run without exhaust flange gaskets?

[vortec]

i just got my new 350 hooked up and running (way out of tune at the moment), last night. but, there is smoke coming from the exhaust manifolds. i'm thinking one of two things: residue from cleaners and rust converter that i used on them several weeks ago, or leaking over-rich exhaust smoke from the flange were the manifolds meet the y-pipe.

when i took the exhaust apart, before pulling the old engine, i found no gaskets there, so it seems i shouldn't need to add them now. anyone else run with just the flared pipe?

it's tough to pinpoint the exact source, since it was a night, and also, the smoke is light and rises around the manifolds quickly. doesn't seem to have any adverse affect on the engine itself.

 

[mouse]

Sounds like normal burn off from the manifolds. If the flare is leaking it would make a sound (anywhere from a tick to a loud roar), depending on how bad the leak is.

 

[vortec]

it is making an exhaust leak type of tick. but it sounds like it's closer to cylinder 2 than to the flange. i just can't actually find it.

 

[mouse]

Make sure its not a valve ticking. An exhaust leak will get louder when a load is applied to the engine. If you have someone drop it into gear (holding the brakes firmly) and give it a little gas, the tick should become louder and easier to locate if its an exhaust leak - of course a loose rocker would get a little louder too, but you might be able to locate the source.

 

[vortec]

i thought about that, but i sure as hell hope not. it's a fresh reman and i would be more than a little annoyed if i had to pull the thing back out and lug it back to the shop. i'll say this, though, it seems very clear, where most lifter, pushrod, or valve ticks i've heard sounded a little muffled, since they are inside. keeping my fingers crossed on this one.

 

[vortec]

i did the good old screwdriver on the valve cover thing, and heard nothing out of the ordinary. then, after hooking my tach/dwell meter, i used my hand to limit the airflow to the carb, to get the engine to misfire, while maintaining fairly consistent rpms. sure enough, the sound became very inconsistent. it would be there, then disappear for several seconds, and so on. at steady rpms, a valvetrain noise would be more consistent, i believe.

 

[mouse]

Sounds like exhaust leak...are you using manifold gaskets? If the mating surface is not totally flat, it could leak slightly. I've had good luck using the small, metal-backed gaskets from Napa.

 

[vortec]

yes, i'm using gaskets. considering the manifolds are 23 years old, from my old engine, i wouldn't be a bit surprised if they are a little warped. the mating surfaces looked and felt pretty good, as far as being smooth and even. but they might be imperfect. i was also going to check the places where the AIR tubes screw in. seems like an easy place to get a leak.

 

[mouse]

Let us know what you find. Good luck!