Originally Posted by mcollinstn (Post 4837886)

There honestly is no reason to chase ghosts here. Don't throw parts at a problem until you have isolated the problem.

It has been established that your needles and seats are .120", so there is no reason to point at those as a restriction

You have told us that your WOT fuel line pressure (measured before the fuel line enters the box) is 12 psi and your WOT boost pressure (measured in the intake manifold) is around 6 psi.

As long as your fuel pressure STAYS above (boost psi + 6 psi) then you are NOT experiencing fuel system inadequacies.

Run WOT. Constantly watch the boost pressure and fuel pressure. Whenever the motor feels like it is starving for fuel, TAKE NOTE of those pressures AT THAT TIME.

If the fuel pressure remains steady and doesn't drop as you experience the "starving" issue, then you DO NOT have a problem with fuel supply.

You MUST get this test out of the way and behind you before you know where to focus next.

It may not be a fuel starvation problem at all.
You could have heat-soak which may be triggering ignition detonation. You may have a weak coil or ignition module which loses output when it heats up (under boost at prolonged max revs).

Originally Posted by mcollinstn (Post 4837886)

There honestly is no reason to chase ghosts here. Don't throw parts at a problem until you have isolated the problem.

It has been established that your needles and seats are .120", so there is no reason to point at those as a restriction

You have told us that your WOT fuel line pressure (measured before the fuel line enters the box) is 12 psi and your WOT boost pressure (measured in the intake manifold) is around 6 psi.

As long as your fuel pressure STAYS above (boost psi + 6 psi) then you are NOT experiencing fuel system inadequacies.

Run WOT. Constantly watch the boost pressure and fuel pressure. Whenever the motor feels like it is starving for fuel, TAKE NOTE of those pressures AT THAT TIME.

If the fuel pressure remains steady and doesn't drop as you experience the "starving" issue, then you DO NOT have a problem with fuel supply.

You MUST get this test out of the way and behind you before you know where to focus next.

It may not be a fuel starvation problem at all.
You could have heat-soak which may be triggering ignition detonation. You may have a weak coil or ignition module which loses output when it heats up (under boost at prolonged max revs).

Originally Posted by SB (Post 4837917)

Bummer.
something else broke (piston probably…maybe valve) , which broke your spark plug.

Originally Posted by SB (Post 4837939)

That spark plug appears to have longer reach than what oe cast iron heads use. (.460”) What heads do you have ?

this is what they should look like with factory cast iron heads:


https://cimg2.ibsrv.net/gimg/www.off...3b50a8c38.jpeg

Originally Posted by SB (Post 4837947)

Okay. Oem GenV cast iron rectangular port heads. Should be using a typical .406” reach 14mm thread tapered seat plug.

Being supercharged, i’d run an acdelco mr42t or equivalent.

Possible that those extra long spark plugs you used caused preignition. You could have other tuning issues too, but this is a serious problem.

Originally Posted by Zole (Post 4837958)

Is there a differenc beetwen GM1 and GM3 regarding sparkplugs....Cilindar that died has a GM1 head

Originally Posted by SB (Post 4837960)

Those are just which castings where used (in the Saginaw foundry i believe) info.

The casting # itself (1409788) is what you go by.