[ZDan]

Originally Posted by 86TOYO2k17

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.

You have to include driver weight! Totally stock power/weight with half a tank of fuel is ~14.2:1 with 165 lb. driver. Lose 120 lb. and it's 13.6 lb/hp. 4% - 5% difference.
I have trouble detecting 10% at seat-of-pants, but for sure a stopwatch would notice 5% given a consistent driver and conditions.

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.

Drag = 1/2 rho v^2 cD A. In awkward 'murican units, drag at 100mph in lb = 1/2 * (0.00237 sl/ft^3) * (146.7 ft/s)^2 * 0.29 * 20ft^2
0.29 cD, 20 ft^2 frontal area, aero drag at 100mph is 147.9 lb.
For 0.27 cD, 137.7 lb.
10.2 lb. difference in aero drag.
The horsepower freed up by reducing drag by 10.2 lb. at 100mph (146.7 ft/s) is:
hp = (10.2 lb)*(146.7 ft/s) / [(550 ft-lb/s) / hp] = 2.72 hp
Around +1.6% vs. rwhp available.

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.

Maybe, maybe not... IMO there really isn't a lot of "low-hanging fruit" to reduce aero drag on a car that's already very slippery from the factory. Pretty much all that's easy to get has been got...

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.

Weight reduction maybe, aero drag reduction, I still don't think you're going to find anything meaningful there.

I do appreciate the idea of doing a little here, little there, *everywhere* to get a cumulative benefit! But for me, due to laziness and being right at the weight limit for my class anyway, I just drive the car to the track and run it, pretty much... My only mods are lowering springs and camber plates and tires, but those mods are worth *seconds* per lap! Hard to get enthusiastic about spending more time and $$$ for *maybe* a tenth or two...
If I had a lot more time and tools and garage and storage space (and skill), I'd be a lot more interested in doing mods for small benefits, or even just for the f of it!