It's all ok in Datsun land...

Agreed, bin the cracked exhaust housing, if it's that cracked then chances are there's pieces starting to flake of on the inside. Anything harder than exhaust gasses is bad for a turbine...

ah yes i must appologise! i forgot about adding the boost hose to the top of the gate!.. it will do exactly what you have said, is the stuffing around worth it? in his case probably not.. i havnt seen gains that high from it though (not saying you havnt). But then again i had my internal gates setup with the correct springs and was using an ebc... in this situation i would get another rear housing and make it all work, makes it a hell of a lot simpler to sort out

Come on dude, seriously??? If you get an decent boost controller, it will add boost to the top of the external waste gate, keeping it completely shut right up to when the gate must open. I've simulated a similar setup with a hob switch and normal boost tap in my car, but the control is not so precise. Obviously there are limitations as to how far you can take it and typical gains are around 500-750rpm, but I have seen applications where they were able to get the boost up by just on 1000rpm earlier than before.

An internal waste gate, or most everyone of them out there, can't have boost added to the top. This means it'll start opening way before it should, costing you valuable spooling time. Yes you can sort of counter it with different springs and stuff, but it's just not as easy as with an external gate. And yes the e-boost can sort of do the same thing on a normal one sided internal waste gate actuator, by preventing it from seeing boost before the time. but it can't nearly take it as far as with an external gate that's nice and large so that you don't get boost spikes.

If the housing is cracked bad I would bin it and get another. Not worth the risk! You can control the boost on either setup so you won't have a problem there. The port for an external gate should be as close to the collector (where all the runners meet) as possible to get it to work efficiently

I must say, i like the idee of controling the boost myself. I understand the idee of bolting the gate shut, but what about the cracks around the mouth of the gate will it not give way, get worse or brake away, and couse even worse damage???

Is there a seacrete way to put on an external wastegate or is it a case of making a hole where you have space??

I disagree, the wastegate won't make a difference in when the turbo will spool, it only exhausts gas when you have reached the set boost level, before then it just stays shut and does nothing. Turbo housing designs, wheel trims, exhaust manifold design and head flow are what determines spool speed. I've tried an external vs internal gate on my old 1600 and the spool speed was the same.
Obviously the wastegate flap, diaphragm, spring and housing would have to be in good nick for the internal gate to work efficient.
However the external gate will control the boost better and prevent a boost spike there isn't really any other advantage. And I have never seen a mod increase the response by 1000rpm! Maybe 500rpm max

Or you could drill a hole in the flange that goes over the wastegate, tap it for a certain size bolt and bolt it down. Just put a nut on there so it doesn't undo itself.

I'd go for external over internal any day of the week. You have much better control over boost that way, even if you are going to run OE/low boost, with a decent boost controller and an external you can probably get the turbo to spool 1000 rpm earlier by opening it at the right time...

i am no expert, but it sounds like i should have dis done profesionaly, how mutch can this cost???

It depends on the specific material. There are many types of cast iron. I think turbie housins have a little more nickel than plain old grey cast iron, could be confusing it though. The nickel would make it easier to weld.

There are generally two methods for welding cast iron. The most reliable is to gently and evenly heat it up till it's just glowing, maintain that heat, weld it and then slowly let it cool. Either bury it in hot sand or control the cool off with the gas torch.

Another less reliable way is to do it cold. Butter each side of the weld with nickel before doing a full weld.

Can also be braised but that might melt in a turbine housing.

Pretty much, if you're not an expert welder it's unwise to try welding up something as valuable as a turbine housing.

Edit: You can always practise on a junk one...

Yea that makes sens, How do you weld castiron?????