I just installed a new header, and under heavy throttle I can hear what sounds like hissing coming from the motor. It doesn't seem like I lost any power (in fact it feels like I've gained power). Is there a simple test to see if there is a leak? Or would it be very obvious? I do have the Mugen CAI, so that might be the culprit, but I had the CAI on long before the header and it never made that noise before.

 

What header did you get? Mugen? If so give it 2-3 days and re-torque all the header bolts.(mine were right on) That noise you hear may just be the thinner walls of the header that you hear the rush of air through the fire wall. Plus there might be some time you need to wait till the Cat/header seals up!

 

[QUOTE]Originally posted by Pinky
[B]What header did you get?

 

I presume you did replace the manifold gasket with a new one?

 

A leaky gasket is usually a fairly loud and unpleasant sound. Checking the bolt torque is a good idea, but the sound you are hearing may just be due to the lighter tubing material, not a leak. I seem to remember noticing it when I installed mine.

 

My car got noisier when I installed the mugen header, there was indeed some hissing that wasn't there previously. I suspect that the walls will be thinner accounting for less insulation.

The mugen CAI also hisses, but I only notice it at idle. It's actually a bit rough (it sounds a bit like the radiator fan is always on), and together with the header and exhaust and uprated suspension, made the car loose that smooth feeling it had when stock. It sounds and feels sportier and the performance improvement probably justifies it, but I would rate these mods just tolerable if this was a daily driver and the main tool of locomotion...

 

Thanks to all for responses.
Yes, the new gasket was used, and I've checked the bolts and they're on nice and tight.
I agree with Luis on everything said. Definitely sportier (less refined) sound
Glad to hear that the hissing is normal.

 

Steven I have the same hissing after installation...damn its such a release to see its a normal characteristic of the Mugen header.

 

That's why this forum rocks!!