Effects of removing the cat on a US 85 QV?

My '83 is de-catted and de-smogged (legal in TX for cars over 25 yrs), Tubi exhaust with small shop-built muffler assemblies in place of the cats. Straight test pipes were way too loud.

Runs fine and smooth; since I had all this done right after it arrived here in jan. '08 I can't compare before/after. My guess is a few xtra hp gain.

 

Don't know about removing it comletely but I am in the process of replacing the stock unit with the Fabsport cat that was on special here on fchat. I will post the results when she returns. Subjective impressions of course.

 

As long as you have a sealed bung for the O2 sensor the FI system will not be effected as everything is measured pre-cat. Noise is a subjective issue and I personally have not found the perfect sound but have have an idea what I am looking for. HP will vary depending on the condition of the cat being removed.

 

I am not as clear on this. The Qv '84 and '85 I thought maintained proper mixture based on the O2 sensor. Doesn't the typical bypass pipe still have a port for the sensor? (hence the K-Jetronic with Lambda control) I think maybe you are referring to the thermocouple bung which will need to be capped? Not an expert just adding my 2 cents.

 

It won't smell very nice with cats off, modern gas gives these cars a real rotten exhaust smell. You want to make sure the wind is blowing away from the car at low speeds. And if it is anything like my 328 it will be a LOT cooler under the hood.

 

... and you can forget about selling it California.

 

It doesn't affect the fuel injection system at all providing all is well in the first place. If you use a test pipe most likely there won't be any bung for the thermocouple. Mine didn't have one. Simply wrap the thermocouple and stick it out of the way.

Great debate on this subject a few years back on here so bear that in mind. You might want to do a seach for this topic as well.

As far as sound... i've found most of the high priced mufflers out there lacking in one form or another. I ended up going with a custom stainless magnaflow set with rolled polished tips for a 1/4 the cost.

+1 on it being a bit cooler and much less worry about about an overheating cat.
HP gain will be little to none. If sound however is the ultimate goal and you don't mind being teary eyed from the exhaust smell then go for it.

 

Ive made quite a few test pipes, what I do is keep the thermocouple and 02 sensor in the test pipe, I just add a (spark plug extender) to the 02 sensor to keep it out of the flow of exhaust gasses, kind of fooling the computer. Everyone I have made works very well. There is a bit more noise though


Wade

 

My appolgies for not clarifying more. I meant a bung that seals tight when the 02 sensor is installed. after 25+ years corrosion deteriates the threads and sealing surface also many times the bungs are replaced and I have seen plenty that have not been welded properly and allow air to leak.

 

I had a '84 QV years ago that I dyno'd with the original cat and a test pipe. It had an increase of 1 hp and a loss of 1.5 ft/lb with the test pipe if I recall correctly. However, with the test pipe there was definitely added drone in the cabin and at stoplights, the smell of fuel was annoying.

 

3 years ago when I did an engine-out major and removed the cat in my US '85, the insides were shredded - large chunks missing (had to shake the stock muffler around for about 5 minutes to get most of the pieces out) so had a straight pipe with O2 bung welded in between the existing flanges I cut off.
No noticeable performance/running difference, I haven't noticed any fuel smell, and sound is if anything a bit more raw and pleasurable to me.
YMMV

 

What? Who? Duh? say again!

 

My 308 doesn't have cats and I have never noticed a smell. at least not teary eyed its car exhaust it never smells good.

 

Steve, you may want to review this discussion before eliminating any o2 sensor:

http://www.ferrarichat.com/forum/showthread.php?t=344238&highlight=lambda+control

 

Turns me ON.


But then again I love the smell of burnt rubber, oil and NITROMETHANE and gunpowder too.