i have a greddy 15g turbo on my 97 civic ex coupe.
where does the efficiency fall off with this size turbo? or...where would i be able to find this information? im thinking about adding pistons/rods/sleeves (i have a machine shop at my disposal) and generally building the block a bit.
i like the fact that this turbo spools very quickly, but was wondering how high the boost could be before it started losing efficiency.
also...anyone know if the greddy 18g turbo bolts up the the 15g manifold and stuff?? finally....how the hell do you spell efficiency?????

 

Do a search on the net for "Turbocharger Volumetric Efficiency Maps". That should point you in the right direction. You'll need to figure out airflow though too... Usually, boost pressure on the maps is rated in BAR, and you'll need to remember to subtract one bar to account for atmospheric pressure. If you're running 15 pounds of boost, you'll want to set your point at roughly 2 bar for the map.

 

Main Entry: ef·fi·cien·cy
Pronunciation: i-'fi-sh&n-sE
Function: noun
Inflected Form(s): plural -cies
Date: 1633
1 : the quality or degree of being efficient
2 a : efficient operation b (1) : effective operation as measured by a comparison of production with cost (as in energy, time, and money) (2) : the ratio of the useful energy delivered by a dynamic system to the energy supplied to it