2018 Tahoe premier flowmaster 40 exhaust

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iamdub

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Just had the flowmaster 40 removed and the XS12 added but did not have the resonator deleted yet need to wait to get more money

It’s so quiet but I’m sure once I get the res out of line and a pipe with tip it’ll be louder?

Some say they heard a big difference with the resonator removed. I can't say for sure if I did.

Also, give that muffler some time. It'll be louder after about 1,000 miles. It'll be a slow, gradual change. So, you might not notice it so much. Or, maybe you're just so used to the noise of the F40?
 

ThisIsLivin

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I put a Gibson stainless 3.5" on my Denali and disabled AFM. With that combination the sound is great and minimal noise at speed. I didn't loose any mileage at all. I get 20mpg at 83mph and 22+ at 70mph. I bought it through Summit for $470 for everything Cat back with a sweet 4" chrome tip and lifetime warranty. I did pitch the cheap clamps that came with the kit and bought some stainless bands.
 
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Ghost10

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I am just curious what would wanna have to deal with to make the exhaust wrap out when reaching max rpm?
 

iamdub

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I am just curious what would wanna have to deal with to make the exhaust wrap out when reaching max rpm?

Huh? Exhaust wrap is for thermal and sound insulation, but mostly for thermal. Doesn't have anything to do with max RPM.


Try again when you're sober! :p
 
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Ghost10

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haha wow. However it is the internet sober or not.

What I was asking you know how some folks do something to their cars that when the engine reaches it's Max rpm before shifting the exhaust I guess you could call it Raspy?
 

iamdub

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haha wow. However it is the internet sober or not.

What I was asking you know how some folks do something to their cars that when the engine reaches it's Max rpm before shifting the exhaust I guess you could call it Raspy?

Ah! I gotcha. I think it's just how different mufflers sound. Unless you're talking about bi-modal exhaust like the Corvette's have. Basically, at lower RPM, you don't need as much flow. So, having a slight bit of restriction, even if it's just that presented by the muffler(s), keeps the lower-end torque. At WOT and higher RPM, you need maximum flow, so the system opens valves to let the exhaust bypass the mufflers. It's just a way to wring out every last ounce of power but not sacrifice it elsewhere. A common mod for this is a "mild to wild" switch. It gives the driver control to activate those valves at any time.

Sound description and appreciation is subjective. I would describe the way mine sounded at high RPM/WOT to have a good bit of raspiness to it and I liked it. It didn't have this until I had put some miles on that muffler. The more I drove it, the more I liked it. It sounded pretty wild near redline, but the sound was still mostly outside. Put the right rear window down and floor it next time you're next to a concrete wall.
 
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Ghost10

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I believe I’ve put about 5k mi on the truck since the new exhaust it sounds good! I still need to drop the v4 res as it’s pointless and hope it makes the exhaust a little louder with some raspy notes
3”in 4”out dual tip arrived however the idiot that boxed it did not do a good job so the black powder coating on one tip is chipped down to the metal so I’ll probably just have a shop when they install it hide it under the truck rather than have it stick out the side
 

hunter7504

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A question for you all, I replaced my stock muffler with an AP XS1259 and had the muffler shop remove the resonator and tailpipe and replace it with a straight pipe out the side (towards the corner, so a little longer than stock). I also had a local guy do the AFM delete. I have been getting some cabin drone, and not sure on how to eliminate it. I still have the stock resonator, so I could put it back on but I don't like the looks of it. The droning noise I hear is in any gear around 1500rpm and 50ish mph. It's only when I have the foot on the gas, so I think it's related to the exhaust. Thought it might be the tip I put on, so I cut that off and noticed no change. Any recommendations on things I could try?

 

iamdub

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A question for you all, I replaced my stock muffler with an AP XS1259 and had the muffler shop remove the resonator and tailpipe and replace it with a straight pipe out the side (towards the corner, so a little longer than stock). I also had a local guy do the AFM delete. I have been getting some cabin drone, and not sure on how to eliminate it. I still have the stock resonator, so I could put it back on but I don't like the looks of it. The droning noise I hear is in any gear around 1500rpm and 50ish mph. It's only when I have the foot on the gas, so I think it's related to the exhaust. Thought it might be the tip I put on, so I cut that off and noticed no change. Any recommendations on things I could try?


I had this muffler at first and didn't notice such drone. But, I never spent much time at 50 mph, either. Drone is mostly a result of engine load, so 1,500 RPM at 50 MPH must be a "trifecta" point for the offending note you hear.

If you have a sound at a particular RPM that you don't like, you can attenuate it with a Helmholtz chamber/resonator and not really affect the overall volume of your exhaust. Basically, it's a pipe of a calculated length that branches perpendicular off the exhaust pipe with a flat, closed end. Extending perpendicular to the exhaust pipe is most ideal, but that's likely not very feasible under a car. It's commonly known as a "J-pipe" since they're often made to run parallel to the main exhaust pipe for packaging reasons. It branches off the main pipe and immediately makes a 90° bend and continues for the remainder of its designed length. This one bend isn't going to significantly its effectiveness at all. Its total length is determined by the particular frequency you want to cancel out. You determine the frequency created at 1500 RPM, determine the length of the sound wave of that frequency then make the tube 1/4 the length of this wave. This will reflect a sound wave 180° out of phase back into the sound's source, cancelling out that frequency.

You said your problem RPM is at 1,500 RPM. A V8 fires four times per revolution. So, multiply 1,500 times four and you get 6,000. RPM is revolutions per minute, so you divide that by 60 to convert it to seconds, leaving you with 100. This is your drone frequency, so it's presented as 100Hz.

Now, you gotta determine the length of this 100Hz wave. Using 1,416 feet per second as the speed of sound (estimating 375° exhaust temp), you divide that speed of sound by 100 and get a 14.16' wavelength. Since you want 1/4 of this length, divide 14.16' by 4 and you get 3.54'. Multiply this by 12 to convert to inches and you get 42.48". I'd round it up to 42.5". This length includes the 90° bend.

KEEP IN MIND: This length was determined assuming a 375° exhaust temp. If the actual temperature is considerably lower or higher at the point where your J-pipe will be interjecting, you should recalculate.


Here's an example pic of a J-pipe:

XaUdpGB.jpg
 
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hunter7504

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Thanks for a great reply and suggestion. Last night I did some measuring under the Tahoe to look how I could get something like this to fit. I did nice that the flex tube that's after the 3rd cat is in bad shape- like falling apart. I just ordered a new one with the replacement front mount clamp. I could of just cut the old one-off and welded both ends on but thought it would be best to unbolt the front and replace it without cutting the mounting tube. Could the defective flex tube piece cause this problem?
 

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