'Trim' Sizes for the Exhaust Side

[Doward]

For the T4, the alphabet trim sizes, (N, O, P, & Q) indicate the diameter of the turbine's exducer and major in inches.

Stock CT26 = exducer 2.047" major 2.677"

N = exducer 2.071" major 2.922"

O = exducer 2.296" major 2.922"

P = exducer 2.544" major 2.922"

Q = exducer 2.693" major 3.111"

GT-R = exducer 2.850" major 3.200"

GT-S = exducer 2.960" major 3.200"

I like the P and Q trim on the 3.0L 7MGTE, but that's just me

 

[frontierguy25]

Can you elaborate on the differences in the Trim for us. Like what is the effect of the wheel sizes regarding spool response and flow. Like the difference between the a O trim wheel and the P trim wheels which one is going to flow more and which one is going to spool up faster and maybe which compressor wheels to match up to the two?

 

[Guyana00]

Hey Doward. I know you've been busy, just reminding you about this thread. Thanks for the info too. You're a great resource to any community you're involved in, especially ours

 

[Mark Conte]

Can you elaborate on the differences in the Trim for us. Like what is the effect of the wheel sizes regarding spool response and flow. Like the difference between the a O trim wheel and the P trim wheels which one is going to flow more and which one is going to spool up faster and maybe which compressor wheels to match up to the two?

I know this is old but to put it bluntly, assuming all else is equal a larger trim (compressor or turbine for that matter) the wheel with the larger trim will generally be able to flow more. However you just have to realize that trim is not the end-all-be-all. There are hundreds of car forums on the planet where I could go say, "Hey I'm looking to make more power, which should I buy...a 60 trim or a 47 trim?" They would all laugh, call me an idiot and say of course a 60 trim. Well guess what, a GT5533R is also a 47 trim.

The same holds true for the turbine side but it is also far more sensitive to A/R than the compressor in that it has a very noticable effect on the tangental versus radial interaction of the exhaust gas with the turbine wheel. In many cases, this will actually yeild a larger flow delta than two otherwise identical turbine wheels - one just with a higher trim.

Garrett is one of the most forthcoming with maps for both compressor and turbine wheels, if you go to the website you can check out most of their GT line up and get turbine charts, you can see the large difference A/R makes in turbine flow.