have you checked the valve clearances while the motor is hot?

My cam with the 1.65 rockers gives 509 thou lift at the valve

yes John Taylor said that he would go back to standard rockers again in the A series same problem youre having give Jeff Taylor a call on +61 2 96238826 and see what he has to say....

yes, I will give jeff a call. The lift i gave was valve lift. the cam spec sheet said .295" cam lift.

It is a very loud noise it makes and the engine just hit a wall and will not rev.

I say again if you don't want your rockers, sell them to me, CHEAP!!!!!!

I wish.

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Yeah, I thought as much, but I did ask for lift at the cam & I went by your response.

I had always thought that an absolute minimum valve to piston clearance of .060" was required with .080" or larger prefered, depending on how much it revs.
Next time you have nothing to do, pull some plugs in the darkness of your garage & have a look at the pistons with a small diameter torch [flashlight] & try to see if there is any evidence of valve contact with the pistons, or even the bore if you are running big valves.
This is the only possible thing that I can think of that would make the noise that you mention.

EDIT. No, it's not the only possible thing, I just gotta learn to think more.

Probably a silly question, but could the rockers be hitting the rocker cover?

If the valves are hiing the pistons...wouldn't you end up with bent valves???

and if you did....wouldn't a simple compression test confirm this???especially if you know that the rest of the engine is not worn out.

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did you use the standard rockers when you built the engine with that .040" clearance, and then change to the 1.55 ratio yella terras later?

if so, going from the standard 1.44 ratio to the 1.55 rocker ratio with .295" lift at lobe, means you have increased lift at valve by .029" and only have .011" static clearance left!

what was that .040" clearance to? piston to valve, spring retainer to guide (or guide seal), or clearance before spring bind?

if clearance is not the issue, it may well just be a valve spring problem. they may not be able to cope with the extra lift and those rpm. how old are they?

Is it possible that with the extra lift the valves are floating into the bottom of any valve releifs in the cylinder wall?