Quote:
Originally Posted by ZDan
That is cool! But still, -24 lb. or -32 lb. just isn't going to make any difference as far as seat-of-pants feel, and barely any difference in measured acceleration or lap times.
It will affect mpg a lot more than acceleration or lap time performance. Even there the difference will be quite small.
I modded the performance analysis spreadsheet I had made for my FD's Texas Mile run to simulate my stock-drivetrain '17 BRZ. I looked at what the elapsed time and max speed would be after a straight at full throttle after exiting 60mph and 80mph turns:
cD = 0.31: 60mph + 1500ft = 11.97 seconds @ 104.1mph
cD = 0.28: 60mph + 1500ft = 11.95 seconds @ 104.8 mph
10% lower cD => 0.02seconds quicker
cD = 0.31: 80mph + 2300ft = 15.26 seconds @ 120.1 mph
cD = 0.28: 80mph + 2300ft = 15.17 seconds @ 121.2 mph
10% lower cD => 0.09seconds quicker
Optimistically you *might* see as much as a 0.25 second lap time reduction at a faster track like Watkins Glen from a 10% reduction in drag coefficient.
Decreasing lift/increasing downforce will influence laptimes much more so than drag coefficient.
For 60mph - 120 mph times for 17+ BRZ, I get:
cD 0.31 60-120 = 19.50 seconds
cD 0.28 60-120 = 18.74 seconds
10% lower drag = 0.76 seconds or 0.4% quicker 60-120 mph.
Background: I did performance analysis at an electric vehicle startup in the 2000s/early 2010s. Developed spreadsheet for 500hp FD that predicted its standing mile performance within 10mph, predicted = 184.2mph, actual = 184.8mph
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-25lbs for rear seat delete will make no noticeable difference, but its a small piece to the puzzle. cost roughly 40$ to drop 25lbs and substantially reduce noise. trunk junk -30lbs for free. Shorai battery was kind of pricy about 300$ for -24lbs for the largest one + custom diy mount. Take out rear floor mats and user manual. round it to 85lbs for 340$. header back removed another 16lbs also added a lot of HP. Also probably a waste of money admittedly but cf driveshaft another -12lbs. 113lbs total. Assuming at least 230crank hp from headerback+tune. stock 2815lbs / 230hp = 12.24lbs per hp. 2815lbs - 113lbs / 230hp = 11.75lbs per hp which is equal to 239.6hp from new power to weight ratio, or about 10 hp for 120lbs weight reduction (almost a passenger) and that will be noticeable.
I did all the equations but don't have them written down or feel like doing them again... but what was the drag forces in lbs going from .29 (stock 86) to .27 (jdms advertised new cd with spoiler + underpanels) at 100mph? i remember it being well over 100lbs which again 120lbs = 10hp on this platform with a few NA power mods.
Also conservatively trans tunnel covers + rear diff covers + rear diffuser + front wheel deflectors should be at least another .01, if the jdm spoiler+underpanels can reduce by .02 those combined should do at least as much.
not saying all this is necessarily a good bang for buck ratio, or that aero is a starting spot. but if trying to stay NA, worrying about warranty, and or wanting to push every ounce of performance out of this platform. Aero and weight reduction do add up and make a noticeable difference.