Looking for as much information as I can get and some opposing viewpoints. I have a '15 Z51 M7 with a CAI and ported TB and I am going to add a ported intake and headers. I have been going back and forth between ARH Long Tubes with hi-flo catted X Pipe or Mid-lengths with hi-flo catted down pipe. My car is currently tuned by DiabLew and he will retune after the install.

My questions are:

What type of gains can I expect from each with the ported intake?
Should I have concerns about passing emissions in New York with either setup?
Is there anything else I should be concerned about with either setup?
Gas smell on startup or idle in the garage?

I really appreciate anything anyone can pass along, thank you!

 

Engine Masters did a video years back, comparing exhaust manifold v. shorties v. long tube headers. Long tube headers made the most power. They were not connected to cats or x-pipe, just straight. I'm not sure how much loss there is on catted x-pipe, but it couldn't be much. With no cats, you'll get gas smell (trust me, this is my current setup). I don't have emissions testing, so not sure how to answer.

 

LTs will give you 25ish rwhp, the mids will likely be 15ish with a tune on an LT1.

Passing emissions with LTs depends on how they test in NY. If it's just visual inspection and looking for OBD2 codes you will probably be fine once your tuner tunes out the CEL from the LTs. Even with cats you lose the rear O2s with LTs and the cats are in a different place compared to OEM so you will trigger a CEL. You will fail a sniff test with LTs, cats or not. Mids are likely the same, not 100% sure but others may chime in.

LTs will be very, very loud compared to the OEM exhaust. Wake the dead loud even with the NPP exhaust when in sport or track. They sound very tinny in tour but the volume is much better. If I'd known how loud they are I likely wouldn't have gone with LTs on my daily driver Z06. The power is great on the LT4 but the noise is significant. It sounds awesome but it's a bit loud for a daily driver imho. The mids will tone it down some. Something else to consider is the LTs will create a lot more engine/drivetrain noise in the cabin. The thin-walled steel transmits a lot more noise into the cabin besides just the increase in volume from the exhaust. You won't be able to talk to a passenger if you're on it above 4k RPMs. The mids probably do something similar but it will be toned down by their shorter length.

You will have a gas smell when cold at startup in the garage with or without cats if you go with LTs. It will be worse without cats though. My LTs have cats and its worse than OEM by a good bit but I am pretty sure I have an exhaust leak somewhere. Something else you may have to deal with once you start monkeying with the headers/exhaust.

Honestly, you will get more gains from a flex-fuel sensor (30ish rwhp conservatively on E85) and tune vs headers/mids/down-pipes and can keep the OEM manifolds so you don't have any issues with emmisions testing. Flex sensor plus install is around $1k plus whatever the tune will cost so it's also substantially less than headers. Just verify your tuner can tune for Ethanol. The sensor allows you to run anything between pump gas ( could be up to E10) and full E85, it will tell the ECU the ethanol % and the ECU will adjust timing automatically once the tables are unlocked for it. Just another option to think about.

 

Great information and very helpful, thank you!

 

GM has probably done the best job on their exhaust manifolds and cats. On my old 16 Camaro before I broke the motor with too much boost I ran 10.00 at 139 with a totally stock exhaust system and a Magnuson 2300 SC. No other internal mods, MS109 race fuel and an Lt4 fuel system. I didn't add long tubes until I built the new short block.

 

I appreciate all three posts, thanks. You guys have given me a lot to think about. The car runs great on the tune I have, I might be better off not messing with the headers/cats.

 

An "advanced search" across the C7 part of the Forum will ID this same or similar question repeatedly. Given that, the bottom-line for me is... if you are going to the trouble why not simply do it right and put on long-tubes (with a tune) so it's worth the effort. However, a tune will potentially cost any remaining drive-train warranty you may have if needed later. Just be aware. And, do NOT get some cheapo no-name headers... you or your installer, like others, will likely regret it during the install. All the best!

 

We usually recommend just jumping right into the long tubes. If you're worried about gas smells stick with the high flow cats as the off road pipes are going to give you a raw gas smell. The cats will also help keep the rasp down and the exhaust rumble smoother. A ported intake should be worth maybe 5-10hp but the headers are usually worth around 30rwhp with a tune.
If you order the headers and a HP tuners kit from us we can send you a free tune.
As far as the warranty goes some dealers may give you a hard time but these days they seem to take all the business they can get. We have a few local to us that will work on just about anything without heavy internal mods. They won't even look twice at a car with headers.

 

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Dave

 

Thanks for all of the feedback!

 

I have catless ARA 2 in Long tubes. The smell is minimal. I'm glad that I went catless! Sounds great! Borla Atak exhaust with NPP black tips.

 

I installed the ARH catted midlength headers on my C7 Z51 about a year ago along with a catless x pipe. I have a very detailed self-compiled (from a ton of research) guide for install if you need it. The whole install took right at 8 hours for me. I've got lots of car wrenching experience but had no specific corvette experience prior. I love the sound -- and if you check my post history you'll see my initial thoughts on the headers. They are as loud as any street car should reasonably be -- and despite what others say, the mids are no louder/quieter than the full-length headers. The ONLY difference in volume between headers is the inclusion/exclusion of cats. I confirmed with ARH and others on the subject before buying -- there is no volume difference unless you opt for NO cats. There IS a slight difference in tone, but it's not significant, and not describable (as everyone has a different ear and definition of words like 'deep', 'throaty', etc). Definitely recommend going with ARH! No issues with CEL. No smell of gas with hi-flow cats either.

EDIT: I should also note that since last year I've put 15k miles on my car -- its my daily driver and therefore I can say that i've got experience with these headers.

 

if you have a install guide for the mid lengths, I would interested in taking a look. That would be very helpful!

 

Found this post when doing some research on ARH mid-length headers. I have a 2014 Z51 with a Corsa (catless x-pipe) + Corsa Xtreme axle back. Would you mind sharing your expertise on the following questions?:
- Did a tune on your car after installation?
- As far as tone is concerned, in your opinion is it deeper or higher pitched than stock manifolds?
- Do the mid-length headers replace the manifolds AND the stock downpipes or just the manifolds?

 

I will answer your questions ....
1 - Installing headers without tuning is like taking a shower with your shoes on , could you , yes , but would you , no , 40 to 50% of the power gain is going to come from the tune

2- With NPP , at idle , its a bit louder , at wide open throttle , it sounds like Satan banging on the gates of hell ....

3- Headers replace the manifolds and the down pipe

So the bigger question is , why are you going with MID Length and not long tubes .... both are the SAME amount of work to install but

Long tubes make much more power and torque

Dave

 

Thanks for the response. Simply put, I'm really only interested in the sound, not making max HP / Tq numbers. My car is a weekend fun toy that I take on drives with like minded people. I don't track it or street race...

Perhaps incorrect, I had read that the mid-lengths were less prone to fitment issues = potentially an easier install. Perhaps this was brand related more than anything.

Also, perhaps incorrect, I had read that midlengths didnt require the tune (again im not looking for max HP / Tq). I would plan on keeping the cats. I'm not opposed to getting a tune, but didn't want it mandatory to avoid CEL's.

Thanks again for the response.

[edit] also and lastly I didn't want to replace my catless x-pipe that I already have with another x-pipe from ARH or Kooks to mate to their LT headers. I was under the impression thats required if using LT's... If that makes sense.

 

Mid lengths might not need a tune , and they have sold them as not needing a tune as an advantage , but that does not mean that your AFR is correct ... . Its like bolting a carburetor on your old small block and not changing the jets , plus the O2 sensors are now in a different spot .... this alone is enough reason to get it tuned .
Running rich or lean is not good ....plus the drivablity suffers

You would have to buy cats from the header manufacturers as the oem cats will not bolt up to mid lengths pipes

Fitment is all about brand .... there are some mid lenght headers that fit terrible

I get wanting to use your x pipe but the installation labor/cost / tune is all going to be the same with mid lenght or long tubes, why would you not want to get the most bang for the buck ...
Dave

 

All great points for consideration. I appreciate your experience with this as its given some new info to think over before deciding. Thanks again.

 

No problem feel free to PM me or email me thru these forums if you have anymore questions !

Good luck

Dave

 

I would like to toss m y .02 in on this subject. for my car I knew it would never make much over 800 wheel hp. had 4 digit power cars to much work.
that said the npp catback oem exhaust is so nice to be able to go from loud to quiet. knew I wanted to keep that. started out with a eos mid pipe. no secondary cats and it increased the sound but not by a bunch. BUT got them on sale for 200$. who doesnt love a deal considering the other brands want 500-700$ for 30$ worth of tubing!! another sale and ordered the catless downpipes. battled with the car getting the oem downpipes off and the new ones on for hrs. sound was awesome!! so loud! then hit the button and nice and quiet. best of both worlds and cost was under 500$ all in. DOWNSIDE... the smell was horrible. stop at a red light and it was immediately overpowering. decided to remove the mid pipe and reinstall the oem . this solved the smell issue. ditched the clunky cats so power gain was who knows 10-15 hp? honestly the oem setup will prolly handle 700 wheel or better before becoming a bottleneck. read a thread about headers and the o/p bought a set of eos long tube headers. 600$!!!! considering the cost off kooks or arh at 2500-3000$ this is a steal. 321 stainless thick header flanges 1.8" primaries as compared to 1.75 on others and read the fitment was good. so I ordered a set.
on backorder of course waited 3 months. and here they are. 2 piece past the collector but WAIT! no mid pipe change needed. you slide the extension on clamp it and it fits oem mid pipe. also fits the catless pipes. other brands you have to use the mid pipe they sell for an additional cost. now im not a fan of clamps so I mocked them up and had my buddy tig weld them into a 1 piece header. fitment was sweet they slide right in place dont hit anything. total cost for my setup is about 900$ (with welding) and if I dont like the smell on pump 93 I cant swap the oem pipe in in minutes.

dont know how much power gain there is yet doing other things but this is a fantastic alternative to the mega high priced headers on the market and for my power goals of 750-800 wheel they should perform just fine . all the hardware gaskets and clamps are included. only thing I didnt get were o2 extenders and im not sure if I even need them since I dont run second sensors.