Mufflers VS Catalytic converters

[special-K]

My girlfriend loves the smell of a car running a QuadraJet. I never paid much attention to the smell and thought she had a sensitive nose

[jdw]

Get an exhaust hose and run it out the door.

[davepl]

Originally Posted by BigRed76

Fuel injection with no cats will do you better than carbureted with cats.

Not actually. I have all three:

- Carb'd car with a cat ('75 Monte factory)
- Carb'd truck with no cat ('70 GMC)
- EFI car with no cat ('69 Camaro ZZ502 BS3 Sequential EFI)

The EFI car still smells like raw gas. It runs at about 14.6:1, but to get near stoich at idle with a cam in a motor like these requires a lot of extra fuel that winds up getting in your girlfriend's hair.

Now a poorly tuned car with cats will stink like sulfur dioxide, so there's no substitute for properly tuning the thing. But properly tuned, cats get rid of the raw fuel smell.

Maybe if gasoline still smelled like it did in 1970 I'd be OK with it, but it doesn't.

[piecesparts]

I may be missing something here. You told us that the truck was a 350, but never talked about the carb brand, the size of the carb, what jets are in the carb, or what the timing is set at, type of intake on the engine, or what temperature of T/stat that you use. There could be changes made here that could make it smell less like an old dump truck and more like a well tuned machine. What grade of gas do you use and what your spark plugs are set at. If you consider a multi-spark unit, like a MSD 6AL; you can get a more complete burn of your fuel since it keeps sparking through the fuel burn. What heat range are your spark plugs and are they burning at the right color? A good set of low resistance spark plug wires will help give you a better burn and a little more HP.

I personally would not put cats on the truck, I would consider a good set of mufflers---I use the Magnaflow stainless mufflers, since I used up several Flowmaster mufflers and had to replace them on a regular two year basis. This was on more than one truck, too--so it is not how the truck was used (daily driving and lots of highway use) Do you have a full exhaust or does it dump out under the truck? There is an advantage in the longer pipes, to get a good purge of your engine's cylinders and give the exhaust gases time to collapse and complete the burn of the fuel. Are you getting plenty of air through the carb to get the proper air/fuel mix for a right burn of the fuel. If your air cleaner is restrictive, then the fuel mix could be rich.

If you have a cam in the engine, then you may not be running in the right air flow area of the venturis. A cam can make you set the idle up to keep the engine running and cause the butterflies to sit in the transition area and not in the idle area, which would make your carb run rich.

[davepl]

I'll add my vote for Magnaflow - I have them on my Truck and my 2+2 because they're quiet when you want to be quiet and loud when you don't, and they don't drone.

[Kennuck]

Originally Posted by BigRed76

Fuel injection with no cats will do you better than carbureted with cats.

I agree with this. I can smell an old carbed car a mile away but my Stock 5.3 without cats has no smell.

[Nima]

Very good information.
Piecesparts, to answer some or your questions, I don't know anything about the engine internal since I bought the truck with it. I have the edlebroke performer intake and eldlebrock 1406 600 cfm carb. I don't know the jet sizes but they are what the carb came with them when I bought it. Downsizing the jets is what I was thinking about as my next step since fuel injection is out of the picture at this point financially. I have the initial timing set at 12-15 and total timing at 35-37 at 2500 RPM. I have HEI ditributor and I changed the spark plugs and gapped them accordingly when I did the upgrade, I don't remember the numbers since it was while ago. I don't know the heat rating or the plugs. Thermostat is 180 degree. I put 87 gas. The air filter and housing is the edlebrock, the one which is open all around.
My exhausts pipes exist behind the rear wheel. It is a very good point to have them exist straight out back. The exhaust pipes and mufflers are JCWhittney (if I remember correctly since it has been few years). Does muffler can make a difference?!

[davepl]

Originally Posted by Kennuck

I agree with this. I can smell an old carbed car a mile away but my Stock 5.3 without cats has no smell.

Yes, when I say "these engines" I'm talking about the older MarkIV BBC and classic peanut-port-era 350 heads. The LS has a fast burn chamber that probably is much more efficient at burning all the fuel.

We also tend to have more aggressive cams in the older engines but a lot of LS guys wind up running factory cam profiles because the motors make enough power in stock form.

I can't prove the cylinder head is the difference, but my '69 Camaro with EFI still smells the same as the Q-Jet car. But it has a fair bit of cam overlap.

[BigRed76]

Originally Posted by davepl

Not actually. I have all three:

- Carb'd car with a cat ('75 Monte factory)
- Carb'd truck with no cat ('70 GMC)
- EFI car with no cat ('69 Camaro ZZ502 BS3 Sequential EFI)

The EFI car still smells like raw gas. It runs at about 14.6:1, but to get near stoich at idle with a cam in a motor like these requires a lot of extra fuel that winds up getting in your girlfriend's hair.

Now a poorly tuned car with cats will stink like sulfur dioxide, so there's no substitute for properly tuning the thing. But properly tuned, cats get rid of the raw fuel smell.

Maybe if gasoline still smelled like it did in 1970 I'd be OK with it, but it doesn't.

I guess I was a bit vague with that statement, since my vehicles are a bit different. What I had in mind was my 5.3 with no cats in my '71, but comparing that to your ZZ502 we are worlds apart

[Z10]

I'm running a complete Magnaflow system on my 72 with cats. The engine is a ZZ4 with FIRST TPI. The stank is gone. The cats are very small and around $85 dollars each. My wife will now not only ride in the truck, but on occasion actually drives it.

Here's a pic of the cats.

[Jack_71C10]

Maybe you can try an alternative route and use one of these.
http://www.powerpluslubricants.com/fuelfragrances.html

[davepl]

Originally Posted by Z10

I'm running a complete Magnaflow system on my 72 with cats. The engine is a ZZ4 with FIRST TPI. The stank is gone. The cats are very small and around $85 dollars each. My wife will now not only ride in the truck, but on occasion actually drives it.

Cool! What's the carburetion on a ZZ4? Holley 3310? [Edit: Duh - I see it's TPI - ignore me]

Does your EFI employ an air-fuel sensor to monitor and adjust the mixture live?

[special-K]

I think this guy already has mufflers. The problem is the exhaust smell and no brand or design of muffler will effect that.

An LS engine is a totally different design, so not to be compared in this situation. A carbureted LS engine w/o cats will likely produce less fuel smell than a fuel injected 350 with cats. Cats are an after the effect mask the issue add-on. LS engines have addressed these issues from within with a more efficient design from the get-go than the one from 1955.

[BigRed76]

I also had a TBI 350 in my 76 K10, it had vortec heads, 10.5:1 compression, edelbrock performer rpm intake, bored throttle body, and headers with no cats, and that truck had zero fuel smell from the exhaust. When I first got it running it wasn't properly tuned yet so it did stink a little, but after it was properly tuned it did not stink.