Ever since I got my headers in last week I have had this noise at idle. It almost sounds like the header is hitting against something. That is what I assumed it was so I am trying to figure out what it is hitting. But I was just thinking... Have I diagnosed this wrong? Is this what "knock" is? Will it go away with an LT4 KM? Is it robbing me of horsepower?
BTW I dynoed 282 horsepower with Hooker LTs and an offroad y, ram air w/ K&N, through a 3200 stall converter. I thought it was low so I changed from stock plugs and wires to NGKs and MSD wires. Could this knock be holding me back also?

 

Knock is actually when the fuel burns off in the cylinder before the spark plug fires. It will make a noticeable knock under acceleration. A knock Module senses the detonation and corrects the timing. Our vehicles are very good at compensating. But at times are too sensitive. Hence why people change to the LT4's KM which is less sensitive. Fortunately for you I think the knock that you're experiencing is more of a rattle. You may only notice it under acceleration because the torque pushed to the ground on take off actually rocks the engine to one side which may allow for a header to come into contact with the chassis. Or since you say its at idle the "torquing" of the engine may bring the header away from the surface it is hitting. There's only one fix, locate the point of contact and adjust accordingly. Good Luck.

 

Thanks for the reply. I understand what you are saying. Actually the knock ONLY occurs at idle when the car is warm. It goes away at acceleration. That is why I was wondering if it was something else. Do you still think that the header is hitting something?

 

You might want to check the motor Mounts. I had a strange rattle/knock come from my car for weeks at idle too. It'd go away once you drive but come again at idle. After weeks of searching I found it to be a loose bolt on a motor mounth. YOu can actually check it by getting under the car and move your exhaust pipe up and down if you have enough clearance under your car to do so. The will move the engine just slightly to create the sound in the mounts.