JRZ RS Pro and Thoughts on STU

I was happily minding my own business earlier this week when I got sent a deal I simply couldn't pass up. It was for a set of used JRZ RS Pros from a 987 Cayman race car with 600lb/700lb Hypercoil springs that have only seen about 3000 miles of track miles since they were last rebuilt. Now, I know what you're thinking. "You said you were committed to B-Street for 2019". Well for starters, buying these doesn't mean I'm installing them right away. They were a good deal no matter what and I plan on sending them off to ANZE Suspension over the winter to have them dynoed and rebuilt as well as add quick disconnects for the external reservoirs. Whether or not I install them on Kay or some future Cayman or flip them, will be decided after winter.

JRZ RS Pro for the 987 Cayman - 10-10-2018

The obvious conclusion some might jump to here is that I'm taking Kay to run in STU instead of B-Street and that would be logical. I've certainly considered it but at this very moment, I have no plans for it in 2019. However, I'm not one to not do my homework to consider all possibilities. I've been spending some time thinking about what STU would look like for a Cayman. In general, I think that allowance for mid-engine rear wheel drive cars to finally go up to 265 width tires makes this a viable choice. Sure you lose out on not having 285s which you can run in B-Street but with better suspension, ability to add lots of camber, plenty of top speed in 2nd and add a bit more power and cut weight then it could be a formidable weapon.

JRZs installed in previous owner's race car

My main concern is that Kay might not be right for STU. Both the 987.1 and the 987.2 Cayman S are allowed in STU and given the same level of prep, the 987.2 (2009-2012) simply has more power. It's not a ton more power but certainly more. It also has arguably a better engine. However, with premium the 987.2 commands over the 987.1, I'm not sure how many people would actually build a 987.2 for STU. It's some serious coin and I can see a full tilt build knocking on the doors of higher mileage GT4 money. At that level of cash, I'd rather have the GT4 and run in Super Street.

Furthermore, Kay is equipped with PASM which is the ideal spec for B-Street and switching to STU and slapping on the JRZs means disabling PASM, completely negating the reason why I paid more for Kay to make sure she had both Sports Chrono and PASM to begin with. Also, with the ND2 in a TBD state of classing for Street Touring, I'd be hesitant to start STU prep only to have it classed in STU later. In autocross, lightness is king and I do believe that the ND2 in ST trim could pose a serious threat to the general higher horsepower but much heavier cars that are already in STU.

Those concerns aside, here are my notes on what I think a decently competitive STU 987 Cayman build would look like for me:

Wheels and Tires

You can go a lot of ways here but for me, I don't see a problem just continuing with XRR spec 18x8.5 and 18x10 wheels I run in B-Street. I don't think 265 square is the right choice. I think the car does like a bit of a stagger so I'd probably run 255/265. This would make the fronts less pinched and feel less squishy as result. I'm only running 265s up front now in BS to balance out the 285s in the rear otherwise, I'd much prefer a 255.

Suspension

I think the stock shocks even with PASM isn't going to be enough. It'll be ok for an "STU Lite" build but will likely still be too soft for grippier surfaces like concrete. You'd also probably want to lower the car a little to get a lower center of gravity and get more negative camber. Obviously, I already got JRZs so I'd run those. The 600/700 rate springs on them now are probably fine too. If it's a fully dedicated max prep configuration optimized for Nationals, I can see wanting more spring rate but I don't think you need to get too stiff to be competitive. It can work, you just have to turn the wheel earlier. Getting good damping is key and the valving and figuring out where the compression and rebound need to be is going to be critical.

I'd keep the Tarrett Engineering GT3 front sway bar and drop links in the front and complement it with the Tarrett GT3 rear sway bar and drop links to be able to fine tune the balance more. I'd also add GT3 lower control arm in the front only as there's adequate rear negative camber but the front needs -4 or more to compensate for the strut suspension and losing camber under compression.

Engine

There's really not a lot more power you can extract from the M97 in NA form and be STU legal. Obviously, sports headers with 200 cell catalytic converters and a "cat-back" exhaust that eliminates the secondary cats is the way to go. A good air filter and a tune to maximize the power would be a good idea too. It should be possible to get the power up to 300hp to the wheels. 

My engine and trans mounts are also 11 years old now and I don't have a high degree of confidence in the state of the rubber in these mounts at this age even with the relatively low miles. The engine is only held down by a single motor mount up front and two trans mounts on each side. I wouldn't go overly stiff here as I've read you can increase vibration to the point where the knock sensor gets triggered retarding power. Personally, I'd probably just go with Rennline HD engine mount and Function First transmission mounts (V2). 

I'd also strongly consider adding in a higher capacity and baffled oil pan. I don't think this is a must but considering how finicky this engine is, it wouldn't be a bad idea given the allowance for some added peace of mind.

Differential

I honestly don't know how much a good differential is worth on a Cayman STU build. With Sports Chrono engaged during my runs, I never once felt I couldn't put the power down or I was spinning tires. I'm reserving comment on this for now but I don't believe it's a must-have item. If I did change it, something clutch type would obviously be my choice but I don't see any evidence in few times I've taken Kay to autocross so far where I felt I couldn't put the power down because of the diff.

Miscellaneous

You can probably save some weight by changing the seats to racing seats. I also think I'd install the Numeric Racing short shifter for a more bolt rifle action like shift engagement for more accurate quick shifts.

Final Thoughts

I've never driven or set up an STU prepped Cayman S before so what I've written above are just my thoughts on this matter. It could very well be a load of rubbish. Am I tempted to do it for the learning experience? Sure! Is it the right thing to do for 2019? That I'm not so sure about.