i need some help
 

I installed an LS2/t56 combo from a 2006 gto into a 67 gto and there is a rattle that I am trying to daignose in the engine, I found this youtube vid with the exact noise (not the car I am working on but the same noise) can anyone tell me what this is?
https://www.youtube.com/watch?v=BB13b9ot6dA

Thanks in advance

almost sounds like a exhaust leak around the header. start it up whenever its really dark out and see if you see any spark coming from the headers

Loose rocker arm or bad piston slap.

thanks for the replys guys, it is for sure not exhaust leak as I have checked that and found nothing, it does not happen at idle only around 1800 rpms and up, I was wondering if the throwout bearing might be wrong but it does not go away when the clucth is depressed. I used a monster clutch with a f body slave cylinder and throwout bearing, could i have a mismatch there somehow?

If your noise is the same as the GTO, then it's the engine. I'm almost 100% that was an engine problem in that video. I say almost because I'm human and not perfect. If it were my car, I'd be going into the heads inspecting the valve train and springs. It's so simple to pull rocker arms and check springs on these engines. There is no valve lash adjustment. You just screw the bolts down and torque them.

If you're going to pull springs to inspect them, I prefer compressed air in each cylinder to hold the valves up. 30-40 psi does fine. You can use a simple lever action compressor or spend the money on a double compressor from Crane Cams.

I agree, valve train from the speed of the tap.

OP, you can pick up a mechanics stethoscope to pin point the area/cylinder. you can do a cylinder kill test. I would not recommend removing the plug wire to maybe disco the injector connectors one at a time. See if the sound goes away.

Thanks all, i will try some of this to see if I can find it. I will keep you posted.

well, rocker arms are fine, push rods are fine, springs are good (however, someone has changed the springs on one side of the engine, yellow springs on right side, plain springs on left side?) Compression check was good, so i am leaning toward a bottom end problem. Still not real sure. Is there any way to test for piston slap?

I pulled the timing chain cover and there is a lot of slack in the chain, enough to be able to move the cam back and forth so I'm thinking the noise is the chain slapping against the timing chain tensioner.

I would install the proper valve springs on both sides. Yellow springs are Z06/LS2 style and are only about $60 new from SDPC.com. Are the head castings the same?

The factory rocker arm trunion bearings are notorious for failing as well. Get the Comp Cams trunion rebuild kit which is about $130. Takes about 10 mins per rocker taking your time with a press. Very cheap longevity/reliability upgrade. I do this on all the LS motors I build.

Also the factory LS2 chain should be run with a GM chain tensioner. As suggested you may want to make sure there is one in there. Good time to replace the crankshaft seal for no future worries. Order a new crank bolt or get an ARP reuseable one as well.