Not So Fast

What kind of exhaust sound change will happen with LTH (with cats) while retaining the NPP ?? Louder, quieter, same?? or any change at all?? I really like the option the NPP offers
Thanks
NSF

LMB-Z

My guess is it will be a little bit louder, and should be a little more throaty. When I put headers on my 05, thats what it did. Just enough to tell you had headers. I think you will like it.

Curt D

I used to run NPP wide open with stock exhaust. With ARH w/cats I run them 1/4 or so open most of the time. It got quite a bit louder with LTH.

MidWestKev

Mine is probably 50% louder. Really noticeable at start-up and WOT.

Not So Fast

50% really that's quite a lot more sound than I would want because with the NPP open its not exactly quiet now, but 50% more, I want more of a sound change than noise increase if that makes any sense
NSF

Turbo6TA

I can only give you my experience with catted long tube headers and the NPP ....

During idle and during normal driving the sound will be about the same (just very slightly louder than with the stock exhaust manifolds), but when you put your foot in it and the NPP valves open up, it's much louder than before ... much!

Personally, I thought it was obnoxious when at full throttle, so I replaced the NPP mufflers with a Borla Touring axle-back system .... much better in my opinion while at full throttle and just very slightly louder at idle and during normal driving than the headers with the NPP.

2011 GS / A6


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Curt D

Check out the 2nd page. This is what I did, just an option. I set the closed position to be about 1/4 open. It still fully opens as normal above 3500rpm

https://www.corvetteforum.com/forums...d-sucks-2.html

2009CSR #45

With the NPP closed I had a small/medium change in sound, not too noticeable unless you really knew your cars. You could hear the factory cam profile a little better. With an open NPP, HUGE difference. I had a factory x-pipe beforehand so I didn't expect too much of a change other than decibel level.

RicK T

Video clip post 1 here:

https://www.corvetteforum.com/forums...-lg-s-m2w.html

RicersRfodder

I am currently running Kooks LT Headers w/ an X-Pipe and hi-flow cats and the stock NPP exhaust. Pretty similar or most likely identical to what you would be running.

With the NPP flaps closed there is only a slight difference in sound, barely noticeable.

With the NPP flaps open the car is much louder with a much deeper throatier sound, it sounds awesome at IDLE and at WOT it sounds downright mean.

I personally love this setup because I still have the option to run very quietly, but when I'm in the mood for the muscle car sound it's one button push away.

CENTVERT

Great news. Mine will be going to the shop tomorrow for those exact mods....plus a cam. Can't wait.

Jaime-Corvette

I too have the npp system... i too also want kooks 3/4 longtube headers. So does the car already have an x-pipe that would fit the headers or? Would i need an x-pipe too. And of i did get the headers and x-pipe, i wouldn't have too replace the "axleback" with the valves?
Someone school me. I would love to learn from you folks

Turbo6TA

The stock exhaust manifolds are much shorter than a set of long tube headers, therefore, you need an aftermarket x-pipe (made for your brand of headers).

Your factory NPP muffler system will attach perfectly to the new x-pipe that comes with the headers you choose.

The other item to consider is whether or not you want cats. You can get your new x-pipe either with cats or without ... Personally, I would get the cats. In fact, you will only give up a couple of HP with them.

Jaime-Corvette

Well im in CA. Already illegally doing this. what is the difference between cats and no cats

Turbo6TA

As you can see, the cats are welded into the x-pipe (not on the headers):

In the photo below, the x-pipe is attached to the ends of the headers with V-band style clamps. The cats are welded into the x-pipe just a few inches in back of those V-band clamps.

Turbo6TA

The system will be a little louder without cats. The exhaust will be a little more smelly without cats. You might gain 2 RWHP without cats.

And in California, you will be in [more] violation of the law driving a car without any cats at all.

Jaime-Corvette

Thank you very much!

Seadawg

I have LG Super Pro 1 7/8" headers, their high flow cats, and their 3" x-pipe, feeding into my stock NPP mufflers, and it is barely louder when in quiet mode. In loud mode, it wakes up the dead. I was having Advance Auto check my battery, starting and charging systems, and mine has the battery in the trunk. I revved it in "quiet", and they wanted to hear it "loud". It was so funny to see them jump, when I hit about 3k RPMs on a hard rev. Several customers came out to see the race car too

Cats did not seem to hurt my torque or HP, this is the 1st and last (6th) of dyno pulls on a 95 degree day here in Florida.

TCW

I've tried it both ways. With and without cats. The smell is terrible without the cats!

This was using LG Motorsports long tube headers with their hi flow cats and without cats.

Tom

Not So Fast

Thanks for al the replies Question answered.
Additionally when I price out, say a "Kooks" 1'7/8" (or about any other system) with catted X pipe, all ceramic coated, that will bolt up to stock axle back system I come up at about $1900-$2000. Members have said they wont run that much or at least they didn't pay that price, HOW SO ?????
I cant quite justify that mark for what the return would be, plus I'm cheap. to me that's a lot of $$$$ for a set of "headers"
Thanks again
NSF