Does anyone have details concerning how the NPP exhaust works.
I understand the obvious which is when the valves open restriction is elimintaed and therefore louder.

I am wondering , if when in open mode, is it the equivalent of straight pipes ( no muffling what so ever ) or is it still muffled some .

 

it is still muffled some, as some minimal back pressure is engineered into the design

 

See here:

https://www.corvetteforum.com/forums...post1587851357

 

do you have a link from the GM engineering department where they say some backpressure is necessary or wanted?

backpressure VS velocity - two different things

 

I am curious if the dmh cutouts will provide a noticeably louder exhaust tone or will it be just like npp in the opened position.

if it is just like the npp ( opened ) it is not worth adding

 

See the picture/Drawing. The green pipes are perforated. No restriction, but some muffling...(like a resonator)

 

From a racing background best is to have NO backpressure period--Looking at the routing of NPP exhaust not all the exhaust goes thru the straight thru pipe--some will still pass thru the muffler--and the exhaust that goes thru the open side is baffled
On my car I simply cut both mufflers OFF and ran straight pipes with 4" Flowmaster tips-----To me the car sounds awesome !! just slightly louder than NPP with more of a growl at WOT---At P/T and cruising ?? unnoticeable----I'm sure this will **** off all the C7 cat back guys who charge $1200 for a system--- I spent $150---and I think it's far superior and makes more HP !!!

 

as long as you think it is superior then that's all that matters.

also, post your dyno sheet of it making more power than.....well, anything. also post a high quality sound clip so we can all agree with you about how amazing it is.

 

Talked with GM people at Carlisle in August and learned the two valves closet to the exhaust tips are for the "performance" mode and open at different settings (sport, track) during driving. You can hear the change, at idle, if you turn your drive selector control. These valves will also open when you get on it even in touring mode. The two other valves, new to the Stingray, and located in the exhaust pipes around the rear axles are for use when the engine goes into the 4-cylinder mode. These valves help prevent the unpleasant drone sound when the engine drops out of 8-cylinder mode.

 

Hopefully you're joking.

 

WHY ? Unusual response--The flowmaster tips are specifically made to fit the back of the C7--they are 4" stainless and similar to the NPP stock 4" tips and hide the huge open panel void in the back of the car . The short pipes are not visible at all either
They look factory and are very hi quality---
These cars have 4 cats--so there is still a little backpressure and the cats quite it down to like I said just barely louder then running your NNP's open---The NPP Option is $1200. !!! So I was able to spend that $$ on other options---as I ordered my car without NPP--

 

I agree the 2 butterfly valves used by the AFM mode close when AFM is activated to get rid if drone However on my car I DELETED the AFM out of my tune so the butterflys are open all the time--
My cat is getting 28-30 MPH even without AFM Before I turned it off it would show 36-38 MPG on 4 cyl. This is not for trips so no worried about MPG as itwill be driven less than 4K a year--
I was more spooked about all the GM AFM/DOD lifter failures of the recent years--So in my case it was a no brainer to tune it out

 

First, if you have a 30 MPH cat, I hope you have a license for it.

Second, tuning out AFM does not remove the lifters.....they are still in there, about to fail.

 

Because a chop/hack/weld exhaust system is best left to the 1984 Z28, not because of your "unique and unusual response." Some things are unusual for a reason.

 

License for a 30 MPH cat ?? what in the hell are you talking about ??

Lifter failures on DOD engines are only occurring when engines are run in 4 cyl mode---In 4 cyl mode the oil is shut off to the oil passages to the lifters on the cylinders that are shut off--so the only oiling those lifters gets is from "splash"--turning out the AFM in your tune will not only prevent the 4 cyl mode but will allow full oiling to the lifters all the time-----
If you want to go to the next step and install a DOD deleted cam that is a whole different thing---With DOD the lift and duration are limited to prevent PYV clearance---so on a all HP build you would totally delete the AFM with a AFM delete kit which will allow you to install a much more aggressive cam---TSP claims on a AFM delete cam you cam gain 121 HP with LT headers---
And if you are NOT in to removing the heads and doing a AFM delete using the STOCK AFM lifter assybly will greatly limit your cam choises and in my experience--put your engine in the risk of lifter failures IF you keep using the AFM---- excessively
I have seen at least 6 2014 engines blow up--Silverados and Corvettes by having the owner continually use the AFM-- The AFM is there strickly to meet CAFE standards--These DI engine have very low oil pressure anyway---so low oil pressure and spash lubrication is a ticket to the dealer for warranty work

 

Just visited a buddy in TX and his shop did the same exact thing to his car...he had no idea until I crawled under to look at his "custom exhaust". I had my suspicions about "custom" since there are plenty of good aftermarket alternatives. To me, it was loud and hollow sounding...like a gutted muffler. I prefer the sound a good exhaust system makes when added to the car (my C6Z has x-pipe & B&B fusions that I run open 90% of the time). Drone was pretty annoying in his car, and even he stated as much and said he was going to look into quieting it down.