I have been looking around and comparing different compressor maps for the T70 and up turbos because someone gave me a big turbo off of a diesel. It is aGarrett turbo and marked .75 A/R on the compressor and .96 A/R on the turbine. It weighs about 50 lbs. The trubine inlet is about 3.5 x 2". The oulet O.D. is about 5". The comp. outlet I.D. is about 2.8" I.D. and the comp. inlet is about 4" I.D. I took it apart the other night and still need to measure the wheels.
I am confused about the compressor map surge line. Suppose I put a T76 or T88 on a stockish 350ci. It won't boost until probably about 4k rpm so how would I figure if the surge limit is going to be a problem. I realize it will spool high at higher rpms and that is OK. I just don't get the surge thing because down low it won't spool so I guess I can't be at the surge limit. Anyone know a simple way of checking if it will be a problem? How do you calculate when it would start to spool?

Thanks,
J

 

I have been thinking about this and it seems like it is all in the turbine for determining when it will start to boost.
I guess I can figure out the exhaust CFM and look at a compressor map with the same size wheel as the exhaust to determine the wheel speed. Knowing the wheel speed I should be about to determine the boost on the compressor side using the correct compressor map. Correct?

Thanks,
J

 

I honestly don't know how to determine when a turbo will begin to spool. Like you mentioned, the determining factor is mainly the drive section (turbine). I have seen some turbine maps, but haven't really seen how to use them to match a turbine. They don't look too useful to me, though I haven't really spent much time trying to read them.

From what I read, the best way to size a turbine is with experience, and then if needed, fine tuning with the turbine housing A/R. With turbine hosuings around $150 for common frames, trial and error may be acceptable to achieve a perfect turbine match.