Gut cat or straight pipe? Advice needed.
 

first off, I've searched and haven't really found the answer I've been looking for. I have a 2 inch by about 18 inch steel glass pack type of muffler ( no packing though, just baffles, I think...) The overall width of it I think is 4 inches.

I'm wanting to give my car just a lil bit of sound, not loud by all means. I plan on running the stock header and stock catback for quite awhile to come. Question is should I just go ahead and chop out the main cat? or just bash the ceremic out of it? I'm leaning towards the straight pipe/muffler but gutting the cat would be easier with being able to just bolt it back in place and not have to worry about welding in a pipe into the straight muffler for the air pump.

Thanks for any advice but I'm torn between these two as I have no money to actually buy anything at the moment. So far the only thing I plan to do is a drop in K&N filter and something with the cat while keeping it all maintained. That's it for now till the motor blows (no time soon I hope) lol, then its rebuild and port work!

It's a daily.

'90 GXL

Thanks.

gut the cat, its really easy...same effects as buying a damn testpipe for 40bucks+, the hardest part about gutting it is onyl just removing it, which wouldnt be that hard if you got power tools, take it out and jab the hell out of the inside of the cat. easy stuff...i bought a damn testpipe resonator for 40 dollars and i feel like an idiot haha

A straight pipe is much better than a gutted cat. The sudden increase then decrease in velocity through an empty cat causes turbulence that restricts flow. A straight pipe might cost more, but you'll get a better result.

Waste of money. You won't see any performance benefit from doing this unless your current filter is extremely dirty, and a new OEM filter will have the same effect for half the cost. Put the difference towards that straight pipe...

Is the new OEM Filter really only $30?

I would get a pre-silencer over the other two options. The most expensive, but the most civil sound.

Straight pipe.

i read an article in an import magazine.
gutting the cat, running a high flow cat and using a test pipe. they dyno'ed all 3 and once befor the changes and the high flow cat yielded the best results. the gutted cat and test pipe actually only gained 1 to 2 HP where the high flow cat gave them around 5HP.

just cut the cat. performance is about the same but it sure looks like you have cat and it will pass visual inspection.

I'd recommend buying a new single cat, there are some really good 'high flow' units out there for not much coin. The noise will remain completely bareable as well as pretty pleasant (in my experience) and you won't have to worry about performance drop or...fumes! :D

Pick up a Bonez or something and call it a day.

K

You don't want to just gut the Cat. It will make the car much louder and will cause backfires when you lift throttle at higher rpm's.

I also would not weld in a pipe. Buy the correct flanges and make a test pipe and uses gaskets. That way you can switch back in forth as needed.

Thanks guys. If I go test pipe I'm going to weld some collars onto the pipe and just get some exhaust clamps to hold it on the rest of the way so I can drop it in and out if need be.

So far just test pipe, I'll do it while the bosses are gone Friday so I have a free lift at the shop.


I appriciate it guys.

Mazdatrix have the OEM filter for $27.59 and the K&N for $54.34, plus $10.17 for the oiling and cleaning kit. So it's really less than half the price.

i'm with NZ on this one. You can go the cheap route and PRETEND like you'll actually pass smog and get mediocre power gains or you can spen a bit of money and actually PASS smog if you leave intact and re-install it when you are mandated to pass the smog test ad get better exhaust flow.

like anything else it just depends on what you want done. a high flow cat by bonez runs $300 but atleast you'll still have your cats when it comes smog time. i had one on my car and it sounds a bit raspy with a stock exhaust and has the easy backfiring.... gutting your cats is cheaper and easy. so whatever works

just buy a test pipe, if for any reason you want the cats back on they will still be functional

gutted my cat, haven't noticed much difference, other that what sounds like an exhaust leak where the split air pipe attached.

I chose not to go w/ a test pipe because it would have been a waste of money since I couldn't reuse it w/ the exhaust setup I am planning.

The filter is pre-oiled so it's just a drop-in, the $10.17 is for re-using it. So you'd only have to drive 200,000-300,000 miles before you break-even! (Assuming changing filters every 100,000-150,000 miles)

You're actually supposed to replace the air filter every 30,000 miles. ;)

Using those prices, and assuming you clean the K&N at Mazda's replacement interval, you start saving money at the second replacement. But you need to drive your car (with it's restrictive stock airbox) for 150,000 miles before you've saved $100. That's probably 15 years of daily-driven use, saving 13 cents a week! Woo-hoo! :D

Every penny counts!

should have taken your cat to the local scrap yard and gone with a resonator... you would've paid for a test pipe and had a couple dollars to spare. I'm still wishing I'd done it with both cats from my fd. could've bought more parts.

Definetely go with the bonez high flow cat. I gutted mine and it sounded pretty sweet but it had a wierd exhaust leak like noise to it and lots of people complained about the smell.

I bought a bonez cat/downpipe for $150 and couldn't be happier. It sounds better and I swear it's faster than the gutted cat. Make sure to have a Napa near by or order some gaskets from mazdatrix. Napa claims they don't have gaskets for our exhaust but they have generic ones that fit perfectly and don't leak at all.

good call on the NAPA.

yeah i got 30 for each of the small cats and 50 for the main cat at my local core exchange thats 110!!! not bad..and for those lookn for a lil extra money from junk parts its a good way to get some extra money.

I'm not convinced you'll feel 5hp gain on a rotary.

i feel special as my shop just became a napa auto care center LOL, free battery replacements for me for the time im working there :) heheh... and cheap parts, everything cost half of the list lol.

FYI: you can get a direct fit, high-flow CAT from performancepeddler.com for around $67. And that includes shipping. You must set up an account before you will see the discount pricing.