*Trim Calculation*

[IJ.]

I was asked by a friend what Trim is and how it's calculated and thought this might be useful to someone and might help demystify another aspect of Turbo's that's often considered black art!

The trim calculation is little diameter divided by big diameter squared x 100
(to get Turbine trim reverse)

so for mine it's 61mm/82mm=0.74390243902439024390243902439024

squared= 0.55339083878643664485425342058299

x 100= 55 trim.

It's just a number to express the relationship between the big and little ends of the wheel.

A few makers use trim a few use inducer and a few exducer so it's always good to find out exactly what size the wheel is.

 

[Stanzaspeed]

thanks for the sxplaination IJ! that makes it much clearer! :icon_bigg

 

[IJ.]

It's one of those NerdyMcNerd things that isn't really of any use in the real world but it's nice to know what they mean when they say "Trim".

Bigger the number the more it will flow.

 

[mkIIIman089]

This might be good for the FAQ I think...

 

[IJ.]

Running the numbers on a stock CT26 I get 49 for the trim!

 

[aye mate]

The trim calculation is little diameter divided by big diameter squared x 100
(to get Turbine trim reverse)



It's just a number to express the relationship between the big and little ends of the wheel.

Little and big diameter of what?

 

[IJ.]

Little and big diameter of what?

Of the Compressor wheel!

 

[Joel W.]

IJ, my 50-trim? dam at least i thought it was 50.. anyways it is supposed to flow 40% more air that the stock trim... and the stock is 49? did i get ripped off lol

 

[IJ.]

LMAO no idea Joel but I can't see 1 unit difference being 40%!

 

[Joel W.]

might have to call and check on this monday..maybe it was 57. hmmm...my math sucks..

 

[IJ.]

Using my "veggie math" 40% more flow would be 19 units change!
(don't know if there is a direct numerical relationship here)
<edit> It wouldn't be as the flow would increase in a non linear rate.

 

[Joel W.]

i could see that the housing was re-machined out to accept the larger wheel. and it sure made a huge difference in boost? seeing if i can find any paperwork on it now..

edited: :dunno: all i found is the reciept and it says upgrade/rebuild special lol
ill call monday..

 

[IJ.]

To go from 49 to 50 trim the difference would be 1.75/44.45mm > 1.77/45mm Joel so I'm not sure if they change the exducer as well.

 

[Joel W.]

ya my numbers must be off.. i had to turn to boost down after i installed it so i know it was upgraded..8psi felt like 12psi did before the upgrade...

 

[IJ.]

Would be interesting if you could measure the inside of the comp cover from the front!

I wouldn't expect going from 49>50 being that much of an upgrade as you describe.

 

[Joel W.]

id have to dis assemble the housing for that right/? or you mean try from the accordian inlet side? these 2 measurements?

 

[trydrew]

What are the stock sizes in mm?

 

[IJ.]

Joel: From the accordian side!

Drew: 1.75"/44.45 and 2.50"/63.50

I posted a bunch of comparison pics in my big thread somewhere around page 42!

 

[Joel W.]

ok i pulled the accordian and best guess with a caliper, kinda had to eyeball it due to ps pump. front small diameter is.roughly 2.25 inches.. cant get the bigger dia. without pulling housing.. and stock small dia. is 1.75 inches.. whew... ahhahaha

 

[IJ.]

Joel: I don't think that's a 50 trim !

Sounds MUCH larger!

It might be a 50 trim but with bigger IN and EX sizes which would explain the difference in power you describe! ie: A much Bigger Comp wheel.