Re: Exhaust Chirping Sound

[jlandry@domain.elided (John A. Landry)]

The aliens commander decided Steve Stegmann <stegmann@domain.elided>
would make a perfect specimen for dissection, and he yelled...

>Fill'er up with best grade premium (I've had good results with Mobil
>Super there **is** a difference) and set the timing to 0-5BTDC.  This way
>you know you won't have any detonation.

I did this already and the premium made no discernable difference in the
sound.  This is what partially lead me to think it might be just an exhaust
noise.

>Go over it with a Stethoscope to be sure nothing's loose inside the
>engine.  Make sure there are no exhaust leaks.  Use the stethoscope
>without the probe.  Just the funnel end.  Then listen to the noise.

There's definitely no exhaust leaks, but I do need to take the time to
listen to the engine with the stethoscope.  The thing is, I can't hear this
sound when the engine is running and the truck is not moving.  Just revving
up the engine doesn't yield any strange noises.  I only hear it (notice it)
when driving maybe 35+ mph.

>When I had the chirping I too thought it was detonation till I made the
>engine ping with a silly timing advance.  

Then the sounds are somewhat similar?  Would you agree that the chirping
sounded like the very start of pinging?

>The chirping was pretty loud on mine, but mine had not been modified.
>Your porting may have cut down on the volume of the noise.

That's what I suspect.

>The only way to stop the noise is to fill the hole for the air injection
>completely.  You can buy the plugs or make them.  Make them may be better
>for you since the std plugs may stick into the exhaust stream (too long)
>on your ported heads.

If it's just the chirping... then it's nothing to worry about.  I just want
to be sure the sound is "normal" then I can ignore it.  It's so barely
perceptible that just turning on the radio completely blocks it.  I have to
strain to hear it... so it's not worth messing with the plugs to change.

>BTW when you've got good premium gas in it try setting the spark at 15
>BTDC and tell me how it runs.  It's an amazing difference on mine.

I'll try that.  I'm currently at 10 degrees BTDC with regular unleaded (87
octane) and so far I detect no signs of pinging.  The difference in
performance and fuel economy between TDC and 10 degrees BTDC is pretty
amazing as it is.  I don't intend to operate with premium gas on a regular
basis, so I figured 10 degrees BTDC was working and pretty safe, so I
hadn't intended to go any farther.  But I guess I ought to find out exactly
where the pinging point is with both regular and premium... just so I know.
My 345 I had would have been pinging like crazy with moderate acceleration
with the timing set to 10 degrees BTDC, so this is really interesting...
same ignition system and same distributor.  I verified the vacuum and
mechanical advance are working perfectly within specs.  At first I thought
maybe the vacuum advance was shot... or maybe the mechanical weight were
stuck.

Thanks,

John L.
-------------------------------------------------------------------------- 
jlandry AT halcyon DOT com      | 
Conservative Libertarian        |  "The road to  tyranny, we must never
Life Member of the NRA          |   forget, begins with the destruction
WA Arms Collectors              |   of the truth."
Commercial Helicopter - Inst.   |                     William J. Clinton
http://www.halcyon.com/jlandry/ |    10-15-95, speech at the Univ. of CT