stock exhaust sound, & valve train noise questions...
11-14-2004, 03:35 AM
#1
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stock exhaust sound, & valve train noise questions...
OK, i've searched the forum to no avail.
As far as i can tell, my '86 951 has a stock exhaust... i have checked it extensively for exhaust leaks, which it has none of.
Now here's the thing: Quiet at idle, as RPMs/load raise, the sound does... under boost, the thing screams. Not WAY overly loud... but loud, none the less. I actually absolutely love the sound- so much that i dont want to change to an aftermarket/custom exhaust... has a very "tuned" note. Have gotten compliments on the sound, as well...
Having limited experience with 951's... i've not heard one that i know to be stock, winding out through the gears. So a stupid question arises: What are they supposed to sound like, stock?
Over 4kRPM, it can be heard from a distance.
On to the next stupid question:
at idle, and partial load/low RPM's there is some (what i suspect to be) valve train noise. Nothing major... if anyone is familiar with BMW's VANOS setup- sounds similar to that... a "is that OK?" sound. kinda a mix of "clicking" and "marbles rattling around in a tin can", but very quietly. As RPM's raise, the noise goes away.
I've pulled the valve cover, checked everything out... all looks fine. Oil pressure has been verified with an aftermarket gauge, and is strong through the RPM range.
So again, having limited experience with 951's... is valve train/upper motor noise common? The motor has 135k on it, belts/water pump done ~20k ago from PO.
TIA,
-dan
As far as i can tell, my '86 951 has a stock exhaust... i have checked it extensively for exhaust leaks, which it has none of.
Now here's the thing: Quiet at idle, as RPMs/load raise, the sound does... under boost, the thing screams. Not WAY overly loud... but loud, none the less. I actually absolutely love the sound- so much that i dont want to change to an aftermarket/custom exhaust... has a very "tuned" note. Have gotten compliments on the sound, as well...
Having limited experience with 951's... i've not heard one that i know to be stock, winding out through the gears. So a stupid question arises: What are they supposed to sound like, stock?
Over 4kRPM, it can be heard from a distance.
On to the next stupid question:
at idle, and partial load/low RPM's there is some (what i suspect to be) valve train noise. Nothing major... if anyone is familiar with BMW's VANOS setup- sounds similar to that... a "is that OK?" sound. kinda a mix of "clicking" and "marbles rattling around in a tin can", but very quietly. As RPM's raise, the noise goes away.
I've pulled the valve cover, checked everything out... all looks fine. Oil pressure has been verified with an aftermarket gauge, and is strong through the RPM range.
So again, having limited experience with 951's... is valve train/upper motor noise common? The motor has 135k on it, belts/water pump done ~20k ago from PO.
TIA,
-dan
11-14-2004, 03:47 AM
#2
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For the exhaust, do you have a CAT there? they are supposed to get louder on boost but not too loud.
As for the valvetrain noise, make sure it's not comming from the valves/head area. The injectors are a bit noisey and could confuse you into thinking it is the valves.
[qote]"marbles rattling around in a tin can"[/quote] that is the sign of a worn rod bearning, you sure you heard that? does the sound increase during acceleration? listen closely to where that sound in comming from.
As for the valvetrain noise, make sure it's not comming from the valves/head area. The injectors are a bit noisey and could confuse you into thinking it is the valves.
[qote]"marbles rattling around in a tin can"[/quote] that is the sign of a worn rod bearning, you sure you heard that? does the sound increase during acceleration? listen closely to where that sound in comming from.
11-14-2004, 04:18 AM
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have a CAT, but it may be hollow (some evidence of it from PO). It's loud enough, that at a 50 MPH to 120 MPH roll-on... it can be heard very well from my friend's audi TT, as he is trying to catch up... even as i gain more and more distance.
99.9% sure the valvetrain noise isnt bottom end noise. The sound's rythm increases with RPM, but the volume of it dies all together by 3k RPM and it sounds nice and smoooooth.
Not a real "marbles in the tin can" thing... just VERY similar to the BWM VANOS sound.
I'm going to take a mechanic's stethascope to it again, as i didnt actually check the sound of the injectors... if they are loud, that could very well be it.
99.9% sure the valvetrain noise isnt bottom end noise. The sound's rythm increases with RPM, but the volume of it dies all together by 3k RPM and it sounds nice and smoooooth.
Not a real "marbles in the tin can" thing... just VERY similar to the BWM VANOS sound.
I'm going to take a mechanic's stethascope to it again, as i didnt actually check the sound of the injectors... if they are loud, that could very well be it.
11-14-2004, 05:47 PM
#5
Three Wheelin'
It sounds like you guys have exhaust leaks, and maybe from multiple areas. Dhallilama, you say it gets louder past 4k rpm. It might have a leak around the wastegate or wastegate pipe area. When the wastegate opens, it will get a lot louder, especially if you dump it to atmosphere. Also, the "clicking" you are describing sounds like your exhaust manifold gasket is leaking. I have the same problem right now. At first I was scared and started thinking it was valve train noise, and that I might need some head work soon. Then I noticed the black discoloration around the last exhaust port, and realized it is just leaking. Now use these leaks as an excuse for upgrades! 
11-14-2004, 08:53 PM
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I know that I have a exhaust leak up there but it is small and nothing to worry about until I have to remove the pipes for my testpipe and new turbocharger which should be after winter!! Already can't wait for the summer to get here!!!!!!!!!!!
11-14-2004, 11:42 PM
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doesnt sound like a leak, in any way... nor does there appear to be any leaks (have felt the exhaust, while running on a hoist, and cant find any soot marks). I believe the cat to be hollow, which could very well add to the volume level. In any case, sounds great.
As for the valvetrain noise... i just cant narrow it down. Doesnt sound "bad" as in it's going to fall apart... but does make noise... much like air-cooled porsche motors do.
plus, i figure if something breaks, good reason to upgrade
As for the valvetrain noise... i just cant narrow it down. Doesnt sound "bad" as in it's going to fall apart... but does make noise... much like air-cooled porsche motors do.
plus, i figure if something breaks, good reason to upgrade
