Kracka

After reading a thread on here about adding an aftermarket X-pipe to an otherwise stock exhasut system (https://www.corvetteforum.com/forums...stock-npp.html) I decided to start looking into it further. There aren't many options on the market yet, but I picked up what is currently the most popular (Corsa Double Helixx) plus another that I think will also prove effective and popular (Borla part #60547) to compare them side-by-side with the stock X-pipe and ultimately decide which, if any, to install on my car (2014 Z51 w/NPP). Until now, my exhaust system was 100% stock. Due to a past history of going overboard on modding my street vehicles, when I ordered this car last winter I promised myself I'd take it slow and only add modifications that don't have any drawbacks to drivability and livability, plus remain somewhat emissions and hopefully warranty friendly. It's not my DD car, but I do take it on quite a few roadtrips, dinner on the weekends, etc. in addition to performance driving orientated events

Stock exhaust specs
-catted downpipes: 3.0" outlets
-X-pipe: 3.0" inlets w/3" cats*, reduces to 2.75" immediately post-cats, single 2.75" X-crossover, expands to 2.875" at the outlets to slip over the axle-back pipes
-NPP axle-back: 2.75" inlets

The stock X-pipe weighs in at 22.6 lbs, which includes the clamps (welded on) so for comparison sake I'll subtract 1 lb. and call the stock X-pipe to be an equivalent of 21.6 lbs.

*The factory X-pipe cats are not monitored so they can be removed without throwing any check engine lights or error codes.

Borla X-pipe specs
-3.0" inlets, smooth taper to 2.75" after the inlet flange
-2.75" piping with the exception of the in/outlets
-single 2.75" X-crossover
-explands to 2.875" at the outlet to slip over the factory axle-back.
-15.8 lbs for a savings of 5.8 lbs vs. stock

Corsa Double Helixx X-pipe specs
-3.0" inlet
-3.0" piping
-two 3.0" X-crossovers
-3.0" outlet (I noticed that this has to basically be crushed to securely clamp over the stock axle-back pipes, not ideal in my opinion as it seems prone to leaks and internal turbulence)
-19.6 lbs for a savings of 2.0 lbs vs. stock (Corsa claims a 2 lbs weight savings so my measurements confirm this)

Corsa (top) vs. Borla (bottom):


Borla (top) vs. Corsa (bottom):


Stock/Borla/Corsa:


Corsa/Borla/stock:



Stock impressions
For factory exhaust piping, it is very nice in design with decent welds, bends, and transitions. If it wasn't for the cats, I'd probably say it wouldn't be worth the bother to replace unless you wanted to be very particular about some of the bends having a slight crush to them.

Borla impressions
This is a very nice pipe, I feel this is what the stock pipe could have been like if manufacturing costs weren't a concern as it has smoother bends than the factory pipe with no crush to them at all. It is similar in design to stock and follows the stock pipe routing almost exactly. One benefit to that is how it looks nearly factory once installed and partially hidden by the stock tunnel brace. Unless a trained eye knows exactly what they're looking for, I can see this pipe flying under the radar when it comes to warranty claims.

Corsa impressions
This pipe is a beast, it's large and heavy, but seemingly designed for excellent flow (Corsa claims +20% compared to stock). This pipe has the fewest and smoothest bends of the three so that is a plus in my book. The double X does change the tone of the exhaust; some say it makes the car sound more exotic or European vs. the throaty rumble of an American V8. I do wonder if it adds unneeded internal turbulence though? This pipe seems to be the most popular on the market right now, but my guess is that's because it was the first one to become widely available and the fact it's straight 3.0" in design.

My conclusion
I decided to keep the Borla X-pipe on my car. I like the design of it, the weight savings, and it's somewhat stock appearance. Considering the NPP axle-back is also 2.75" in diameter I do not feel I'm giving anything up in regards to the Borla 2.75" vs. Corsa 3.0", but that is just my somewhat experienced guess. The exhaust tone sounds similar to stock, just a bit louder and sharper with the removal of two catalytic converters. They all install very easily with simple hand tools, 1 jack, and 1 jackstand. I'd suggest a 3/8" drive ratchet with an extension or two, sockets in the 13-18mm range, a 15mm wrench (ratcheting if you have it to speed things up), a flat head screwdriver for prying off the gaskets and rubber hangar, and a hammer to pound the gaskets on to the new pipe. You can just jack up one side of the car; I jacked up from the passenger side rear point (just in front of the rear wheel) and put the stand under the passenger side front point (just behind the front wheel).

VetteLT4

didn't happen to take any before and after sound clips did you?

Kracka

No, sorry, I did not.

VetteLT4

i have a corsa sitting in my garage waiting to install. after ultimately deciding against headers, im hoping the xpipe and open valves will be enough to satisfy my sound requirements. when i had my c4, i removed everything from the 2 cats back. just manifolds, 2 cats, and pipe out the back. it sounded like a nascar(well almost) when i was on the pedal. this xpipe seems the closest i can get to that architecture, assuming open valves is relatively close to being straight through...

Kracka

With a catless X-pipe, the car does have a serious bark when firing up. I think you'll be happy with it, it definitely puts the stock exhaust on steroids when the valves are open, yet still quiets down nicely when closed

I say crawl under there and get it installed then post back with your thoughts!

js1977

Very nice detailed review on this!!! It's got me thinking.... Hmmmm

Kracka

Thanks!

balpo

Nice write up and photos. How about a dyno comparision? Anyone?

Kracka

I'll be on the dyno next weekend for some other testing, but unfortunately won't have anything back-to-back for just the X-pipes. Corsa claims 5whp/4wtq which is probably accurate enough for an otherwise stock exhaust system; I'd attribute that to the removal of the two cats more than anything else (piping diameter, design, etc.).

It's the little things that add up though, 5 here, 10 there... I'm not out trying to break any track records, but it makes for a very nice street car!

snakepit

Will the check engine light come on.

Kracka

No, no tune required either. The rear (X-pipe) cats are not monitored, as long as the front downpipe cats stay in place there will be no check engine lights or error codes. The stock o2 sensors are up- and down-stream of only the front cats.

I'm building on my setup to stay 100% compliant with the stock tune so I have no issues when flashing back to stock (Diablo InTune) for trips to the dealership (warranty work, free oil changes, etc.). Next up will be a set of ported & coated OEM exhaust manifolds. In addition to the X-pipe I also already have the AFE intake, Weapon-X ported throttle body, and DiabLew-tuned Diablo InTune.

Jason 98 TA

Great results Kracka! We need to get you to try long tubes some day!! HAHA

I never considered building a x only because I didn't think many of them would sell.

Do you think this is a popular mod to get rid of the rear cats?

Jason
Texas Speed
www.texas-speed.com

Kracka

Thank you! Maybe some day! I actually have a set of AFE PFADT long-tube headers coming, but I'm not totally sure what to do with them yet since they don't fit into my original plans. They appear to be very nice though so who knows, the temptation may get the better of me

I think the X-pipe has the potential to be a very good seller for the guys wanting to just do simple DIY bolt-ons that remain somewhat stock tune/warranty/emissions friendly. It's seems like the Corsa is selling pretty well...I sold my used one the same day I listed it up, and had multiple guys wanting it. I also have another shop (the one that did the ported & coated exhaust manifolds for me, and working on a ported intake manifold) looking into fabbing up their own X-pipe taking certain aspects of both the Borla and Corsa and creating what they feel combines the best each have to offer. Considering your price on the long-tubes, I'd have to imagine you can get an X-pipe to market at a very reasonable price as well. Competition is what makes this marketplace great, and I always look forward to seeing more of it since it not only benefits the customer, but also pushes companies to make the best products possible!

ErnieD

Another data point for you, Jason: If a double x-pipe, like the Corsa, was available, with plenty of "communication" between the two sides, and a price in the $300 range, I'd buy it. Either 3" or 2.75" would be fine. If 3", though, the rear pipe size should be swaged down to 2.875" for a good fit over the axle-back pipes (an issue mentioned relative to the Corsa pipe by Kracka in his post above).

Ernie

Kracka

Out of curiosity, why do you prefer/want a double-X as opposed to the traditional single crossover point? My personal opinion is that would just change the exhaust tone while adding weight, turbulence, and complexity. I view that as Corsa's C7 signature to make their systems unique in design and tone vs. the competition. Again, just my personal thoughts and I'd love to hear what others think.
I fully agree with this, excellent point.

0v3rc10ck3d

Anything you can do to increase volume. Currently axle-back exhaust systems are extremely expensive and headers usually require a tune. A lot of us just want more volume to our exhaust.

ErnieD

That's mostly personal preference. Some folks believe that the X in an X-pipe should be as close to the engine as possible for best performance. Without a lot of real foundation, I tend to subscribe to that idea. When I had an X-pipe fabricated for my C6 Z06 , I had the X placed immediately behind the flanges. If a pipe is fabricated with two X's, one of them is necessarily quite near the front of the pipe.

I think two X's also provide additional exhaust gas blending over what one X would provide. That should result in a slightly smoother (and perhaps slightly quieter) exhaust note -- sometimes stated as more "exotic" sounding rather than "muscle car" sounding. Having said all that, one X near the front of the pipe, with plenty of side-to-side "communication" should work just fine.

I've changed three Corvette H-pipes to X-pipes (an LS1, an LS2, and the above mentioned LS7). In all cases, regardless of location of the X, the X-pipe resulted in a slightly smoother and slightly quieter exhaust note.

Ernie

Kracka

I've heard the same regarding placing the X as close to the engine as possible. I don't fully understand it either, but that's besides the point; hotter exhaust gas, etc. I think a single X near the inlet flanges then a brace between the two pipes that also doubles as the exhaust hanger mount would work well while also keeping the weight down. Borla did a nice job bracing their X and Corsa went almost overboard in rigidity (two X's, brace bar, plus exhaust hanger mount).

One thing to add, I really like how the Borla is NOT polished! Not flashy and doesn't draw any attention to itself once installed above the tunnel brace.

David Borla

Thanks for the feedback!

VetteLT4

pretty much the only reason I did it. little concerned about the size of corsa for clamping over the stock exhaust as mentioned, but I guess ill see how that goes when I install