[Anthony]

Thanks everybody who's contributed information. If you would like to add information, please link your source of information, or better yet: post a photo of the part on a scale like in the official weight thread. If you don't give me a source, I will use your post as the source. We're thorough around here!

I've also decided to color code parts by diameter. Matching colors = less turbulence = minimized loss of horsepower
2.118"/53.8mm, 2.25"/57.15mm 2.36"/60mm, 2.38"/60.5mm, 2.5"/63.5mm, 2.76"/70.1mm, 3.15"/80mm Unknown

***Note that some measurements may be inner diameter, and some may be outer diameter. Check your sources if diameter is a concern to you, which it should be if you want hp/tq gains***

Headers:
30.00lbs - FA20Club (Source)
21.10lbs - Greddy Catted (Source)
20.90lbs - Stock (Source)
16.30lbs - Greddy Catless (Source)
14.00lbs - Hotpipes Forceworks UEL Header (Source)
13.89lbs - 1320 UEL (Source)
13.65lbs - HKS EL (Source)
13.00lbs - JDL (Source)
12.65lbs - T1R (Source)
12.00lbs - Rev Works (Source)
10.90lbs - Nameless Stepped 1.500-1.625 Catted (Source)
10.20lbs - Borla UEL (Source)

Over Pipes:
11.4lbs - Nameless Over/Front Pipe Combo catted resonated (Source)
6.70lbs - Borla Cat Delete Pipes (Front & Over combo) (Source)
4.50lbs - Stock (Source)
3.50lbs - Milltek Sport (Source)
3.50lbs - Perrin (Source)
3.13lbs - 1320 (Source)
3.00lbs - PLM Overpipe (Source)
2.94lbs - Avo Turbo World ceramic coated (Source)

Front Pipes:
12.2lbs - Stock (Source)
11.4lbs - Nameless Over/Front Pipe Combo catted resonated (Source)
09.0lbs - Avo Turbo World catted (Source)
07.8lbs - Tsudo (Source)
07.2lbs - Invidia catless resonated (Source) (Diameter)
07.0lbs - PLM with high flow cat (Source)
06.7lbs - Borla Cat Delete Pipes (Front & Over combo) (Source)
05.2lbs - T1R (Source: PM from FT-86 SpeedFactory)
03.1lbs - Tomei (Source)
02.2lbs - Amuse (Source)

Mid Pipes:
12.40lbs - Stock (Source)
12.35lbs - Tsudo (Source)
08.60lbs - Invidia as used on N1 and Q300 (Source) (Diameter)
07.50lbs - Tommy Kaira Titanium (Source)

Catback Exhausts:
40.80lbs - MXP Prototype (Source)
39.00lbs - Invidia Q300 (Source) (Diameter)
38.50lbs - Stock (Source) (Diameter)
36.60lbs - HKS Legamax Premium (Source)
36.40lbs - Magnaflow (Source)
34.80lbs - GReddy EVO3 (Source)
33.95lbs - Tsudo (Source)
33.60lbs - Isis Street (Source)
33.60lbs - Perrin Dual Single Tip (Source)
33.40lbs - Berk (Source)
33.00lbs - TRD USA (Source) (Diameter?)
31.00lbs - Milltek Sport Resonated (Source)
30.80lbs - GReddy/TRUST CS GTS V2 (Source)
29.20lbs - Dezod Motorsports Dual Exit (Source)
29.00lbs - Invidia N1 (Source) (Diameter)
28.00lbs - Milltek Sport Non-Resonated (Source)
28.00lbs - Borla (Source)
26.00lbs - FT86SpeedFactory V2 (Source)
25.20lbs - Agency Power (Source)
22.00lbs - HKS Hi-Power (Source) (Diameter)
22.00lbs - Tanabe Concept G (Source) (Diameter)
21.60lbs - Tommy Kaira Titanium (Source)
18.00lbs - Buddy Club Spec II (Source) (Diameter)
17.08lbs - This Thing
16.53lbs - Panda Performance Titanium (Source)
16.10lbs - Tomei 80 (Source)
15.43lbs - TO-YO-07 (Source)
14.10lbs - Tomei 60S (Source)
<12.0lbs - T1R 70RT Titanium (Limited time group buy, get it while you can!)
10.20lbs - Tomei 60R (Source) Although mine weighs 9.98lbs - photo
09.70lbs - STM Aluminum Dual Exit (Source)
08.40lbs - Amuse R1000 Single Exit (Source)

2.118"/53.8mm, 2.25"/57.15mm 2.36"/60mm, 2.38"/60.5mm, 2.5"/63.5mm, 2.76"/70.1mm, 3.15"/80mm Unknown



Based on all this information, the factory engine back system weighs 76.1lbs. The current lightest combination is:

Borla UEL headers, Avo over pipe, Amuse front and catback sytem for a total of 23.74lbs, saving 52.36lbs from stock.