I got my brand new Stillen cat-back today and had it installed with before/after dynos and air/fuel. Those of you who know about my previous mods will be happy to hear that the before dyno generated just about the same amount of power, 235.9 whp and 216.1 wtq with just 32% humidity and 57 degree weather (my first dyno was very humid and hot so maybe it's a testament to how well the car deals with heat). After the cat-back was installed we did three more runs with just about the same conditions and the car made the same if not less power, 231.7 whp and 222.9 wtq being the best (228 whp and 230 whp were the other two but I don't remember the wtq). Plus I got laughed at by the installer. I'm not sure if it's the combination of mods I have on the car or if the exhaust on the 05s are exceptionally well designed. My air/fuel ratio did not change between before and after modification, running 14.2-14.3 for all runs and hitting 13.6 at the richest point at 6400 rpm. The power curve is exactly the same as before mod. I'm not exactly pleased with the sound, as I'm probably getting old and it's a bit loud for me on take off and acceleration, but there is no drone at highway speeds (it's silent, actually quieter than stock). The exhaust looks splendid and at some rpms sounds good, but for me the low tone rather than the sexy growl was a disappointment; nothing like the pulsy growly VQ note I kept hearing about but more like a smoother Civic. I'm thinking about swapping it back out for my stock unit. The car does feel more eager to move but I'm not sure if it's more power or if it's just a benefit of freer flow. I may just sell it at a discount of 600 to 700 bucks to local G35 sedan owners who care more for sound than power. Or maybe it just needs to break in. For those who don't know, here are my modifications for comparison:

Stillen Z-Tube, MD plenum, MD 1/2" spacer, DC Sports headers, Stillen TD

 

you need a reflash

 

The tuner was unsure how much good a reflash would do since air/fuel did not change and looked acceptable. With new equipment he was hoping to see the ECU over or under compensate for the exhaust. It's still baffling as to why power and a/f were unchanged.

 

Agree, you need to have new maps in your ECU that will take advantage of your mods. Let the exhaust break in a bit. The sound will change in a month or so.

 

^+1, you'd probably be ok without the headers, but most people get a tune after getting headers.

 

I see. So headers and plenums and such add 30 whp without a tune but the cat-back is the straw that breaks the camel's back? I heard the 07s are even worse about mods.

 

u put on the exhaust and go on dyno with no ecu mod. Hmm COoL. lol

Ur ecu wasnt even resetted and car wasnt even used to the mod. Nice try tho rookie lol

go getta tune, that car shouldnt put down nothing less then 250whpand 240+ tq with the mods u have.

 

Or, maybe it just shows how well designed the OEM exhaust is.

 

Headers won't give you anything without a tune, they actually rob you of power until you get it tuned.

You also need to account for the weight you lost when you swapped out the OEM with the Stillen.

 

One would think he would be running pretty damn lean with headers.

 

In that case, the Motordyne spacer and plenum gave me way more than 30 whp. If you remember my post, I installed the spacer, plenum, z-tube, and headers then dynoed for a gain of about 30 whp.

Original post here:
https://g35driver.com/forums/engine-...-mod-info.html

 

With a gain of 30whp over stock, shoudnt you be pushing more than 230whp? That's approx 265hp at the crank which puts you right around stock output. Thats 287hp at the crank if taking drastic 25% drivetrain loss into account. The stock cars make just about 275-280hp I believe and were underated by the factory.

 

Saying the mods should net "30whp" is a pretty generic statement because of the differences in dynos and the numbers they spit out. I think some tuning would take advantage of the mods, but the fact that his AFR is nearly perfect leads me to believe there isn't a whole lot of power left on the table. The catback should have made some gains. I think the hard truth has been revealed that these TD catbacks just aren't where they're cracked up to be. To0 many people on this site believe the masses that tout the Stillen/Borla TDs put down 10-12whp easy, but the reality is there really aren't many dynos out there that support this claim. And then there's the trade-offs with noise, drone, and vibration. I had the Borla TD on my G for 2 weeks a few years back. I tried to love it, but I couldn't stand the drone under load from 1800-2300rpms, the noise from 1000rpms to 4000rpms, the major drop in mpgs, the cabin vibrations caused by the systems lack of flex sections in the y-pipe, and most importantly, not a lick of perceivable gains. If anything, the car felt flat from idle to 3500rpms and then came alive. With the stock exhaust, the car felt more responsive. I'm far happier with the 05/06 sedan midpipe and HR y-pipe. The sound is far better, the car feels far snappier, no weird vibrations , no drone, and OEM fitment.

 

Well today I took off the DC headers and stuck the factory manifolds on to see what the dyno would be. I was back down to 219 whp with the Stillen cat-back, and 229 whp with the headers back on.

 

I got the stillen gen2 as well and love it. Waiting on a few more mods then I'll get a reflash or some sort of tune.