Ok finally got the six pack tuned in and running on the idle circuit. But my concern is this 496 sounds like a diesel. I had the short block put together by a local shop. It is a mild .040 496 with a Mr Six Pack cam. Roughly 471 I 490 E hydraulic. Diamond dish pistons, eagle rods and crank.
It doesn't sound like it's coming from the rocker area. I even pulled a valve cover and everything looked good. It sounds like from the block area. Under the intake maybe. Sounds like piston slap.
Timing is 18 initial. And has 40lbs oil pressure at idle warm. With a standard oil pump. The motor doesn't miss or stumble at all. Seems to run good. Just sounds like it wants to fly apart. Any ideas before I pull it back out? Thanks

You could pull a plug wire off each cyl.one at a time and see if it goes away.
Does it have file fit rings that maybe didn't get files?
I bought a 400 one time that someone put together and raised hell when I started it and found the rings butted because no one filed them.

My guess would be piston rock. There's most likely not a whole lot of skirt in the bore relative to the pin at BDC. I've heard a few strokers that sounded like a coffee can full of rocks at idle. Don't know that I would be all that worried, but it's hard to say without actually hearing it in person. The "diesel" description is common with this issue, not necessarily a problem.

Yup sound like BDC piston rock.

I have to work tomorrow. But I'll try and get a video up Thursday.

diamond pistons/straight pins/ loose clearances when cold, short stroker pistons. piston slap", part of the territory. it should shut up when the engine is warmed up. if not the pistons are too loose.

^^^^^I 2nd the above, a buddy of mine built a 383 w keith black pistons that were too loose and it sounds just like a diesel.

all those hypers are noisey when cold but if they're a couple thousands too loose then you really need to turn the radio up.

Are the pistons 2618 (low silicon) alloy? They're gonna be looser at idle than 4032 and you'll get a bit more noticeable slap. Plus you're running a smallish hydraulic Flat Tappet so the valvetrain is quieter than a solid lifter motor so the bottom end noise is going to be more prominent since you don't have much top end 'clatter' compete with it (LOL). Run it, put some load on it and it should quiet down a bit...but it'll never be as quiet at idle as a cast OEM offset Piston. 2618 is used for race/blower/nitrous so they don't (by design) expand fully unless you're building some significant load (heat) in the holes.

FWIW I was worried about this until I put dozens of passes and a couple thousand miles on it. These are Ross pistons, and a 588 solid roller. I pulled everything apart, checked lash a million times, compression and blah blah blah. To my knowledge it is still running strong.


https://www.youtube.com/watch?v=OPPjBNwdHfA

This one is a 517" low deck with 2618 Alloy Nitrous slugs and it's quite a bit noisier than the last 508 RB I did with 4032 slugs. It also revs a lot quicker ( Some of my friends called it a Comp eliminator motor) and makes quite a bit more power too.

If the vital signs (oil pressure and temperature) are good run it for a while and even go out and Dog it a bit.

https://www.youtube.com/watch?v=t6gtdpu5MqA

https://www.youtube.com/watch?v=uO4qlTvI9Vo

My Arias pistoned 400 rod, 3.75 stroke 400 sounded like that for 19 yrs. I finally traded it for a 6.1 Hemi. Piston slap ala mode. Goes away with RPM in my experience.

i think the key here is; does the noise go away after the engine starts to warm (pistons get some heat and expand). if so; then forget it and move on. it won't break, but don't hammer it until the pistons are warmed up. nature of the beast.

Does it go away when warmed up ? My 493 has a little piston slap when cold since I run the pistons on the loose side but when warm its all gone. Its been no problem at all. It should go away when the eng is warmed up. Ron

Streetwize what cam is in that 517? What exhaust? Sounds awesome!

Ok, here is the video. Does this sound extreme? https://www.youtube.com/watch?v=V5D8pq0OGgk

doesn't sound much different than my 440 solid lifter, light piston, street engine. is some of that noise valve train related? what type of tappet? any oil restrictors? what rockers?

496, diamond dish piston, comp cams pro magnum rockers and hydraulic Mr Six Pack cam. Has more piston noise then my 470 stroker build. The main reason for concern is this is my original six pack block. And I'd hate to ruin it.

Same here.

that cam should be quiet and idle smooth. strokers use shorter pistons and should be fitted a little tighter. check what the recommended clearance is vs what the machine shop set them in at.