Does anyone know what the pressure is inside the exhaust manifold at say, 30 psi of boost?

 

Depends on the turbo...maybe just slightly less....but most commonly the same or higher.

 

When turbos blow, does the turbine or impeller disintegrate first?

 

Hopefully just the shaft gives out if not hope its the turbine....If its the compressor wheel.....Houston we got a big problem...

The Drive pressure is usually above the intake pressure. I have a gauge on the exhaust manifold the intake manifold and on the big turbo compressor housing. I've had drive pressures over 85 psi and the intake was only 75 or so psi....most times the intake is a couple of psi lower. On a quick rip I've seen 60 psi on the intake and only 30 or so psi on the intake until the pressure stabilizes and squeezes through the small turbo compressor outlet and through the stock intercooler. Unless you are fireringed it is best to keep drive pressures below 90psi max. If you are on the stock turbo.....48psi will take out the shaft especially if you hammer it to 48psi then brake. ks

 

If I increased the drive pressure significantly over stock, say to 80 psi, would I have to use a blow-off valve to prevent the stock turbo shaft from breaking in two?

I'm thinking of artificially raising the drive pressure on the turbine to get more boost from the impeller; I know the stock turbo lays down over about 50 psi, but I still want to follow this idea to see if it has merit on a bigger/more efficient turbo.