C3 - 76 - Catalytic Converter Question

[Steve B.]

[Harmon C.]

Re: C3 - 76 - Catalytic Converter Question

The water in the exhaust may be the result of not going for a ride long enough to heat the mufflers up. Some people drill a small hole at the low point of the muffler so the water can leak out all the time. The smell may be their if you put a converter back on as most times they stink. The smell could just be from the carb. running rich during warmup with the choke on.

[Joe L.]

Re: C3 - 76 - Catalytic Converter Question

I have a 1976, L48 which a prior owner has replaced the stock exhaust system, including the catalytic converter, with straight through pipes, circa 1974 and earlier. My questions stem from the fact that besides the bad smell there’s a noticeable amount of water, at start up, below each exhaust pipe with a black carbon looking film on top – only noticeable during the first several minutes of operation. I’m guessing that both the smell and the strange looking film are the result of there being no catalytic converter. So what’s the bottom line… with the catalytic converter removed is there enough gain in performance/horsepower to offset the unpleasant items above or is it worth putting a stock exhaust system back on?

As always thanks in advance for your help.

Steve Boyd

Steve-----


The water with slight amount of soot is very normal. It's condensation which mixes with soot in the exhaust system and is blown out on engine start-up/warm-up.

I don't know what you mean by "bad smell". However, a car with a catalytic converter removed along with, likely, other emissions components, is going to generate a lot more exhaust emissions. Of these, the unburned hydrocarbons (HC) are going to be very noticeable and unpleasant.

My recommendation: return the engine to stock emissions configuration and re-install a stock exhaust system with catalytic converter.

[Peter G.]

Re: C3 - 76 - Catalytic Converter Question

Steve, I remember back when I had my "new" '76 Corvette and back then we would remove the "cat" and replace it with a straight pipe or it looked like a very small "glasspack" that had the four bolt flat flange on both ends so it would bolt right up to the existing stock exhaust.

The "cat" is also like a small muffler and does quite the sound of the exhaust so back then we took the "cat' off not just for the small added horsepower, but also for a little deeper exhaust sound. I believe some of the repo companies do now sell the little "cat" replacement pipe.

I am a purist so I would put the exhaust system back to the correct stock configuration.

But that's me.

[Joe L.]

Re: C3 - 76 - Catalytic Converter Question

Steve, I remember back when I had my "new" '76 Corvette and back then we would remove the "cat" and replace it with a straight pipe or it looked like a very small "glasspack" that had the four bolt flat flange on both ends so it would bolt right up to the existing stock exhaust.

The "cat" is also like a small muffler and does quite the sound of the exhaust so back then we took the "cat' off not just for the small added horsepower, but also for a little deeper exhaust sound. I believe some of the repo companies do now sell the little "cat" replacement pipe.

I am a purist so I would put the exhaust system back to the correct stock configuration.

But that's me.

Peter-----


The catalytic converter "replacement pipes" or,as they were usually called, "test pipes" have been illegal to sell in the USA for several years now. The EPA clamped down hard on this. I'm sure they could still be obtained in the "underground" market, but I don't think you'll see them advertised or available from any "mainstream" suppliers.

[Duke W.]

Re: C3 - 76 - Catalytic Converter Question

Dave McClellan, in his book, stated that the single catalyst exhaust system beginning in 1975 added "half an atmosphere" to exhaust backpressure, so it went from 3-4 psi up to 10-12, which took a huge toll on output. Up to that point Corvettes had one of the most efficient exhaust systems on any production car.

The old "bead bed catalyst" was mostly to blame and modern monolithic replacements significantly improve the situation, but the car still effectively has a single exhaust system.

There were only a handful of catalytic converter part numbers used on those vintage GM cars, and bolt on monolithic replacements are commonly available for a about $150.

Duke

[Larry C.]

Re: C3 - 76 - Catalytic Converter Question

I took off my 1976 L-82 catalytic converter in about 1978...thought I was doing something good then...ha...now would like to replace the converter back into my system so the car would score better in ncrs judging. Where could I find such an item?

[Duke W.]

Re: C3 - 76 - Catalytic Converter Question

Any online parts catalog - like NAPA - should yield a functionally correct replacement, however, it will not look like the original.

Obviously, if the catalyst is not installed it will be a full deduct, but a current aftermarket replacement should only be a partial deduction, which you should be able to figure out from your JG and JRM.

You might also be able to find a used original, but they are hard to come by. I don't think junkyards are allowed to sell used catalytic converters.

Duke

[Greg A.]

Re: C3 - 76 - Catalytic Converter Question

I remember a thread some time ago that mentioned a company that bought old cat converters, remanufactured them to current specs and materials and then sold them as replacements. They were physically the same as original OEM cats, but functioned like current styles.

I couldn't find the website of the company I looked at before, but here's one I did find: http://smithcat.com/index.htm

The point is there is a source for a remanufactured original...we just need to find it. Maybe someone will chime in who has experience with these.

BTW, I think there's a market for old converters, so don't just throw one away.

[Larry C.]

Re: C3 - 76 - Catalytic Converter Question

Duke and Greg, thanks for responding, I am brand new to the NCRS and look forward to having the car judged..your information will sure help me out..I hope my best friend that was with me the day I bought the car brand new will be with me at the October Frisco event. The car and friendship both have stood the test of time..

[Rich W.]

Re: C3 - 76 - Catalytic Converter Question

You may have luck finding a cat from another car or truck that will at least look the same pancake style converter..there are a good bit of those around still..might be able to trade a mono for a pancake style..it will be hard to find one because you are not supposed to be able to buy one from a salvage yard..which drives me nuts..but you may be able to talk them into it..can always try..good luck and welcome.

[Larry C.]

Re: C3 - 76 - Catalytic Converter Question

Rich, thanks for sharing the info, I need to check out a long shot on an original converter that a fella was going to cut off and give to a muffler shop and havent heard from them...probably wont be that lucky but who knows! Would the converter for the 76 be the same as earlier or later models and how do you tell if it meets specs the judges are looking for?

[Rich W.]

Re: C3 - 76 - Catalytic Converter Question

Well the only way to be correct is to go by what the judging guide or aim says..I don't have either for your year car so I don't know what years may be if at all interchangeable..I got the manuals for my years..there is so much info in there it will make you dizzy..which I feel is part of the fun..if you can get your hands on the one you talked about would or should be the way to go..maybe get the whole exhaust from the buy before he hacks it up..bribe him by getting him some replacement exhaust..good luck on the hunt.