NASA ST4/TT4 Build
12-05-2017, 12:46 PM
#76
Registered
See, I looked at the ST5 rules and got worried immediately. I've never done a dyno test on my car, but looking up stock figures and assuming a 2900lb race weight I couldn't get the calculator anywhere near 14:1 lb:hp.
12-05-2017, 02:17 PM
#77
Hmmm, something's missing. Quick review:
- HP used in the calculation is not crank HP, but RWHP - so that's about 85% of advertised crank hp from stock figures
- Max RWHP can be used, but the rules allow for AVE RWHP over a large RPM range
If the car alone is 2900 lbs, add another 180-200 lbs and it's well under the figure for the class - which is good since you're going to need to make up 0.7 points off of the ratio due to the A-arm deduction. For example, if your comp. weight is 2900 lbs, then your 14.5 would be 13.8 due to the A-arm hit. Thus, you'd break out of the class - unless you used the OEM aero allowance and recouped 0.4 points, bringing you back into the class at 14.2:1. Those modifier points are how they try to equalize the cars now.
However, that's all using MAX RWHP...in reality, a Renesis rotary peaking at 200 RWHP is likely averaging something closer to 195 RWHP over the specified range. So...comp weight of 2900 lbs is 14.87, easily soaking up the 0.7 hit and landing safely at 14.17 even without the OEM aero bonus. That means you can run a rear wing of your choice...and trim some additional fat...
Last edited by R(ace)X-8; 12-05-2017 at 02:19 PM. Reason: math...
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hufflepuff (12-12-2017)
12-05-2017, 03:29 PM
#78
Registered
I was going with RWHP, and using a conservative figure of 180ish.
2900 pounds is my assumed race weight, all in, with me in the car.
Maybe I need somebody smarter than I am to use that calculator for me. :P
2900 pounds is my assumed race weight, all in, with me in the car.
Maybe I need somebody smarter than I am to use that calculator for me. :P
12-12-2017, 06:04 AM
#79
Registered
Yes, I agree – the RX-8 is a much better fit for the new ST5 class. I was going to open a new thread for this car’s (now) ST5 build. I had a couple of things to wrap up for the ST4 build (mostly cosmetic stuff), but I knew I was going to be under-powered. So that was about all I needed to switch directions once the rules came out.
Unfortunately, due to the rather harsh penalties imposed on aero, I’m going to have to lose the front splitter. You take a huge points hit for it – and that’s on top of the built-in points hit you take for a non-OEM rear wing and the ridiculously harsh hit taken for an upper A-arm style suspension. Added up, I’m “overpowered” and/or “underweight” with the resulting adjusted weight-to-power. So something has to go, and I can’t undo the upper A-arm architecture…
The plan is to keep the rear wing, add a bit of ballast (mostly w/a passenger seat, something I’ve wanted anyway for track days), and take advantage of the front air dam allowance. The current splitter frame can stay, since they allow a flat tray forward of the wheel centerline. The only thing that will come off is the front blade (the support struts can be strapped to the bumper and tucked under the fascia). For track days I can easily put the blade back on and run it, so not as much fabrication lost as it seems. The new front air dam will bolt in the same place as the splitter blade, but it’ll extend up to the leading edge of the fascia – much like the typical Miata practice seen when they use the same rules allowance.
I’m hoping the RX-8 will be competitive. Some of the sample adjusted calcs in the new rule set surprised me. I expected to face the Miatas, E36 M3s, and stock-ish S2000s, but looks like I could also face early Porsche Boxters. The real flexibility of the class was on display with their example of a built-up 2009 Hyundai Elantra w/motor swap, aftermarket brakes, etc. Should be an interesting class if folks come out to play. =)
Unfortunately, due to the rather harsh penalties imposed on aero, I’m going to have to lose the front splitter. You take a huge points hit for it – and that’s on top of the built-in points hit you take for a non-OEM rear wing and the ridiculously harsh hit taken for an upper A-arm style suspension. Added up, I’m “overpowered” and/or “underweight” with the resulting adjusted weight-to-power. So something has to go, and I can’t undo the upper A-arm architecture…
The plan is to keep the rear wing, add a bit of ballast (mostly w/a passenger seat, something I’ve wanted anyway for track days), and take advantage of the front air dam allowance. The current splitter frame can stay, since they allow a flat tray forward of the wheel centerline. The only thing that will come off is the front blade (the support struts can be strapped to the bumper and tucked under the fascia). For track days I can easily put the blade back on and run it, so not as much fabrication lost as it seems. The new front air dam will bolt in the same place as the splitter blade, but it’ll extend up to the leading edge of the fascia – much like the typical Miata practice seen when they use the same rules allowance.
I’m hoping the RX-8 will be competitive. Some of the sample adjusted calcs in the new rule set surprised me. I expected to face the Miatas, E36 M3s, and stock-ish S2000s, but looks like I could also face early Porsche Boxters. The real flexibility of the class was on display with their example of a built-up 2009 Hyundai Elantra w/motor swap, aftermarket brakes, etc. Should be an interesting class if folks come out to play. =)
Agreed! I just created a ST5 / TT5 thread for all of us to discuss plans, share advice. It is by no means meant to prevent you from opening your own dedicated, detailed build thread. Hope to have you there!