Observation of NPP Exhaust / Crimped Exhaust pipes - Page 5

doc212121 · 02-27-2016, 07:59 AM

LOL Brilliant? I had to laugh....sorry bud no offense intended.
Its not going to be worth the hassle unless you upgrade the entire system, and for a muffler shop to do it right without leaks you would need to drop the entire section to make sure your welds are 100% around, most "muffler shops" dont do the quality of work needed to do it properly......

jimmypop13 · 02-27-2016, 08:13 AM

Quote:

Originally Posted by doc212121

LOL Brilliant? I had to laugh....sorry bud no offense intended.
Its not going to be worth the hassle unless you upgrade the entire system, and for a muffler shop to do it right without leaks you would need to drop the entire section to make sure your welds are 100% around, most "muffler shops" dont do the quality of work needed to do it properly......

I think it would be a pain simply bc of the hanger placement. It seems that in order to do a perfect job that you'd have to cut off the hangers and redo them bc the pipe is still a little flattened where they are

KaBoom1701 · 02-27-2016, 08:22 AM

Might be there to help reduce drone...

oldman · 02-27-2016, 08:26 AM

front cat is only 2.25 and the exhaust is very hot there, you know gas law P=VT, just remember we are talking Kelvin. So 2.75 squash at the rear is pretty much a wash when it comes to flow area vs volume.

.9453 x PI for the rear crush assuming it has 1/2 smashed
1.27 X PI for the front cat
so front has 1/3 more flow area
about say 450 degrees F is 505 K
about say 180 F at the crush is 355k
so the front has 50% more volume of exhaust
so off hand calculation on back of napkin the front cat diameter is the primary restriction.

I would use a touch and a slide hammer to pop it out and then mig up the holes. I fixed many a header from a smash.

Tr6 · 02-27-2016, 09:10 AM

Quote:

Originally Posted by KaBoom1701

Might be there to help reduce drone...

Nailed it! It reduces the drone significantly at Idle but especially under WoT.

What you can do is to replace the secondary cats with 2.75'' pipes. I got rid of mine with 2.5 but that was temporary as will Borla came out with something. Npp and xpipe are all 1 pipe so it'll require you cutting the stock part off and most likely clamping the borla xpipe on (like they did for C7 non-npp).

Kevjud · 02-28-2016, 04:25 AM

As many have stated, the restrictions, or "dents", were put there for a reason. Bigger isn't always better when it comes to exhaust systems. There is a lot which goes into the design of exhaust systems. As the diameter of the exhaust pipe increases, the velocity of the exhaust gases flowing through it decreases which could have a negative impact to the scavenging of the exhaust gases. The system relies on this exhaust scavenging to aid in overall exhaust flow. As some others have stated, they could also be there to reduce drone. That being said, there are many stock exhaust systems which are too restrictive because quiet exhaust tone is more of a priority than HP to the design engineers. It is always a trade off, but in the case of these cars, the exhaust systems have been engineered pretty darn well or the cars wouldn't be putting down the HP numbers they do. That being said, could gains be made by altering the system? Maybe, but you do run the risk of sacrificing HP for sound. Unless you have made modifications to the engine which requires a higher flow system, you are probably best off with Cat back systems if your objective is to just change the exhaust "sound". I have seen many Harley guys swap 2 into 1 systems for true duals and end up with lower numbers on the dyno because the exhaust scavenging afforded by the 2 into 1 system is lost when you run a true dual exhaust. While these aren't Harleys, the theory is the same which is why H and X pipes are used on automotive systems. As far as eliminating the cats, a word of caution here, some of the corvette guys have done that and for some the added smell wasn't worth it.

02-27-2016, 08:22 AM	#59
KaBoom1701 KaBoom1701 Drives: 13' ZL1 Red M6 Join Date: Dec 2012 Location: I.E. SoCal (Yucaipa) Posts: 8,631	Might be there to help reduce drone... __________________ Mods: Roto-Fab Intake, WW Res. kit & Big Gulp Air Scoop, Elite Catch Can, ATI Super Damper & 18% OD Pulley, LF Idler pulley bracket, Metco CC breather, ID850 Injectors, Stainless Power Headers w/ ceramic coating, TR71X Spark Plugs, JMS Fuel Pump Booster, Bo White TB, Tuned by Ted @ Jannetty Racing, Ron Davis HX, D3 Reservoir, Pfadt 1" Springs, Moreno Camber Plates, ZL1 Addons Splitter guard washers, Tow Hook kit & rock guards, Hurst Shifter Billet Plus 6 Speed Short Shifter, ZL1 DRL lighting harness, ZL1 Recaro Seats.

02-27-2016, 08:26 AM	#60
oldman Drives: SS 6 speed of course Join Date: Jan 2016 Location: Hilo, HI Posts: 4,346	front cat is only 2.25 and the exhaust is very hot there, you know gas law P=VT, just remember we are talking Kelvin. So 2.75 squash at the rear is pretty much a wash when it comes to flow area vs volume. .9453 x PI for the rear crush assuming it has 1/2 smashed 1.27 X PI for the front cat so front has 1/3 more flow area about say 450 degrees F is 505 K about say 180 F at the crush is 355k so the front has 50% more volume of exhaust so off hand calculation on back of napkin the front cat diameter is the primary restriction. I would use a touch and a slide hammer to pop it out and then mig up the holes. I fixed many a header from a smash. __________________ Forged short block, large duration sub .600 lift Cam Motion cam, 7200 RPM fuel cut, Pray Ported Heads, 3.85 pulley D1X, stage II intercooler, DSX secondary low side, DSX E85 sensor, Lingenfelter big bore 2.0 pump, ported front cats, 60608 Borla, LT4 injectors, ZL1 1LE driveshaft and Katech ported TB, ported MSD intake, BTR valvetrain, ARP studs, ProFlow valves, PS4 tires. Last edited by oldman; 02-27-2016 at 08:37 AM.

02-27-2016, 07:59 AM	#57
doc212121 Drives: 2016 Camaro 2SS White/White Join Date: Jan 2010 Location: Michigan Posts: 351	LOL Brilliant? I had to laugh....sorry bud no offense intended. Its not going to be worth the hassle unless you upgrade the entire system, and for a muffler shop to do it right without leaks you would need to drop the entire section to make sure your welds are 100% around, most "muffler shops" dont do the quality of work needed to do it properly......

02-28-2016, 04:25 AM	#62
Kevjud Drives: Hyper Blue 2SS Join Date: Oct 2015 Location: Granger Posts: 35	As many have stated, the restrictions, or "dents", were put there for a reason. Bigger isn't always better when it comes to exhaust systems. There is a lot which goes into the design of exhaust systems. As the diameter of the exhaust pipe increases, the velocity of the exhaust gases flowing through it decreases which could have a negative impact to the scavenging of the exhaust gases. The system relies on this exhaust scavenging to aid in overall exhaust flow. As some others have stated, they could also be there to reduce drone. That being said, there are many stock exhaust systems which are too restrictive because quiet exhaust tone is more of a priority than HP to the design engineers. It is always a trade off, but in the case of these cars, the exhaust systems have been engineered pretty darn well or the cars wouldn't be putting down the HP numbers they do. That being said, could gains be made by altering the system? Maybe, but you do run the risk of sacrificing HP for sound. Unless you have made modifications to the engine which requires a higher flow system, you are probably best off with Cat back systems if your objective is to just change the exhaust "sound". I have seen many Harley guys swap 2 into 1 systems for true duals and end up with lower numbers on the dyno because the exhaust scavenging afforded by the 2 into 1 system is lost when you run a true dual exhaust. While these aren't Harleys, the theory is the same which is why H and X pipes are used on automotive systems. As far as eliminating the cats, a word of caution here, some of the corvette guys have done that and for some the added smell wasn't worth it.

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