Ok, some of yall remember me posting about 2 weeks ago that my 01 z28 a4 dynoed 295 at the wheels. That was with a lid and fast toys ram air system. I told yall i had flowtech LT's, y pipe, and random cats that i hadnt put on yet. Well we put everything on and took it to the dyno. My car ONLY PICKED UP 7 RWHP with the LT's, ypipe and cats!!!!!!!!!! What is going on guys? Please tell me that is not the end of the road for me, because if it is then that was the biggest waste of 900$ i have ever spent. THE CAR HAS NOT BEEN TUNED OR RE-MAPPED YET. Is this the reason why i only saw an increase of 7 rwhp? Does the computer just not recognize that i have put all these bolt ons on, and after tuning it, will i then see the hp increase? Please someone have good news for me! Heres how we did the set up. LT's were bolted in, then we took the y-pipe, cut it in half on both sides (after the y when the pip splits into 2 seperate pipes) and welded the cats into place (along with o2 sensor holes and all that emission legal crap).

 

dyno's don't go down the track, go see what she runs before you get pissed

 

Did you dyno the 2nd time around on the same machine?

 

I'm by no means an expert on this stuff but i think there is something wrong with that dyno or the dyno's operator. I don't see how on earth you could put full exhaust on a car and only gain 7 horses. Hell, my CAI and home-made ram air scoop netted me enough to feel a difference (probably 10 rwhp) so I would think that full exhaust on an LS1 would gain way way more than 7 rwhp. One way to tell without a dyno is to run a buddy that you've run before without the exhaust and see what the outcome is. I was half a car back with my friend's stock '98 LS1 A4 2.73 Z28 from a 10-110 roll and after I installed the CAI and ram air scoop I pulled roughly 2 cars on him in the same situation. Hope I made you feel better.

 

Lids and ram air produce horsepower when you are moving and forcing air into them. On the dyno you won't see hardly any gain. You added longtubes, cats, and a high flow Y-pipe but it's exiting through the same muffler. The muffler is probably the main area of restriction. I suspect that adding a decent cat back system and tuning would show the horsepower you are missing now. Don't get discouraged, LS1 engines make great horsepower with only a few mods and are extremely reliable.

 

nah, a lid will give HP regardless of whether the vehicle is moving or not, it's a way more efficient piece. The cat-back could be an area of concern, as well as the lack of a tune, but you should still be seeing higher numbers than a 7rwhp increase. Drive the car for a few days and go back to the dyno, sometimes the computer just needs to relearn its curve. Any professional shop will disconnect the battery during the install, so this could be part of your problem, there will be a temporary loss of power while the computer relearns it's timing curve. I say give it a few days, redyno, and if that doesn't cut it, go for the tune and a quality cat-back. that 2 1/2" pipe isn't helping things going from your new headers/ypipe. You could see up to an additional 10 rwhp just swapping out the cat-back... a good tune should be good for 7-15+ rwhp on top of that.

 

Stock cat backs are 2 3/4" tubing. It's more the sucky stock muffler than the tubing size.
Everything else that Birch said was dead on. Run it a while and see if it improves. Some LS1s don't like headers with the stock tune so a real tune after a good catback will help even more.

 

My car actually felt a little sluggish after the header install, and it was running extremely rich. Got it tuned, and she's been a screaming bitch every since then. Gained 20 horsepower from the headers, but the area under the curve on the dyno was significantly larger. I say get a cat back, its definitely choking up the system...and if need be, get a tune. You'll probably have more of an improvment than I did.

 

That sounds about right. They will help more if you use a supercharger or N20. The exhaust on the car is already very efficient. If you go to WS6.com they dynoed a full exhaust w/ff cats and gained only 14 hp for $1400. I know it sucks but it all adds up with each mod. Hang in there.

 

I believe you answered your own question, GET THE VEHICLE DYNO TUNED, that should solve all your problems.

SteveC

 

If you plan on keeping the stock catback, throw a cutout on the car. That should get you in the neighborhood of another 7-10 hp. The stock catback will kill you. Get the car tuned as well.

 

So it sounds like a cat-back would be a good investment. The exhaust sounds really raspy too comming through that flowmaster thats on it. What is the best flowing cat-back out there? Will i be pleased with Corsa? Are the cat-backs a bolt on system, or will i have to weld them in? I can definatly feel the difference while driving the car, and to be honest i think i have gained more than what the dyno showed. the guy at the shop told me the same thing u did birch. he said he had the batt. unplugged and that it may take a couple days for the computer to relearn its curve.

 

Pick which catback you ant to spend your money on. Plain and simple. I've done quite a bit of catback dyno testing, Granted between different cars, but all of them saw about the same gain in RWHP with the tune. Headers greatly amplifies the catback gains as well. I would get a cutout. would work the same and cost lots less.

Chris

 

Does anyone run their car without a muffler? I know several friends that do not and their cars sound really good. I really dont have the $ to by a cat back exhaust right now. I might buy cut out... but what if i ran a 3 inch pip from my cats back without a muffler? I thought about just "y'ing" the pip right over the axle that'a way i would have dual tips. Good idea or no? If it would sound like **** then i dont wanna do it.

 

CUTOUT. They're dirt cheap. I run longtubes with no cats to open cutout. That way I can have a really mean sounding car with more horsepower than a catback, or I can cap the cutout and have a quiet(er) ride.