Gerard, boost is generally harder to control the lower the boost set point.
So for high boost pressures, a small wastegate might be enough, but if you want to run low boost then a larger wastegate will work much better.
Horse, that's what I'd be doing aswell buddy.
I'm not talking about boost creep up top, trying to keep from increasing towards redline, the larger flap and as cast poring of these gt pump rear housing will prevent that.
I'm talking about trying to keep the turbo to hold boost around 25psi all the way to redline and also not have it spike of say 2psi when you drop it down a gear back right on boost.
I never ran my gt pumps 20g with that cast ported rear housing, but when people push 16's they spike a few psi normally if you downshift and as they come on when your running a decent boost level, and i also experienced it on my td05-20g in a well ported 070 16g rear housing, i get a 1-2psi spike with it running 22psi, but tuning in the higher load cells accounts for that. People seem to go external when you need to get more stable boost and hold it all the way to redline.
So to push the turbo you going to have to look at tuning, the internal wastegate will easy get you to where you need to go before you need a better method of tuning than a generic chip that's not at least written on the dyno for your car, and then you can push the turbo and look an external gate to control boost.
Also, good luck trying to push the turbo over 20psi on a generic chip, my guess is it'll be too aggressive. I had a chip not from them, another good writer,and it'd knock all the time when turning the boost up over 14psi, it had aggressive timing and relying on the ecu to pull timing all the time after getting knock. The car felt great but i recon chips have their place in running moderate boost levels, unless the car it tuned on the dyno with the chip, or your stuffing around with a safc trying to tune the afr's i think you'll have trouble getting it tuning safe around and over 20psi, on a generic chip.
Im pretty sure chips cant add more load areas top the map than the number on a stock map, you just changing the tune, if im correct....
If you did tell them how much boost you want to run they could have made the made the high load points are a lot softer tune, but after the load points for roughly 7psi, then the next row is 10psi, then you have one more row and that's it. So after this you have run out of resolution. You'll be starting to interpolate into this load area as you start running over 10psi. There was no need for more rows as boost cut is around 14psi stock.
So for example when you running 15psi, you'll be in the same load cells as when you run 25psi as you have no more room to move on the map.
If they have wrote the chip tune to run 25psi on pump fuel, it'll be quit slow running anny less boost.
Or if its aggressive and you try run over 20psi it'll likely you'll knock its head off, especially if it has octane reset so it cant "learn" and reduce timing as its get a lot of knock quite often, its reset every time the car is switched off.
Have a look at the 1g timing map on this guys site, shows the 1G timing map load cells and roughly what boost level they correspond to. http://www.jeffgst.com/id20.html
The chip will likely do you good running 15psi and maybe approaching 20, depending on how aggressive they wrote it. But is far from ideal trying to push the turbo past this, if you relying on the engine to knock, then ecu to retard timing all the time, you letting it knock hard in the first place so putting stress on the motor.
The only way to get more resolution is go and ecmlink or some other ecu.
