Need4Camaro

iTrader: (1)

99 Z28

Late last year my 4L60E died so I replaced it with a FLT Level 6 4L60E and it shifts like a dream.. well.. my car has 212k miles and just today I got an SES light.. one of my cats is bad and I live in an emissions county. It may be partially responsible for a lack of power in the lower RPM's Im experiencing as well.

Anyway... I have been saving up for a stronger rear axle to accommodate my goals for 600 - 700 WHP and Im alittle more than half way there. My emissions aren't due until June, however; I'm "thinking" of switching my plan and upgrading my entire exhaust (its all bone stock) and including a catted Y-Pipe and doing the rear end later.. Not sure... one thing Im mildly worried about is the additional power of the exhaust may uncover more problems ... what do you think?

RPM WS6

iTrader: (3)

Clogged cats would not be responsible for power loss in *only* the low rpm range. The more exhaust the engine tries to pump out, the more of an obstacle any blockage would become. By the time you're seeing problems at idle or low rpms, the engine would probably have a hard time even reaching high rpms, much less make good power at WOT. Flow is less critical at low rpm, so that's not where you would feel the power loss first or only. On the other hand, cats can go bad in other ways - such as the coatings wearing off the substrate leading to a reduced ability to "scrub" the exhaust. Or they can break apart and blow out the tail pipe as well. Either of these situations would lead to a P0430/P0420 code which is the common indicator of cat failure (simply meaning that they are no longer able to reduce tailpipe emissions by an acceptable amount). There is no code which directly and specifically indicates a clog or blockage.

Based on what you mentioned in your other thread about this, I think the hesitation problem is more likely MAF related.

LT headers and Y-pipe won't give you more than about a ~20rwhp bump on an otherwise stock car. That's not going to break anyone's rear if it's holding under the current conditions. Having said that, as you have an A4 car the rear isn't really a big concern at any power level on street tires (sans wheel hop), especially if you take it easy during launch. Here's a thread that shows just how much the stock 7.5" can handle behind an A4:

https://ls1tech.com/forums/gears-axl...ock-7-5-a.html

Lastly, does your emissions test include a "sniff" portion? If not, you might want to skip the cats so you don't have to worry about issues with them later, and also save some cost, reduce routing complexity, and gain a bit more power by omitting them. In fact, for the near term, you could even use O2 sims or custom tuning to pass with the stock cats if it's just an OBD scan test (and they would obviously pass a cursory visual if they are still present).

HCI2000SS

iTrader: (2)

Like mentioned above the 20 hp gain that you'll see from changing the exhaust isn't going to make a difference to your stock 10 bolt. Also you mention wanting to make around 600-700 hp...well you will need a nice free flowing exhaust to do so.

Need4Camaro

iTrader: (1)

I'm ganna replace the MAF anyway just for safe measure because I really don't trust the MAF in there right now. I just haven't gotten around to it. For the sniff test, I can't recall for certain honestly.. I "think" last year I went and got it tested and it failed (becuase it hadn't been driven in a long time and the PCM wasn't ready) and I think the first emissions station did everything, he checked under it to make sure there were cats, did sniffer, even checked under my hood..then failed it because the PCM didnt register.. later.. after driving it 50 miles I took it to a different emissions station and he just plugged it into a scanner and didnt check a damn thing and passed it. So Im not really sure.

I heard driving without cats gives a bad foul odor while driving though. Any truth to that?

As for the rear I was mainly focusing on it because I believed it was a weak link but I it does seem kinda dumb to dump 3 grand and still have clogged cats..I'll probably do exhaust first.

RPM WS6

iTrader: (3)

In my state, they only do a more comprehensive check if you're applying for a wavier after completing repairs that exceed a certain dollar amount but still can't get the car to pass. And that's only done at "full service" centers. For a standard inspection, the test is the same at any center (OBD scan only here). Not sure why they would follow a different process within the same state but, if it were me, I'd investigate your state's EPA site and figure out exactly what sort of test you need to pass. That will tell you want you really do or don't need. For a scan only test, O2 sims or custom tuning is all you need to pass.

Well that's mostly subjective. Prior to 1975, no domestic vehicle had cats, so it wasn't anything that folks couldn't live with. IMO, the smell isn't much to deal with when the cam is still stock. With a healthier cam (e.g. more overlap) the fumes will be worse. But it's still subjective. My '71 has a mildly built 355 with an upgraded cam and I don't find the smell to be a problem, I don't even notice it on the road (not even when idling at traffic lights and such). This becomes a bigger concern for guys with dumps under the cabin, but if you have tail pipes at the bumper, or at least behind the rear wheels, it shouldn't be an issue unless you're particularly sensitive. I've owned pre-emissions and/or emissions delete cars my whole life, so I'm pretty used to it.

Quite frankly, the cats are not clogged if the problem goes away as soon as you unplug the MAF (and I think you said this was the case in that other thread). There is no way that unplugging the MAF could clear any exhaust blockage. And, again, any exhaust blockage that causes issues at low rpms would only get worse at high rpms/WOT, which I don't recall being the case based on your description. So I don't think you're experiencing that particular type of cat failure at this point.

But I agree about the rear. If it comes to the fact that you *have* to do some exhaust repair to get the car to pass emissions, there would be no reason to first address the rear if it's still working fine. However, again, you might not need anything more that some tuning or sims to pass the e-test if it's just an OBD scan - and if so, you could do that for the next test and delay the exhaust work until you're ready.