Okay I need some clarification here on this whole exhaust system and power no power issue. Trying to approach this from a common sense point of view, there are a few things that don't make sense to me.

On multiple threads I have read where a Cat Back system will not give you any HP increase over stock but headers will give you a sizable increase. This just does not make sense to me. The whole idea behind headers is to improve exhaust flow by reducing back pressure or resistance in the flow path of the exhaust gasses. I understand that headers can be tuned by using different size tube diameter, equalizing or changing the length of the tube runners, etc. and this will be different for each engine type. However, the main goal of the header is to improve flow by reducing the amount of restrictions. Porting heads is another example of doing something to improve flow by making the ports larger, smoother and matching the head ports to the intake ports. With all that said, how is it possible that you gain no HP when you install a less restrictive exhaust system on the car even if it is just from the Cats. To me it is reasonable to think that any reduction in the restriction of exhaust gas flow has to provide some kind of improvement in performance via increased HP.

To prove this point, I would love to see a dyno run with headers, Cat Back system, and CAI installed as the base run ( I think many already have this), then install the factory mufflers back on the car and dyno again. The final dyno run would be with the factory mufflers and stock air intake with the factory filter. Do a comparison and see if HP was lost. I know this is kind of like reverse engineering but it should prove a point.

I have changed the intake and mufflers on my car, but kept the rest of the stock exhuast system. Seat of the pants tells me I did find some good HP increase compared to what the car was stock.

Sorry for being so long winded on this and I am hoping for input from the forum members that have far more knowledge and experience than I do. Your thoughts and comments would be appreciated to help me better understand this issue.

 

The stock exhaust system, though much quieter, is engineered decently to be non-restrictive. Most I have seen with comparative dyno's is 3-5 HP increase with aftermarket cat back.

 

If you can STOP ANALYZING the HP/NO HP exhaust thing and just use this equation it'll be much clearer....THE PEOPLE on here that are telling you there is little to NO GAIN in just an exhaust have spent THOUSANDS in exhaust systems to learn this !!! Myself included.HEADERS work for 20 or 30,more w/a tune.Headers/tune/exhaust on my c5(6spd) put rear wheel HP at around 398-400.So,that's around a 60 HP gain or so. Exhaust is for BETTER SOUND more than anything else.

 

Yep, stock cat back is pretty good. The money for the HP in headers is worth it, for the cat back and mufflers not worth the money, unless you are going for as much HP as you can get. Also, many like the sound through the stock mufflers after adding headers.

 

And that is about what one can expect to gain with less restrictive cats too.

There is more to headers than just less restriction. Sequenced pulses actually can help extract cylinders and that helps gain midrange torque. There are also differences between long tube and short tube headers with where in the rpm range they help. Larger diameter headers move the boost portion up the scale and help with more HP but on the street one drives with torque not horsepower.

 

Analyzing your car to get the most performance for the dollar spent is what everyone on this forum does including me. Hopefully it is also understood that not everyone has thousands of dollars to spend on just an exhaust system right from the get go, but do want to do all they can to improve performace while they put a little back for the really good mods. The idea here is to slowly upgrade over time by taking small steps. Handing someone a car with 400 HP at the rear when they have been used to driving maybe 250 could get very interesting. However, taking those small performance improvement steps and adjusting to the changes a little at a time may prove to be a wise approach. Anyone that thinks you do not need to respect the power these cars have is in for a rude awakening. I appreciate your comments on the performace gains you found.

 

Well, this isn't exactly following your scenario, but this test is on the same dyno on different days, however.

My car with LG Pro Long tubes, Lingenfelter CAI, and stock mufflers dyno'd 382rwhp/380tq

I later added the Borla (Sport) Stinger exahust. I dyno'd 386rwhp/383tq.

Exhaust was a net gain of 4rwhp.

 

i wanna add to this.

sequenced pulses can help extract but in a longer style tube you will not see this benefit. it's actually the diameter and the maintaining of exhaust gas velocity directly out of the port that maximizes scavenging. that said to maintain exhaust gas velocity you need a smaller diameter tube, but a smaller diameter tube will choke off high end mass flow. so what you need is just enough diameter that will handle the max flow of your engine (within reason of diminishing returns) and no more so you get maximimum exhaust gas velocity.

now i mentioned that it doesn't help extract in a long tube, but for sure it helps in short tube. and a final note on long tube, it will still help at the collector but if the header is sufficiently long you will notice the least of benefits there as the critical flows near the head are doing good. that said a perfect header would incorperate all these aspects. i would take a long tube of this sort every time.

so it makes total sense what you said about larger diameters move the boost portion up the scale because they're favoring higher end flows.

while it's tru that torque is important, ti's not seperable from horsepower. it's mainly an issue of gearing but we'll all agree that if you have a torque or horsepower band that falls off and it's not a result of more gear loading, that's a bad thing.

 

Thank you for the post as this is what I was trying to explain..you did pick up HP as well as some torque on top of the gains the headers and intake already gave you. The question now is would those gains have been more or less without the headers and CAI. I ask this because the headers and intake already provided a substantial inprovement in your flow and I think you could assume at some point you are approaching an optimum flow level. The closer you get to this level the harder it will be to gain power from flow related modifications. BTW congrats on the good numbers you achieved with the modifications made.