im looking here in summit, and they have these open exaust converters where you can uncap it, and you will have open headers, does anyone have these, do they hurt exaust flow when there capped off?

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Trent
---Car---
89 Firebird
305 L03 TBI A4
t-tops
Open Element Edelbrock Aircleaner w/ K&N air filter
Summit Chrome Valve Covers

---Stero---
Pioneer DEH-P730 Premium
Infinity 2way 4652 4x6's
Pioneer 4way ts-a6985 6x9's
profile cl640 110x4

Future:im profile 1200sx 900watt x 1, and a pioneer cdx-p1270 12 disk cd changer