Help me understand turbo compressor maps.
11-02-2011, 11:54 AM
#1
Help me understand turbo compressor maps. I have done so much reading but its so confusing. Maybe some one on here could help me understand. I have read on forcediductions.com, garrets website, and even some random ones on google. Can anyone help me understand?
11-02-2011, 10:01 PM
#6
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Compressor maps are not useless.
They don't plot engines, because there are THOUSANDS of engines. That is why they give you a map for the turbo you are looking at. It is your job to plot YOUR ENGINE.
The bottom numbers reading left to right is how much air the turbo can move. This is usually in lbs of air per minute. 1lb of air/min typically can make roughly 10 wheel horsepower. So you can consider a 100lb/min turbo to be a 1000whp turbo. Keep in mind that this is a ball park figure and not on the money info.
On the left side of the map you have your pressure ratio. This is a combination of variables including your atmospheric pressure and boost pressure. Basically, it adds up to the amount of pressure you are going to run.
Knowing those two things will tell you if your turbo is in the area of what you need. I know that I want to make 800whp, so first off, I should be looking for a turbo that will flow at least 80lb/min. Next, I know that I need to do it at 20psi. If you were to look at the compressor map of a tiny T3 turbo, you would see that you can achieve 20psi, but there is no way in hell you could achieve 20psi and flow 80lbs a minute.
The rings in the center of the graph are the turbo's efficiency range. The very inner ring is where the turbo is performing at peak efficiency. Anything outside of that ring, and efficiency falls off.
If you know how much air your engine will move at a given pressure and a given RPM, then you can plot your engine on a compressor map/graph. If you connect your lines and you get your line to go right in the middle of that efficiency range, then you have a pretty good turbo for what you are trying to do.
Oh also, the horozontal-ish lines on the compressor map are telling you how fast the compressor wheel is spinning. If you look at the number on the right, it will be something along the lines of 60,000 up to say 140,000 rpm. The bigger the compressor wheel, the lower that RPM number will be. Big turbo's cannot spin as fast.
They don't plot engines, because there are THOUSANDS of engines. That is why they give you a map for the turbo you are looking at. It is your job to plot YOUR ENGINE.
The bottom numbers reading left to right is how much air the turbo can move. This is usually in lbs of air per minute. 1lb of air/min typically can make roughly 10 wheel horsepower. So you can consider a 100lb/min turbo to be a 1000whp turbo. Keep in mind that this is a ball park figure and not on the money info.
On the left side of the map you have your pressure ratio. This is a combination of variables including your atmospheric pressure and boost pressure. Basically, it adds up to the amount of pressure you are going to run.
Knowing those two things will tell you if your turbo is in the area of what you need. I know that I want to make 800whp, so first off, I should be looking for a turbo that will flow at least 80lb/min. Next, I know that I need to do it at 20psi. If you were to look at the compressor map of a tiny T3 turbo, you would see that you can achieve 20psi, but there is no way in hell you could achieve 20psi and flow 80lbs a minute.
The rings in the center of the graph are the turbo's efficiency range. The very inner ring is where the turbo is performing at peak efficiency. Anything outside of that ring, and efficiency falls off.
If you know how much air your engine will move at a given pressure and a given RPM, then you can plot your engine on a compressor map/graph. If you connect your lines and you get your line to go right in the middle of that efficiency range, then you have a pretty good turbo for what you are trying to do.
Oh also, the horozontal-ish lines on the compressor map are telling you how fast the compressor wheel is spinning. If you look at the number on the right, it will be something along the lines of 60,000 up to say 140,000 rpm. The bigger the compressor wheel, the lower that RPM number will be. Big turbo's cannot spin as fast.
Last edited by SATAN; 11-02-2011 at 10:14 PM.
11-02-2011, 10:47 PM
#7
Compressor maps are used for a "guide" so you can choose the correct turbo for your application that will make the h.p. goal you have set while being the most efficient.
if the calculations for the motor you have can only handle 50lbs/min...a turbo that produces 120lb/min would be overkill. and buying a turbo that produces 20lbs/min would be too small and would overheat/overspin to produce the desired boost/h.p.
To the O.P.:
post your setup & h.p. goals and I'm sure that there are plenty members here like cobrakiller that would steer you in the right direction
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11-02-2011, 11:00 PM
#10
Well, I have a forged AES 390 sitting in my living room now lol. With a ls9 head gaskets and all I should be around 9.0 compression. My goal is 1000rwhp on e85. I have already made a thread about picking a turbo and was recomended a s91 and GT91. But I just wanted to understand the map and how to read it lol. My engine is sort of new compared to the 408 that most use, so I don't know the pressure
11-02-2011, 11:23 PM
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The surge line is where you don't want to go past. Any time you plot your points and you cross the surge line, it means that the turbo is trying to move more air than the engine can ingest. For example, 20psi at 1,500rpm is typically considered a bad thing, and you are most likely surging at that point. This is very hard on the turbo and it will not live very long in these conditions. Typically this is happening because the exhaust side of the turbo is too small for the engine it is mated too.
The same thing happens when you are making a lot of boost and you suddenly close your throttle. If you do not have a blow off valve, that air has to go somewhere. It will try to go back into the turbo. You will hear a ch-ch-ch-ch-ch-ch sound. Hard to describe the sound while typing.
Is an S91 a 91mm inducer turbo? Cause I'm willing to bet that thing flows quite a bit more than 100lbs/min. Not that running a turbo to the ragged edge of what it is capable of, is a good thing, but going too big, isn't really a good thing either.
Then again, I don't know what an S91 is either, but it sounds big... considering a Garrett GT5533R is rated up to 1500whp and it has a 91mm inducer.
EDIT: S91 as in Borg Warner S400 91mm? That is quite a bit for only 1000whp. Unless your plan is to hit more hp in the future (and it usually is LOL).
Last edited by SATAN; 11-02-2011 at 11:30 PM.
11-03-2011, 07:28 AM
#12
No I'm not planing to go past that because my heads will start lifting from what iv been told. But even Dr turbo recomended those to me. They are both rated around 1500hp but is that number rw or crank? If its crank then its probably only 300 more go then I need.
11-03-2011, 07:52 AM
#14
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the compressor map is usefull based on what PR ratio you plan on running and how much airflow your targeting at that PR. you generally want to find a compressor that puts you within the highest efficiency ring given those two factors. its actually very simple. Its just a tool though to get you close, by no means can you plot on a map and determine at this PR and rpm i will have x amount of HP. far too many variables come into play. VE, exhaust flow and turbine A/R and efficiency etc.
11-03-2011, 11:26 AM
#15
The truth is, compressor maps and turbine maps are really first and foremost for engineers. Their primary use is for simulation purposes along with general engineering such as component sizing and in certain cases, material sizing. A lot of good engineering firms (even the smaller ones), will have some sort of simulation code that uses compressor and turbine maps for predictions on boosted engines. With good maps, you can be in a position to transiently predict how many milliseconds it will take to spool your turbine to max speed among many.
This isn't to say that the maps aren't useful to the average person. As Satan and others have pointed out, they can be extremely useful in sizing your setup. A few approximations based off of NA airflow can get you in the right ball park.
11-03-2011, 11:39 AM
#16
Well, I have a forged AES 390 sitting in my living room now lol. With a ls9 head gaskets and all I should be around 9.0 compression. My goal is 1000rwhp on e85. I have already made a thread about picking a turbo and was recomended a s91 and GT91. But I just wanted to understand the map and how to read it lol. My engine is sort of new compared to the 408 that most use, so I don't know the pressure
The problem with the large frame turbos is that space is at a premium under the fbody hood. It's tough to get one of those guys in there and still have room for your cooling system. It all depends on how crazy you want to get with the fab work.
11-03-2011, 06:02 PM
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390ci engine with a boosted 600whp goal. THEN the S91 would be extreme overkill, even though it is still the same engine.
11-03-2011, 11:20 PM
#20
The compressor part is easy, take your lbs per min required for a given amount of HP(i.e. 100lbs per min = about 1000fwhp) and your desired boost level (pressure ratio) and pic a Turbo where those two points fall in the efficiency range of the Turbo. Its choosing the right turbine side that's tricky... a 76 mm Turbo can move 100 lbs per min but if you have a 68mm turbine wheel it will choke out way before that on a 390ci v8. On a 2.0 4 cylinder or v6 its possible. Why don't they have turbine maps?!