While doing my research on the FI 2.0 turbos I looked high and low for dyno graphs with a built motor and 11:1 compression. I couldn't find any. It looked like SOHO push the FI Stage 2.0 the hardest on a stock block. From what I remember they were at 72x whp at 16psi of boost from what they posted. The best I can figure is that the FI 2.0 turbo's will fall off at 17 psi of boost. Now the question is why. Is the turbine housing of the GT28 frame turbo too restrictive or are they starting to push hot air on the compressor side. If I had to take a guess I would say it is the turbine side that just can't flow the exhaust gases out fast enough causing excessive drive pressure. There is a way to test this but nobody has done it. You can look at EGT pre turbo (drill the exhaust manifold before the turbo) to get a good idea or (you can drill a hole in the exhaust manifold before the turbo) take drive pressure readings. You can even do both. Here comes the issue. Testing is not cheap if you are not doing it yourself. So what I did was just look at Justin's build with the GT3076 turbo's. I picked a point on the dyno graph to look at boost pressure. I picked 4000rpm. The only problem with this is Seb was hold it back due to it being a stock block. Well, most of the FI 2.0 kits were on stock block so I decided the data would be close enough. I looked at the Boost psi at 4000rpm for several graphs. They all came up to be approximately 10 psi. What I don't like to do is push a turbo to it's max. Heat is the enemy and pushing it to the max will generate a ton of heat. I am not sure where the new FI 2.5 turbo's will start to fall off but I am sure MA will find out for me and let me know. I have a few more thoughts rattling around but this is the bulk of why I upgraded.
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