3 inch duals vs Y pipe - results
TECH Fanatic
Joined: Jan 2022
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I love everything about that hat! 
As mentioned above, it’s not that you can't make more than 310hp (it's not a brick wall), it's just that this is the point at which some amount of restriction begins. But it's actually worse than this because the various factory pipe bends, and flow restrictions in the stock muffler, might not maintain optimal flow for a 2.75" system in the first place. This is why we often see gains of 7-10rwhp with just a catback - because there are obviously some restrictions in the stock system that hinder, to some degree, even a stock LS1 (~350hp level).
As mentioned above, it’s not that you can't make more than 310hp (it's not a brick wall), it's just that this is the point at which some amount of restriction begins. But it's actually worse than this because the various factory pipe bends, and flow restrictions in the stock muffler, might not maintain optimal flow for a 2.75" system in the first place. This is why we often see gains of 7-10rwhp with just a catback - because there are obviously some restrictions in the stock system that hinder, to some degree, even a stock LS1 (~350hp level).
Yep, there are multiple restrictions in a factory exhaust system. Like RPM WS6 said, in addition to pipe size, you have number of pipes, the transitions/merges, muffler flow, converter restriction, and bends. The estimates on the tables above give a good estimate for a "lossless" system based on pipe size are just that, estimates, and have assumptions baked in. Also, the chart that bthomas posted is more accurate as it uses actual ID (pulls out the wall thickness) in calculating cross section area. In my case, it made a lot of difference. I still got the best decision for my power level so it's academic, but points to some restriction, which was probably inevitable anyway IRL. I thought the lossless amount initially was 812, it's actually more like 680 (I am assuming crank HP). Given my engine is making 700-750 flywheel, it matters, but probably not a ton given it's lossless up until the last 20-70hp. I'll have a better idea when I get it dyno'd this Saturday. Wish I could have afforded to do dynos before and after but there IS a limit I can tolerate...and one the wife tolerates, which I already roared by. LOL
Joined: Nov 2001
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From: Schiller Park, ILL Member: #317
If you're coming from the factory (SLP) dual/dual setup (standard on Firehawk, optional on SS) then the gain probably would be about 0 as that's already a 3" system with a good flowing muffler. The base systems aren't as good; more restrictive muffler, 2.75" I-pipe, and only 2.25" muffler outlets & tail pipes for non-SS/WS6 cars.
Ok, likely the final iteration. SUPER happy with the sound and overall volume and the Magnaflow 6 inch round mufflers killed a majority of the 2k rpm 129hz drone. It's still there but to my ear, 80% is gone...SO much nicer to drive. I may still do J-pipes if the wife complains but it is SO much nicer to drive, volume and tone, I doubt she will. This is to my assometer also with no change in power (both mufflers are straight through). Now, off the dyno!
Teching In
Joined: Oct 2021
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Ok, likely the final iteration. SUPER happy with the sound and overall volume and the Magnaflow 6 inch round mufflers killed a majority of the 2k rpm 129hz drone. It's still there but to my ear, 80% is gone...SO much nicer to drive. I may still do J-pipes if the wife complains but it is SO much nicer to drive, volume and tone, I doubt she will. This is to my assometer also with no change in power (both mufflers are straight through). Now, off the dyno! https://www.youtube.com/watch?v=2nCHvOYVy0s
The J-pipes were done, aimed at drone at 129hz, and results were amazing. Can have a conversation and enjoy the exhaust note and it takes much longer to make your ears ring, but that happens with tops off anyhow.
