I have just finished a complete rebuild on my car. 355 with all forged internals, CC306 cam, custom tune and a few other things. My question is, I have what sounds like a horrible exhaust leak only under load. We have tightened everything on the exhaust side and it is still there. My question I guess is...If I have a couple of rockers that are loose or out of adjustment, would they make a noise like what sounds like a exhaust leak. I only ask this because you can hear some ticking coming from the valve covers and then it only makes this noise under load. Also would it cause the car to have a miss if they are out of adjustment....like tightened to much? the plugs/plug wires and opti were changed out with brand new one's when I rebuild it. I didn't change the O2 sensors they are only about a year old and figured they were still good. Any help on this would be greatly appreciated, and if I forgot to mention something feel free to ask. Thanks in advance.

 

Ttt

 

My guess would be a failing header gasket. You say you've tightened everything on the exhaust side, but once an exhaust gasket is compromised,even a little, its usually done and will only continue to get worse...tightening it won't help. Try feeling for airflow around the header gasket at idle, as usually even small leaks are detectable.

 

Maybe you do have an exhaust rocker down too tight. It does kinda make a "tish" noise when you've got one down too tight and its not closing all the way and the compression/combustion is just blowing by the valve, but i don't think you would be able to hear it from inside the car, you have to open the hood and get right next to it to hear it. But then again my car was loud as hell I had true duals dumped before the axle and I couldn't really hear anything without opening the hood and gettin right on top of it. Oh, and if you have too many rockers down too tight it will run like crap (duh) but not as crappy as you might think. I noticed when i got em down too tight the "lope" of the engine would change and the idle RPM changed a bit. It seemed like it was running a little rougher. Once they were all on the way they were supposed to be the engine idle rpm "smoothed" out but with a cc306 its hard to say "smooth". This was with 1.6 self aligning RR's. Which side does it sound like the leak is coming from? I noticed that on mine, and 2 of my friends engines (all had headers/cam/heads/ 1.6 RR's) it sounded like there was a rocker down too tight on the passenger side coming from the #6 cyl. but i'm assuming it is just these motors, as they all had the exact same noise.

 

Thanks for the suggestions, I haven't had a chance to go out there and looka at it yet, but I'll keep you all updated. Thanks