I was messing around under the car today - getting some photos to upload here. While I was there I tied stuffing/wrapping rag around different parts of the headers. Also, I decided to try the “hose” trick to locate the sound. My lack of hands made the hose trick difficult so I ended up using a long funnel like a listening trumpet.
From all of this my new theory is I have leaking manifold gaskets… I hope, because I went and bought a set of genuine gaskets to install. If I get the lifters replaced with enough of the weekend to spare I’ll replace the manifold gaskets.
Here’s how I came about my latest theory; I wrapped rag around where the manifolds meet the cylinder head - to capture any leaks there. The mating surface of the cylinder head is hidden behind the flanged plate of the headers, so I assume any signs of leaks would be hidden also. The rag wrap did seem to quieten the hissrattle, but I couldn’t repeat the test on the rear bank - heat, and getting my hand up in there proved too challenging in the limited amount of time I had free today.
Since headers do little or nothing other than make a lot of noise and underhood heat, why not just put the stock manifolds back on and stop beating your head against the wall…
Headers on this car have been proven to show results. The stock y-pipe is very restrictive.
Having said that, Caddyman, I do see your point. It’s come down to the fact A) I’ve done this job half a dozen times before without issue, and, B) I can’t let this beat me.
I’ve just fitted new genuine manifold gaskets and the hissrattle and ffffffft noises persist. This has convinced me it’s not an exhaust leak.
But it’s not an intake leak either.
In desperation now I’m wondering if the noise is the dead lifters I’m replacing today? But, I’m trying to get my brain to understand why the noise stops with standard headers… more positive exhaust manifold pressure taking up the clearance at the valve quicker? The rocker arms will be replaced today also - all rocker arms, shafts and lifters as the current ones looked burnt to me when I changed the valve cover gaskets last year. The rocker arms use a roller at the camshaft end.
Wesw - no hear shields on the car. I even removed the plastic engine cover and front half of the intake.
Sparkplugs - new. Oxygen sensor - new (tried two different brands).
Intake manifolds upper and lower replaced then ceramic coated. New gaskets each time. New bolts and washers the second time. Injectors cleaned and re-kitted.
Wesw - thanks mate, appreciate it, The car has been to every exhaust shop in town and all of my mates, and my dad, have all either had a look at it or helped with fitment of the headers. None of us are complete amateurs either, my dad and I were mechanics in our youths (though I was a motorbike mechanic). The rest of my mates are either mechanics are just gearheads who have cars and enjoy working on them.
I’m about to start pulling the car down to replace the valve gear. We’ll see how it goes after that. If it’s still noisy I’m going to admit defeat… and maybe cry a little.
I’ve tried the proper stethoscope AND the hose trick. Both with the tail pipe blocked and unblocked. All three exhaust shops I imagine tried the same also.
Some cars (mine) have a valve in the muffler to reduce restriction under the pressures of acceleration in order to improve gas mileage a wee bit. Perhaps since the new pipes are offering lower restriction, they’re allowing enough pressure on the valve to keep it open some even at idle. That might explain the passing-air sound (hissing) at idle and could also explain the loud exhaust-leak sound under acceleration.
If my guess turns out correct, the system may require a lower restriction cat-back system. Perhaps that would change the acoustics. Confession: I did not read back through the thread to see if you’d also modified the muffler & pipes.
Mountain bike - the only valve linked to exhaust system is the EGR valve/plumbing. I’ve run the car with and without the EGR completely as well as with the EGR “disabled” and “enabled”. No change to the noise.
I’ve just finished replacing the rocker arms and lifters in the front bank. Just going to take a break and do the rear bank.
I had two very dead/collapsed lifters and one arm with the top section of the lifter stuck in there.
From your audio clip one would believe there is an exhaust leak. Have you ruled out induction noise as the problem?
With customers vehicles that I have driven who have installed a “cold air intake” there is always a very annoying whistle during part throttle and closed throttle operation. These “performance” air cleaners should be called unsilenced air cleaners, as there is usually no cold air available in the engine bay of a vehicle. Throttle bodies whistle, that is why factory air cleaners are so big and enclosed.
I’ve long had doubts about the term “Cold Air Intake”. The one for my car, which I suspect is typical, would take the air from exactly the same cavity under the fender that the original snorkel did, and it also has no restriction in the entry of the passage that would create expansion of the air coming in and thus a bit of cooling. I designed my own that takes air from a now-opened (formerly plugged and purely decorative) vent in the front bumper. “Ram air” is actually more accurate in my case. I also designed in much higher flow capacity. The improvement in acceleration above about 40mph is surprising, with improvement passing performance on the highway impressive. All for less than $50 in materials. And I removed that dumb induction system carbon filter that nobody knows exists. Without a dyno it’s impossible to know numbers, but it definitely worked.
But to get back to the OP’s problem, I sure wish I could help hands-on. It’ll be interesting to know how much the valvework affects the sound. I hate to say it, but I have a sneaking suspicion that the rushing air sound will be even more noticeable. I sincerely hope I’m wrong.
Half way through the rear bank valve gear replacement. Intake valve side done. It all looks pretty good. The old lifters are a by stiff feeling.
The intake side is all completely stock. As is the air filter. I don’t do cold air intakes either. Too dusty over here.
Intake side has been through the mill also - every gasket and part has been replaced. Apart from the air box and plumbing and the actual throttle body itself. The vacuum test is within tolerance. The brake booster connected/disconnected makes no difference. Same with the cruise control. Replaced the ISC o-ring.
I tip my hat to your diligence. Sounds like the sound is simply a characteristic of headers on that engine. “Porting” (opening up the exhaust ports) might be the only solution. Emphasis on the word “might”.
