How To: Read Compressor Maps

[e36'n]

They don't spool almost as fast... It might only be a few hundred RPM difference, but it will have a lower turbine inlet pressure(35R).

Plus if you're talking about on an S50/S52, I've already shown that a GT30R is a horrible choice for those engines at the beginning of this very thread. It has an inefficient compressor towards redline on both engines.

Say we're talking about the m50.

[Def]

Run the calcs - I give you all the tools and knowledge you need at the beginning of this thread.

[e36'n]

Run the calcs - I give you all the tools and knowledge you need at the beginning of this thread.

I've mapped out my engine probably 100 times or so on different maps.

I'm probably not explaining what I'm trying to get after well enough, my apologies.


Say you have two turbo's with the same compressor housing, but different sized exhaust housings. I'm assuming the one with the larger hot side, 12cm2 opposed to 9cm2 (let's talk holset's since I've got one coming), is going to make more power at the expensive of a slower spool, ceteris paribus.

Is there a way you can figure out how much more power & airflow the larger one is going to put out at a certain rpm? Or would they both roughly make the same because the compressor are the same size (and assuming the compressor is efficient all through the power band).

Sorry for my ignorance.

[Def]

The one with the freer flowing turbine will put out a bit more massflow due to the higher volumetric efficiency at the same pressure ratio. Probably on the order of a few percent max.

[e36'n]

The one with the freer flowing turbine will put out a bit more massflow due to the higher volumetric efficiency at the same pressure ratio. Probably on the order of a few percent max.

As in a power difference of under 5%?

That could be why all the HX30's on ebay are selling for a fairly high price. I'm quite sure they have the same compressor housing as the larger HX/HY35. I've seen some good numbers from DSM and honda guys on those Holset's.

[Def]

As in a power difference of under 5%?

That could be why all the HX30's on ebay are selling for a fairly high price. I'm quite sure they have the same compressor housing as the larger HX/HY35. I've seen some good numbers from DSM and honda guys on those Holset's.

It's impossible to give firm figures when I'm not even sure how much the A/R is changing. The power difference will change drastically depending on the boost being run and if the smaller turbine housing is at a choked flow condition or not.

[e36'n]

Thanks. I'll have to figure out the Holset to Garrett conversion before anything.

[techno550]

Thanks. I'll have to figure out the Holset to Garrett conversion before anything.

conversion?

[e36'n]

conversion?

Figure out what a Holset's turbine size which is in cm2 equates to in Garrett's a/r values.

Here's the conversion between Mitsubishi's cm2 and Garrett's a/r:
6 cm2 = 0.41 A/R
7 cm2 = 0.49 A/R
8 cm2 = 0.57 A/R
9 cm2 = 0.65 A/R
10 cm2 = 0.73 A/R
11 cm2 = 0.81 A/R
12 cm2 = 0.89 A/R

Now, I know that mitsubishi's figures are only the "A" in the A/R ratio, but do Holset and Mitsubishi measure at different places? The Holset HX35 with the 12cm2 housing is massive and I'd imagine it's bigger than a standard T3 turbo with a .89 a/r.

Here's a diagram, although I'm sure you guys know what I'm talking about.

Picture 001.jpg

[Def]

You can't "convert" and compare turbine housings. They each have unique geometries. Just as a Garrett T2 housing is NOTHING like a Garrett T3 housing, and similar A/R ratios can support vastly different HP - you can't go comparing other manufacturer's area specs to a Garrett housing as far as when it'd spool or how much power it'll make.

[e36'n]

Question for you Def regarding reading the Holset maps properly.

Do you just start reading at 2.0 bar rather than the 1.0 on those maps or...?

[Def]

Question for you Def regarding reading the Holset maps properly.

Do you just start reading at 2.0 bar rather than the 1.0 on those maps or...?

I'm not sure what you're asking.. The Y-axis scale on the compressor map you posted is the pressure ratio across the compressor. Refer to the first post on how to properly read it.

1.0 = same pressure across compressor
2.0 = double the pressure at the outlet compared to the inlet
etc.

[e36'n]

You posted earlier that:

PS - I'd berate the engineers at Holset for using those units. Total pressure is *COMPLETELY* different than absolute pressure(which is what they are actually referring to on the PR axis).

and

Looking at the corrected mass flow, without correcting the massflow in my spreadsheet I'd say you could run somewhere in the 20-22 psi range as a safe maximum and would probably be somewhere around 450ish rwhp(maybe higher, depends on how the engine breathes).

So what I'm asking is how I would properly read the Holset maps.

[Def]

The answer is the same - that's the ratio of absolute pressures across the compressor. Read it exactly like I described in the first post in this thread.

[Bav///Man]

Does anyone have the compressor map for the t3/t4 t60-1 .82 A/R? I know Garett may not as it is a hybrid.

What trim do I have?

[Def]

It's a T04B 60-1... commonly referred to as just a 60-1. Just search for 60-1 compressor map in google.

[TonysBologna]

Yeah I know.... BF.c changed the attachments to not include any data/zip files now, so I couldn't update mine. I have you email bro, I'll send you the most up to date Excel spreadsheet I've made. I changed the values to show an exponential change in boost/rpm, meaning it shows boost psi increasing on a closer axis to what my actually happen to a turbo spooling up. I'll forward it to you!

I'd like a copy as well.. Thanks
infrntofu@cox.net

[sixsick6]

I just posted the 60-1 compressor map but since I'm a new member, wasn't allowed to link it. Oh well. How long does this n00bban last?

[niks325i]

Have patience with a relative noobie please. I'm working on learning to read these things, but wondering if anyone has any comments about this map. Interepretation, I guess.

Nik

[dave reader]

Hi all,
Def, I'M new to the forum, i have been looking at the topic reading compressor maps,
i have a questions for you if you dont mind, in that SURGE, you say to check you draw a line from a pressure ratio of 1, at 2000rpm approx 11.42lb/min, from pressure ratio of 1.6, 8.7psi boost, my question is why is the line drawn on a angle approx 45,deg, and not straight up, is there a reason for this,
the rest of the info is very good just wondered why you have the line at angle? and does it work, regards Dave ,uk.

[kawgomoo]

love this thread! but im having trouble determining how much exhaust flow my engine will produce.. the turbine maps on garrets site are very simple. anyone have any idea how to guesstimate the exhaust flow of my engine so i can make a somewhat educated guess on which turbine housing to run?

[Def]

Hi all,
Def, I'M new to the forum, i have been looking at the topic reading compressor maps,
i have a questions for you if you dont mind, in that SURGE, you say to check you draw a line from a pressure ratio of 1, at 2000rpm approx 11.42lb/min, from pressure ratio of 1.6, 8.7psi boost, my question is why is the line drawn on a angle approx 45,deg, and not straight up, is there a reason for this,
the rest of the info is very good just wondered why you have the line at angle? and does it work, regards Dave ,uk.

The 45 deg line is a very rough estimate of how a moderately sized turbo would build boost(i.e. it's not an on/off thing like a vertical line would be). In reality there is a curvature to the line(going upwards), but I think the 45 deg line is reasonable for most cases.

That said, feel free to adjust the RPM/boost to something more in line with reality, this was just a very rough look at the basics of compressor maps - it is not meant to be set of hard rules you have to follow for every case.

[Def]

love this thread! but im having trouble determining how much exhaust flow my engine will produce.. the turbine maps on garrets site are very simple. anyone have any idea how to guesstimate the exhaust flow of my engine so i can make a somewhat educated guess on which turbine housing to run?

Intake mass flow + fuel mass flow = exhaust mass flow


Garrett's turbine maps are in corrected flow, so you'll have to look up how to calculate that. When the line goes horizontal it means the volute has choked somewhere(velocity of the exhaust is sonic), and you have to then raise pressure to get a 1:1 increase in flow that corresponds to the change in density since you are not going to go past sonic at the choke point.

Garrett usually states the formulas they use for corrected flow, so you'll just have to back calculate it knowing your turbine inlet pressure and temperature to see what your actual flow rate is/was for a given combination. Too bad they don't give an actual turbine map with efficiencies and speed lines though...

[benjy]

Ive been floating about reading up on FI and Ive got a question. What would be the difference in choosing a turbo for a 'torque' engine rather than max power output?

[Def]

Ive been floating about reading up on FI and Ive got a question. What would be the difference in choosing a turbo for a 'torque' engine rather than max power output?

One would be smaller than the other one...