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1985 Corvette Stock muffler mods.

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Old 04-16-2018, 11:54 PM
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Markever234
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Default 1985 Corvette Stock muffler mods.

Evening fellas,

So the other day i read that stock c4(1985) mufflers had a dummy
exhaust port, so I go out to my project car... lo and behold... my
vette is a dual exhaust, not a quad exhaust. Needless to say I was a little devastated... This got me thinking though.. can the stock mufflers be modified? specifically.. what is behind the dummy port? Can I drill it out and make it a true quad exhaust? Why did GM do this? Where can I find a
diagram of stock muffler?... but alas... there doesn't seem to be that much info on the topic.. or I suck at searching. Either way.. any info on
this abomination to american muscle would be greatly appreciated.
Thanks as always.

- Mark
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Old 04-17-2018, 12:03 AM
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84 4+3
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I believe I have read about people knocking out the second port back in the day... probably won't notice much of a difference though.
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Old 04-17-2018, 01:46 AM
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Originally Posted by 84 4+3 View Post
I believe I have read about people knocking out the second port back in the day... probably won't notice much of a difference though.


Oh no no no ... with factory mufflers it gets real loud when you open that blank port, I had my dumb half hour of the day when i did that. She was way too darn loud, had to buy new mufflers.
The exhaust enters that section and has to travel through the baffles to exit the other side, open that and you have straight out not muffled exhaust.. very very loud.. the noise police will make a bee line to you..
Some come with a small hole in the blanked off section, to get the same color as the other outlet.

Last edited by gerardvg; 04-17-2018 at 01:52 AM.
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Old 04-17-2018, 08:30 AM
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84 4+3
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My much of a difference was in performance/power. Should have clarified that one lol.
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Old 04-17-2018, 09:20 AM
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In all truth it isn't a true dual exhaust on an early C4 anyways, the exhaust comes together at a y-pipe in front of the catalytic converter. If you're looking for power there's more to be found at the front and middle than at the back.

Louder exhaust might help the butt dyno, but so do hard tires, it doesn't make the car faster though.
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Old 04-17-2018, 10:38 AM
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vader86
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I lost the mufflers to rust before drilling mine out.
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Old 04-18-2018, 04:19 AM
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I'm not looking for extra power out of the car just yet. I wouldnt mind a little extra sound, but nothing extreme.. Does anyone know what is behind the blank? If I knock it out will
it damage any muffler internals? Also.. recommend method to removing the blank?
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Old 04-18-2018, 11:28 AM
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No it should just be a thick plate, you can drill through it, you might cut into a baffle. I believe there are some baffles oriented behind it, but I'm going by old memory of what mine looked like when rusted through.
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Old 04-18-2018, 11:36 AM
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Originally Posted by gerardvg View Post
I had my dumb half hour of the day when i did that. She was way too darn loud, had to buy new mufflers.


When you do look for more power, those mufflers, drilled out or not, cannot flow more than the most restrictive upstream section.

Last edited by whalepirot; 04-18-2018 at 11:39 AM.
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Old 04-18-2018, 12:20 PM
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Originally Posted by gerardvg View Post


Oh no no no ... with factory mufflers it gets real loud when you open that blank port, I had my dumb half hour of the day when i did that. She was way too darn loud, had to buy new mufflers.
The exhaust enters that section and has to travel through the baffles to exit the other side, open that and you have straight out not muffled exhaust.. very very loud.. the noise police will make a bee line to you..
Some come with a small hole in the blanked off section, to get the same color as the other outlet.

Did this once and the drone was so bad I put a plug in to put it back stock, Get headers and catback if you want better sound and a small bump in HP.
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Old 04-19-2018, 06:52 AM
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Thanks for the responses, guys ! Since mine seems to be in pretty good shape, I think I will
hold off on drilling them and wait until I can purchase a a full 2.5inch system.
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