5.3Avalanche

I've test driven many C6s and a new Camaro with the NPP exhaust system which opens and closes exhasut bypass butterfly valves depending on vacuum pressure and engine RPM.

This got me thinking. Why can't I just make this system myself on my C5 and wire it to be manually controlled? I searched the forum but can't see that anyone else has done this before to a C5.

I have a mild-sounding magnaflow axleback but will soon be adding a set of LG longtubes. The extra hp will be nice, but I want to make sure it sounds good without having to swap the exhaust out, and sacrifice the quiet sound during highway trips with my better half (she hates drone and cabin noise). I was going to just do the bypass mod to my magnaflow system, but figured it may be a good idea to install butterfly valves in the bypass pipes. I would control the valves with a simple toggle switch that I would conspicuously mount in the cabin.

Have any of you done this before or have heard of anyone else doing this? Anything I should be aware of?

Cheers.

Patches

madmatt9471 incorporated the B&B Fusion version of this into his C6 ZR1 exhaust mod on his C5.

https://www.corvetteforum.com/forums...sion-pics.html

I had a set of cutouts in my setup for several years. Fairly straightforward exhaust bypass setup.









Control switch in the cabin

5.3Avalanche

Thanks for the reply and pictures Patches, but you're showing straight cutouts rather than inline butterfly valves on the bypass like what the NPP system uses.

I want to perform the bypass mod just like the Z06 guys do to their Ti systems, only I want to install a butterfly valves like the NPP system has. Preferrably the exact same part number too as I have more faith in an OEM part than the aftermarket valves.

I'd rather apply this to the bypass pipe so that it's no so obnoxious when it's open. I want a controllable quality sounding exhaust, not a crazy straight pipe no muffler sound.

Is there room when doing the bypass mod to install butterfly valves?

Patches

That's why I also included the link to Matt's B&B Fusion setup which is the closest mod to the NPP setup for the C5 without actually using that setup. There is a member here who cut out the center well section of his C5 to install the C6 catback setup. That was quite a project to get those in. I would imagine you could figure out a way to adapt the NPP to a set of C5 mufflers.

5.3Avalanche

Thanks for your help Patches and the link. The B&B link was interesting.

I'm surprised nobody has done what I'm proposing.

martysauto

I wouldn't do it to the magnaflows. You'll find out after you put the headers on, you'll have drone, especially w/o cats. Do the header install and drive it for a week or two. Then you'll know which way to go. It would be ashame to do the work on the magnaflows and not like it either way.

5.3Avalanche

Thanks marty. So you're saying if I put headers on I'll have drone no matter what? Even with my whisper quiet magnaflow? I was planning on putting on LG'ss high flow cats and x-pipe along with the LTs if that makes any difference.

martysauto

From personal experience and what I've read hear, the odds are good it will drone. What i am suggesting is to wait and drive it after the header install to do muffler mods. It eliminates the possibility of spending time and money on a mod you don't like.

5.3Avalanche

Fair enough. I may not even install headers if there will be drone. I thought that a mild exhaust system would contain that increase in resonant noise.

dr_whigham

LT's, catless X-pipe, and a Corsa extreme here. No cabin drone.

I'd attribute that more to the Corsa than anything else. Even with the Sports I had there was no drone. All catbacks are different though...