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Discussion Starter · #1 ·
Reading Compressor Maps

I'm trying to understand turbo dynamics better and I need a quick tutorial on how properly read a compressor map.

I'll attatch two compressor maps. The first is the TD04L-13G. This is the stock turbo for the WRX
 

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Discussion Starter · #2 ·
The next one is a T3 Super 60 that I've been told is very close to what I have in my car now.

Can someone translate these maps into laymans terms and give a quick demo of what is being portraid in these charts?

Thanks in advance.
 

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Well, for starters, you have different units on those two maps, which makes things a bit more difficult, but, i'll give you a general overview.

The vertical axis is pressure ratio, meaning how much the air is compressed. Here a ratio of 2:1 means it's compressing the air to twice the normal density, giving you 1bar of MAPressure.

The horizontal axis is actual flow. The TD04 map is in cubic feet/minute (CFM) while the T3 is in LB/MIN. This makes comparison a bit tough between the two maps.

The lines that are curving across the middle of the map are turbine RPMs.

The lines enclosing area on the maps are efficiency rates. If you look on the TD04 map, you can see the percentages written on the map.

Now, reading the TD04 map, we see that peak efficiency is 76%. The area enclosed by the 76% line includes all of the area in which the turbo is operating at peak efficiency. That said, the most you can get out of the TD04 at peak efficiency is about 0.9bar of pressure and 225 CFM of flow.

The T3 map is rather crappy. While we can still tell where peak efficiency is, we aren't quite sure exactly how efficient the turbo is inside that area. You can, however, see that you can run about 1.25bar of pressure within peak efficiency and flow around 25 lb/min of air.

A direct comparison of the two turbos can't be accurately made with these two maps because a cubic foot of air will weigh different amounts depending temperature.

That said, you can push the turbos out of peak efficiency range. You'll heat up the air quite a bit as you move farther out on the maps though.

One last thing youc an tell from the maps is what the turbo is capable of at certain rpms. If you follow the rpm lines across the map, they show the exact CFM for a certain pressure at a certain rpm. For example, on the TD04 map, there is a point included that shows that with the turbo spinning at 150,000rpm, the turbo will push out 360CFM at 1.0bar of pressure. This also puts it in the 60-65% efficiency range. (bad)

Hope this helps!


Now...what we need is a compressor map library!
 

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First go to
My CFM calculator

Enter the peak boost you plan to run and the rpm in which you plan to reach it (or leave blank for simplification) and the displacement in CU (there is a check box to change it to CC units).

This will give you two numbers for each rpm point: Pressure ratio (PR) and air flow (in cfm) for your motor.

All you have to do is look at any compressor map and plot PR vs air flow (in cfm or lb/hr). You want your plot to stay withing the most ideal part of that compressor map.

The map has rings. The rings represent the compressor effeciency at a given point. There is also a line show compressor rpm. The higher the compressor rpm, the hotter the air will be and the harder the turbo will be working (read: longivity). If your plot gets to the left of the chart (off of the chart) the compressor will surge. This usually happens when you try to put a turbo that is too big for a car.

Now the links!

This is what you should read first. It pretty much teaches you everthing you need to know about turbos and maps:
http://www.badbricks.com/main_files/faqs/turbo_size.htm (link not currently working)

here is a site that plots it for you on top of various charts:
http://www.bsmotor.com/turbo/kalkuler.html

on the sites that don't plot it for you, or if you find a chart elsewhere, you just print out the compressor map and draw it in with ink.

turbonetics compressor maps:
http://www.turboneticsinc.com/comp_maps/fig1.html

garret compressor maps:
http://www.bsmotor.com/turbo/tabell.html

Mitsubishi turbos upgrade guide and well as some GOOD tech info http://www.3si.org/member-home/jlucius2/j2-2-turboguide.htm (link not currently working)


After reading all of this and understanding it, you'll pretty much know all you need to about turbos (beside actually getting hands-on experience).

-C

This almost seems like a FAQ.

[EDIT] I forgot I added the cfm to lb/hr conversion checkbox on my calcuation page.
 

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Turbo info thread (flow, compressor maps, etc...)

Compiled by Hotrod on NASIOC:

Last updated 12/28/02
Turbo Type ----------- Approx flow @ pressure
Stock Turbo ---------- 360 CFM at 14.7 PSI
IHI VF 25 ------------- 370 CFM at 14.7 PSI <--- estimated
IHI VF 26 ------------- 390 CFM at 14.7 PSI <--- estimated
T3 60 trim ----------- 400 CFM at 14.7 PSI
IHI VF 27 ------------- 400 CFM at 14.7 PSI <--- estimated
IHI VF 24/28/29 ----- 410 CFM at 14.7 PSI <--- estimated

========= 422 CFM max flow for a 2 Liter at .85 VE pressure ratio 2.0 (14.7 PSI) 7000 RPM =======

IHI VF 23 ------------- 423 CFM at 14.7 PSI
FP STOCK HYBRID -- 430 CFM at 14.7 PSI <--- derived from HP potential listed on web
IHI VF-30 ------------- 435 CFM at 14.7 PSI <--- estimated
SR 30 ----------------- 435 CFM at 14.7 PSI
IHI VF-22 ------------ 440 CFM at 14.7 PSI <--- refigured
T04E 40 trim -------- 460 CFM at 14.7 PSI

========= 464 CFM max flow for a 2.2 Liter at .85 VE pressure ratio 2.0 (14.7 PSI) 7000 rpm =======

PE1818 -------------- 490 CFM at 14.7 PSI <--- estimated from max flow numbers
Small 16G ------------ 505 CFM at 14.7 PSI
ION Spec (stg 0) --- 525 CFM at 14.7 PSI <--- per vendor post 12-27-2002

========= 526 CFM max flow for a 2.5 Liter at .85 VE pressure ratio 2.0 (14.7 PSI) 7000 RPM =======

Large 16G ----------- 550 CFM at 14.7 PSI
SR 40 ----------------- 595 CFM at 14.7 PSI
18G ------------------- 600 CFM at 14.7 PSI
PE 1820 -------------- 630 CFM at 14.7 PSI <--- estimated from max flow numbers
20G ------------------ 650 CFM at 14.7 PSI
SR 50 ---------------- 710 CFM at 14.7 PSI
GT-30 ---------------- 725 CFM at 14.7 PSI
60-1 ----------------- 725 CFM at 14.7 PSI
GT-35R -------------- 820 CFM at 14.7 PSI
T72 ------------------ 920 CFM at 14.7 PSI <--- Note you would have to spin a 2.0 L engine at about 14,000 rpm to flow this much air.

IHI VF 25 ----------- 395 CFM at 18 PSI <--- estimated
IHI VF 26 ----------- 400 CFM at 18 PSI <--- estimated
T3 60 trim ---------- 410 CFM at 20 PSI
IHI VF 27 ----------- 420 CFM at 18 PSI <--- estimated
IHI VF 24/28/29 -- 425 CFM at 18 PSI <--- estimated
IHI VF 23 ----------- 430 CFM at 18 PSI <--- estimated
IHI VF-30 ----------- 460 CFM at 18.0 PSI <--- estimate based on trap speeds of cars running this turbo
AVO 320HP -------- 465 CFM at 17.5 PSI
T04E 40 trim ------ 465 CFM at 22 PSI
FP STOCK HYBRID- 490 CFM at 18.0 PSI
IHI VF-22 ---------- 490 CFM at 18.0 PSI <--- refigured
SR 30 --------------- 490 CFM at 22 PSI
Small 16G ---------- 490 CFM at 22 PSI
ION Spec (stg 0) - 500 CFM at 19 PSI <--- per vendor post 12-27-2002
PE1818 ------------ 515 CFM at 22 PSI <--- estimated from manufactures rated max power
Large 16G --------- 520 CFM at 22 PSI <--- upgraded flow some on review of compressor map

========= 526 CFM max flow for a 2 Liter at .85 VE pressure ratio 2.5 (22 PSI) 7000 rpm =======

========= 578 CFM max flow for a 2.2 Liter at .85 VE pressure ratio 2.5 (22 PSI) 7000 rpm =======

HKS GT2835 ------- 580 CFM at 22 PSI 400 hp
MRT 400 ------------ 580 CFM at 16 PSI
AVO 400HP -------- 580 CFM at 17.5 PSI
MRT 450 ------------ 650 CFM at 19 PSI
AVO 450HP -------- 650 CFM at 20.0 PSI
SR 40 ---------------- 650 CFM at 22 PSI

========= 658 CFM max flow for a 2.5 Liter at .85 VE pressure ratio 2.5 (22 PSI) 7000 rpm =======

HKS GT3037 ------ 670 CFM at 22 PSI 460 hp
PE 1820 ----------- 680 CFM at 22 PSI <--- estimated from manufactures rated max power
20G ---------------- 695 CFM at 20.0 PSI
HKS GT3040 ----- 710 CFM at 22 PSI 490 hp
AVO 500HP ------ 770 CFM at 22 PSI
SR 50 ------------- 770 CFM at 22 PSI
GT-30 ------------- 790 CFM at 22 PSI
60-1 --------------- 800 CFM at 22 PSI
HKS GT3240 ----- 830 CFM at 22 PSI 570 hp
GT-35R ----------- 880 CFM at 22 PSI
T72 --------------- 1000 CFM at 22 PSI <--- note you would have to run a 2.0 L engine at >40 PSI boost to flow this much air

Conversions used where I had control over conversion factors:
1 HP approx equals 1.45 CFM

1 CFM approx equals 0.0745 lb of air/min

0.108 Lb/min approx equals 1 hp

1 Meter cubed/sec = 35.314 CFS = 2118.867 CFM

1 KG/sec = 132 lbs/min approx equals 1771.812 CFM

power coversions:
1 PS = 0.9859 HP = 75 Kgf m/sec
1.3405 HP = 1 KW
1 HP = 746 watts
 

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Discussion Starter · #10 · (Edited)
This info is awesome. Thank you very much.

Convert CFM to lb/min: Mass Flow(lb/min) = 0.0756 x Volume Flow(cfm)
 

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Discussion Starter · #11 ·
Thank you very much, both of you, for this information. I'll be sure to review it.
 

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See? When Rez doesn't sleep, good things happen! :D :cool:

Breaking out in cold sweats...is that a sign of sleep deprivation or caffeine overload? :eek: :confused:
 

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Discussion Starter · #14 ·
Let it be heard thruout the kingdom that ClubWRX is the greatest car site of all time.
 

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Just wanted to expand further on the comments regarding the pressure ratio (y-axis) on the compressor maps. Although a PR of 2.0 logically equates to around 1 bar of boost, there are some factors that you need to take into account for an accurate calculation.

The formula I use is as follows:

pOut/pIn = (Pm + Pic + Patm) / (Pit + Patm)

Where Pm = Relative boost pressure @manifold.
Pic = Pressure drop through IC.
Patm = Absolute ambient barometric pressure.
Pit = Pressure [email protected]

Units of measurement are PSI.

So let's say there is a 3psi drop through the stock intercooler (not outlandish for a small tube-fin IC), plus a 0.5psi drop at the turbocharger inlet (guesstimate). Sea-level barometric pressure is 14.7psi

Given these conditions, a PR of 2.0 would figure as follows:

2.0 = (Pm + 3 + 14.7) / (-0.5 + 14.7)

Solving for Pm:

Pm = 2 . 14.2 - 17.7

Pm = 10.7 psi

This is important in the selection of compressors based upon flow map data because you generally need to run a higher PR than it might first appear. i.e Your turbo needs to work to overcome the pressure drop across the IC (and at the inlet). 1bar of boost at the compressor outlet does not necessarily equal 1bar of manifold boost.

-Pace
 

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To add to that, you can download a PDF of altitude pressure correction factors here.

Also, a nice pressure unit conversion calculator can be found here.
 

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TypeC said:
There is also a line show compressor rpm. The higher the compressor rpm, the hotter the air will be and the harder the turbo will be working (read: longivity).
Tons of excellent info in this thread!

This particular point is, in my opinion, an overgeneralization... the islands of efficiency have MUCH more bearing on outlet temperatures than the compressor speed. If a compressor has 78% efficiency at 200,000 RPM, the outlet temperature will be no higher than another compressor that makes the same pressure ratio at 78% efficiency at 120,000 RPM. In fact, below a certain speed it becomes very difficult to attain efficiencies as high as 78%, which is why compressor design is leaning toward smaller and faster compressors. Watch your efficiencies above all else. Chances are, if your compressor has peak efficiency at 150krpm, you WILL be making too much heat at 200krpm, because you will be operating at a reduced efficiency. But if your peak efficiency is at 200krpm, don't let that scare you off. And if the turbo is designed around a peak efficiency point up at 200krpm, that speed is certainly not going to harm your turbo's longevity. These things are made to go fast! As long as your oil and cooling system is adequate, the bearings should not take any more wear and tear regardless of speed. The real problem is, if the turbo is designed for a PEAK speed of 200krpm, it's likely that the shaft has a vibration problem somewhere a little way above that speed. If the shaft starts shaking, you WILL potentially get metal-metal contact at the bearings or at the compressor wheel/shroud interface and then UGLY things start to happen.

I'm not talking completely out of my ass here, I am a mechanical engineer working in centrifugal compressor design for the past year. Not a ton of experience but I've learned a lot, and took coursework specializing in turbomachinery and bearing design when I was finishing up my degree. I've also got a few very useful excel worksheets I've put together that I'll see if I can upload and share if they'll be of use to anyone else. Turbos are FUN! This thread remains the best summary of turbocharger info I've seen on any auto forum!
 

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1x2 said:
djrez4,

this is nuts! Thanks! (can't send money, saving for mods...) :D

And nuts are tasty...start digesting my friend ;)
 
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