arnott1t
SILVER Star
So off i went trying to get into the more technical turbo stuff. I read that a turbo should be sized based on airflow. Then using the known airflows of an engine at various RPM and Boost pressures you can map your engine on a turbo map. You try and stay centered on the main turbo islands since they are the most efficient. I found a handy dandy spread sheet that does most of the stuff for you. Here http://www.mez.co.uk/myturbocalc.xls
It is based on a gasser engine using to turbos but can be tweaked a bit to suit our 3B.
I had to make a few assumptions though my calculations. The first was volumetric efficiency. I assumed it to be 85%. This seems to be a common conservative assumption. If it was better our stats would shift to the right on the turbo maps. If worse to the left. The other assuption was adiabatic efficiency. Most sites said it was normally around 70% so thats what I used.
I also assumed atmospheric to be 14.7psi and used that number to get my pressure ratios.
So in that spread sheet I set Cubes to 208 VE to 85% max power to 3500 and max torque to 2200 and boost threshhold to 1500
It then spouts out the flows on the left that are corrected byt tempurature.
Lower in the sheet it does all those calcs again but an an rpm you set in the red RPM line.
I went from 1000-4000 rpm in various increments. You can also set the differnt boosts you wish ot achieve. It again takes boost into its flo calculations.
I then went mapping from here. I set three points on each graph to make a line. The first point was at 1000 RPM and 1psi boost. The next was at 2200 and 8psi boost and the last was at 4000 and 12psi boost. these number are probaly a little high in the bosst department but you have to start somewhere. After that I made a squarish area on each map with my minimum boost and min RPM, Min boost max RPM, Max Boost Min RPM, and Max Boost Max RPM. This method seems to be a little easier. You try and get as much area as possible centered on the middle islands of each map. At first it seems troubling that the Min RPM Max boost is normally below the surge limit but it is a fairly impratical case. I used 1000rpm min and 4000 max and 4psi min and 12psi max boost. I thought 4 would be good since that kinda the minimum that I would like to see and 12 is proably higher than i would run too but this is just for an idea.
I plotted these number on a couple garret T3 maps and here what i found. I did the 40 45 and 50 trim maps.
Hers the 40
my interpretation seems that it wouldn't provide enough flow at higher rpm. Or atleast not 12psi. Not a bad thing maybe.....
The 45 trim
Looks a little more balnced...
The 50 Trim
Again this one seems good too..
I would think you would want the smallest turbo possible to minimize lag. I would try the 45 trim model i think.
Just have to find out what kind of car had one.
Let me know what you guys think. Maybe some of my assupmtions are wrong or im doin something really wrong not sure.
Thanks,
Tyler
It is based on a gasser engine using to turbos but can be tweaked a bit to suit our 3B.
I had to make a few assumptions though my calculations. The first was volumetric efficiency. I assumed it to be 85%. This seems to be a common conservative assumption. If it was better our stats would shift to the right on the turbo maps. If worse to the left. The other assuption was adiabatic efficiency. Most sites said it was normally around 70% so thats what I used.
I also assumed atmospheric to be 14.7psi and used that number to get my pressure ratios.
So in that spread sheet I set Cubes to 208 VE to 85% max power to 3500 and max torque to 2200 and boost threshhold to 1500
It then spouts out the flows on the left that are corrected byt tempurature.
Lower in the sheet it does all those calcs again but an an rpm you set in the red RPM line.
I went from 1000-4000 rpm in various increments. You can also set the differnt boosts you wish ot achieve. It again takes boost into its flo calculations.
I then went mapping from here. I set three points on each graph to make a line. The first point was at 1000 RPM and 1psi boost. The next was at 2200 and 8psi boost and the last was at 4000 and 12psi boost. these number are probaly a little high in the bosst department but you have to start somewhere. After that I made a squarish area on each map with my minimum boost and min RPM, Min boost max RPM, Max Boost Min RPM, and Max Boost Max RPM. This method seems to be a little easier. You try and get as much area as possible centered on the middle islands of each map. At first it seems troubling that the Min RPM Max boost is normally below the surge limit but it is a fairly impratical case. I used 1000rpm min and 4000 max and 4psi min and 12psi max boost. I thought 4 would be good since that kinda the minimum that I would like to see and 12 is proably higher than i would run too but this is just for an idea.
I plotted these number on a couple garret T3 maps and here what i found. I did the 40 45 and 50 trim maps.
Hers the 40
my interpretation seems that it wouldn't provide enough flow at higher rpm. Or atleast not 12psi. Not a bad thing maybe.....
The 45 trim
Looks a little more balnced...
The 50 Trim
Again this one seems good too..
I would think you would want the smallest turbo possible to minimize lag. I would try the 45 trim model i think.
Just have to find out what kind of car had one.
Let me know what you guys think. Maybe some of my assupmtions are wrong or im doin something really wrong not sure.
Thanks,
Tyler
