I have recently installed a used HKS Carbon Ti Exhaust system on my 2004 WRX. I paid 1/4 of the new price, it has about 5000 miles on it.

Anyway, there are some pros and cons.

Much less turbo lag, due to less back pressure and it sounds awesome.

However, I am not sure it there is any more power available from it. It almost feels like less.

With the stock exhaust, you can feel when the turbo spins up and boosts the power. With this much freer flowing exhaust, I'm almost wondering if there is not enouch back pressure.

The acceleration with the HKS exhaust is smoother, and the turbo spins up sooner, but it feels like the acceleration flattens out, when normally it would continue to pull.

Has anyone else experienced this situation? Would I be better off with a slightly more restrictive exhaust, say the STI exhaust.

Would anyone be interested in purchasing this one from me?

Any thoughts on this would be appreciated.

 

Im not pretending to be an expert, however I did lots of research befor I bought my cat back system for my 04 sadan(same color, nice!!!!) I think what you are experiencing is the 3' factor. The HKS and meany other aftermarket systems use 3inch pipe... this defenitly takes away some backpresure and lowend torq. What you do get is better high end HP numbers(which the HKS has, the highest numbers)...this does not nesicarly translate into more usable power.

I bought the Hayward and Scott exhaust system. This is the old scoobysport setup. It uses 2.5' pipe from the cat to the back box. I sware I have more lowend grunt now......

Anyways... check out this site about half way down and he talks about how 3' is over kill for anything under 350hp or so

http://www.rallyperformance.com/engine.shtml

Im sure the exhaust is high quality...this just might help you understand whats goign on a little better......

 

I have an 02 WRX I experienced the same thing when I first put it in...

I also did a lot of research.. and in that research was some dyno graphs.... with a completely stock WRX Vs one with just the HKS catback the one with a catback has improved HP and Torque at every point in the power band... infact it makes a minimum of about 9 HP and 3 torque at any given point. That "less boosting" you're feeling is actually the engine not having to try as hard to accelerate. they have all the graphs and explinations right on the HKS website.

 

I experienced the same phenomenon, low end power felt weak, but top end was great. I got rid of mine because I do a lot of city driving, and I now enjoy my low end power more. I have heard that reseting your ecu may help, (I sold mine before I heard that one ) The power is great on top and the sound is intoxicating, , I will buy another one when my warranty runs out and I can go turbo back!

 

yeah you DEFINITLY NEED to reset your ECU...

also you should notice you can drive all the way down at 1500RPM

I dont know about anyone else but before I put the catback in driving so much as a hair below 2000RPM the car would pretty much just choke. after the cat back you can drive just smooth and dandy all the way down at 1500

you do get more low end according to the REAL dyno... the but tdyno dissagrees untill you try driving at stupid low RPM and realize there's new power where there wasn't before

 

Yeah, I'm and idiot, the more I think about it the more I wish I would have RESET MY *#@%ing ECU, maybe I would not have sold it for $500. The exhaust made my idle dive down to almost stall rpms when I came to a stop and put it in neutral, and then it would climb back up. The down up wavering and nearly stalling when letting off the gas inand putting the car in neutral did worry me. GUESS I SHOULD HAVE RESET THAT NICE, OVERLY SMART ECU. Oh wait that was just me being in idiot. Live and learn. Get the exhaust, you'll love it! Twisted Symphony, you are 100% right! Thanks for the knowlegable insight!

 

This is a good post because I just bought a blitz nur spec cat-back and noticed similar results, but (idiotically) just ignored it because it sounds awesome!

Just one question....HOW DO I RESET MY ECU??? Will be any forseen problems in resetting my ECU?

Thanks!

 

you can reset it by disconnecting the battery for an hour and a half or longer (might be shorter but better safe than sorry)

or and I could be mistaken about this. you start your car then shut it off but put the key in the on position then quickly push the brake on and off about 20 times

I could be wrong about this but I'm sure you could find it on a form somewhere. I tried it once when my car was giving me a check engine light for trying to drive with out the gauge cluster in (heh; dont do that) and it seemed to work. but definitly leaving the battery disconnected will work.

You should note you're car will run a littl crappy for about a week until it learns but DONT DRIVE ANY DIFFERENT because how you drive in that first week will determine how your car reacts to your driving. oh yeah and be sure to write down your stereo presets because you'll loose that and your clock time and everything when you disconnect the battery.

also if you dont reset your ECU your car will eventually learn but it will take months instead of just a few days

 

Thanks to all for your posts, I'll try it this tonight and post results in a few days.