Catless exhaust, EFI, stink?

My catless Miata smelled pretty good with a little fuel fragrance added.

Although it never bothers me normally.

Oh good grief, the PO of my '92 OCC gutted the cat. TBI350. It smells horrible. I notice it when I'm in traffic, or if heaven forfend I go through any kind of drive-thru.

Keith Tanner wrote: Because the cat will reduce the amount of CO exiting the exhaust along with NOx and HCs. It's kinda the point. Want to make it smell better? Use E85.

E85 makes me gag. At least when it is processed by a Buick engine it smells absolutely gross. C16 smells way better. Costs a tiny bit more though (Last time we bought some it was $95 for a 5 gallon pail)

I like the smell of my catless exhaust on both the zx and miata. Maybe Im just weird

I hate the catless exhaust stink from my brother's RX8. I've had a couple cars that were catless and I didn't mind too much.

The older I get the more I dislike the smell of catless cars. Currently, everything I own runs cats. The F350 I just sold was missing the cats. It didn't smell horrible, but it still had a distinctive smell.

My rabbit is quite stinky with it's catless setup... Not too annoying except when running in the garage for tuning.

I have a bad cat on my rover. When I bought the truck, the passenger side cat looked a bit.. funky. Not knowing Rover, I did not think much of it until a month ago when the CEL came on for a bad O2 sensor.

With 90,000 on the clock, I figured they were all due and bought all four. That's when I discovered the downstream sensor on the passenger side has been spaced out from the flow. Now I know why that cat looks funky, it's a cheap aftermarket one welded into the system.

Next month she's getting a full SS Magnaflow from manifolds to tip. This is a ULEV vehicle and I want to keep it that way.. until then, the exhaust really stinks with untreated exhaust an excess of fuel

Try an RX7 with no cat.

Back to the OP. Two options on routing to consider. First is extend the tips further. If the exhaust tips aren't extending past the bumper you might be blowing the exhaust into dead air under the body and its pooling under there.

Another option is side exhaust instead of rear. Some cars just have funky airflow and it rolls up the rear into the passenger compartment. More of an SUV thing but possible either way.

That, and don't rule out an exhaust leak somewhere else. Doesn't take much of its in the right spot under the body.

Cats or no, you shouldn't be getting the fumes into the passenger compartment, no matter how smelly they are.

I have to shut the engine off of my Corvair (high turbulence heads that is very stinky at idle) before I get fully in the garage or it will stink for a half an hour. I could run the Speed3 with the door closed for 10 min and you could hardly even tell!

Sometimes I feel bad for people following me in traffic. The exhaust shoot straight back and is well below the bumper so I don't smell it. As noted above, if the exhaust stays in the dead air it will recirculate up, which is even worse with a Corvair because if it gets pulled back into the motor by the fan, it goes into the heater.

dean1484 wrote: Try an RX7 with no cat.

After being away from my RX-7 for a while, I went back to driving it and the first thing I thought was "oh JEEZ this thing is a pollution nightmare" and I started going back to looking into Ecoboost swaps.

I would put a cat on it but with the porting it has, the cat would melt down before I got out of the driveway

When the midpipe failed on my Volvo, I bought a Magnaflow pipe with cat, even though the rear cat isn't even monitored by the computer. It doesn't hurt power any, so why eliminate it?

I also have a cat for my '86 VW if/when it ever gets finished. Has a stock cam so there's no reason it can't have a cat.

But the RX-7.... oy vey!

kb58 wrote: If you're getting a headache due to carbon monoxide and a cat is put on, how does that keep you from still getting a CO-caused headache?

You would be shocked at how little CO is left in a properly running catalyst equipped car's exhaust.

Knurled wrote: When the midpipe failed on my Volvo, I bought a Magnaflow pipe with cat, even though the rear cat isn't even monitored by the computer. It doesn't hurt power any, so why eliminate it?

One doesn't need control over the second catalyst for it to work. But controlling it can really do a lot of good. I personally prefer having the sensor prior to the last brick, though- you can really use it effectively, making SULEV/PZEV a lot easier.

hhaase wrote: Back to the OP. Two options on routing to consider. First is extend the tips further. If the exhaust tips aren't extending past the bumper you might be blowing the exhaust into dead air under the body and its pooling under there. Another option is side exhaust instead of rear. Some cars just have funky airflow and it rolls up the rear into the passenger compartment. More of an SUV thing but possible either way. That, and don't rule out an exhaust leak somewhere else. Doesn't take much of its in the right spot under the body. Cats or no, you shouldn't be getting the fumes into the passenger compartment, no matter how smelly they are.

Pre-emissions days, many firms had plumbing requirements to prevent exhaust recirculation.. I know one firm had a rather dark name for the test (not F).

Part of the reason I parked the MGB GT is because I got tired of smelling like a refinery fire when I arrived at my destination.

I am looking at a Fitech EFI for the Molvo, and when I read the reviews, one of the big revelations is that the car no longer stinks of raw exhaust. All relative I guess.

I don't think it stinks much really. It's just headache, it only started after the header and up pipe swap. I can smell it a little here and there, but it's not stinky.

Exhaust tip vs bumper

alfadriver wrote:

Knurled wrote: When the midpipe failed on my Volvo, I bought a Magnaflow pipe with cat, even though the rear cat isn't even monitored by the computer. It doesn't hurt power any, so why eliminate it?

One doesn't *need* control over the second catalyst for it to work. But controlling it can really do a lot of good. I personally prefer having the sensor prior to the last brick, though- you can really use it effectively, making SULEV/PZEV a lot easier.

My point was, I could have replaced the rear cat with a section of 2 1/4" pipe and the computer wouldn't have thrown a hissy-fit that would prevent me from registering my car.

Mind you, I did replace the front muffler with a straight pipe and a mandrel bend, but this wasn't an option for the pipe with the rear cat on it. And the car isn't any louder, which is odd, but pleasing. (There's still a mid muffler and the rear main muffler, and a resonated exhaust tip... and the two catalysts... and the teeny tiny turbo which is a muffler unto itself... I like quiet cars)

In reply to java230:

Didn't change the tip, headaches started after the swap? Look for evidence of exhaust leaks where you did that work. Dollars to donuts says there's something leaking fumes and you're sucking carbon monoxide plus other exhaust fumes. Really want to get that fixed if you're already having exposure symptoms as CO takes a long time to clear out of your system.

In reply to hhaase:

I couldn't find any leaks.... New gasket at the block, and ball fittings

Oh and did I.mention that with the cats removed and on deceleration followed by a hard acceleration all the unburnt fuel in the exhaust explodes. I had to get a special exhaust system from Japan from Mazda that could take the huge backfire. It was also loads of fun to do this in underground parking garages as you would set off every car alarm in the place.

In reply to dean1484:

A huge ass port will do that....

It sounded like two six ga shotguns going off together and shot flames two feet out the pipes.

I can't believe how many of you pantywaists can scarf down bacon and soft drinks without a care, yet set up a chorus of pitiful whining at the thought of smelling a little raw exhaust. Surely, one of the great joys of our hobby is standing behind a 1960's Corvette with a carbed 327 at startup and getting a whiff of that eye-watering exhaust, rich with unburned hydrocarbons and the promise of unbridled speed. You should be truly ashamed to call yourself men.

dean1484 wrote: It sounded like two six ga shotguns going off together and shot flames two feet out the pipes.