F-body catylic converter question...

[Nemesis_y2k]

How many inches is it???

I want to know if stock F-body exhaust is a full 3" exhaust(including cat)... and if so, are there spots for 2 O2 sensors in the stock cats?(for OBDII)

Thanx!!!!!!!!!!!!!!

[Joe 1320]

After the Y, the stock exhaust is 2.75 inches. There are indeed 4 02 sensors on an OBDII setup. One on each exhaust manifold just proir to the Y pipe flange, and one just after each cat.

[Nemesis_y2k]

Great reply, thank you... BUT...

Your cat(or one of them) are they 3" or 2.75"?

I'm a Sunfire GT owner, NOT a F-body driver, so I don't know where the Y is... and what it is before the Y... ?

I am looking for a 3" alternative to a universal cat that I'll have to drill and weld...

or can the 2nd sensor just be welded in the piping after the cat???

Thanx!!!!!!

[wolfdogs]

Originally posted by Nemesis_y2k
Great reply, thank you... BUT...

Your cat(or one of them) are they 3" or 2.75"?

I'm a Sunfire GT owner, NOT a F-body driver, so I don't know where the Y is... and what it is before the Y... ?

I am looking for a 3" alternative to a universal cat that I'll have to drill and weld...

or can the 2nd sensor just be welded in the piping after the cat???

Thanx!!!!!!

why are u doing this?

[Nemesis_y2k]

Because I'm planning ahead for turbo and will require a full 3" exhaust and am looking for the best alternative to having to drill through a universal cat. I will also require a 3"x18" resonator... and I have my borla 3" straight through muffler...

Just gathering information to do it right the first time

I know how to custom build an engine/exhaust... now its to find my parts...

[Kevin - Blown 95 TA]

You might want to skip the after-cat O2 sensor and plug in a simulator. If you need a 3" cat - the OBD1 cat will work, but there probably isn't room for it on your car cause it's big. I don't think the small OBD2 cats are near 3" in/out. I just got done welding my OBD1 cat up to a 3" header flange, and it fit perfectly, once I made it round with a expander where it was cut off from the Y-pipe. The reason I did this was for emissions. Normally I have on a Random 3" converter, but it won't pass emissions with the Random. The Random is slightly smaller, though, and is less restrictive, so it stays on there the rest of the time. Also, you could look into Walker converters, or Brown. They are said to be OEM quality. I'm sure you could find a more compact 3" aftermarket model, but it might not scrub the emissions good enough to pass.

[Nemesis_y2k]

Thanx for the amazing info... What kind of information will the 2nd sensor send and what do I lose by using the simulator(wich I was trying to avoid)???

[Injuneer]

Surprised no one asked this question before asking... but what year F-Body are you talking about? Your screen name indicates "y2k".... but you say you don't even have an F-Body.

Each year of the 4th Gen F-Bodys can vary as to the number, size, location of cats and number of O2 sensors. Without stating a specific year, it is almost impossible for anyone to give you the correct answer.

Additionally, if you are talking about using a turbo, the size of the stock exhaust configuration has got to be the least important issue you are facing. You will need a full custom exhaust to support the turbo, and you will need to oversize the exhaust to suit the need of the turbo. Whether you would even use the stock PCM to control a high output turbo is subject to debate, so the issues of number and location of the O2 sensors becomes a moot point, until you decide specifically what you are doing.

The OBD-II (96 and later) LT1 and LS1's have dual cats (one in each branch of the Y-pipe), and a pre-cat O2 sensor in front of each, and an after-cat O2 sensor behind each cat. The PCM utilizes the pre-cat sensors to control A/F ratio. The after-cat sensors are utilized only to verify the efficiency of the catalytic convertors. If you remove the cat, you MUST use a "simulator" to provide the required signal to the PCM, indicating the cat is still there. That will have no effect on the operation of the engine management system, because the sensors are only used to measure the cat performance.

[Nemesis_y2k]

YOu must have missed that lil part...

I drive a Sunfire GT...

THat's exactly what I'm doing is building a full custom exhaust

going from 2" to 3 is quite the step

Most people run their turbo's with 2.5-3" on our cars... so I'm just looking for the right sized cat with both o2 sensor holes and am wondering if gm had a stock cat I could use of a 3" size... that's all

Thanx tho for clearing up what the second sensor does I actually just found someone selling a j-body simulator for 60 bucks... I'll lookin to that.

Thank you all again...


I just want a yes or no, is your cat exactly 3" :P

[Joe 1320]

Originally posted by Nemesis_y2k



I just want a yes or no, is your cat exactly 3" :P

no

Also, cats do not have bungs for 02 sensors. The bungs are located in the exhaust tubing regardless whether they are factory or aftermarket. Some cats have the provision for an air injection tube, but that's it.

[Nemesis_y2k]

My work is done here...

Thanx so much, you guys are

[Injuneer]

What a huge waste of time... where do these trolls come from.