When running a turbo, how much boost can the plastic diaphragm covers take on the b2 converters?
do they need to be upgraded to the steel type?

I don't think this is anything anyone has measured as such but its considered a preventative step to swap to the alloy covers. Finding alloy B2 covers is the hard part as even a 2nd hand B2 usually brings $50-$80 at the wreckers or on Ebay.

Here is a tip, OHG X1 convertors are exactly the same as the B2 and already have alloy lids. Last gas job i did i scored a couple of phucked X1's just to use the lids on some new B2's. I double stacked the convertors ie: drilled the 4 mounting holes in the lid of the lower convertor and used countersunk holes so the diaphragm had full movement without hitting the heads. I had to have the diaphragm purge buttom drilled out and welded over and also tapped the vent for brass fittings running to the balance lines. I have pics laying around but you get the drift.

This was alot of work but given the nature of the engine that was built it was deemed necessary. On a fairly mild boost level (ie: up to 12psi) the plastic lids *should* be ok. If not you will hear them leaking air but this is still going to pushing against the diaphragm so won't upset mixtures or anything. Like alot of things, people hear about this stuff without actually knowing WHY you change them.

Aaron

I am only looking at 6 psi maybe 8psi in the future so hopefully it should hold up ok.

my cars seen 9psi and my converters have been mine.
Rmyers s/c EA has B2's aswell and they were fine with the 9psi pulley he's got on it.