Boost pressure and cylinder pressure
 

I've seen the phrase "it's not boost pressure, but cylinder pressure that damages engines" used several times, with reference to lifting the heads. This sort of makes sense, the peak cylinder pressure is experienced during combustion, though I assume there must be a relation to engine load - more air, more fuel, more combustion, higher peak cylinder pressure.

I have a Hawk Sti with a forged 2.5 build, with uprated head bolts and gaskets etc, that I'm told is good to roughly 420hp. In parallel I'm told that using the stock VF43 turbo, it won't get there, which is fine!

In it's simplest form, does that mean that the VF43 turbo simply is not capable of creating combustion conditions with peak cylinder pressures high enough to move the heads, at any RPM? Or have I massively over simplified the logic?

if you put a bigger turbo on and ran more and more power at some point the heads would eventually lift, the bigger the bang effect, but the advice on your power level sounds good to me.
Trev

So basically a vf43 can't blow enough air at any rpm to risk lifting the heads?

No mate a vf43 can't blow enough air to lift heads on a forged 2.5

I'd be quite confident to be honest. If going on trackdays just keep an eye on the expansion tank for any abnormal displacement of coolant, i.e. raised above the high mark, as the movement of coolant between low and high marks should always be consistant and raised would indicate an issue.
Trev

That is good to know! Cheers guys.