To get started in autoX, it's not terrible. To keep the car reliable/robust on track (cooling upgrades, hubs, brakes, etc), it starts to add up. I'm not sure if the muffler/intake add any real power, but they sound cool and add to the bottom line. There's a minimum weight requirement (2500 lbs w/o driver), so there's not much point in trying to save weight with super lightweight parts (carbon fiber seats, mufflers that make your ears bleed, etc). It gets pricey, but pretty much any TT build can get pricey pretty quickly.
In reply to Keith Tanner :
Thanks for the insight! Any chance you know anyone running a Spec MX-5 build in the metro area here in Colorado? I'd love to take a ride.
Would you be willing to drive one of these things on, let's say, a 4 hour ride to a further-than-normal track?
I sell and service their motorcycle shocks. They list a 15 hour service interval on those but I commonly see 40k between services on sports touring bikes. Not sure about the car shocks though
In reply to roninsoldier83 :
I don't know anyone who's running a Spec MX-5 in CO, but of course they wouldn't be talking to us because most of our parts are illegal for the class :)
We were testing the shocks as a potential addition to our product line - we had adjustable ones built. When adjusted properly, they were very comfortable for street use and with a different adjustment, quite effective on track. Very spendy, though. And we went through several upper mount designs to try to quiet them down.
Driving a race car 4 hours to the track? I'd do it no matter what the suspension :) Earplugs take care of noise. But based on our experience, I'd shy away from recommending them for a daily driver. That's based on a modified version of the NA/NB setup, remember. The original track shocks were definitely a track setup with short travel and little NVH control. The NC is less constrained for travel from the start but I'd want to see some dimensions on shock body and shaft length.
If you want to know about SCCA legality of the Hard Dog bar, ask an SCCA tech inspector. There's a lot of FUD out there without specifics. And it's the tech inspector who actually determines if you can run.
The only concern with SCCA legality of a roll bar in the NC would be for hillclimb. You can run the factory hoops or better for Time Trials so there's nothing that excludes the hard dog.
roninsoldier83 said:
I am considering building an SCCA Club Spec NC Miata using your specified Mazda Motorsports Penske shocks. I am trying to figure out how long the service intervals on the shocks are? The car will be used for autocross (likely 7-10 events a year) with the occasional 1-2 times a year time trials. As my local tracks are pretty far away the car will see mostly street miles (likely ~3000 miles a year on the street). How many street miles should I expect to see out of the shocks before they need to be rebuilt? Thank you!
So, I received a response from the folks at Penske. For reference, I'll list the question I asked them above.
The response I received:
"Sorry, but there’s no definitive answer to your question. In this case, the street miles will be more important than the track miles. I can’t really say how many street miles is too many, because so much depends on the type of roads you drive. Smooth interstates, they might be good for 50k miles. Rough city streets or backroads, it will be a lot less because there’s much more energy being put into the shocks. We tested the shocks to 100hrs when they were being developed, but that’s extreme, it’s not a recommendation."
Based on that response, it looks like the Skynet-esque-ChatGPT response is probably pretty close to the truth.
I'm sure performance will drop off to some degree within X-thousand number of miles. I'm not sure if someone as ham-fisted as myself would even notice a slight drop in performance, but it doesn't quite sound like the alarming "they need to be rebuilt every 1000 miles" claim I was concerned about.
I run the Penske Spec Miata suspension package on my 1990 Spec Miata. I definitely do not want to drive that setup on the street with the spring rates specified for the MX5 - 700f/400r. It's 700/300 for the NA and NB SM. They probably are a bit noisy too.
As far as longevity, it will depend on your track (and street) conditions. Officially, Penske says about 100 hours. Unofficially, some start leaking oil before that. I probably wouldn't go longer than 2 full seasons (16-22 ish weekends plus test days) without a rebuild based on my experience.
Take a good hard look at the parts options and decide if you intend to use the car to compete frequently or to drive on street and occasionally track or compete with the car. You can build a better street car that perform well on track cheaper - and be more comfy.
Intervals definitely vary, and it isn't just an external contamination or temperature issue. I'm not sure what the shock body materials, coatings, or bushing/band materials are, but over time, wear particles will become entrained in the oil from the action of the shock. Typically the piston band and the seal head bushing are coated with teflon or a similar anti-wear metal, which tends to embed wear particles. Over time, these surfaces become more like very fine grit sandpaper due to the embedded metals. Steel body shocks can handle some of this, but aluminum body shocks will wear through anodizing and require new shock bodies. The chrome shock shafts can have similar issues over time, and of course seals will eventually start to leak.
Your average street shocks are built with materials that offer inferior performance in a tradeoff for more stable performance over a longer life and with the expectation that they'll be thrown away and replaced after 50k miles.
dps214
SuperDork
12/10/24 4:46 p.m.
Just for reference, 3000 miles at 60mph average is 50 hours. So even a 100 hr rebuild interval with 3000 street miles per year would mean a 1.5-2 year rebuild interval.
