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4" downpipe dual exhaust

Old 10-10-2018, 02:30 PM
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Default 4" downpipe dual exhaust

I am running a LQ4 with a t6 1.10A/R s475, with a goal of 650 to the wheels, with a 4" downpipe and need/want to split it into duals to be able to run it out the back of my truck. It is going to just be a street truck and don't want the noise and drone under the cab. If I split it into dual 2.5" will that kill the flow? I could possibly step it up to 3" but will have to get creative.
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Old 10-10-2018, 05:39 PM
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IMO yes it will hurt flow. Where do you plan on splitting it and how long will it be 2.5inch? I think you'd be better off with dual 3"
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Old 10-10-2018, 06:17 PM
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Do the dual 2.5 with a 4" cutout.
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Old 10-10-2018, 06:18 PM
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Originally Posted by Burnett03 View Post
IMO yes it will hurt flow. Where do you plan on splitting it and how long will it be 2.5inch? I think you'd be better off with dual 3"
it will be 4 until the end of the transmission so probably 3 or so. The rest will be 2.5 or 3
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Old 10-10-2018, 07:55 PM
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Full tailpipes with enough power will kill some horsepower but a loud valve before the dual exhaust would make quick work of that. I don't really think you'll lose that much power, 650 or even 500whp on the street is going to destroy tires anyway.
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Old 10-10-2018, 08:25 PM
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I would try to make dual 3” work, dual 2.5 is about equivalent to single 3”
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Old 10-10-2018, 10:44 PM
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Dual 3" or single 4 or 5" all the way to the back. Consider a cutout after the downpipe if you must run full exhaust so you can open it up if need be.
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Old 10-11-2018, 09:02 AM
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I think you'd also be hard-pressed to find a pre-made single 4" to dual 2.5" merge pipe. You might need to have that custom made, if so. Not sure what someone would charge for that. I think you could find 4" to dual 3" though.
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Old 10-12-2018, 11:00 PM
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Originally Posted by 03sierraslt View Post
I would try to make dual 3 work, dual 2.5 is about equivalent to single 3
are you talking tubing volume, exhaust velocity, or a balance of the two?
because dual 2.5" = 38% more volume than single 3"

overall though, dual 3" is still about 13% more volume than single 4", so it won't restrict it (particularly if running straight-through mufflers instead of chambered)
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Old 03-22-2019, 02:00 PM
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Why not find a take off Duramax exhaust or a take off Denali exhaust and run a Borla muffler? I have the left over Duramax exhaust pipe from my dually with a Borla that's not terribly long on my Yukon and it sounds good with O drone. Where my Y pipe merges is where the Duramax was l
flattened so it would seal around the cut. It was done a year ago and even with my Yukon dropped 5" it isn't a problem.
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