[twiceblown]

i come up with:

flapper diam / diaphr diam / flap area / diaphr area / Flap PSI / turbine housing PSI / ideal acutator spring pressure
20.00 50.80 0.49 3.14 19.49 40.00 6.20
23.00 50.80 0.64 3.14 25.77 40.00 8.20
27.00 50.80 0.89 3.14 35.51 40.00 11.30


but note, that's at 40psi manifold pressure. if we increase that to say 50psi (not unlikely since we saw a 10+psi decrease manifold pressure by going to a 3" exhaust!) then these figures become:

20.00 50.80 0.49 3.14 24.36 50.00 7.75
23.00 50.80 0.64 3.14 32.21 50.00 10.25
27.00 50.80 0.89 3.14 44.39 50.00 14.12


So, it actually looks like stock may not be bad if you've only got manifold pressure of 40psi. higher than that, and you'll get flapper lift prior to the intended moment.

Also, it's interesting to note that you SHOULD NOT increase the size of the flapper on a TD04!!! Ideal spring pressure increases greatly for minor porting of only 3mm!!!

NOTE: flapper and actuator diameters in MM, spring pressures, manifold pressures and seat pressures in PSI.