I put this question in the Tech section too...but since we are dealing with a SC too I thought you could help.

Ok I know it will come down to my ear ultimately but still looking for your input.

My stock 05 Z51 M6 is getting an E-force supercharger at the same time my axle back Borla S Type II will be installed. Lot's of thought went into selecting the Borla's with #1 concern being NO DRONE at highway cruising speed but nice note when I put my foot into it. Lot's of feedback from those that seem to be like me that they really love their Type II so rest easy.

So I'm not chasing a RWHP number with the SC and it is what it is when it is all tuned up but I totally understand that the engine is a big pump and now will have more pumping power. I'm questioning my plan to leave the stock exhaust manifold and cats on, knowing this will be the choke point for back pressure and I'm only going with mild boost 6-8 lbs. vs. making the pump more efficient with headers and open mid pipes to the Borla's.

Why don't I just put the headers on and mid pipes let my tuner have a little more fun, put a smaller pulley on it to get back the 2 lbs. I'd have to make up and get a little more RWHP (who doesn't want that) all while the car is conveniently in the speed shop getting work done on a rack and dyno? Why...because I am DRONE-APHOBIC!

The conservative me strategy is to see how the Borla's sound with the stock exhaust and if I even will miss the 20-40 extra HP the headers & pipes will give me if I am happy there is NO DRONE! I can always go back and put them on later...but probably a few coins more expensive to mobilize the shop again for the install than if they did it while already on the rack.

My tuner said the headers and pipes would definitely change the tone of the Borlas making them a bit deeper...and louder! I don't need louder and a DRONE I told him and he countered with we could put a mild resonator on them to tame them down if that was the case. Obviously he would like more airflow to play with from a performance standpoint.

Your thoughts? Anyone go down this path before?

 

Since nobody else seems interested, I'll add my 2 cents.

You can definitely have a free-flowing exhaust that has no drone at cruising speeds. As long as you choose the right mufflers, you'll be fine with a set of long tube headers and high-flow cats. I don't have any personal experience with the Borla S type mufflers, so I can't really help you there. I thought I remembered a lot of Borla systems having noticeable resonance, but don't quote me on that.

"Drone" is caused more by muffler style/design than headers based on my experience. Sounds like you're mostly worried about interior resonance when cruising, and that is understandable. You definitely have some options though.

Corsa Sport mufflers are a great choice if you want something that is aggressive sounding during acceleration, but has basically zero drone. I've ran them with stock manifolds and with headers, and it's really hard to tell the difference when cruising with the windows up. I wasn't a huge fan of the tone they produce, but that's really a subjective thing.

If you want the best of both worlds, pick up a set of factory NPP dual-mode mufflers. They will be quieter than a regular C6 muffler when the flaps are in the "closed" position, and have a nice throaty sound when they are "open". Even with headers and high-flow cats, they are extremely quiet with the flaps closed. With this type of muffler, you can choose if you want it whisper quiet or very noticeable.

If it were my car.... I'd throw on a set of headers and NPP mufflers. It'll be quieter than the Borlas and stock manifolds when you want it to be, but make more power and likely hold up better than the stock cats will.

 

Thanks for taking the time to reply Street. Good to hear your opinion about the headers and long pipes...I am committed to the Borla S Type II after many hours of reading so I think I'm good from the axle back mufflers and sound. I have to use my imagination about what tube headers and long tube or cat through pipes might do to the resonance so your comments certainly helps.

 

My car is identical to yours. I do not have an eforce kit, but I have an A&A kit. Along with that I have kooks 1 7/8 headers with catted x pipe, and borla s type II mufflers. I do not experience any drone with this set up.

The car is fairly loud under heavy acceleration, but no resonance.

 

With the blower my npp setup is louder at WOT than most the other vettes around and near silent cruising. Still my favorite for vettes.

 

I love this site....thanks Blk Beauty...doesn't get more specific than that!!!

 

I guess my point was that I'd be more concerned with the engine performance, and make adding a good set of headers your priority. Then you just need to find an axle-back system that fits your needs (tone, sound level, drone level, etc.). Sometimes it takes some trial and error to find one you really like.

Just realize that if/when you add headers, it will make whatever mufflers you go with louder overall. I'd imagine the Borla S Types with long tubes will be pretty loud at WOT. I like being able to have a "stealth" mode, so the NPP or ZR1 exhausts are great for me.

 

I pulled out the Dork mode when I posted to you last time when I went back and read it. I have the Borla's in a box and have had for a few months so returning them is not an option...they are going on because...well...they are paid for... And I don't mind loud when I put my foot into it because it's a Vette I just want it to mellow out when I'm cruising at highway speeds. Many reviews gave me the confidence to go with the Type II so really I'm down to leaving more known performance on the table with my stock exhaust pipes & Borla's and experience the sound...or just go for it...you know.

 

I'm sure the Borlas and stock manifolds will be pretty mellow overall. Headers tend to make whatever muffler you have louder and more aggressive sounding, but are pretty much a must do mod when adding a blower. You're leaving quite a bit of power on the table and a lot of guys have problems melting the stock cats, so it's something to keep in mind.

Loud at WOT and quiet at cruise is why GM engineered all the dual-mode exhaust systems. They're pretty hard to beat in that regard. Most performance mufflers add some drone at cruise. Corsas are the only ones I've ever had that didn't.