Gutted Pre Cat

[twizyours]

Alright boys and girls I gutted my pre cat today. Why? Well yse one in hopes of getting a performance gain. Two after reading about how phantom cruisers on the other board when installing their header spaced their o2 sensors and didnt get a cel light and how some of the awr headers arent getting cel lights I wondered if my theory of the o2 spacing is what makes the difference then just the cats themselves actually being between them. Well my theory was that the second 02 sensor is more like a flow sensor. What I mean by that is it is really yheir to check if the pre cat gets clogged or not , so if the pre cat got clogged the second 02 sensor would get a real low signal and throw a cell, which is why if you put the second 02 sensor after the second a real cat it would throw a cell. This is my theory.

Well after gutting my cat I drove for maybe 40 minutes and no cell so far.

As for performance it does feel better to me but nothing gigantic but I am also having misfirng problems though ( I was hafving misfiring problems before the gutting), but it does feel a whole lot better to me at idle.

Now I havent reset the ecu yet I want to drive a little longer before resetting the ecu to see if it pops up that way first. Will keep yall posted

 

[twilightprotege]

very good. yeah i've been thinking of doing that myself for a little while or just by getting a dump pipe from the stock header to the 2nd cat.

and just a quick q, reset the ecu? is there an easier way of doing this than by disconnecting the battery? like on my previous car all i had to do was take out a fuse for 10 minutes

later

 

[twizyours]

The fuse could probally work but to be certain I would just disconnect the cable for 15 minutes and hit the brake pedal like 5 times. That is to just to be sure.

 

[twizyours]

Well still no check engine light and I have been driving alot. It does pull better and throttle response feels better. I will say that this is the first time I gutted a cat and could say I was happy with doing so. Not the best but it was free. I dont think a cel is going to pop up either. I reset the computer a couple of minutes ago. I will let you guys know if a cel pops up, but I dont think it will.

 

[RAAZ227]

You should reset the ECU anyway. It's a good idea to reset it after any mod you do. It lets the computer reconize the change.

 

[twizyours]

I did already I just wanted to see if it would pop up without resetting it first. I resetted it and still no cel.

 

[snowman4us]

whould this efect emitions allot? and how hard is it to do?

 

[PHRiSCo]

I think its incredibly stupid to gut your cats, my reason is that my warranty bill for a new 3-way Hi-Flow mazdaspeed cat system was $2600 canadian, I dont know how much the US bill would be. Getting a straight pipe made is much cheaper in the long run, I paid $170 Canadian for a muffler shop to make one for me with the proper flanges and sensor housing, etc... I can swap back the straight pipe with the cat system in a matter of minutes.

 

[twizyours]

Well I dont know how much it would Effect emisions. The way the cat is designed it is really easy and should take you maybe a hour and a half.Detach the o2 sensor connectors I found the best way is to first unbolt the brace that holds the cat to the block, take off the heat shield on top of the manifold, thyen take of the heat shield underneith on the downpipe and then unbolt the downpipes bolt that hol it to the frame. The next step is to unbolt the 2 bolts from the downpipe to the cat. Then unbolt the 5 bolts from the cat to the manifold. Try to slide the downpipe of from the cat and slide the whole piece out from undernieth the car. Unbolt the downpipe. To get all the stuff out it was pretty easy, I used a long pole about a inch wide and a 15 in lb. sledge and made a whole down the middle. To my suprise it was all cracked inside and slid it out from the bottom. Some people recommend using a long drill bit, but I always used a metal pipe. Be carefull not to inhale this stuff because I think I heard it is like abestious. Then just put everything back together. It is really easy.

 

[twizyours]

First you should still pass emissions, and I gutted the precat not both cats. I have had my a friend who guttd both cats on his cobra and still passed emisions. 2 cats is not needed. Also alot of shops in america wont mess with getting rid of a cat.

 

[twilightprotege]

PHRiSCo, $2600 canadian dollars for an exhaust system? i think someone got ripped off big time

hell you could get a full on race system, header, cat, muffler all with mandrel bent piping for less than that

 

[twilightprotege]

ok, well i've finally got around to gutting my pre-cat....took me about 45 minutes just taking my time. was pretty easy. did almost exactly what twizyours did....the crap just came out. nice and easy.

and the result? the butt dyno doesnt say much, but small increases never do, but the thing i am most impressed about is the idle. much smoother...my car used to drop to 500rpm every now and then then pick back up...but i've had no problems so far and now the engine idles just over 700rpm and is smooth where before it used to idle at around 750-800rpm and was rough

so all in all a good mod, it's free, doesnt take long and improves the idle.

later

 

[CruzinAltitude]

I know this is a tad off topic, but I have gutted a Cat befor also, but I did it becuase it was causing a exhaust blockage and I cut it open, took everything out and had to leave it open for a couple of days. I never knew a 4banger (it was an 85 chevy cavalier wagon) could sound so raw out loud and mean. It was way beyond rice. I was ashamed driving it around town!

"We now bring you back to your regularly scheduled thread."

 

[twilightprotege]

my car doesnt sound any different now, no body could tell if i had done it or not...

but back to twizyours idea, i agree with your idea that it's the spacing of the o2 sensors that is what throws cel's on the awr headers etc...because when you think about it, there is really no real benefit of having two o2 sensors...i'm sure it is just a safeguard incase the pre-cat gets blocks (like if someone puts through leaded fuel or something) it would throw a cel and as with most sensors that throw a cel, it wants to SAVE THE ENGINE AT ALL COSTS

later

 

[SpicyMchaggis]

uh the pre-cat is just for when you start the motor up...it has that rattle sound to it and just burns off all the extra crap in your motor..once it gets to operant temperature its completely bypassed..gutting your pre-cat will do absouletly nothing for you..once the motor gets hot, it will be the same old deal..as for your main cat...that gutted, WILL NOT pass emissions..I can assure you of this.. RacingBeat makes a universal kit for miatas/proteges,etc...When I ran straight pipes on my Syclone..I didn't pass emissions..wasnt even close..Do yourself a favor..get a hi-flow cat and just stop costing yourself money in the long run...

 

[twilightprotege]

well the consensus is that the first cat does most of the work and the 2nd cat mops up what the first cat doesnt

but i dont think you're right about gutting the pre-cat doing nothing....after all we are removing restictions from the exhaust flow

 

[PHRiSCo]

Twilight, looks like you don't know how to read. I said my warranty bill for the 3-way Hi-Flow Mazdaspeed Cat system was $2600Cdn. The key word here is "warranty". In engrish...that means I didn't actually pay that, that what the bill stated. So that means if you gut your cats, and you don't pass emission, that's how much it would cost you to put the stock back on.

Doesn't anyone learn how to read in school anymore?

 

[SpicyMchaggis]

possibly..and the FIRST cat is what we call the pre-cat..it only runs when the motor is first started..after is up to the right temp..its rendered useless...the second cat is the main cat...it was the same deal on my 626.. for instance..the AWR header removes the first cat and relies on the second cat (main) for emissions..now why would they put the warm up cat after the main cat? doesnt make much sense to me...

 

[twilightprotege]

PHRiSCo, yeah i did realise that after i wrote it (woops)...i wrote that very late at night (here in australia)

SpicyMchaggis, you are right, the first cat is a warm up cat, i just checked the shop manual, but it still does play a role in reducing CO emissions even at normal operating temps....but still removing the stuff inside of it will help exhaust flow...and you cant argue with that

 

[SpicyMchaggis]

that might be true..but your talking a gain in flow of in the small of degrees..get the racing beat cat..you'll notice the difference...that or a header..but again, for a free mod..I can't argue results..so no CEL warning huh?