bypass pipe or hollowed cat? (long)

Teutonics · Teutonics's Garage

After yet another nerve-wracking emissions inspection today, I think I may need to re-evaluate my exhaust setup.

I currently have a bypass pipe, and have gotten through inspections before because no one ever knows what it's supposed to look like on a rear engined car (maybe they always thought the heat exchangers were the cats?). Anyway, here's what happened today: Drove into the station and leave the car with the tech, go to watch from the waiting area. Guy pulls the car onto the rollers and then gets out the inspection mirror.... looks under the car on the drivers side (where cat is supposed to be), moves around to several different places, and then goes to get a second tech (I'm starting to sweat now). Second guy gets the mirror and works his way all the way around the car, shakes his head "no", and gives the mirror back to the first guy (uh-oh!). Tech proceeds to test car and comes in and tells me I pass, "$25 please". Whew. I can't take this again next year.

Anyway, to my question.... I have a completely hollowed catalytic converter (ain't NOTHIN' in there!) that I could put on the car. Will there be any issues or appreciable loss in performance as compared to the test pipe?

Sorry for the long post, I had to get it off my chest!

jmohn · jmohn's Garage

I have been told that a gutted cat. is less effective (performance wise) than a "test" pipe. I have never verified this.

Jerry M
'78 SC

masraum · 12-20-2003, 07:57 PM

A gutted cat is worse than a test pipe is worse than a Euro style pre-muffler.

Thomas Owen · 12-21-2003, 03:58 AM

Get the pre-muffler and put it on. It has the cat-like bulge.
Regards,

911nut · 911nut's Garage

I did a back-to-back between a test pipe and my hollowed-out cat.
Using a hollowed-out cat made the car feel like it was tied to a tree.
Do what Thomas said. A Fabspeed muffler looks like a cat.

Teutonics · Teutonics's Garage

Thanks all!

1987C1 · 09:08 AM

I keep reading that a euro pre-muffler gives you around 5 HP but
a test pipe gives none. I don't understand how a pipe in place of
a cat gives no additional HP. The back pressure and flow should be improved with a test pipe - giving additional HP.
I have read the test done in Bruce Anderson's book - does anyone have any other tests on this?

Jeff Alton · 12-21-2003, 09:55 AM

I have the Fabspeed pre- muff and it does indeed look like a cat. However, if you have 30min of spare time why don't you put your hollowed out cat on for the test and them just take it off after??

Jeff

Teutonics · Teutonics's Garage

Quote:

Originally posted by catca
...why don't you put your hollowed out cat on for the test and them just take it off after??

I thought about that, but my "butt dyno" isn't calibrated to 100% accuracy.

The only way I would be satisfied with the decision was if it was tested on a real dyno, and was hoping someone on the forum had already "been there - done that".

However, I'll probably end up swapping and trying it for the next emissions test!