07Txlex

Has anyone removed the second set of cats and the sliencer and left the rest stock instead of just going for aftermarket exhaust? Other than the removal of the cats being illegal are there any other downsides? as in will it hurt the car? I live in Texas where we do not have to pass a smog test simply because we have OBDII cars and they just check for warning lights. I am kinda thinking of doing this.. comments?

lobuxracer

iTrader: (2)

Comments about the performance or the legality?

Performance - Dropping the cats and resonator will definitely make more noise even with the stock mufflers. It might make a little more power, it might not. There is a small chance it will lose power.

Legality - It is a Federal crime to remove a working catalytic converter. This is why most shops won't even consider it. The EPA amended the law to include private individuals, so it's 100% illegal in all 50 states for anyone to do. Getting caught is a separate issue for those who would consider the marginal gains worth the risk of legal consequences and those who would ignore the benefits of such devices with respect to public health and the environment. Personally, I don't need the 3 or 4 horsepower when I know that it really is better for everyone's health to leave the cats in place. JMHO.

Gernby

iTrader: (1)

Wouldn't removing the 2nd cats effectively just degrade the emissions back to a non-ULEV2 standard (ie. still pretty damn good)? I don't know what the differences are for LEV, ULEV and ULEV2, but as you said previously, the 1st cats do most the work.

Regarding power, how could it not help performance? I don't see how it would change the "tuning" of the exhaust (like changing pipe diameter or length), but it would require less energy to pump the exhaust through.

07Txlex

Awesome the one of the knowledgeable people I was hoping would respond did.. Yea I know about the legal stuff and as you said it would be a decision one would have to make. I just was wondering if it was an easy way to increase performance seeing how many people say the cats rob alot of power, but if you are correct in saying 3-4 horsepower or a loss then obviously it's not worth the risk.. Thanks Lobux

07Txlex

And the other person i wanted to chime in did.. lol I was just thinking that in texas they really don't check emissions on new cars, this being said once you found someone to do it you could probably get away with no reprocussions.. If the performance gains are there then I just may do it.. Any thoughts on how it would sound with the above mentioned items removed using stock mufflers? Crappy or similar to aftermarket?

al503

what bux said.

Since the primaries would be untouched, I don't know if this would apply but many owners of the g/z have removed their cats (they only have 1 set) and they put the cats back on (or aftermarket ones) after they smell their exhaust at a stop light or something. I guess it's really bad. Perhaps people with the LMS exhaust could chime in here.

Bux also alluded to power loss. What many don't realize is that a certain amount of backpressure is a good thing to produce torque down in the rpm range, where most of us do the majority of our driving. The advertisements/claims from the manufacturers of +20 rwhp (whether exaggerated or not, which is a different story) are usually at the top of the power band in a very narrow rpm range. It sure sounds good but on the aggregate, you may be losing more on the bottom end (again, where power is most useful to most of us) than gaining up top.

07Txlex

Yea I have always heard you have to have some backpressure.. But I was thinking this car really only has two sets because they wanted lowest the lowest emmission rating, so by removing the 2nd set I thought it would still retain enough backpressure.. I could be completely wrong tho

lobuxracer

iTrader: (2)

Actually that whole thing about "backpressure" is dumb. A bigger pipe without cats actually shows more backpressure to the engine than does a smaller pipe that is able to retain heat better particularly at low rpm when flow (and heat) are relatively small. Never forget, there is atmospheric pressure pushing into the end of the exhaust unless there is enough heat and flow (the T and n in PV=nrT) in the exhaust flow to cause a pressure reduction. I've written some really long posts on other forums about this, but suffice it to say, there is an optimum size, and just as al503 said, bigger tends to favor high rpm torque at the expense of low rpm torque and smaller tends to favor just the opposite.

Gernby - exhaust is a funny world, and a LOT of it is counter-intuitive. As I mentioned before, I learned more about engines after taking a high vacuum course than I ever thought I would simply because I learned to change my thinking about the way gases behave. This too would be a stupidly long post starting with gas molecule behaviour and ending with why many of those terms - vacuum, backpressure, suction, and others are really meaningless to understanding what goes on when an engine breathes. The concepts those terms represent are valid, but the terms make your thought processes confused.

Evitzee

If Lexus ever put it up on the lift for servicing and saw you removed the cats your warranty would probably be toast. Can't see why anyone would want to do it .... for a couple of hp that you would never see in operation?

linh811

It would also be better for everyone's health if you drove a Prius instead of a 306hp gas guzzler

Lexmex

My RX300 no longer has precats and I am in Mexico. Just has a high flow cat and I passed voluntary emissions here in Mexico City (think California in terms of standards). Bad gas down here and precats don't mix, plus road debris knocked a hole in my OEM cat. OEM Resonator was gone also.

GUESS WHAT? NO CHECK ENGINE LIGHTS.

In Mexico, people will strip out the cats if they don't live in an emissions area. The rules just don't exist here.

Why voluntary emissions? Because if not, you can't drive every day in Mexico City, they have some strange driving rules here to minimze pollution...it is based on your license plate number.

lobuxracer

iTrader: (2)

Tell that to the people who refined the battery's metals, assembled the battery, added the electrolyte, and those who will also be exposed to those metals and corrosives when the battery is reprocessed. I doubt they will agree.

Hybrids are a shell and pea game. I drive 95% highway, a hybrid would only benefit me for its ability to use the carpool lane. I would not get good fuel economy from it.

Gernby

iTrader: (1)

I wasn't aware of the temp thing as much as just tuning the exhaust for specific flow / resonance characteristics. Exhaust works similarly to the intake, and intakes often cause losses and / or gains at certain RPMs due to the helmholtz effect (standing waves). That's why an open header causes such huge power losses (higher back-pressure).

clubfoot

I think you're both right as intakes and exhaust have a "sound" behavior component that makes pure calculations based on temp, pressure,...etc, tricky.

linh811

I think you're missing the point... not that any of us would drive one, but a Honda fit will get you 38mpg highway..