Sorry to ask such newbie-like questions but here goes:
How do you read a compressor map?
How and in what units are turbine, compressor wheel and housing sizes measured?
Is there anything else I need to know?

 

anyone, PLZ?

 

Get the book Maximum Boost. It explains how to read compressor maps. I am sure there are other books that explain it as well, but Maximum Boost is the one that I am familiar with. Perhaps someone will take the time to explain it in this thread, but it's going to be a long thread to cover what it all means if you don't have the background knowledge to make sense of the answer. Maximum Boost will explain everything you need to know.

This is a good question, it's just that the answer can be pretty involved depending on what else you need to know to make sense of it.

-Max

 

The most common values refer to the size of the compressor wheel in mm, the A/R, and the turbine wheel design.

for example - T66 .7 Q-trim

Bigger A/Rs spool slower but make more power up top. Some more common wheels are P-trim, Q-trim, GT-Q-trim.

The P-trim is a smaller wheel so it tends to spool quicker... but it doesn't seem to make as much power up top as the Q-trim. The GT-Q is a new wheel that Garrett has just released... so far it looks very good with larger turbos (74mm).

Keep in mind that every mfg. has their own nomenclature. A Greddy T-78s compressor wheel for example is very close to a T-66 Garrett.

A Greddy T-88 is close to a T71 or 72. It is very confusing when everyone uses different ways to describe their turbos.

 

I have an issue of European Car from 1995. It explains these things, but it is really confusing. A/R ratio is the size of the housing to radius of compressor? How are T3/T4 hybrids made, anyways? Thanks A LOT!

 

The A/R ratio is the ratio between the cross-sectional Area of the housing to the Radius of the center of that cross-section to the centerline of the turbo shaft. Basically, think of the housing as a cone that has been curled up. The AR ratio is the taper of the cone. The cone acts just like a nozzle. Both the compressor and turbine housings can be described with an A/R ratio.
http://wwwrsphysse.anu.edu.au/~amh11...s/trim%20ratio

A "hybrid" turbo is one that is designed to both spool up quickly and also flow well at higher flow rates. The T3/T4 Hybrid turbocharger is composed of a turbine section from a fast-spooling T3 turbocharger, and a compressor section from a higher-flow T4 turbocharger.

 

Do you actually chop up a T3 and T4 catridges or does Garett actually make them this way? Thanks for the link!

 

They make them that way, but I guess a custom shop could make one to their own specs. The Turbonetics web site has a lot of good turbo information, and they sell Garrett-licensed turbos, including the T3/T4.
http://www.turboneticsinc.com/index01.html