Performance nut

I know there are cat backs but has anyone taken a saw to their exhaust and put a pre-fitted X/H pipe and called it a day? Just curious as the stock "muffler" seems ridiculous.

ArizonaZ06

Here's the NPP in the wild with the muffler insulation chamber removed. Could be wrong but looks like an H pipe cross-over is incuded with the performance NPP stock C8 exhaust.

Performance nut

Thanks for providing. This is what I was thinking if you wanted to keep an X-pipe. I'm not sure why they went with a vented pipe and an open ended pipe where the valve goes. Seems... odd. I would think that if you wanted the concept of a valve that opens up more flow, you would have attached the second set of pipes somewhere where you can take advantage of the flow (through a Y for example). Then lose the clamshell and thermal coat the pipes/wrap for temperature control.

Turboalky

I was looking at a way to modify the factory Z51 NPP exhaust also. Valves are there to restrict flow and quiet the exhaust I believe. Not to add more flow

Performance nut

When they are closed, yes. Though it gets louder when I open them. Can't prove the ad power but I imagine it does due to added flow potential when open.

gtpvette

This explains the flow pretty well.

Waterline

Do I understand correctly that the mild to wild remote valve system doesn't work on the C8? I liked it on my 08 C6. Does the track setting keep the valves open? If I remember correctly, the mild to wild system would keep the valves open and retain the +3000 RPM operation as in the C6. I miss that thing.

Andybump

If the engine sound setting is track, then the tailpipe flow control valves will be open almost all the time. There are some conditions where they will close to meet "federal bypass" noise limits. However, those conditions are difficult to detect - some have experimented with forcing the to stay open regardless, and they report that there is no perceived difference exhaust sound between that and the track setting. Those valves will also close if AFM kicks in. For example, in Z mode, you can set the engine sound to track. But if the engine/shift setting it Tour, AFM can still still activate. If/when that happens all 4 valves close (AFM and tailpipe).

And folks report that the mild to wild is not effective. Also, there is the pulling the fuse method- but its a shared fuse with the mirror. There is a workaround by splitting the fuse but it is not worth the effort for the reason noted above. And it will set a DTC and an MIL on the dash.

ArizonaZ06

Have a deep sound idle with the Z51 NPP. This with added HJS 200 cell wrapped Cats and 1 7/8" Cerakote Glacier Ice Kooks headers.

E85 tuned with AFM delete adds to the NPP growl especially with an aggressive throttle. Shift pops are not as loud with corn 104 octane but worth 486 to the wheels. Also have a few other intake mods.

However, if a used Fabspeed Valvetronic cat- back should become available, I would WTB if any member would like to move theirs.

Performance nut

There are folks who say headers don't make a difference but they really do make a sound difference. I am honestly debating about whether a catback is truly worth it or not as I'm seeing just a weight difference with questionable power changes. Though if you took off the suitcase and opted for other thermal solutions, that alone probably would give you weight savings. You still have to solve the hole issue and the hanging pipes that lead to nothing. Normally I would say it isn't worth it but dang... catbacks just got really expensive all of a sudden. Redesigning stock seems more feasible now with minimal material required (though more labor if you can't weld).

Gary barnes 1098

I’m all over this performance nut if you get something figured out with the stock npp.
Im with you 100% this aftermarket exhaust borla etc is just stupid outrageous.

ArizonaZ06

There's no doubt C8 headers improve on a number of different ways.

A set of Cerakote ceramic coated headers will create a deeper tone and an improved exhaust sound. Unless you street and track your Z51 and have a non valved X-Pipe Exhaust, paired with the smell of a straight pipe Cat delete system you probably wouldn't hear a header difference anyway, or for that matter what anyone else riding along might have to say.

You would also improve on compartment airflow and weight, by the removal of 15-20lbs of heat sheilding and adding a Cerakote coated lighter T304 Stainless Steel header versus stock.

Headers have proven for years dyno gains. Especially the low torque LT2 engine across the power band shows gains with it's 470 stock torque.

For me seeing the engine in the C8 Coupe is a deal breaker. My opinion is headers especially look great with no sheilding in an opened up engine compartment.

I prefer keep with the highly heat protected NPP, like the exhaust valves and feel it's a good performance exhaust. Add a pair of Cerakote coated headers and possibly a set of Kevlar covered HJS 200 Cell cats or Corsa Cats with Cerakote. With these combinations the engine compartment run's cooler than stock. Prefer to go this route and keep the NPP as I have now for almost 4 years.

Performance nut

Thanks for posting! I think headers are next for me if I'm being honest. I see the rest of the exhaust the same way though. Ditch the shielding, replace some pipes, and then coat/insulate. I think when I finish closing on my house, I'm going to look for a stock NPP exhaust in the area and start cutting and welding on it to see what I get. I got a feeling ditching the shielding alone will save significant weight.

Performance nut

I checked out Borla and this is exactly what I was thinking. Y pipe after the bellows but the addition of the mufflers is interesting. I was thinking small resonators but a dual entrance/exit muffler... Hmm. Have to research this. Straight piping it probably would be loud as heck but efficient for piping, routing, and support.

Gary barnes 1098

Plz keep me posted. I have access to all weld and fab work and once I have something to kinda go off I may start playing with this.

ArizonaZ06

Your definately on to something! After finding yourself for next to nothing a NPP test mule, with welding skills you could be amazed the sound and extra flow you will find. Guessing that this could be what C8 engineers at the beginning stages of the NPP originally came up with, only to be shot down for lower cost, regulators and future corporate advantageous plans. The original conceptual C8 First Gen NPP could be to be discovered. Certainly get your house closed and test these waters.

Is it possible today's quite pricey C8 Borla program is along the lines of what the original C8 NPP was created to be? The C8 engineers perhaps lowered cost and scaled down the NPP by containing open pipes and creating holes to avoiding the use of twin mufflers with higher cost. Thinking also at the time engineers were highly focused on mid-engine heat and elected to use a substancial dose of insulation on the final NPP that tested out on lower compartment and trunk heat.

Performance nut

No problem. I'm thinking of cutting flush with that big ol' honking mounting bracket just to the inside of the exhaust tips. Replace from the catalytic converter flange to a few inches past the bellows with 3" flanged piping (and likely a 3" bellows) to a 3" inlet, 2.5" outlet Y (or whatever the stock piping is). I was thinking of putting a resonator on the non-valved pipes with some sort of H/X back to the stock tips. Then the other side of the Y, go straight down to the valved tips without any muffler/resonator and with minimal length and bends. To me that is a real race worthy exhaust once you open up those valves. Even partially opened it should sound awesome. Probably free up some ponies too.

And the best part is, if you cut well, you can likely reuse some of the stock piping. Won't know until I get my hands on one.

I never thought of it like that but it totally makes sense if Borla/someone else picked up an older design filed in the GM circular file cabinet. I honestly don't understand the design at all but know there had to be a cost/EPA/sound ordinance reason for it.

itsonlyairandfuel

2M Fabrication Cat-back Exhaust for C8 - CorvetteForum - Chevrolet Corvette Forum Discussion

Andybump

Borla is using technology to tune the exhaust notes with pipe lengths and other features. Its not just louder, but enhances certain lower tones while preventing drone. Its both volume and character. Below is an example but there is more about it on the web site.

"Polyphonic Harmonizing

Playing the right notes together on a pipe organ creates a satisfying textured sound with dramatically more acoustical depth than a single note. This is the basis for the patented technology of the twin Polyphonic Harmonizers within our C8 system. Using the same principles as an organ, pipes of different diameters and lengths within the Harmonizers are tuned to create our signature ATAK® or S-Type sounds for the C8. A straight-through design ensures zero performance loss."

GTS Bruce

I have heard every system. Cat back,no cats,hp cats,headers.... On a cross plane crank the difference in sound is NIL and expensive. Louder sure. Couple more HP maybe. Couple lbs lighter sure. Never going to sound like a FPC. Worth it very questionable.