Lets pretend I decide to completely get rid of my cat, and have muffler elims. What could I possibly do to get by emissions? Run it off everclear and retard the crap out of the timing?

 

mufflers dont do anything for emmissions... as far as eliminating the cat goes... do they hook a sniffer up to it? You didn't say what year you have, do you have precats?

if they hook a sniffer up, and you don't have precats... it'll be tricky... but someone will probably give you an idea... I think alcohol was mentioned the last time this came up

 

Lets pretend a "visual" is a part of your smog test. You're DEAD!

RACE ON!!!

 

precats will help more in the morning... the main cat is best once things warm up.

however, if you remove the precats and install a REAL GOOD main cat - re: Random Technologies - you should be ok.

Oh, and don't forget lots of methonol.

I would not remove the precats, as much as gut them...

One last thing... precats, like cats, are no where near as restrictive as they were 20+ years ago. modern cats draw no more than 3~5 hp, whereas the original bead style cats of the late 70s early 80s drew 20 hp! Real power theives!

 

If you go on the rollers, you'll need a cat to pass. You're in the Phx area, I assume they'll put you through IM240, aka, "the rollers". But looking at some posts here in the last few days, it sounds like Phx is like Chicago, no real visual inspection, just a scan for the OBDII cars and rollers for per-OBDII cars. You don't need precats to pass the rollers, you do need a main cat. The precats are just to help emissions in the first few minutes, until the main cat lights off. If you have a nice new modern cat, it'll light off fine, besides, your car will be warm when it's tested.

Eric

 

On my 85, i swear i picked up about 15 hp because of the difference i felt by eliminating the cat (which was partially clogged)... that whole exhaust system is such a poor design though.

Corvetteaholic- i see you have an '85 as well. So that means you have one cat, if you gut it, or eliminate it, you wont be able to pass a sniffer emmissions test.

 

How about rodding out the pre cats. They would still be there, but not restrict flow at all.

 

I'm pretty sure I don't have pre-cats in my 85, which is good I guess. From another thread I saw an exhaust system which is true dual, and NO cats at all. Thats what got me thinking about trying to get through emissions without a cat. Does retarding the timing help at all with emissions? I had a buddy who ran straight everclear instead of gas for emissions in his old truck, and by some miracle the poor thing passed. He wasn't required to have a cat though.

 

My 85 has a single cat from the factory. I replaced it with a small 3" carsound cat, and it passed easily.

Use fuel additive, pull timing back to 4 degrees, put in a clean paper filter, and get her warmed up, you'll pass. EGR helps the most, when it opens you'll see the CO drop like a rock. You might get by without a cat.

What you should do, is pick up one of these cats for $50, weld some flanges to it, and make a test pipe to match. Then just bolt it on every two years.

 

ah, the answer here is "partially clogged".

The old bead style of cat used a metal box full of platinum coated beads. The exhaust air passed through the voids between these beads. It was highly restrictive, and, very disorganized. Creating backpressure and horrid scavaging ability. If you want to imagine it, think of a fish tank filter with charcoal. The water passes through the voids. But, once it gets clogged, forget it!

Fast forward to the modern metal matrix monolith. Those ROCK. Image a lattice work of ceramics. This is very fine, very small holes, but lots of them. The exhaust passes through this matrix, coated in platinum.

That matrix is very efficient, very non-restrictive. The air passes, creating little backpressure and not harming scavaging at all.

Performance cats use the exact same technology. However, they make the cat larger, with more holes, to allow more air through.

The best way to describe these is much like a screen door. The air passes freely. So will water. But, the downside, if the matrix gets blocked, or, in the case of this example, the screen gets blocked, not much will pass.

I understand the need on purpose built race cars to run open exhaust. That's fine, but I don't understand the desire to remove a device that works SO well and causes so little problems, just for 5 hp.

Sure, the entire single tube Vette exhaust sucks, but, install a 3" center pipe, with cat, good y-pipes and longtubes, you will still be legal, and won't loose all that much power. The center pipe will work more like an x-pipe or such. Another option, that should pass visual everywhere but CA, is to do a disguised dual system, with an x-pipe, and bullet cats.

Sure, they cost $$$, but you know something, it's a cheap price to pay for clean air. Without the advent of the catylitic converter, there would be no place in this country safe to live in... or this world for that matter. Modern cats actually CLEAN the air, compared with what they take in, versus, what they take out. That was proven in England several years ago. The quality of the air being used by the engine was worse than the quality of the air coming out the tail pipe. Sad, ain't it?

The other upside to the cat - they act as mufflers, meaning, we can have loud cars that are not so loud we cannot deal. mufflers have shrunk (look at the muffler on a 50s or 60s caddy!). There are trade offs.