Hi Plumma,
Always the big question isn't it!
Have a look at this link in the forum by my mate Graeme who has led me astray with the mods I have done to my IP.
No, I didn't get any baseline readings on the motor before making changes. Free and easy access to a dyno with readout would be a nice thing to have.
Standard boost is 7psi and I've been running 12.5psi for a year or so. It all went fine and all I needed to do was watch EGT's when towing.
When I added the big exhaust I immediately noticed more torque. I drove from Perth to Geraldton, 450km, and could hold gears on the long slow hills on the highway much more than I could before. I used to lose speed if I couldn't maintain 2000rpm and full boost going up a hill, power would drop off quickly once it went. After the new exhaust this wasn't the case and the increased torque was quite obvious. The big exhaust is essential I believe in enabling excess gas to escape quicker. I found EGT's are less with the big exhaust, perhaps 100°C at full power.
In Geraldton I unwound the fuel screw first one, then two full turns. Boost was left at 12.5psi. Power increase was immediately noticeable and the fully loaded car zipped up hills. I really had to keep an eye on EGT as with all that extra capacity for fuel, EGT rose if overfuelled.
Once I got back to Perth, I did my other tests with removing the waste gate control and found EGT's did not rise as much with the extra air supplied by the turbo. Power was, umm, substantial!!!
I've pulled back to 15psi boost and don't get to that very often. I mostly don't rev past 3000rpm as there is plenty of torque and max boost from 1800rpm to 3000rpm and well beyond.
Am I risking my engine? Maybe a little, probably not so much. There is plenty of reports around that 14 - 16 psi is fine for these engines. Extra fuel is always controllable by your right foot. High EGT's are the nasty thing to avoid that will melt stuff, load up your coolant and oil systems.
Yota put a light on the dash that switches on at 14psi, called the overboost light. I figure that Toyota say 14 psi is enough for them, so why not increase boost to that level? I've also got a posting at
this link on power boosting, showing how I did it.
Tim