high-flow cats?

[Dora The 4x4'a]

i am in the market for a high flow catalytic converter. i am subject to every 2-year sniffer tests in Md. my concern is still to be able to pass these tests unfortunately. but i am no stranger to swapping exhaust systems in order to pass tests lol. so my question is does anyone have one of these on ther ex?

what gains did you get. did you like the sound any CLIPS?!

and wher can i find a "good" one for my application.

thanks as always
-chris

 

[IZwack]

If you have access to a welder, I'd just hit up E-bay or summit and buy a set of those universal cats that matches your tube diameter -- they are usually around $40-$55 per cat. Some already come with the oxygen sensor ports but if it doesnt, you can also find weld-in bungs (both on E-bay and summit) for maybe $5 each.

 

[Dora The 4x4'a]

thanks

so our diameters are 2in? i believe you suggest gettin a highflow cat and gettin it in 2in and welding it. i do hav access.

i hav never messed w/ on o2 sensor. are those welded in? so ill hav to replace it totally or would i be able to pop it out of the old cat and pop it in the bung on the new cat.?

also. if i do not immdiately take care of the sensor. what will happen? just throw a code and mileage affecteD?

thanks
-chris

 

[HahnsB2]

Yes it will pass. No there wont be any power gains, only sound. Modern cats are all "high flow" and designed the same, the inside of your stock cat is the same as any aftermarket unit.

 

[IZwack]

i hav never messed w/ on o2 sensor. are those welded in? so ill hav to replace it totally or would i be able to pop it out of the old cat and pop it in the bung on the new cat.?

Yeah the bungs are welded onto the tubing.

Basically you drill the proper size hole, place the bung centered to the hole, and run the bead.

http://store.summitracing.com/partdetail.asp?autofilter=1&part=SUM-G2990&N=700+115&autoview=sku

 

[seth247]

Yes it will pass. No there wont be any power gains, only sound. Modern cats are all "high flow" and designed the same, the inside of your stock cat is the same as any aftermarket unit.

If theyre the same why does the sound change?

 

[Dora The 4x4'a]

sweet thanks fellas.

-chris

 

[Willard]

You should know, you don't have to worry about O2 sensors. None of the first gens have more than two, and I think a '92 would only have one. Regardless, they will be up on the Y-pipe, so it's not something you need on the converter.

 

[Dora The 4x4'a]

thanks
we shall see

 

[Dora The 4x4'a]

this is the cat i ordered off of ebay from "performance-curve"

http://cgi.ebay.com/ebaymotors/2-25...038170025QQitemZ380038170025#ebayphotohosting

the cats w/out the o2 bungs were 5 bucks less but i figure ill just plug it if need be i went ahead and bout the one w/ the o2 sensor nut.

 

[HahnsB2]

If theyre the same why does the sound change?

Because you're removing 1 cat from the system. Anyone who thinks the factory cats are restrictive on relativly stock engines is smoking something. I even run a single "high flow" cat, for sound, not performance.

 

[Dora The 4x4'a]

i am embarassed to admit until now i did not notice that at the y-pipe there are 2! cats!
so my ? is:
i have a 2.25 highflow cat to put on w/ an o2 bung. where should i put that? should i cut out both cats and install the highflow cat after the y pipe and run plumbing to the muffler and than a tailpipe and call it done? (deleting the 2nd cat and obviously the resonator that was already deleted)
thanks
-chris

 

[HahnsB2]

i am embarassed to admit until now i did not notice that at the y-pipe there are 2! cats!
so my ? is:
i have a 2.25 highflow cat to put on w/ an o2 bung. where should i put that? should i cut out both cats and install the highflow cat after the y pipe and run plumbing to the muffler and than a tailpipe and call it done? (deleting the 2nd cat and obviously the resonator that was already deleted)
thanks
-chris

Remove both factory cats, as I'm told, the factory cats are made in such a way that they work in 2 stages and the first one treats the exhaust to be "processed" by the second cat, remove 1 and the other is not effective, single cats have both "stages" in the same unit. My rig has the same oval flange as yours, a 2 1/2" pipe was ovaled and welded to the flange.

 

[glfredrick]

The new single high-flow cats will offer some exhaust flow improvement, and they will take the place of a dual-cat system.

We've seen good results with the eBay ones.

Oh, and the deal with exhaust and back pressure is typically misunderstood... The best exhaust system has NO back pressure. But, a system build TOO large will not allow scavenging, which is what actually hurts performance. Scavenging is the pulsing of the exhaust flow that pulls the next cylinder's gas out the tail pipe with it. A good set of headers and a properly designed exhaust setup will actually pull a slight vacuum on an engine just from the exhaust pulses scavenging the system. A system too big just dumps the exhaust into a pipe, and it has to get pushed out of the system. That's the whole nature of a "tuned" system.

 

[Dora The 4x4'a]

ok so consensus is remove BOTH cats and replace with ebay*special highflow cat. great. heres a lil more specific of a ?.

w/ both cats gone, im left to connect my 2.25 cat to the y pipe and then that to some plumbing till i get to my muffler.

what is the best way (after the y-pipe) to connect to the 2.25 inlet on the new cat (cut/weld? flange?

part 2: cat placement. now i have the freedom to place my cat anywhere i would like along the truck. is there a "better" place for it to be placed to be most effective? like should it be closer to the y-pipe or further away?

i would assume it would be best to get rid of both cats and mount my new cat right behind the y-pipe and above trans crossmember there.

any suggestions?

many thanks
-chris

 

[HahnsB2]

Here's my exhaust. I didn't weld the pipe to the flange, it was like that when I got it. Everything else I did. Generally the closer to the engine the more effective the cat is.
I used a band clamp to clamp the cat/muffler/exit pipe assembly to the pipe off of the flange. They are easy to remove and seal well (mine doesn't since the pipes don't align perfectly which is why there is foil in here, seals really well actually), it really helps if I need to pull the whole exhaust assembly off for any reason. The u-bolt clamps (which suck BTW) on the cat are not needed since I welded it, I just haven't got around to taking them off. It appears now looking at these pics I have an exhaust leak at the flange, I haven't been able to find that damn thing!

 

[Dora The 4x4'a]

sweet..what are those measurements hahns?

after gettin under ther today im gunna need to cut or grind my cat off the flange from the y-pipe. so i figure ill make a clean cut and weld a short pipe off the y pipes to the cat and then a pipe to the cat and plumb it out over the crossmembers cleanly to that big heat shield where i can work in open space from there..

question is. what are those measurements? the y-pipe to a new pipe into my cat (2.25 inlet/outlet). is the y-pipe 2.25? so it would be a straight weld?

 

[seth247]

make sure you put the cat under a heat shield.


They get HOT

 

[Dora The 4x4'a]

yeah itll be where the other cat was.. there are the stock heatshields there