brillo

I know pulling the cat would free up some HP, just b/c its a restriction, but I was wondering if it would also improve mileage in any way...all environmental issues aside....

mysql101

definately if your car stopped dumping fuel on it to keep it cool. but then you wouldn't need to remove it

Rxdriftingaction

it won't got a big help. don't do that man.. maybe will increase 2~3hp. but u won't get some good deal with mpg. maybe will got worst.

MELRX8

Which is the greater restriction, cat or stock exhaust? In other words which will improve flow the most a high flow cat or after-market exhaust?

robertdot

Go read racing beat's site. They talk about all that.

Rxdriftingaction, where are you from?

brillo

bump

StealthTL

iTrader: (1)

I am running that experiment this week, will keep you posted on the results.

I removed the 'oxidation' bed of the catalyst, by far the biggest restriction. I retained the 'reduction' bed, (the first bed, before the secondary sensor) thus avoiding check engine lights.

I just finished my first tank of gas after the switch over, but don't want to quote results based on just one fill......

Will post next week.


S

(Anyone interested in detail can P.M. me, but don't go carving up your cats just yet.)

brillo

Interesting, how is the noise level?

robertdot

The problem with the gas mileage is the ECU fuel maps, not restrictions. It still going to run rich if the cat is there or not, and it is still going to get bad mileage.

StealthTL

iTrader: (1)

Sounds louder, no doubt, but not any 'harsher'.....

I have a cat-back, it just makes the grumble and 'poppage' louder, if you know what I mean.

s

Felix W.

So how can you remove the cat, yet not get CEL codes? Do you use an O2 fooler?i don't understand which part of the cat you removed to reduce backpressure.
felix

robertdot

Trick it with an O2 "fooler". Remove the whole thing. Cats are restrictive by their nature. You are shoving exhaust through tiny "honeycomb" holes. Remove it, replace it with a straight pipe, and it flows better. It's not going to increase your mileage (at least not enough to deal with the extra sound), and your HP increases are only marginal (according to Racing Beat).

shelleys_man_06

Agreed. Removing the cat will cause some gains in power, but I don't think it will increase gas mileage. You're freeing up more area for flow. I believe your engine will increase in thermal efficiency on the order of 0.001%.

shelleys_man_06

Okay. I'm seriously thinking about removing my cat, permanently, but I'm worried about my upcoming emissions exam. Yeah I call it an exam; it's worth 30% of my RX-8's grade for the semester. Seriously, are there any solutions to passing the emissions test without a cat in Texas?

Aoshi Shinomori

Someone on here posted once about how they passed their tests without their cat. I believe it was something along the lines of a heat sheild? or something encasing his mid pipe, so when they pull out the mirror and look under the car, it looks like there is actually a cat. Don't take my word for it, as I don't know the regulations for emissions testing in Texas or any other state. But if all of what I just said was wrong(good probability) couldn't you just strap the cat back on the day of the test? Again I don't really know how long or how much work it would take to switch back on. Hope this helps.

IZoomZoomI

isn't most the restriction from the exhaust manifold and not the cat?

shelleys_man_06

Well, rotaries are pretty damn loud without cats. As for the RX-8, I really don't care at this point in time. Like I said, I don't want to have to crawl under the car the day before the test just to put my cat back. I'm a lazy SOB. Plus, it would've been a clear sign I should've just kept it there in the first place. I'll figure something out. shelleys_man_06 always has a solution, even if it's crazy.

Aoshi Shinomori

It's just one day a year, c'mon. But seriously if you are really against having to do that, there is always the high flow cat option.

shelleys_man_06

I'll admit the exhaust manifold is of a log-type. I prefer a long-tube header, but I don't know if that would fit. I know some aftermarket companies have them, but I'm looking forward to designing a turbine header.

What part of "I'm a lazy SOB" do you not understand? J/K p

Rasputin

Correct, unless you also make the following changes :

- disable catatyst temp protection (not advised as it also protects other exhaust hardware and sensors!) ;
- enable part throttle lean running in the map governing requested AFR (I'd love to be able to do this).