It amazes me how few people actually understand what a turbo’s trim is. I have asked several people on eBay as well as this and other sites about what the compressor trim of their turbo is. I usually get back an A/R number…


So, I went through this myself and took some pictures. This is how to calculate trim.



This is the compressor side of my Garrett T3 with a 40 trim. You have to take off the compressor housing, which is usually not very hard; just a few metric bolts.



Begin my measuring the Exducer diameter. On T3s, it is 60mm, but it doesn’t hurt to see how far off yours is. Measure it and record the number.



Next comes the Inducer. Measure the smaller diameter carefully; a few mm makes a huge difference. Record that number too.



Next, all you have to do is use this equation


As you can see, my turbo comes out to .40, which is a 40-trim T3.



Here is an example of how not to measure trim. The inlet diameter doesn’t tell you much, because they are usually tapered and allow for clearance in the fins.


Thanks for reading!


-Alex

 

hey, good write up... I just learned something new

 

Definitely a good write up. Hopefully someone will stickify this?

 

I vote sticky. Lots of people might know this on here, but there are TONs of noobs who can benifit from this. Good writeup!

 

good stuff

 

very good, thank you

 

Some people have asked me if it works the same way for the exhaust side, and the answer is yes.

 

wow a noob that actually knows something on this site, good job.