The info in the following link is 8 years old, but it is of value.

I personally used some Borla XS muffs on my '61 with 427 SB motor. Very quiet at idle,and you only really hear the exhaust at WOT. The H pipe helps, also.

http://www.ls1tech.com/forums/genera...al-street.html

Doug

 

If your chevy like mine, a 76, has the original rams horns cast iron exhaust manifolds it is not unusual for one of them to crack and crack so that you can only see it from below. The casting is brittle and any past exhaust system hanger failures can put pressure on them.

Jack the front up and look from underneath at each. Both mine have been replaced now. Both cracked. Both cracked because P.O. ran an exhaust system with two broken hangers and it's just enough pressure under the right circumstances to cause a crack. The cracks you can hear if you know what sound you are listening to. My y pipe into the pellet cat converter was loose at the fittings and the cat converter had corroded as well as various rust holes in the pipe behind that.

Huge difference in sound and where it came out once we put the new exhaust manifold on, straight duals through bullet cat converters which are low restriction and flowmasters. Sound is deep but behind the car and disappears at 40 mph way behind you. Cruising is more wind noise than anything.

Lance

 

I'm pretty far over 50. Come an listen to my 69 BB sometime.

 

Can these cracks generally be seen? Or just heard?

 

It depends on the crack. Some cast manifolds/headers literally crack from top to bottom and are very obvious. The one I replaced on mine (p.o. had replaced the other one 6 months prior) had a crack on the passenger side parallel to the collection down part of it that was only about 2/3's of the way around the collection port at the second port from the firewall and near the mid line and it was on the underside of the exhaust Manifold. I dont have a photo but I did put the high temperature repair material in it which shut it up for maybe a month at a time but a crack 1/32" wide doesn't allow much material in it to fill it and the expansion and contraction pretty quickly gets rid of the fix. I was told you can take them off and a good welder reweld but they aren't that expensive so a new one is a better choice or was for me. You'd be surprised at the noise that comes out of it and really notice it once you replace it. It was very easy to see from underneath the engine with a bright flashlight once I looked carefully and added it to the list for modernizing the exhaust and did so. It also can fry the plug boots, wires, etc. with the escaped heat. The crack I saw was never 1/8" wide, much smaller than that...much, much but any crack lets gasses out for sure.

 

when i first got my 76 friends who owned vettes and were knowledgable with the hood closed immediately told me I probably had a cracked exhaust manifold. Once heard you pretty much know the sound as it's somewhat distinctive once you've heard it. If the sound of a fully muffled system isn't coming from the back of the car you have openings in the system is the basics I would say.

 

Your wife says the car smells, if she's talking about the inside thats a definite clue!!!!

 

This is the new manifold coated with vht silver and a red arrow pointing to the area the crack was on the old manifold before replacement. The crack started at about the arrow and went down, across towards the block then turned up in a "U" shape. it was essentially two pieces of metal butted against one another at the crack but when hot air came out of the engine there was plenty of escaped gas and sound.

Lance

 

Wow, nice looking manifold. And thanks for all the info.

Here are mine. As you can see, they look original. Probably need to go.

Didnt notice any cracks from above, I'll get underneath and see what I can see.

 

Did you change your exhaust manifolds yourself? is it a big job?

 

Check for leaks. If you don't find any, install a balance tube connecting the left and right pipes. That will make a huge reduction in noise. Those mufflers should not be loud, but will be much louder if you have true dual exhaust.

 

"The car is loud even sitting in the driveway. "

Perfect!

 

You should be able to hear and know what exhaust "leaks" sound like. If you can't maybe your friend with the TA can help. Exhaust leaks are distinctive in sound like "ticks" usually and can get very loud when you accelerate. Also, your wife said the car smells. Like what? Exhaust inside the car?? That would be a clue you have exhaust leaks. If you can't find them, a muffler shop can. It might be worth taking the car to a shop and have them look at it.

 

The P.O. had someone change the driver's side but for some reason missed the passenger side. I'm 67 and don't do the heavy wrench work anymore, just the light work, so had the knowledgable shop that I use for that change the exhaust manifold when we redid the complete exhaust system from the 2-1-2 epa crappy one to true duals which more than doubled the exhaust flow cross section area from the necked down part in the old system. The original manifolds on mine were more orange colored all over but all that depends on where it's been and what road chemicals, humidity, etc. the car has seen. I think they get the car up, move the a/c out of the way and then remove and put new on. Mine did not have the AIR pump nor did it have a heat riser in the joint between the exhaust manifold and the exhaust pipe on that side which simplified it. I'm not sure if aging effects the brittleness of the original exhaust manifolds but they are cast iron which is not ductile but brittle anyway.

The instructions say on new ones to put a gasket between block and manifold. My guys all race and use big block Chevy engines to do it and they do not, they just snug it up to spec without and save the eventual destruction of the gasket in place. No noise there, no gas escaping. The new system sounds all come from the downturned end of the pipes not the myriad leaks of an old exhaust system with so many weakenesses due to age and corrosion. I'll attach a clip to mine from you tube so you can hear it now.

Once a new manifold is in you can make it look new by buying a can of VHT silver spray paint, spraying some well off to the side in an empty can and then with a disposable 3/4" wide paint brush just paint the COLD exhaust manifold and it will look like mine in the photo. You could do it to your existing ones but perhaps finding the source is first most important then engine detailing can begin since it looks like you can make significant progress doing that if you want to do it.

Good luck. Remember, it is a sports car, not a sedan for grandmothers and other little old ladies!

http://www.youtube.com/watch?v=N8V7VonBfmI

 

Fix the exhaust leaks.

Put dynamax insulation on the floor.(heat and minimal sound damping)

Replace carpet.



That should cover everything.

Oh, almost forgot; take pictures off the wall.

 

Thanks Lance and damoroso,

I hear ya on the sports car. I had a 6 speed 2002 c5 convert and loved it. This 76 is cool too. This is my first c3 so maybe I'm a little naive. I doubt that everyone who has an old vette has their ears ringing for hours after driving it. I think that's an indication that something is wrong. I want this thing to sound good, just not so much that I can't enjoy driving it. Again, one of the other posters on this thread said he had my mufflers and when driving he can hear the fan. This is proof to me I have a problem since all I can hear is the engine/exhaust.
As for the smell, It really doesnt smell when I'm driving it, just when it sits in the driveway and runs. I am pretty sure I have some leaking around the valve covers. I tightened the bolts a couple times since they were a little loose. I plan on replacing them and the gaskets at some point. Maybe that is why the car smells a little. Or maybe exhaust. I think I'll take it to a shop and have them do a leak test.

I'll try getting a video clip up on youtube so you guys can see/hear it.

Thanks again

 

Thanks Dannyman. Ya then I get new carpet too. Nice.

 

Does Dynomax max floor insulation? Is that the best one?

 

Oops! My spelling won't help you much if trying to search.

"Dynamat" is one of the popular brands used and I have not heard any negative comments about installation or performance. Cost is at the high end when doing comparisons; but the product is value for price.

 

No worries, I really think you have some exhaust leak problems. I have a BB in my car, with Flowmaster 40's and at idle or cruise, it's not loud in the car at all until you stand on it. Outside the car, well that's a little different... You really might want to take the car to a muffler shop for an opinion.