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This is a post I made a long time ago, but I don't think it ever made it over here... enjoy

This post is to help you get past the Honda-Tech mentality of "bigger is better" when it comes to turbos, and get you thinking "properly sized is better". Who'd a thunk it?
This will make some assumptions that you under stand some basics about what a turbocharger is and a what it does.

So, lets take a look at a compressor map. This is the map for the T3 super 60.



Ok, thats it go build a turbo system.

You can see this is a basic 2 axis graph (x and y)... but what does it all mean?!?!?
It's really pretty simple.
Pressure ratio is just that a ratio of pressure.
Pr= (Bp+Ap)/Ap
Bp = boost pressure
Ap = air pressure (14.7psi you should know this, if not go back to school)

so if we want 10 psi PR= (10 + 14.7)/14.7
or 1.68 (we will round to 1.7 for ease)

pretty simple right?

Now the column on the bottom is Air flow lb/min, but sometimes they will be in CFM.
Oh no's what to do?
Here is how to calculate CFM

CFM = (L x RPM x VE x Pr)/5660

and to convert CFM to lb/min simply multiply CFM x .07

L = engine size in liters
RPM = what rpm your plotting the point for
VE = volumetric efficiency
2 valve engines 85%
4 valve engines 90%
ported 95%
race heads like whoa 103%
these are just estimated numbers, but should get you pretty close to what you need.
Pr is taken from the calculation we did earlier.

So if we have a d16 what kind of CFM do we need?

CFM = (1.6 x 7000 x 90 x 1.7)/5660
CFM = 302
and that in lb/min is 21

so lets plot that point.



Not bad, at redline that turbo at 10psi is just at the end of the center island. (that’s a good
thing) but there has to be more right? Yep, we are going to have to plot 2 more points. With these next 2 points we are going to make a few assumptions. (but that’s ok, because they are almost always right.)

The 2nd point we need to plot is 50% max rpm.
Assumption 1. The turbo will make full boost by this rpm. Usually it will, or it will be really close. This is easy oddly enough the engine flows 1/2 the CFM at 1/2 the rpm (yea yea, that’s an assumption too, but again its fine)
So to plot this point we keep the Pr the same, but divide the CFM or lb/min number in half. That gives us a new lb/min of 10.5.



this is good, the point falls on the right side of the surge line. Had it been on the other side, all hell would break loose, cats and dogs living together, real wrath of god kinda stuff.

A quick note about compressor surge… If that point (or any point) falls on the other side of the line, it is similar to letting off the throttle to shift and not having a BOV. (only a little different) The other side of that line is where the turbo isn’t pushing air out of the compressor housing. Instead the air is just spinning with it, and with the exhaust side still spinning it, it can/will create pressure build up at the turbo outlet. This is where damage to the turbo can occur, as the air can/will try reverse flow and go back though the impeller.

The last point we need to plot is the 20% air flow to make sure we don’t cross that surge line between then and 50%.
We will plot this point at 1 Pr (atmospheric pressure, no boost) and take 21 and divide that by
5 (20%) roughly 4, and then run a line from there to the 50% point.



By looking at that map with these points, you can see that this turbo on a D16 is a pretty damn good match.

So figure those 3 points out, and go to town plotting compressor maps and find the right turbo for your application.
 

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Finally! I've been wanting to learn how to read maps for ages but just hadn't gotten around to it. Thanks for this write up.

SHOULD BE STICKY'D!!!!!
 

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I have a question about the pressure ratio. Sorry but I got confused is pr the same as bar. I'm thinkin no but still had to ask


Edit: it took a few minutes but I got my head out of my ass. Its different. Nice write up.
 

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Well, if your turbo is on the list, this is a better easier way.

Garrett
BW
Holset
DSM

Squirrel Performance

^
Just put in your figures and it does the math for you.

This is just a ballpark as manifold design, engine add ons, etc.. has a different effect


EDIT:

This is a Super60 on a 1.6L at 250 hp at sea level
Every dot is an RPM point to 8k
 

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I understand that the ovals on the map are efficiency islands, such as 74, 70, and 66 percents, and that the horizontal lines are the turbocharger's rpms. How much does the rpms matter? I'm assuming that it is important to not over rev the turbo. I was playing around with the Excel file that Zer0DazE posted and it was possible to get an efficient plot of points (on islands 70% and higher) but with varying turbo rpms.
 

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I was hoping you would tell me! I read somewhere that it's not good for a turbocharger to be spinning too fast. If the range on the map goes from 80,000rpm to 150,000rpm, does that mean that anywhere inside that range is fine? Or should one shoot for a lower rpm either by running less boost or getting a bigger turbo?



Maps were produced using Zer0DazE's Excel sheet. The one on the left is 16psi on a t3 60 (not super 60) and the one on the right is 10psi on a t3 60 again. Note how both plots of points appear to be in the turbo's efficiency range but the turbo's rpm is much higher with 16 psi. I just wanted to know if this mattered that much.
 

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The compression of air. As air is compressed there is less room for the air molecules to move around, causing them to rub against each other. The friction between them generates heat but I do not know if this is a substantial factor at all. The engine utilizes the heat as energy in the combustion chamber.
 

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This was originally posted by Craig and has been the top thread in Archive for the past 4 years.

But, its good info to know, as you can actually calculate almost everything in an engine from this. Knowing the turbo air flow will help with basemapping and getting damn close with fuel, possible timing based on pressure at certain RPMs, etc.

Also, sizing according to goal and building the engine to goal are all very important as everything on the engine needs to work in harmony.
 

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air is compressed to increased density of the air, more oxygen to burn more fuel, heat needs to be removed from compressed air as it aids detonation, thats why we use an intercooler to lower IAT
 
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