: A "T28" that is somewhat popular here will have more lag, and feel 'less torquey' than a proper set of 650's. Sorry, engineering and physics win here. The trouble with the T28 that is somewhat popular on this forum is that it is a 65 trim T-3 compressor wheel in a stock carved out compressor housing. What this does is effectivly eliminate the diffusor that is built into the compressor housing. A diffusorless housing is how the very first turbos were built in the 40's before we has as much understanding of aerodynamics as we do now. The diffusor is where about 30% of the turbos compression takes place and eliminating it causes the adiabatic efficeny to drop to 50% or below, or about as good as a bad roots blower. What that means is intake charge temps nearing 300 degrees F at 20 psi or so! I have seen these turbos literaly boil water off intercoolers. Ingesting this hot air is not the greatest for the engine either. A Sport 650 for example will only heat the air to around 170-180 degrees. This loss of efficency from the reman T28 also makes for more work to to done by the turbine, causing more backpressure, less VE, more lag and more reversion. The exhaust side of the reman T28 is usualy a 68-79 trim T25 turbine carved into a stock .63 T2 turbine housing. The housing to wheel geometry is usualy not as critical in the turbine as the compressor but the T2 housing is smaller than the T25 and is not optimal. The reman T28 can produce more flow than stock but it is not a high quality flow. It is hot, laggy and bad for the motor. That is why the popular aftermarket T28's suck big rocks. Notice how no one actualy prints dnyo charts with these turbos? I bet no one has made much more than 470 wheel hp with these and if they do, they don't do it for long. Notice how so many people blow up there motors with these? It is the heat and the reversion encoraging detonation. If you look at the engineering build sheets, a Sport 650 is actualy a true T28, with the proper housings and wheels. It is very simular aerodynamicaly to a Pulasr GTI-R turbo SR20DET. A sport 650 will kick the shit out of those reman T28's in both power production and engine relaiblity. Mike
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