I live in Alabama where we don't have emission tests. Instead of buying a sport cat, midpipe, or midpipe with a silencer. Why can't I just gut the factory cat? Would a sport cat still be better? Also are people with midpipes with silencers still getting fumes like a straight midpipe?

Big question: What does the air pump do and how does it relate to the cat? I hear that every time someone removes the stock cat and go with a midpipe they take off or disable the air pump? Why?

Is there a downside to not having a air pump? Usually there is always a downside to every modification so what will I be giving up?

 

Fumes are still there with the midpipe.

Air pump supplys oxygen to the cat at idle to help burn off harmful emissions. Without the air pump these go unburned and are released freely into the air. Air pump only works at idle and disengages at low rpm...never on while under throttle.

No cat, who needs an airpump...saves 9 pounds of weight. Downside is you will have (or most do) have a bad idle as the computer will try to compensate for no air pump. I just adjusted the idle to run at 1000 instead of 750-800. Smooths it out. Also, without the air pump you will need to get a new pulley for the water pump and alternator with a shorter belt.

Gut the cat....but may get better flo with a midpipe or high flo cat and it will weigh less too.

 

Stock cat weighs 30 lbs

MP weighs 10

 

On a 89+, you need the airpump to run the VDI. As for why get a pipe instead of gutting it. Well the factory pipes are small, plus it is not smooth. Also think about what the big hole in the middle can do to your exhaust flow

 

 

gutting the cat will allow more flow and youll deffinetly feel the difference the mid pipes are a better design, designed for straight thru flow when you gut the cat it will be better flowing better exhaust but not as good as with a good mid pipe.exhaust is not all flow thers also sound you tend to get a tin can sound slightly coming out from under the middle of the car after that .Plus the weight difference ,the cats weight is due to the cast flanges and the converter honeycomb material the rest is a thin sheet metal ,Ive seen it cause i unwrapped one to fix a buddies cat I welded the seems back together for him no leaks from that now...also when you gut the cat you also get rid of the ability to actuate the six ports properly on an 88 and below ...I see that you have a 89 so thats not a problem

 

I don't have a 89' car but a 94 3rd gen. So know I'm wondering like the post below if I should go high flow cat or midpipe with a silencer?

 

Save your cash for now and spend your time. I've heard using acetone to remove the cat material works. Just fill your cats with acetone and let them sit overnight. The next day they should be ready to be cleaned out and ready to go back on. I have an '89 TII that I gutted the cats on. I just used a long screwdriver and small hammer to tap the driver with. I was getting big backfires with the airpump still engaged without the cats. I disengaged the airpump and now the backfires are not bad at all. My idle wasn't affected much. Just a bit lumpier now at idle which is still at 750RPM. The person that told me about the acetone trick for the FD cats is "RX7_Kelvin". He is on this forum everynow and then. He can tell you more in greater detail.

jerk_racer@hotmail.com

 

Aside from putting out 10X as much pollution with a midpipe, the other advantage of using the highflow cat+airpump is you don't have to worry about boost creep. If you have a dp+mp+cb that is reasonably high flowing, you'll need to port the wastegate and get a good boost controller to take care of spiking. Some people have reported they can control the boost properly with a PFC without porting, but you should really do it to play it safe. The downside of the of the high-flow cat is you loose a little horsepower (maybe 10hp, they flow pretty well), you can't blow flames, and of course, its another failure point.

 

I gutted my cat and if you want I will sell it to you.

 

...a third gen cat (w/all the heat shielding etc) weighs at least 60 lbs, in my expert opinion . It's heavy as ****. When I get home I'll put it on the scale to find out.

 

60lbs!! I realy don't think it's that heavy. I'm only 140lbs and I picked it up with ease. Probably more like 30-40. Maybe you're just a wimp

 

alright....enought insanity with the guttiing of the cat. i feel that its a waste of time and energy. ok a cat is not the same size in diameter as the regular piping why in the world would you want to increase pressure, slow gas velocity down, and create turbulante ambiance just to bring the gases pressure back down and the increase vel. i mean people spend the extra money to put mandel bend tubing for the exhaust and then gut the cat...WTF. anyways my rant and rave.....just do it right and replace the cat with a midpipe.

 

I really don't think you have any experience with a gutted cat. After I gutted mine my boost spooled up alot faster. So fast that for the 1st time I spun the tires in 1st under accel. which I could never do before. A faster spooling turbo means better flow. I guarantee my gutted cat flows way better than when it wasn't gutted.