Hi guys,

Quick question to your Mod pros. Im thinking of an upgraded exhaust for my C5 coupe. I've got No mods so far. I've been told Exhust/Intake are the first mods most ppl do. So here are the 2 questions -
#1. By laws of physics, shouldn't the smooth (free flow) breathing increase HP and gas milage for a car? (Free flow/less restrictive air intake and free flow exhaust) ? If this theory is True, then why do some ppl say changing the exhaust makes no improvement to HP, and gas milage goes down a little?

#2. I'm debating between Z06Ti, Borla & Corsa (maybe GHL). I'm not looking for something too noisy or loud. Just something that had a *lil* deep tone to it, and would be aggresive at WOT. Also should look nice. In terms of looks I want the wides pipes in the back, at least 3.5 inches to 4 inch tips. (Having an aggresive look, but not too aggresive in noise). Is there something you can suggest?

Thanks for answing my two questions. You guys are the best. This forum is more informative than a Vette magazine...

 

The reason people say exhaust change by itself makes no improvement, is that in C5s, the stock intake is the weakest link.

It's like a one lane road feeding a four lane highway. Widening the highway won't increase flow through the one lane road. At some point when you improve intake flow, then exahust flow becomes a limitation as well.

Bit of an extreme for an example, but hopefully it demonstrates the point.

 

I am taking a 'moderate' approach to this...First I put on a Halltech Stinger intake filter and airbridge. This gets rid of the small intake aribridge and accordian flex pipe. Blackwing is another setup that a lot of people use with similar results. THis alone made a feelable difference in throttle response. FOr best results, you want to do a 'relearn' procedure too so your computer can adjust to the lower restriction filter/intake. These types of systems will also breath well enough to work with better intake manifolds and cams, if you ever get that far. After the engine, exhaust manifolds and cats are the restriction point. The muffler section will have a lot to do with noise but not as much to do with power or effenciency. I just installed a ZO6 Titanium muffler setup, and even with stock manifolds and cats, I can feel a little better throttle response at lower RPMs, and the sound is just a tad louder that stockers. I plan to do L-G or Kooks long tube headers and higher flow cats sometime later. This is when the HP at mid and higher RPMs will come on. Don't bother with shorty headers, the long tube ones will help wth mid-band HP and torque, whichis what your after. At the same time as the headers/cats, plan on a real Dyno tune to reprogram your engine computer to take advantage of the better breathing. If you have an A4, the shift points can also be made more optimal, as the transmission is computer controlled. Results seem to vary, but there is a large body of evidence that improving the flow before and after the stock engine really helps the quickness of response, and to some extent the total available HP. There are plenty of cheaper headers than Kooks and L-G Motorsports, but this forum is filled with stories of problems of fitment and longevity with many of them. There are some that have a real problem history and are to be avoided, and some that seem to be just fine, but that are not on my personal list to choose from. I am choosing to save up and get the 'reputed best' , cause they will FIT and they will LAST. Freedom from hassle has its value to me. It will be intersting to see what others here have to offer, many of the members are much father along in the mods than I am, and can speak from direct experience, rather than 'parrot' what other have done. Good luck!!!!!!!!

 

Your theory is incorrect insofar as C5's are concerned.

Intake will give you an immediate increase in horsepower. Cat back will not. Why? The restrictive exhaust manifolds, horrible cats (4 in some cases!!) and inefficient H pipe.

That is why a complete HEADERS systems makes such a huge difference (30+rwhp in some cases). You would be replacing everything from the heads to the cat back system. At that point, a free flowing cat back will net you a few ponies.

With the stock system (or the Ti) or any restrictive cat back, you gain very little.

Stingers, B&B Bullets, SLP Loudmouths plus headers will give you the biggest bang.

EG

 

I have to fully agree with EG on this one. If you have to go step by step, go with the biggest bottleneck first and you will see the best increase soonest. The bottlenecks are (IMHO and in order of restriction) headers, filter/airbridge, mufflers, cats, H-pipe.

 

If I can gain a simple 30+rwhp with new header back exhaust, why doesn't Chevy do that for me at the factory? They know I was not looking for a creme puff when I bought the vette. Why do I have to spend the time and $$ to do it right?

...just a thought.

 

Cost. Complexity. Warranty. EPA. Mileage. Environmentals.

Should I say more?

 

Bureaucracy always cost me $$

 

And emissions.

 

Bottom line is there is probably 125-150rwhp going begging in your C5 that just needs releasing.

New heads, headers, intake and cam will release that power.

It is completely unrealistic to expect GM to sell a highly tuned car at the volumes that they sell the Corvette (300,000 units) and honour the warranty, reliability, pass emissions, avoid gas guzzler tax, idle, be quiet, make the Sunday Drivers and Garage Queens happy and sell for $50,000.

That is just not reality.

 

I had the same dilemna when I was deciding on those mods. I finally decided on the GHL Magnum Plus system with dual 4" tips(6" mufflers). I am certain that you will love that setup. They have a nice low rumble and are definitely not too loud. Plus, with those giant dual tips they really look mean. I also added a Z06(2002+) airbox and with those mods I definitely felt a difference in acceleration. Good luck with your decision.

 

If you get intake and exhasut mods, particularly headers, etc., be sure to do the the LS1 edit/dyno tune to optimize the performance of your mods.

 

So for a stock Z06, the last thing I need to get for more hp is the exhaust I take it?

should I not even bother with exhaust? I mean, everyone seems to say the Ti exhaust is just as free flowing as the borla/corsa.. etc... if not exact, almost... and not enough to tell

So should I just free up the intake and headers and x-pipe and leave the Ti? would that yield just about as much as the same setup with borlas?

 

For a stock Z06, you won't gain much with an aftermarket exhaust. From an HP standpoint, you're fine sticking with the TI if you're adding headers and x-pipe. I'd suggest that you'd add hi-flo cats as well.

Now, if you have future plans that will make tons of power, then you might want to consider a better flowing exhaust such as Borla, B&B, GHL, or MagnaFlow. The TIs will not flow as well as these aftermarket exhausts once you get over 450 rwhp, especially in twin turbo applications.

 

It's not as simple as just making as smooth as possible the path for the exhaust. Remember, in any internal combustion engine, the exhaust isn't coming out in 'smooth' and continuous streams, but is coming out in puffs from each cylinder, as a result of a combustion process which is carried out under controlled (but not perfectly controlled) conditions. Due to the valve overlap of the cam intake and exhaust lobes, a certain amount of backpressure is beneficial to the system, both for emissions purposes and power purposes. A straight through system is most beneficial at high rpm (drag race) conditions, but not so good for daily running. So an exhaust that is too "free flowing" may (and usually does) lose significant amounts of low end torque in exchange for high end performance. Efforts to balance back pressue to each cylinder are evidenced by the design of long tube headers to be as much as possible "equal length", which explains the goofy curves some of them have in the rear tubes.

So, unless you're running ballstothewalls all the time, you probably want some restriction in your exhaust system.

 

at this point that's exactly what you should do.

 

here is my .02

Skip the Headers if you are not going to change the stock cam and heads. For the cost you would get more bang for the buck with changing your gears and your 1/4 mile times will drop more.

If beyond that you want a bit deeper sound then change your cat-back only. This will give your car a nice sound without being too overly loud (well if there is a such thing as too loud)....

I would also suggest swapping out the stock air filter system for something that will give the car more air flow in.

 

Although I prefer Z06Ti or GHL...
Magna flow has great WOT V-8 sound and quiet when not wanting to be agressive! ..and prolly among the best made exhaust...
It is one of the least restrictive systems you can install too...
...with documented more rwhp...

Intake should provide the coolest air possible...
...Id take cool air or compressed air over "smooth flow" of air...

If your looking for more hp...make those changes and then dyno tune the vette to yank 25-30+ rwhp

 

You will get much better seat of the pants improvements going with a higher stall torque converter and gears rather than headers and catback system if you do not plan on modding the engine. Swapping out the air intake is a no brainer because aftermarket systems are so cheap and provide very good gains. So many people here are focused on peak horsepower numbers, but this is only a piece of the puzzle. Despite that fact that you wont see the real differene on the dyno, a 3600SS Torque converter and 3.73s will keep you in the high rpms between shifts and drastically improve acceleration whether you currently have 2.73s or 3.15s.

Yes, the better exhuast flow will be necessary if you go with a heads/cam etc, but if you do not plan on going this route, the gains you will experience will be dissappointing compared to the nearly 2 grand you may choose to spend on a set of LGs. However, sound may also be a consideration. Personally, I have the dynatechs and love the sound. It is incredibly mean and, when combined with a good catback system, may be worth the money for just the roar.

 

Great post! also do not forget about scavanging that improves exhaust system performance. A properly tuned exhaust will utilize air momentum from each exhaust valve release to aid in scavanging the next cylinder, which is why bigger pipe is not always better. Too big of pipe and you lose any scavanging capabilities. This is why a matched system is so important.

Another reason for no major gains on catbacks is that the factory catbacks (especially Z06) are not very restrictive in the first place. At least not the primary bottleneck as stated above.