Okay, since we have started the topic, I'll join in with some questions. I was planning to start a thread asking my questions on the entire exhaust system as my warranty got closer to expiring but might as well start now. I kind of have a problem with basically throwing away a perfectly good exhaust system. It looks like Chapel has answered a lot of my questions.
First, do any of these answers change with a L99 vice a L3?
I am pretty sure they are the same. I have never seen any company offer a different part number based on the trans. So they should fit regardless.
My perception is that long tubes give better performance because the individual tubes are longer and the exhaust turbulence is not as bad by the time the individual tubes are combined, correct? (I think this was sort of answered but want to make sure) Similarly, larger tube diameters lessen the restriction for the exhaust, thereby bigger is better efficiency (conditional on the installation as mentioned)
Some of the headers have a longer collector. I guess this would cut down on turbulence. I haven't seen this brought up or compared in a test so I don't know if there would be any significant difference. But I would stay away from any brand that has a noticeably smaller collector length-wise. LT headers excel over STs and OEM manifolds in flow and scavenging and they allow the engine to operate with less exhaust restriction and more efficiency.
As far as bigger is better, it does seem that way. A test was done comparing 1-3/8th vs 1-7/8th vs 2 inch headers. The 1-3/4 made the least power. The 1-7/8th made more power everywhere in the RPM range over the 1-3/4. The 2 inch made more power in the higher RPMs than the other two...but in the lower RPMs the 1-7/8th was neck and neck. So it came down to the price. At the time of the testing the 2 inch headers were a lot more expensive than the other 2 sizes. And the performance gains on a N/A car did not really justify spending that extra money. TSP now offers the 2 inch at the same price as the 1-7/8th inch. So again, it comes down to possible fitment issues. On a highly modded car the 2 inch would have more of a difference. And obviously with boost the 2 inch is better.
High flow cats perform the same as OEM with regard to emissions? I may have to pass an emissions inspection one day (don't now, but could be in my future). I don't think I can completely remove the cats without getting in trouble or taking the chance.
I doubt they perform the same. The OEM cats have a higher count substrate or something like that. And there are 4 total. There will only be 2 HF cats. And the count is significantly less than OEM. So while it does still work fine, the HF cats will not be equal to OEM. You will notice this in the smell. It won't be terrible, but you will always be able to tell HF cats from OEM just by the smell. Catless will give you all but unbearable gas fumes...especially in traffic in warmer weather.
I heard about these Green cats. They are supposed to flow just as good as regular HF cats and I heard they work almost just as good if not just as good as OEM. I will have to look them up.
Can you give a quick tutorial on what a tune actually does and how it is accomplished? I see it referenced a lot and think I get the gist that you have to take it somewhere to get it done and it is based upon the mods you make, but that is about it. Why might it void your warranty?
Tunes are either canned and generic, or custom, or a dyno tune to up the performance. Diablosport handheld tuners that have a basic tune from Diablosport. These simply alter the timing, shift points, shift firmness, AFR, and other parameters to give better performance. Additionally, they can get rid of some of the annoying performance robbing features (like skip-shift) that come programmed in the ECU.
The next type of tune is a custom tune. This is better than a pre-programmed handheld tuner in that it is specific to your car. A tuner will ask you to datalog with specific instructions and specific parameters. Once you datalog you can download the file to your desktop/laptop and email the file. The tuner then creates a tune based on those results and emails the tune to you. You then load the tune onto your programmer, into your car, and then drive it for a certain amount of miles to let the ECU learn and adjust to the tune. The process is done again, usually 2-3 times or until the tuner feels the tune is at it's best and safest performance potential. These tunes require you to have a handheld tuner. And the tuner usually gives you a certain amount of time that you can have free updates based on mods. You will need this type of tune when you get headers. So for now you can get a handheld and use the pre-programmed tune. Then get a custom tune when you get headers. And then you can upgrade with a CAI, cat-back, power wedge, etc if you don't already have those.
A dyno tune is the most accurate and specific. This is the only way to go if you get a cam. A supercharger like Vortech usually comes with pre-programmed tunes that are trustworthy. But if your car is not otherwise bone stock, then you cannot use that tune as it will not be correct. And even still, a dyno tune will be better as far as performance. But a dyno tune also costs a lot more. Usually $400-$700 dollars.
Any altering of the ECU will result in the dealer voiding your warranty. Basically because you risk damaging your engine and trans. So they don't like the ECU getting effed with. Some tuners claim and guarantee that their tunes cannot be detected. On the other hand, the dealers all claim that they can and will find any tune if it is written in the ECU. There was a huge debate a few times over this with neither side providing substantial proof to support their claims. So you basically have to take the risk. If you tune, then return the car to stock before going in for warranty work and pray to god the tuners are right. If you have a good relationship with your contract holder, then maybe talk to them and see if they'll allow tuning. Sometimes they will if you buy the parts from them and let them do the labor. But this will negate any money you could save. But if that engine blows then it may be worth it. It's all up to what you feel comfortable with.
On a scale of 1 to 10, with 1 being OEM and 10 being LT, where do ST rate? A lot closer to 1 or closer to 10 or simply a 5 in the middle?
OEM manifolds are pretty decent these days. And the factories are gonna start making STs optional soon if they haven't done so already. STs will flow better than OEM. I would rate them about a 6 or 7. See, LTs get high numbers on the dyno because they need custom tunes and HF cats/test pipes. So that 30 hp you might see is not all from the headers themselves. STs with an otherwise stock exhaust and stock tune might get you about 5-10 hp. Add in a custom tune and those HF cats and the gap will close. But LTs will still have a huge power advantage. If you ever wanna go turbo tho, you will need the stock manifolds...just to let you know.
And finally, what are the properties of a good exhaust, cat back, bigger tubes? I'm totally at a loss here, but I think VA is pretty restrictive, so I am assuming I probably cannot delete anything related to the emissions and maybe some restrictions on noise.
Any help would be appreciated. TIA
You can get a cat-back in the stock size which is 2.5 inches...or larger than stock at 3 inches. I am pretty sure the 3 inch will be louder. But that is all depending on the muffler. Some mufflers are super loud and some are quiet. My exhaust roars when I get on it. Otherwise it has a good amount of sound to it. Some others will be able to chime in. You could look into the GMPP axle-back which has a great sound and should give you no problems with inspection. I recommend getting an entire cat-back tho...that is just what I personally prefer.