This is a continuation of this thread, I recommend reading it first if you haven't already.
https://www.oilburners.net/threads/...o-components-specs-and-compressor-maps.83966/
In the last part I talked a lot about air flow, focusing mostly on peak airflow to decide if a turbo is useable or not. Hopefully from the previous discussion, yall have a few turbos in mind. This thread will help you decide which will suit your needs the best.
Lets start of with the factory turbo compressor map as our first example
As we can see by looking at the furthest right point of the compressor map, this turbo peaks at about 52 lbs/min so it could support 270 hp at the crank, and would live a short life at that power level, but theres a lot more to this compressor map than the peak airflow.
On the vertical axis located on the left side of the map you will see pressure ratio. Theres a lot of science behind these numbers, but to quickly find where you are at on this axis, take the boost level you are seeing add 14.7 to it, then divide the total by 14.7 again. This gives you your pressure ratio.
So lets say you own a factory turbo idi, with some mild mods and are seeing 15 psi of boost at 3000rpms out of the stock turbo and you want to see where you are at on your compressor map to figure how hard you are pushing the stocker, using the equation above 15 psi puts you around 2.00 PR.
Now to find air flow for that boost and rpm we will need a new equation, since the previous air flow equation used horsepower as a factor, which we are not using in this scenario.
Here us the equation we will be using
So, using the info we know we get
7.3x3000xVEx2/81,032
VE is volumetric efficiency, and is normally expressed as a percentage. For non intercooled setups, use 70% and 75% for intercooled. For the sake of this equation, drop the percentage sign and do not express it as a decimal, just use 75 or 70. Working the equation out as an intercooled setup, we get about 40lbs/min.
So, like a game of battleship (or battle shots) we use 2 on the vertical axis and 40 on the horizontal axis to draw lines that intersect on the edge of the 72% efficiency island. Not bad.
Well lets say you like the power you have, but you want to replace the turbo with a more modern design to get a bit more performance and a boost of fuel economy. We discussed the R&D Stage 1 turbo, the s257 sxe in the last thread, lets see what just changing a turbo would do for our IDIT
With just upgrading the turbo, I usually see as much as a 5-7 psi increase in boost without any fueling changes, so this will change our values a bit, putting it on the high side and using 22 psi at 3000 rpms, we get 2.5 pressure ratio and 50 lbs of air. This sets us in the 72-70% efficiency range and further into the map than the stocker, but could definitely benefit from some more fuel/higher boost pressure.
Well lets say youre not happy with stockish power numbers, and you want 400 hp at the crank, still very easy to do on the idit internals, and within reason on na internals. Since we have a horsepower goal and not a boost goal, we will need to use our original formula from the first thread.
Looks like we are going to need a minimum of 145cc of fuel and 75 lbs/min air. If we wanted to stay with a big single, an s364 would be a good choice, we know our pressure ratio will be higher than 2.5 with more fuel and air, likely between 3-3.5 PR, so we can use that to get an idea where we will be on the map
Looks like the air flow is there, but how will this turbo respond down low? How can we find the characteristics of this turbos air flow? Well, say your factory turbo is spooled all the way by 2200 rpms, and you want to keep that responsiveness. So, using our air flow calculation using boost pressure, I get:
7.3x2200x75x2.4/81,032=35lbs/min
That sets us perfectly in the middle of the map at 76% so this turbo is more than capable of spooling just as well as the factory turbo, but will be making around 20 psi at 2200. You will note I used 2.4 as our PR, thats an educated guess at were it will be, I will show how to prove later on if the guess is plausible.
Well lets say you want to know just how low in the rpm range the turbo will start making boost. The factory turbo with no leaks and a turned up pump usually starts making boost at 1500 rpms, so lets use that as our first calculation.
7.3x1500x75x1.6/81,032=16 lbs/min
Looks pretty good, that would be just under 9 psi at 1500 rpms, but thats guessing the PR would be in the neighborhood of 1.6. Knowing our airflow, we can see how close our guess was by moving our equations around and setting PR as the variable, instead of air flow-
Luckily, there is this handy online calculator for finding out cfm from displacement and rpms:https://www.widman.biz/English/Calculators/CFM.html
I inputted 444 ci, 1500 max rpms, and 75 for ve, calc spits out 173 cfm which sounds about right. So if 14.7 psi of atmospheric pressure is able to force 173 cfm into a na engine, then 9 psi of boost would be 161% of the total air flow, since 9/14.7=.61
So we multiply 173 cfm by 1.61 and get 278.5 cfm, divide that by 14.47 to convert it into lbs/min and we get 19.2 lbs/min. This doesnt align with our 16 lbs min calculation so we know the engine will need more air flow to get 9 psi of boost at that rpm level, at this point you can keep playing with the numbers by guessing PR until you get a close number.
Lets say you want 600 hp at the crank, and you dont want to loose that responsiveness of a stock turbo. At this power level, a single will not be able to accomplish this, but a properly matched compound setup will. First, set some goals for where you want to make boost at, lets say you want:
5 psi at 1500
10 psi at 2000
20 psi at 2500
30 psi at 3000
45 psi at 4000
A large charger is never going to make boost below 2000 rpms, so we got to look at something small.
An s252 wouldnt be a bad choice, It would spool very hard up to 10-15 psi so a large external wastegate with a 10 lbs spring would be perfect. We then need to look at turbos that will start spooling in the 25-35 lbs/min range and will suit our peak power needs.
A quick search looks like an s472 sxe would suit those needs.
Thanks for reading, hope this has been informative to yall!
Wes
https://www.oilburners.net/threads/...o-components-specs-and-compressor-maps.83966/
In the last part I talked a lot about air flow, focusing mostly on peak airflow to decide if a turbo is useable or not. Hopefully from the previous discussion, yall have a few turbos in mind. This thread will help you decide which will suit your needs the best.
Lets start of with the factory turbo compressor map as our first example
You must be registered for see images attach
As we can see by looking at the furthest right point of the compressor map, this turbo peaks at about 52 lbs/min so it could support 270 hp at the crank, and would live a short life at that power level, but theres a lot more to this compressor map than the peak airflow.
On the vertical axis located on the left side of the map you will see pressure ratio. Theres a lot of science behind these numbers, but to quickly find where you are at on this axis, take the boost level you are seeing add 14.7 to it, then divide the total by 14.7 again. This gives you your pressure ratio.
So lets say you own a factory turbo idi, with some mild mods and are seeing 15 psi of boost at 3000rpms out of the stock turbo and you want to see where you are at on your compressor map to figure how hard you are pushing the stocker, using the equation above 15 psi puts you around 2.00 PR.
Now to find air flow for that boost and rpm we will need a new equation, since the previous air flow equation used horsepower as a factor, which we are not using in this scenario.
Here us the equation we will be using
(Air Flow)lbs/min= LitersxRPMxVE%xPressure Ratio
81,032
81,032
So, using the info we know we get
7.3x3000xVEx2/81,032
VE is volumetric efficiency, and is normally expressed as a percentage. For non intercooled setups, use 70% and 75% for intercooled. For the sake of this equation, drop the percentage sign and do not express it as a decimal, just use 75 or 70. Working the equation out as an intercooled setup, we get about 40lbs/min.
So, like a game of battleship (or battle shots) we use 2 on the vertical axis and 40 on the horizontal axis to draw lines that intersect on the edge of the 72% efficiency island. Not bad.
Well lets say you like the power you have, but you want to replace the turbo with a more modern design to get a bit more performance and a boost of fuel economy. We discussed the R&D Stage 1 turbo, the s257 sxe in the last thread, lets see what just changing a turbo would do for our IDIT
You must be registered for see images attach
With just upgrading the turbo, I usually see as much as a 5-7 psi increase in boost without any fueling changes, so this will change our values a bit, putting it on the high side and using 22 psi at 3000 rpms, we get 2.5 pressure ratio and 50 lbs of air. This sets us in the 72-70% efficiency range and further into the map than the stocker, but could definitely benefit from some more fuel/higher boost pressure.
Well lets say youre not happy with stockish power numbers, and you want 400 hp at the crank, still very easy to do on the idit internals, and within reason on na internals. Since we have a horsepower goal and not a boost goal, we will need to use our original formula from the first thread.
Looks like we are going to need a minimum of 145cc of fuel and 75 lbs/min air. If we wanted to stay with a big single, an s364 would be a good choice, we know our pressure ratio will be higher than 2.5 with more fuel and air, likely between 3-3.5 PR, so we can use that to get an idea where we will be on the map
You must be registered for see images attach
Looks like the air flow is there, but how will this turbo respond down low? How can we find the characteristics of this turbos air flow? Well, say your factory turbo is spooled all the way by 2200 rpms, and you want to keep that responsiveness. So, using our air flow calculation using boost pressure, I get:
7.3x2200x75x2.4/81,032=35lbs/min
That sets us perfectly in the middle of the map at 76% so this turbo is more than capable of spooling just as well as the factory turbo, but will be making around 20 psi at 2200. You will note I used 2.4 as our PR, thats an educated guess at were it will be, I will show how to prove later on if the guess is plausible.
Well lets say you want to know just how low in the rpm range the turbo will start making boost. The factory turbo with no leaks and a turned up pump usually starts making boost at 1500 rpms, so lets use that as our first calculation.
7.3x1500x75x1.6/81,032=16 lbs/min
Looks pretty good, that would be just under 9 psi at 1500 rpms, but thats guessing the PR would be in the neighborhood of 1.6. Knowing our airflow, we can see how close our guess was by moving our equations around and setting PR as the variable, instead of air flow-
Luckily, there is this handy online calculator for finding out cfm from displacement and rpms:https://www.widman.biz/English/Calculators/CFM.html
I inputted 444 ci, 1500 max rpms, and 75 for ve, calc spits out 173 cfm which sounds about right. So if 14.7 psi of atmospheric pressure is able to force 173 cfm into a na engine, then 9 psi of boost would be 161% of the total air flow, since 9/14.7=.61
So we multiply 173 cfm by 1.61 and get 278.5 cfm, divide that by 14.47 to convert it into lbs/min and we get 19.2 lbs/min. This doesnt align with our 16 lbs min calculation so we know the engine will need more air flow to get 9 psi of boost at that rpm level, at this point you can keep playing with the numbers by guessing PR until you get a close number.
Lets say you want 600 hp at the crank, and you dont want to loose that responsiveness of a stock turbo. At this power level, a single will not be able to accomplish this, but a properly matched compound setup will. First, set some goals for where you want to make boost at, lets say you want:
5 psi at 1500
10 psi at 2000
20 psi at 2500
30 psi at 3000
45 psi at 4000
A large charger is never going to make boost below 2000 rpms, so we got to look at something small.
You must be registered for see images attach
An s252 wouldnt be a bad choice, It would spool very hard up to 10-15 psi so a large external wastegate with a 10 lbs spring would be perfect. We then need to look at turbos that will start spooling in the 25-35 lbs/min range and will suit our peak power needs.
A quick search looks like an s472 sxe would suit those needs.
You must be registered for see images attach
Thanks for reading, hope this has been informative to yall!
Wes
