need new ideas on source of engine noise. 383 stroker, aftermarket crank, 5.7 rods, stroker pistons, 218/224 cam. dart iron eagles, approximately 9:1 ratio. running tpi with 950 commander and wideband 02. engine runs great but has a chatter at low rpm that sounds almost identical to a diesel engine. my understanding of diesel engines is limited but i've read that the diesel chatter is caused by the sonic blast of the fuel igniting. this is the second block i've put together with this combination and both have had the same chatter at low rpm.
any ideas would be greately appreciated .

 

my *guess* would be something at the flywheel/flexplate.

 

i did run into that problem , actually i've broken three flex plates
with that setup ,put a hd flexplate in and it hasn't broken yet.
the broken flexplates were fairly easy to locate and they sounded more like a metalic knock. i forgot to mention i'm also running
sandersons cast iron headers . when the engine is cold is when
it is the loudest , the sound gradually decreases as engine temperature increases. thanks for the response!

 

Exhaust leak ?

 

Whats weird is mine sounds identical at idle to your situation. I'm also running a 383. We found out it was a tuning issue with WAY to much fuel problem and the injectors were ticking deeper and slower then normal, until operating temp. It was eather way to much fuel or not enough. One of them.

 

pull the valve covers and check your valve adjustment, pushrods and lifters .

 

Did you check for any misalignment issues? I had similar symptoms because the CL of the crank and trans didnt line up. It also visibly distorted the flexplate once the TC was bolted up to it. With the flexplate out, it was as flat as a pancake. I imagine that if the misalignment was bad enough it could break the hub of the flexplate from all the alternating stresses. Granted theyll certainly break from the torque but if youve broken several of them its something worth looking into.

All the clanking noises where due to the TC and front pump getting chewed up. It was hard to locate as well. The sound came from all parts of the motor and trans. Easy way to eliminate this as a possibility is to unbolt the TC, slide it back and support it so it doesnt drag on the crank, and start the engine. No more clanking sound=blown trans. This also wasted the boss in my crank since the TC dug a deep groove into into it.

 

Didnt see that youve actually put together two motors and had teh same problem. Makes teh trans issue less likely.

Is there any one place that the sound is coming from? Is it only at idle, high loads, or at all loads at low RPMs?

 

yep , i've got an exhaust leak, had this motor out of there plenty of times. unfortunately there aren't any leaks around the block area, they are about three feet back under the seats.sealed up good n tight at the heads and collector. i installed an 18" piece
of steel fuel line in the end of a stethiscope this afternoon ,seems to make that device extremely directional without making contact.
i was able to pin point the noise. its loudest at the top of the
cylinders and disapates as you move to the bottom of the block,
it does this on all cylinders but the right bank seems to be noticably louder. thanks for the help!

 

my afr ratio seems to be ok,13:1 to 14.4:1 from cold to hot.
valve train issues could be worth looking into,the first engine
was torn down at 10k and phosphorus bronze guides showed signs of premature wear mostly on the exhaust. took them to the machine shop had them drilled and liners put in. i've never dealt with that type of valve guide, they came with the heads as well
as teflon seals. The machinest said the teflon might be sealing too well because the valve guides were very hard matal and not
likely to wear quickly. the tops of the valve stems had the scrub
area centered in the stem. replaced the stiff valve springs with stock springs and stock lifters due to lifter noise ,the performance lifters seemed to colapse quicker. rocker geometry still looks good
thanks for the reply.

 

Seems a lot like forged piston slap to me.

 

at this point i believe all my flex plate problems have been resolved with the heavy duty flexplate. i know what a broken flex
plate sounds like now. i think those hard tuning sessions were killing the stock flex plates. i hope i dont have to pull the tranny again .thanks.

 

piston slap could be very possibe. the pistons insalled are hyper pistons with teflon coated skirts . there is not alot of clearance
in the bores ,if i recall correctly the recommended clearance was
.002 in . if piston slap was occuring what would it sound like and would it come from the top or bottom of the cylinder ? how can i check for that?

 

The cast pistons do not expand as much as forged so if the actual clearance was too much then they would indeed rattle and the problem would likely never go away with the increased temp.