Crate Engine Knock

Hi
I have installed a brand new crate engine in my 1957 Chev Pickup however it has a loud “knock” that makes it sound like a diesel at idle. Increasing the rpm to high idle makes the knock go away and advancing the static timing decreases the knock. Other than the knock, the engine starts and runs perfectly. All the usual stuff, like bearings, rod clearances etc have been checked.
The engine was purchased as a 1996 to 2000 383ci Vortec Truck Engine and has 9.25:1 compression, roller camshaft and flat top hypereutetic pistons. Static timing is set for 10 deg.
Instead of the fuel injection, we have carburetted the engine as it needs to run and be repairable in very harsh, out of the way places.
Our best guess, at the moment, is piston slap. So, what are people’s guesses on what the “knock” is ?
Can it, in any way, be caused by running a carb on a late model engine like this, that has a long stroke and short piston skirts ?  

what kind of Distributer do you have????

there can be several issues with various distributers..

are the back two drivers side spark plug wires separated ...?????  #5 and 7 are only a 1/4 crank turn apart and when the wires are too close.. the magnetic field created by the #5 spark voltage will create an early spark in the #7 cylinder.. this will KILL the engine shortly... as it destroys the piston and rings...

is the crank damper center bolt tight..
who torqued the flex plate bolts . who tightened the torque converter bolts..

any chance of a vacuum leak.

i know these were done...  but its an important thing to ask..


the link below is on this site.. your user name and password work there also..  

you might want to cross post this over at

http://forums.chevyhiperformance.com/active-posts/index.html


thats one of the most active forums and there are a lot of smart engine builders there..


please add as much detail as you can...

toss some photos up on photobucket..     its free.. so we can see any errors.