A4 1.8T with 034 stage 3 - T3/T4 57 trim - Unitronics BT

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My friend bought a 97 A4 with 1.8T. Available info: 034 motorsports Stage 3 turbo kit Garrett T3/T4 57trim turbo 3"Stainless steel downpipe 3" exhaust with 12" vibrant resonator Custom FMIC Forge 004 BOV Boostvalve MBC Unitronics 440 Big turbo software Delphi 440cc injectors Innovate Wideband AFR gauge I drove the car yesterday: nice power - FROM 4500 rpm on, NO drop all the way up. NOTHING (literally, not even 5 psi) under 4000 rpm. a) To be expected from 57 trim? b) Assume .63 A/R (considering the behavior) c) To get SOME low/mid power: change to smaller turbine. What is likly the current wheel? 57? 54? d) If A/R is 0.63, how much will .48 help? Looks like the stock FR is installed (I think 4 bar is stock). Wideband showed no lower than 13. Assuming this is true: way to lean, or? I noticed a 'pop' from the exhaust. Misfire? Friend says it happens quite a bit. I appreciate your input/thoughts/suggestions how to give him some mid range power (even at the expense of top end power), and a 'save' setup.

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Aside from driveability issue(some like it 'peaky'), I also noticed the turbo inlet
- has no filter or screen
- sits at best 6 inches above ground

Is that safe? It seems to me it is sucking dust, sand, snow, water mist (or worst case: pure water in a anything deeper than 4 inches) like Hoover on steroids.

I can't believe 034 Motorsport designed it this way.

What can be done to make it safe?