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What's the thickness of the uprights?
My eyechrometer says 1/4" and if this is indeed the thickness I'd be genuinely concerned, it's not a lot of material.
Big downforce numbers at high speeds plus side loads when cornering, add a bump and you might exceed the ability of those uprights to handle the load.
Car looks good, looking forward to see how it does @ SLB!
My god. You are doing beautiful things. Whats wet weight with all the aero additions looking like?
Parked, about 2400 lbs w/ driver.
At 140mph, around 4000 lbs I'm guessing. That is based on the pyrometer readings and pressures we saw at VIR with a lot less aero.
Not bad for what is basically a full tubbed endurance car with over zealous cooling. Not a partially tubbed, full carbon body time attack special designed to almost hold together for one lap.
Non boosted brakes
M/C sizes F 1.00", R .875", Tilton pedals. Took one big adjustment on bias bar to get balance right. Not having a booster and also having aceel map dialed meant I no longer needed to fan the clutch for downshifts.
This meant full two pedal driving. So left foot braking once rolling. Gotta tell ya, it's f'ing fantastic. So easy to threshold brake and either feed in maintenance or spooling throttle early, while blipping for downshifts when and where you fancy.
No fear of downshifting and upsetting the car. Also, as before, upshifting exiting turns without worrying about a money shift from the lever moving around. SOW CCW has a long, steeply banked increasing radius exit that leads onto a short but important straight. Banging two shifts while WOT and max G cornering. Crack, Whooosh, Crack, WHOOOOSH. Sublime.
Pedal effort is typical unboosted. Meaning initial response isn't touchy, but lower torque. The difference is now you get a steady and linear increase in brake torque with pressure, not travel. Some Porsches are like this. Pedal doesn't sink as you apply pressure. Initial drop of maybe 1/2" then it stops.
Can't promise whatever pedals you try will deliver the same feel but thos M/C sizes are apparently the correct ratio. I modeled the ratio on OEM bias valve and caliper piston areas. Overall, modulation is vastly improved now. And it wasn't bad with the booster.
Suspension
Springs were a bit too stiff for SOW, which is a low-ish speed track and really bumpy. BRP (Buttonwillow) is also lumpy but not nearly as rough as SOW. BRP is also much faster min speeds on average. We were working through a list of things and I sorta spaced on shock settings. Ran too soft so it heaved on a few of the rumply sections. 1800/900 rates should be spot on for SLB and fresh tires. We ran 1400/700 at VIR which felt really good on 245's. Now with significantly more aero and 275's, we know we will need a bit more spring. I took the big jump in hopes of maintaining a better aero platform. Big roll or pitch changes play havoc with AOA of flat bottom, splitter and wing. If the springs are too stiff, we have a set of 1600/800 on standby as well as the 1400/700 we had in it at UTCC.
Power
The power. Jeebus. It was fast before but the boost hits sooner and doesn't dip with the TPS malfunction we had before. It seems to have a boost leak right around 24 psi. We briefly saw 32psi on the dyno yesterday but it blew the spark out. Regapped from .043 down to .032 fixed the spark blowout. The used OEM D585 coils unfortunately lived through a period running about .4ms too much dwell and some spurious voltage spikes around 18v. The new AC Delco coils were worse so we switched back to the used ones. Ordered some MSD 8286 PnP coils overnight. After Super lap we'll switch to AMP EFI coils.
We saw a brief spike of 412tq at 3940rpm when it hit 32psi before it blew the spark out and I aborted the run. Extrapolating that incomplete graph, it's clear that it would have topped out around 420tq and 440~450whp. We were never able to get the boost to stay there. Instead fluctuating between 22 and 26psi. So we turn the boost D/C down a touch to keep it steady around 24psi where it makes ~415-420whp. We also pulled some timing out, down to around 18.5° on top IIRC.
Tires
Tires were a bit rooted but we wanted to save our freshies for SLB. Just getting some run time to see how the heat was being managed. Trans stayed around 170° max, lower as soon as I backed off. Oil temps barely 220° when hammering on it. Coolant never went above 202° as far as I could tell.
Melted some of the coroplast substrate in the flat bottom. Distorted the thing a bit but nothing major. Everything else seemed happy.
Aero
When we first mounted the aero kit, I drove around the skid pad for a bit, gradually building speed. Checking to make sure the tips of the splitter didn't drag and the flat bottom didn't uh, catch fire. Didn't and didn't (woot). Doing a big circle at around 70mph I could feel significant downforce already. Weird feeling. Like you suddenly received way better tires. We ran the big **** at min AOA. Balance between low speed mechanical grip and higher speed aero grip seemed about right. Light mid corner push at really low speeds that could be reduced with a little lift or annihilated with a brush of the loud pedal.
Corner exits nice and neutral-ey tight. Car became more planted and a bit tighter at speed. Again hard to really dial in because SOW only has one fast turn and it's just a kink with non existent - car totaling runoff. So I lifted each time through T1 though the car would clearly do it flat without breaking a sweat. I thought "now is not the time to test and maybe find the limit of traction in this turn".
Other stuff
Really like the OMP HTE-R400 seat. MXG dash is sweet. Have it configured with full data dweeb display style. I think nine little fields with data from the MS via CANbus. Plus the graph style tach like and S2000 and pretty shift lights.
A few things left to button up and we're off to BRP for Superlap tomorrow.
Lovely write up and keen to see more.
Is it a requirement to run windowless? Not ideal for aero I would assume.
Have you heard of anyone else running spring rates at that level on a miata before? It is a difficult game when aero is added to the mix
I have heard suggestions on theories around WTAC class cars running lower rates to provide compliance and mechanical grip for the low speed corners and then essentially letting the areo sit the cars on the compressed springs & bump stops acting as the spring at anything higher speed where the aero comes into play.
This thing is quite similar to my car, except everything turned up another notch... and a working engine.
Also, some cars at WTAC are actually using smaller diameter "bump springs" that suddenly increases spring rate a ton when the car gets going fast enough to fully compress the main spring.
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