joey bagadonuts

While this mod may seem commonplace to our British counterparts, here in the States, I'm not sure a lot of p-car owners remove their catalytic converters (it's an illegal mod for street cars, or something like that). Well, I've read that a cat bypass or sport cat might deliver more power, so I thought I'd take my chances.

Conclusions: It's certainly a deeper, booming exhaust note, but not unbearable. I already had the secondary bypass and the cat bypass didn't really add much to the interior noise. Open the windows and rev it up in a tunnel and you'll definitely make your presence known--pure race car!

For me, the performance gain I'm most interested in is increasing torque further down the rev range. Coming out of the slow corners at the track, that extra grunt comes in very handy. And according to the butt dyno, the cat bypass definitely adds some low-end pull.

I don't want to get bogged down in the hp/torque discussion, I just wanted to pass on some pics and let you know that the cat bypass is a mod worth considering. (Special thanks to Lefty's Deceiver for his assistance with the installation.)

Here's what you start with ... yuck!!!


As you can see, the orginal cat contains some sort of honeycomb filter.


I bought a nice B&B bypass, secondhand off eBay. Notice how the sensor plugs right in.


Yes, I got rid of a lot of mass! The original weighs 14 pounds--this one weighs only 4!


Here's a look from underneath. Nice fit, don't you think?


Not a great shot, but the other end of my primary muffler connects to a u-shaped bypass and then on to the tailpipe.


Questions? Comments?

Ruairidh

Joey, what happens for annual state inspections? Does this impact the emissions aspect? Purely hypothetically would one simply put the cat back in before testing and remove after?

More Torque is always welcome!

Doug H

Joey:

Very cool. I don't have to pass inspections and am very interested in this modification. The guy at my shop Friday told me that I would loose too much back pressure to by pass the cat with my new GHL exhaust. Is he incorrect. Sounds like it. Does the car idle and run as smoothly. Don't need it for everyday use so not to worried about the noise.

How much and were do I go to get what you got. Do I need to get my chip modified if I do the cat bypass also.

SPIKES

COOL JOEY

you have way too much free time on your hands


is the rest of the emmisions stock.....no lights comming on the dash etc..?

joey bagadonuts

Oh, I forgot the coolest part! On the way to the track yesterday, an RSA driver spotted me and followed for a while. In the paddock, we started talking about our cars and then he asked why were there flames shooting out of my tailpipe.

R-,
That's correct. I'll slap the cat back on when I go in for emissions testing. I took care of it earlier this year so I'm set for two years.

Doug,
I got my part for $175 + shipping off eBay. You can get a new Bursch test pipes for around that amount from Vertex or GRParts . Along with B&B, you can also find one at Fabspeed if you want to buy direct. The back pressure thing is beyond me but that hasn't been a problem--my car's pulling stronger than ever. I've read that removing both mufflers might create problems but not the cat. Maybe someone more knowledgeable can comment but this is your basic plug-and-play mod.

SPIKES,
Emissions have not been a problem. How'd that cup pipe work out for you?

SPIKES

hi joey
did not like it. too quiet at low revs. saves a lot of weight though.
i need a deep grumble on start up.
i did a conversion on my 930 years ago and it sounded great.

i like your latest idea.

johnfm

Can't beat the low rumble, eh Joey. I shudder to think how it sounds with the secondary bypass as well though.

joey bagadonuts

Yes SPIKES,
If you need more rumble on start up, this is definitely the way to go.

John,
I must be losing perspective ... a problem most likely caused by too many trackdays. I even discarded the engine sound pad during the summer (it fell apart during a cleaning), and I still don't think the noise is that bad. With two bypasses, the sound is starting to resemble an American muscle car--think Cobra SVT--only with a lighter, flat six ... if you can imagine.

Joe@Fabspeed

Hi Joey
Catbypass pipes do work........great for track applications.......FYI the center muffler BEHIND the license plate is more restrictive than the 2ndary muffler behind the passengers tire. In addition, removing the center muffler is better as you are removing the most weight at the BEST area in terms of better handling and inertia...........lastly when you are corner balancing the muffler that is riding "shotgun" counterbalances your weight.
take care
Joe Fab
Fabspeed Motorsport

Doug H

Apparently, running the bypass pipe for the muffler behind the license plate to the secondary side muffler is not a good idea. My shop apparently believes that this leads to popping or blowing that big tub of a side muffler. My car was set up this way and also blew the side muffler. The single GHL at the rear, according to G-Tech if that means anything, improved upon my 0-60 times over the set up with the bypass pipe in the rear and only using the side muffler.

rsa

Joey, I completely agree with your assessment about the sound. The deep rumble especially traveling thru underpasses is priceless. I'm not sure if the car is quicker, but it sure sounds that way. My RSA has had the secondary muffler and cat bypass since I bought it this spring, so I've never experienced it any other way. I suspected it made the car slighltly quicker though. Do you really think it adds to low end torque?

Also, have you noticed any crackling/backfiring? Mine does only very occasionally.

P.S. I think I met you this summer at the Willow Auto drive up to Lake Geneva. Since I'm only one town north of you, maybe I'll see you on 41 some time!

joey bagadonuts

Oh sure, Jeff. I remember meeting you at Willow. Nice car, by the way.

As for low-end torque, I think a "real" dyno is in order but here's what I've noticed. In stock form, the engine becomes pretty torquey at 4,000 rpm or higher. After the various mods, I'm pretty certain that my car starts pulling hard around 3,200 - 3,400 rpm's. I'll probably hit the 11/9 PCA dyno day at The Exchange to see what the curves say, but the pull is so noticeable it actually makes the car feel lighter.

Ruairidh

Ok, now you've really sparked my interest Joey! Thanks for the post - you've just added another thing to mull over for my car!

BrokeAss

Nice mod Joey! I've been thinking about junking my cat with a similar mod.

I tried to get a local shop to "give" me an old cat from their parts heap, with the idea that I'd "core" it out. They wanted more for the old cat than you paid for a used bypass pipe, so needless to say that idea just died. (Hmmm, maybe its time to rummage the parts pile at another shop....) Coring out a used cat may be an exercise in futility though. The cat is one solid, very dense mass of cells and doesn't look as if it's going to yield easily to the hammer & chisel treatment.

My list of mods for '04 includes overhauling the exhaust completely. Since I leave in South Florida, I plan to dump the heat exchangers and go with pure headers, no cat and dual exhaust outlets - oh yeah and removing the engine fan and replacing it with a bypass pipe. (I got a very good price from GHL for the parts a few weeks ago, but alas while the spirit is willing the wallet and the spouse have ruled on the side of common sense)

joey bagadonuts

R-, Do it! Your neighbors will love you for it!

Thanks, Terry. Looks like you're working on a cool list of mods yourself. The header swap IS expensive and I think I have enough straight-line speed at this point that I'll stick with the current setup for a while (yeah, we'll see how long that lasts). NOW I want to focus on cornering speed.

During my last track outing, I was doing my best times ever but I still couldn't hang with those "prepped" cars in the corners. Evidently, big sway bars, R-compounds, -2 degrees of camber and trail braking can only get you so far. Next up are new shocks and springs ($$$). I might opt for wider rubber as well, i.e. 245's and 275's, and try to shed a few more pounds ... from my car, that is.