Cat replacing pointless?

ok dudes listen... i think replacing the stock cat is pointless because i just did that and took off my old on and there is nothing inside, there is nothing in it that will stop the flow, its almost like a straight pipe... i doubt u will get any gain in HP from aftermarket ones, unless u replace the header because there is a section on there that looks like it will play a role of a second cat...

im kinda mad right now because then whats the point of buying after market cats that replace a good flowing stock cat as it is? Some people pay big bucks to hallow out their stock cats so the cops wong say nothing and here we have stock hallowed out ones on the 240sx...

whats the deal ?

Hmmm...I've never considered that. Does anyone know the answer?

here is another thing... the stock cat is 2 3/4 in and 2 3/4 out... the header is 2 3/4 and stock cat back exhaust is 2 3/4 so pretty much it all flows smoothly... now i put this cat one wich is 3" in and 3" out... NO i will not leave it like that im doing the header and cat back exhaust as well... but whats im saying is the cat is already hallow stock... the pipe i bought is a straight pipe as well... but since the outlet on the cat is 3" and the exhaust piper after the cat is 2 3/4 then i wouldnt be surprized if my car actually loses HP or 2 because the air coming from a 3" pipe will hit the edges of the 2 3/4 pipe and kinda bounce back and wont have as good of a flow as that stock hallow cat allow because both connecting sides are same size..

so if you are going to change the cat do the exhaust at least, or just the exhaust or just get new exhaust without the cat , just straight from header .... this is why people say that their 240s pass smog with their new test pipes because seems like the stock cat doesnt really help anyhow with emissions... i honestly dont even know why they put it on... just because all cars need to have one for the cops to see that its there??

if your cat was a straight pipe inside the guy who had it previously modified it.

cat's have two honeycombs in them that restrict airflow a lot. if you could see right through your cat either it isn't a cat or someone poked a hole through it.


cat's are extremely restrictive on turbo cars.

Seems like a previously modified car, My s14 and s13 had cats (which were direct from factory) had honey comb type filtering. There is only 1 cat in a s-chassis car. What appears to look like a cat is actually a unit called the reverberator, and theres also a second dummy reverberator located on the header. Do not mistake these for catalic converters.

Replacing your Cat for a high flow or test pipe will get you pretty much no gains as far as performance if your car has not gone through the higher stages. I strongly reccomend a larger cat for those running forced induction systems, OR I.H.E. otherwise...its a mod you dont need if your not there yet.

Hollow cats dont add power on low displacement N/A engines and I will never belive anyone who tells me about the "Power gain on the top end but lost low end" they are just hearing the added noise and hey! everyone knows that noise equals power

Funny story... I walk in to autotech to see some kid going at his exhast with a prybar. Upon closer inspection he was "gutting the cat" with it on the car and just letting the honey comb fall into the garbage can below... best part is that it was a four cylinder Jeep. get ready for that Hard hitting top end spanky :gay:

My old 91 240 SX Coupe had a nice Injen CAI and a sharp (I think it was Stillen?) SS exhaust that featured a "test pipe" & 2.5" back to a stainless muffler...
It ran MUCH better & faster then ANY other 240 I have owned (4) or driven...It had nice 16" rims & hi-po tires on it and it would still easily get it sideways on dry pavement...(I wish I still had that babe!) Anyway all I can say is, in my experence the 2.4 DOHC does benefit from easier air flow, in & out but does still need some backpressure, the right amount is the key...

& yes, you guys are right, GT500's cat had already been "whacked out"

if your cat was a straight pipe inside the guy who had it previously modified it.

cat's have two honeycombs in them that restrict airflow a lot. if you could see right through your cat either it isn't a cat or someone poked a hole through it.


cat's are extremely restrictive on turbo cars.


DUDE no its its a stock cat....the car was not modified in any way EVER!! the guy who i bought it from was the first owner... hes this old dude who has been driving it nicely since day one... everything is 100% stock, i mean there is no way he modified the cat lol... plus the cat is all rusty and worn out and the bolts were on really tight so i know it wasnt taken off since 95... and it passes smog with that stock hallowed out cat.. im telling you guys, stock cats on our cars are hallow.. because i heard it from other people as well... maybe just certain years, ... because i know 95s are... i had people confirm.,

hollow

Dude, your car looks like a FWD drag car, nie rims in back, shitty up front, or a drift car, ecxept then the nice rims would be up front lol.....but I'll look sick when it's done, btw how did you paint the rims?

could you post some pics maybe of your cat that you have taken out? i believe you that its hollow and everything, im just curious as to what exactly it looks like....Also, when are you getting the new rims up front? it should look awesome when you get em!

yes i will take a couple pics of it tomorrow and post it up here, make sure to check it out ... i might do it around noon or something...

about the rims i already got all 4 rims... got them on ebay for $150 :biggrin: its getting the hubs that was and still is a pain in the butt!! i got the rear ones with no probs because they are direct blt on from 300zx its the front ones that are find to find...

I ordered a pair from AZ pinnacle Nissan dealer they had them in stock for $96 a piece... so i should get them Wednesday and will do the fronts next week as well...

I already painted all 4 wheels and ready to go... ill still have to paint the calipers and put the drilled rotors on and new pads...

As to how i painted the wheels.. first i scuffed the wheels all around with some scuff i got from Home Depot.. then i blew all the dust off with air compressor. After that i then got a can will Fuel and i put some on the wheel and cloth and wiped off everywhere i could to get it clean and not greasy so paint will stick better... then i taped off the tires with tape and paper, let it sit in the sun for a bit to warm up the aluminum... then i sprayed a light layer then some few minutes another layer, then another... i did about 4-5 coats on each wheel... i did the inside of the wheel too because i think it would look weird not painted on the inside, you would be able to tell its painted... since i had a set of wheels on teh back already i was able to drive with my 5 lug convertion on the back... an once i got my other pair painted i just swapped them and painted the other 2 today ...

its pretty easy to paint them but people that dont know or never done it before will have a few trouble a few runs and maybe a few missed spots, thats how i learned lol...

logik23 are you planning on painting rims or something?

Anything that restricts air flow into or out of the engine robs power (not torque). Simple as that.

as i promised id post pics of my stock cat... sorry it took a little time, i said around noon, but i did it when i got a chance, as you can see its a stock cat, and its hollow inside.... i inspected the cat and there is no signs of anything being inside the cat either, there is no scatches .. NOTHING that will show the cat being hollowed out before or something, i would guess some took might atleast scratch it inside or something, but its completely stock.... and like i said i have ren into other people with 95 240s saying the same thing...

So i think replacing a cat is good when u do the header and exhaust to get it slightly wider to breath easier , So if you ever go to a smog location and they say you need to replace the cat, think again, because you will be replacing a hallow cat for a hallow cat, and yet i bet these cats cost up your butt!!... you know this almost makes me want to go to an exhaust shop or even the dealer and see how much they are asking for these stock cats?!!

because if they cost same price as the "actual" cat then they are ripping people off and i dont see how they cant get in trouble for that. All it is , is for looks from what i can see...

Plus if you ever replace the cat with a test pipe or something, keep ur stock one because if you get pulled over and the cop happens to check the cat and you get in trouble.... i personally think you can actually fight it in court... considering that the stock one is hollow and you replace it with a hollow pipe ..... thats just my :2cents:


http://image20.webshots.com/21/2/16/91/219921691yvJVVe_ph.jpg

hmm i think thats why you would of needed a new one. The cat should not look like that, my stock cat you could not see through. My aftermarket cat you could not see through either. My aftermarket one is made by Random Technology. Now people have been known to drill out all the shit in there stock cats to "free" up the air flow. We did this to my boys eclipse just for shits. Couldnt notice anything though......prolly cuz its a piece beater but.....

[QUOTE=Chuki_breath]hmm i think thats why you would of needed a new one. The cat should not look like that, my stock cat you could not see through. My aftermarket cat you could not see through either. My aftermarket one is made by Random Technology. Now people have been known to drill out all the shit in there stock cats to "free" up the air flow. We did this to my boys eclipse just for shits. Couldnt notice anything though......prolly cuz its a piece beater but.....[/QUOTi

its stock dude im telling you, there is no drill marks or scratches on the inside that would implicate anyone messing eith the inside of the cat... and like i said before... this car is bone stock... the ONLY owner of this car was an old dude!!! he didnt even know how to change oil or anything period on this car... he would just always take it to a dealer for it to be done... an old fart is not gonna drill out the cat because he wants that extra couple hp hahaha... and then leave the entire car stock completely...

look at the front wheels of my car... thats how it was all around when i got it.. yes gay!! i almost want to go see a cat at a dealer to see what they sell and what it looks like..

Nah, I'm not ganna paint rims, I got no rims to paint, but if I get some and they need painting, I'll have an idea about how to do them. Looks like yours came out pretty good.

My cat was hollow too. I replaced the header and the cat-back exhaust. My mechanic said my cat was completely hollow. I think GT500916 is right dude.

ok here is what i think i know... the cat is hollow, i know this because when i replaced my cat with a cat pipe i saw this and i thought, then whats the points of replacing these? then i know of other people who also had hollowed out cats stock... then the post above me had a hollow cat so obviously im not hte only one....

but... the other day i replaced my header and believe it or not, but the cat is actually right after the header not under the car but right on the section where the pipe is going down from the header and right before it evens out horizontally.

I had to take that section off to replace it with my long header , and its not hollow at all there is stuff inside that would block air like a cat would. So the thing is when you do replace the cat pipe and a cop says something about it and is about to write you a ticket, you tell him and say... "you freaken noob thats not the cat i replaced, my cat is over thuure!! "

so you can replace that wanna be cat at the bottom of your car with a test pipe and you wont have probs with passing smog because your cat is actually else where... this is why guys told me before htey replaced the cat and passed smog, i now know why...

There were a few 240sx that had cats, and hollow cats. Usually a VIN number can distinguish the changes, kinda like trims. My S14 and many others iv worked on had honey comb cats. Other S14s and S13s iv also worked on had factory hollow cats. But the point remains, weather your car has one or doesnt have a cat..it will make no difference off the bat.