CraigS

Anyone ever done this without shop tools, how hard is it? How much louder was it after? Dont worry I dont have to deal with emissions around here!

I would really like to do this myself because my dad is refering me to his friend who is supposed to give me good deals but is charging $40 per/hour + supplies!

NismoPick

Why waste time & money trying to gut it? Just fab or buy a replacement "test pipe."

CraigS

Could you drop me a line to that site! Will it be a direct fit? THANK YOU!!!

NismoPick

The site is www.ebay.com That pic is for an S13 240sx. I posted it as an example. You can fab one yourself for about $8 if you have a welder. Just go to Midas (or any muffler shop) and get the right size flanges & a pipe that's the same length as the cat you are replacing.

nismo619

I have degutted the cats before i used a tire iron and a rubber hammer or a steel hammer it takes about and hour if u do it right start at the sides of the honey comb and work your self around try to hammer the tire iron all the way to the other side if not crush out then when u worked all the way around 360* cut a "+" in the middle of the cat to easliy get out the big chunks,,, of honey comb when u get about half way threw u will find your self getting stuck from a " metal wire screen " turn the cat over and do the same to the other side.. after about 20 or 30 min of beat the hell out of it, it should be done.. any more questions ask me...

HybridS130

Damn it only took me 20 minutes to do three. . . . .

RodMoyes

Yeah, but he said "if you do it right..."

Rod.

lww

I'd rather spend the $8 and weld a clean straight through pipe together.

A gutted cat will most likely not improve your performance, but I'll bet it will increase the droning at cruising speeds.

You're basically creating a resonator which doesn't flow as well as a straight pipe. If not designed properly, it will create turbulence in the exhaust flow and probably create a slight performance decrease.

thxone

One of my friends and I hollowed out his cats on a 1978 Camaro with a propane torch a hammer and a piece of rebar...took about 10 min per cat, we heated up the honeycomb inside then knocked out the chunks...painted them silver and had a friend weld them back in place. At the time Fl still had emissions testing. The car was a bit louder but more hollow sounding...SBC 305cu, headman long tube headers and 2 1/2" ID stainless pipes. Passed with flying colors. WEAR GLOVES!!

HybridS130

By doing it right I can only imagine nothing left inside the pipe and in which case it's really not that hard at all, especially for a mexican. . . . . .

NismoPick

For anyone that missed it....

WildmaN

I gutted mine, but I didn't have the money for the straight pipe. And I am not really looking for performance right now. My Z is plenty fast enough as it is. I also didn't want to play switch around every 2 years. Also the fact mine was shot anyway, because I was told that by techs. Even though they were Pep Boys. But my Z did blow worse after they got it running right. All in all, it was the Z guru, that helped me get my Z through. Mad props to him

All aside, I used a crowbar, and a sledge hammer. It took about a 1/2 hour or so. Now this weekend I am going to put my new metal gaskets, at the front and back of the gutted cat. Because I am tired of breathing the exhaust coming through my driver window.

HybridS130

I bought my 1980 with a straight pipe already installed

CraigS

Well i talked to the shop guy and it kinda really sounds weird the way he said he wanted to do it, he said that the cat was rusted on and wouldn't be able to get it off he would cut off the cat before the bolts on one side then after the bolts on the other, then gut the cat and weld a straight pipe?

Hes done work on my dads truck and I just really get a hunch he's screwing me over.

So, I think ill just gut the cat.

jfairladyz

Take the time it would take you to gut the cat and either go get the stuff needed to put in a straight pipe, have someone fabricate a straight pipe, or forget about the whole thing and spend that time playing some video games or actually improving the performance of your car

A couple laps in GT4 will benenfit you more then gutting a good cat. If it's plugged then atleast you'd have a reason.

CraigS

Suprisingly thats the whole reason I wanted to gut the cat, its annoying pulling up to a car show and people looking at your car because something is rattling underneath and not because the car looks good, and I can definitly tell this isn't the full performance of the car. If I end up disliking the performance then I'll willingly go crying back to the guy to get a straight pipe. Call me a stubborn but for some reason I just think everyone is out to steal my money .

jfairladyz

If thats the reason then go for it. Thats why wildman did it. You cant get any worse then a plugged cat.

I just think it's funny that people take the time to gut a perfectly good cat in hopes of gaining some extra performance only to find out they've most likely lost power in the process. The REAL proper way to gut a cat
is to put a length of pipe inside the cat. That way you get the benifits of a straight pipe and still retain that emissions legal look. You dont want that huge resonating chamber in your exhaust stream. Especially that close to the exhaust source. It's those that dont understand the way the exhaust system really works that think hollowing out a good cat is going to gain them power.

Now note I said good cat because obviouslly if a cat is plugged then you can only gain performance by removing that restriction.

lww

^^^ ^^^

WildmaN

I would like to know more about putting a pipe inside the cat. Enlighten me man, that would be cool. If it isn't too hard, I would probably do it.

lww

Get a piece of pipe long enough to go through the entire cat to the flange and has an OD smaller than the ID of the cat and weld it at both flanges.

I used to do this all the time back in Oklahoma where the 'emissions' check was merely a visual inspection of the OUTSIDE of the exhaust system to verify the cat was installed. They didn't care if it worked, was hollow or had a pipe through it, only that it was installed on the car.

3XAZOWNER

Same in Georgia. We don't have emissions checks in the state but the city of Atlanta does cat checks at traffic stops from what I have been told by a muffler shop. He suggested to put the pipe inside the gutted cat, so if you go through a traffic stop anywherethat slides mirrors on a pole under your car to check the cat, it will be there. My cat is gutted, but the pipe is not inside yet. He told me that the gutted cat will decrease performance, since the exhaust gases rush into the cat and swirl around in an empty cavity before being forced out the back by gas coming in. So if that theory is correct, then I AM losing power by running a gutted cat.

nismo619

U dont loose power by useing a degutted cat... ... but that idea of the pipe inside the cat sounds like a freeking good idea.. LLW is right thou about the " turbulance " the exhaust gas would have.. a straight pipe is better but the proper way to do it is yet to be done hear on zdriver... wait until my next pay check and i will make someing happen.. " WITH THE POWER OF DREMEL !! " I WILL MAKE ONE ! LOL HA HA HA

jfairladyz

The proper way to do it is to leave the cat alone or get a high flow cat. But if you have a solution better than sticking a pipe inside the cat then I'd love to hear it. I hope it's not to dremel a hole through the honeycomb roughly the diameter of the exhaust pipe. Thats got enough negatives to make it not worth while either.

lww

Dude, you're gonna go through $20 worth of Dremel cut-off wheels if you're planning to do what I think you're planning to do.

And YES, you will loose performance with a gutted cat. A real 'resonator' has a perforated straight through pipe going through it that prevents the turbulance from impacting the performance of the vehicle in any perceptible way.

I've tested this on a dyno back in the early 90's when I was club racing with sponsors in SCCA. I don't care what the 'butt dyno' or your ears tell you, a REAL dyno says you loose torque and a little hp to the wheels with a gutted cat on a 1980 280ZX.

Stock exhaust + cat = 119 whp & 124 wtq
Stock exhaust + gutted cat = 117 whp & 118 wtq
Stock exhaust + gutted cat + straight thru pipe = 121 whp & 129 wtq

I could be wrong, since I didn't test it on all of the model years, just the one I had, but I suspect you'll get the same results with a '79 or an '81-'83 280ZX as well.

lww

I'm betting he's planning to remove the shell with a Dremel and wrap it around a pipe of the same diameter as the rest of the exhaust.

This would actually be the ideal setup if you want the best exhaust flow and still need the cat. It would be so much trouble though, I can't imagine I would spend the time. You're going to get 99.999% of the same power with a very slightly smaller ID straight through pipe.

I wouldn't use a Dremel though, you'll be horribly disappointed by it's ability to cut REAL materials with any level of efficiency.

A Makita 4.5" or 7" grinder with a cut-off wheel would make the process go MUCH faster.