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Another Long Tube question...

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Okay folks...  what is the consensus numbers on what a good set of 1 3/4” primary long tubes (Kooks, ARH, etc) will get you on an basically (maybe a CAI and a cat back) stock L83?  Info/numbers on catted vs non-catted would be cool too.  So would before and after tuning...  even though it’s pretty much a given that you need a tune if you do long tubes.  Thanks y’all!

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I dont have specific numbers to give you, but the consensus with long tubes, catted or not, and a good tune, (obivously intake, and exhaust) would net you about 25-30hp and 25-30 tq.

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All I can tell you is mine hauls a lot more ass and gets a lot more MPG than when the exhaust was stock.


I have a test spot that's about 1000 ft from a stop sign to a merge sign . When I cut out the flapper and swapped the stock muffler for a magnaflow I picked up a couple of mph and MPG, truck was already tuned but it was not retuned for cutting out the flap and new muffler.


 When I went headers and the stock 6.2 catback with the flap cutout and tuned, I picked up another 3 MPH over the previous setup. Which is a total of around 5 MPH from stock exhaust. 


I do get near 5 more MPG total than when my truck was untuned and had the K&N on it, it was bone stock except for the K&N. On my work commute stock with the K&N I got 14-15 MPG on gas and 11 on E85. Got it tuned and the v4 (AFM) turned off. Got the same mileage but made more power/went faster.


With all my exhaust changes I've seen as high as 19 MPG on gas and 16 on E85, going the same roads that I used to get 14.5 and 11. 


I had a decent highway drive the other day and the 25 mile MPG chart showed I was getting a little better mileage on E85 than the best I previously had with the stock manifolds and the flap cut out with the magnaflow and tuned. I gained considerable mileage and power just cutting out the flap and swapping the stock muffler for a magnaflow, I gained a lot more power after the headers and 6.2 catback, but again since then I've stomped on it all over the place so I'm not sure if I'm getting better MPG, but it's not worse. (with the headers and 6.2)

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Also, you probably wont get a lot of power numbers here since the driveshafts pop on the dyno.


But I've heard approx 25 from headers, and approx 25 from doing a cutout ( I assume a really good catback will be near the cutout numbers). Talked with a tuner from Dubai about it and he said that you may see up to 50 hp. Sounds crazy, but if you read through this thread about how much back pressure that damn flapper creates it's not too hard to see.



Edited by 00pooterSS

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I have Speed Engineering Long Tubes and love them


Not expensive and fit perfectly, im planning on making a full review video:



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On ‎2‎/‎19‎/‎2019 at 5:49 PM, 00pooterSS said:

Also, you probably wont get a lot of power numbers here since the driveshafts pop on the dyno.


But I've heard approx 25 from headers, and approx 25 from doing a cutout ( I assume a really good catback will be near the cutout numbers). Talked with a tuner from Dubai about it and he said that you may see up to 50 hp. Sounds crazy, but if you read through this thread about how much back pressure that damn flapper creates it's not too hard to see.



The Flapper...  where is it?  I'm wondering if my Flowmaster Outlaw kit already got rid of it and if I would need DiabLew to do an update if it is still there but goes away.  Pics would be very much appreciated.

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The flapper is in the stock exhaust and in the borla GM catback. I don't think it is in any other catbacks but I really only know about the OEM setup. I don't know about all the aftermarket setups

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L83 5.3 2017 z71.  I installed Corsa cat back, then afe cai, then tune with blackbear performance.  That was a great set up.  I literally just installed kooks lt 1-3/4 about three days ago.  Haven’t retuned it yet but let me tell u, it is the most noticeable butt dyno upgrade yet.  Easily as much as cai, cat back and tune gave me combined.  But it is friggin loud.


This set up does stick down below the frame about 3 inches so be aware of that.  That’s a concern of mine if I go offroad. 


Right now I am enjoying the upgrade and can’t wait for the retune.  But can forsee adding a resognator in the near future to quiet it down. 

Edited by Stonehenge

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