Unless you've got a 2004.5 and beyond! I learned that after I had already purchased test pipes .

 

O2 sensor no likey?

 

My SES light came on after a week.
A friend of mine did the pedal ecu reset and it went away.

Just waiting for it to kick back on... whatever, my chits quick.
I'm happy.

 

No lucky I found out before I put them on their.

Cliff Notes Version (courtesy of Neffster):

G35's with builds dates after 10/03 are revamped for ULEV status. This means a more complex ECU and different sensors. Vehicles prior to 10/03 had O2 sensors with 4 wires, where as those afterwards have 6. This makes the sensors much more sensitive to emissions so indefinitely they'll throw a code with test pipes. So yea, no likey.

 

That is correct.

I had stillen send me an interceptor box for my race pipes. It connects/splices into your O2 sensor wiring under your car. My ECU does not even know the difference now!

 

How much did Stillen charge you for a pair of O2 simulators?

 

Yes, I'd like to know how to modify the heat shield too. I just got my Crawfords and like to know before installation

 

There is no pair. It is a single box that at $50.00.

 

I am curious to the answer to the original question...will hi-flow cats with the stock exhaust give a better power increase than the stock cats with an aftermarket exhaust? I'm thinking about doing one or the other, but not both, in the near future. What is the most restrictive portion of the stock system...cats, y-pipe, cat-back? (Don't even say header cuz that ain't happenin!)

 

A lot depends on how much you want to spend. True dual exhaust from the cats back will undoubtedly give you the most gains, but this can be a little expensive.

 

It has been held for a while that the cats because of their 2 stage design are the largest restriction in the exhaust system, so in my opinion you could free up more power by replacing them and sticking with the stock exhaust than going with the original cats with an aftermarket exhaust.

I don't actually have any numbers to back that up though.

 

I don't have an aftermarket exhaust, but I've dynoed against several people with them.

General concensus (proven time and time again) is that exhausts give anywhere from -2 to +7rwhp when independently dynoed. This means throw out all of the "my butt dyno says that the Stillen gave me 20-23rwhp" and the "dude, the manufacturer says..." posts.

I gained ~18rwhp from z-tube, plenum and cats. Others with CAI and exhaust LOST 2rwhp from stock.

I've ran the Crawford cats for just shy of 1 week now and I do not have ANY rattles or unwanted vibrations. I also ran the RT cats for ~1 year and didn't have any rattles, just a very slight rasp (and I'm being critical). If you want vibrations buy a borla, 16+ piece exhaust and try to 'align' that.

Also, just because an exhaust is "true dual" doesn't mean that it is "better". There are many factors like back pressure, weight, cost, exhaust gas flow path, etc... to consider.

Esemes has the borla exhaust and a VORTEC S/C. He swapped out the borla for the Fujitsubo (went from true dual to single exhaust) and GAINED rwhp, and he was running under boost. I'd be inclined to believe that the same would have been true for a NA vehicle, but this has yet to be proven.

 

neffster, you said that your crawford cats don't make any rattle. Did you bend the heat shield? coz mine rattles when I accelerate. Doug told me that probably it's because of the heat shield. If you did bend the heat shield, how did you bend it?

 

The heat shield is actually kind tough. I took a small adjustable wrench sized down to fit over the edge of the shield and bent it down. You really don't have to bend it too far. You could probably do the same thing with a set of channel locks.

Most likely it's your left (drivers side) cat that is rattling against the frame when the engine "twists" under heavy torque so it's the only one you should need to bend. It's accesible from underneath the car, you don't have to remove it or anything.

 

BTW, did anyone notice how freakin heavy the stock cats were?