50 trim is NOT to small for a B series. lets do a little math here

airflow = displacement x rpm / 1728 x 2
for a type r
108cu in. x 8,000rpm / 1728 x 2 = 250cfm

thats 250cfm @ redline @100% VE or volumetric efficiency. no stock cammed motor runs 100% but the C5 is great so we'll assume 95%

237cfm base under normally aspirated conditions
convert to lb/min
237 x .069 = 16.38 lb/min

now to add on the boost. what boost shall we run today? lets say 10psi. we need to find the pressure ratio
10+ 14.7 / 14.7 = 1.68 or 1.7

so to find out airflow at redline under 10psi of boost

16.38 x 1.7 = 27.5 lb/min i'll round up to 28

28lb/min @10psi @redline

but this is only redline. we need to find out the turbo thats gonna have the best efficiency across the board not just at redline. whats a type r hit full boost at now adays on a street setup......4,500 ; 5,000

lets give the benifit and say 4500

16.5 lb/min @4,500rpm @10psi


now we have to plot the points on the compressor map to find out which one is best.

heres some maps to plot points with. what you will be doing is finding the pressure ratio of 1.7 on the left and the airflow on the bottom.

so everyone is looking for pressure ratio 1.7 on the left and plotting dots for 16.5lb/min and 28 lb/min and then connecting those dots.

this is the 50 trim t04e. its a wonder full compressor for a small motor at moderate boost levels. people doubt this compressor i have no idea why. max efficiency is 78 % and look at where you plot your points. it dives right through that island making the most of the highest percentages. the lowest efficiency it drops to is 74%

(edit look at next post)http://www.majesticturbo.com/30375.html


now for the 60-1. you plot those same points on this graph and you find yourself almost surging this compressor. you also find that you DONT EVEN REACH THE MAX efficiency island of 78% you dig through all the low ones starting at 65% and ending at a MAX of 74%

(edit look at post after that http://www.majesticturbo.com/20177.html



now lets do a fully built motor with 20psi

4500rpm 20psi(which i doubt will make that...lets go to 5500rpm)

pressure ratio= 2.4
5,500rpm @20psi = 27 lb/min
8,000rpm @20psi= 39 lb/min

if you use the 50 trim you are going through a 76% efficiency island the whole time with a little dip into the 78%

if you use the 60-1 you are starting at the 65% and step up for about 500rpm of the 70% island.

we are taking into account HIGH ve so these numbers may be to the left a little, making the 60-1 a worse choice.


am i clear or should i go more in depth with variable VE calculations and temperature and air density as well? i spent nearly the last 3 years learning this turbo math to find out many things about turbos and one of them is believe none of what you hear. i'm in the process of buying two turbos to battle them out on the dyno

T04E 50 trim with a O trim T4 turbine in divided T4 housing
T04S (T58) with a O trim T4 turbine in a divided T4 housing

i'm testing where the motor will be sitting at a certain RPM on the compressors map. finding out if these calculations are as close as i've thought them to be for ALL my turbo selections i've ever made.