How to Read compressor maps (slightly more useful than how to draw them)

[jfallen]

After hearing that not many people had much use for learning to Draw compressor maps (fair enough, there are very few which haven’t been done properly and most of these are from IHI) I’ve decided to do a how to make use of a compressor map. Eg: how to size a turbo correctly for your application rather than go, GT28RS’s are sic I want one for my GT4, or your mate going “Just get a T78 for your supra it’ll do.”

For this exercise we will be modelling the CA18DET motor and the VJ23 Turbo charger, which uses the RHF6 IHI compressor. The CA18DET is a Nissan twin cam turbocharger motor (83bore/83.6stroke,) and the RHF6 compressor has a 65mm, 64Trim wheel. For completeness it is worth pointing out that the VJ23 the BB turbo off the Mazda Familia GTR from the Group A days. Compressor flow on this map is in metre’s cubed per minute (m3/min.) When doing your own motor finding the correct compressor may take some time for your desired application.

Step 1: Using anEngine Calculator such as my spreadsheet fill in the required values, remember to set realistic targets. You can either set a kW/Hp target or as I have done selected a boost level and use goal seek to determine the likely power.
In this example I have chosen a Rev limit of 9000 (not unreasonable for CA18DET,) with a boost level of 20Psi, or a P/R of 2.4. With those limits imposed it is expected that the motor will flow close to a total of 14.9 m3/min. It is likely that the motor will produce somewhere around 350BHP or 265crank kW.
Here is the compressor under the microscope:
It’s a revised drawing of the other map I posted (it’s much more accurate in my opinion


Step 2: Along the corresponding pressure line (2.4 in this case) I like to draw a green line to show exactly where the load on the compressor will be. This will be more useful later on. Then plot each 1000 RPM points on that line using a pencil.
Looking something like this:


Note: That between 4 and 9m3/min at a PR of 2.4, in order for the compressor to maintain a constant pressure ratio of 2.4 the wheel must Slow down.

While this is a hand drawn map using the best available information and cannot be considered perfect, even so this phenomenon is seen on many compressors. But when thought out it makes sense:
-Once past the stall point the compressor becomes more efficient towards the RHS of the map before tapering off.
-At an equal speed, at a higher efficiency, a higher P/R will be achieved at a constant airflow.
-This is shown on the map by the lines of equal speed rising slightly towards the point of peak efficiency and then falling off.
-This is also the reason why (I believe) that small boost spikes are seen just after the desired boost pressure is reached, before settling out under heavy load. It is also to point out that not all compressors show this phenomenon, but a great many do, and it’s nothing to be concerned about.

Step 3: Now recalibrate your engine model to a boost level of Zero. Place marks with a pencil along the P/R 1 line. This is important to see when and how boost is likely to arrive.


Step 4: Connect the dots so that you get lines of equal RPM across the map. I like to use read pen because it’s easy to see. It’s also a good idea to extend these lines beyond your desired/ required boost level to see if the compressor has further capability that you may wish to use in the future. Label the end points.
Looking like this:


Observation I have drawn lines out to 10,000 RPM just for completeness. What we can see is that Mazda got it right when fitting this turbo to it’s 323 Familia GTR with a 1.8L motor. It is extremely well sized for moderate boost levels <15Psi with a stock limiter of 7500, but it also has great potential as shown by this test. It must be noted that the limits of this map are 100% accurate (eg stall line, choke line, and over all shape) but the efficiency and speed lines are “best guess” using available information. That said they’d be Dam Close to the actual figures.
We can see that keeping our 9000 limit we could push boost up to a P/R of 2.55 (23Psi,) which could potentially raise power to over 280crank kW or 380BHP. However any higher boost level would risk over speeding the Turbocharger.
It is likely that positive pressure would be seen just before 3000RPM with full boost showing up just before 4000RPM. This is because we have to wait for the turbo to speed up. Remembering that this turbo came standard on a 1.8 this seems about right.

This turbo would be excellent for a weekend track car/hills thrasher with peak efficiency seen through the hard acceleration phase. However there enough room to not be concerned about over speeding the turbocharger and going into the choke spiral of doom.

Hope you’ve enjoyed this article.
Jordan

[Sam_Q]

nice work, any idea on where I can find a compressor map for a TD-05 turbo?

[jfallen]

Which TD05 are you after? there are at least 6 different ones.

Cheers
Jordan

[Sam_Q]

TD05H-01450 is the code on it, I will do some research on to what it came off

[Sam_Q]

I found some maps here:

http://www.rbracing-rsr.com/turbotech.html

but I dont know which one of these is mine:

TD05-14B
TD05-14G
TD05-16G small wheel
TD05-16G large wheel

I might make a forum post asking people what it is

[jfallen]

to finod out exactly what you've got you have to measure the compressor wheel using a set of viner calipers. To do this properly it requires that the compressor cover is removed. But you can sort cut it slightly and just measure the inducer.

Name / Trim / Inducer / Exducer
14B / 55.0/ 1,695/ 2,285
14G/ 62.1/ 1,800/ 2,285
15G/ 59.9/ 1,707/ 2,205
15T/ 56.3/ 1,654/ 2,205
15C/ 57.2/ 1,638/ 2,165
15C/ 57.2/ 1,654/ 2,187
15G/ 55.2/ 1,625/ 2,187
16G/ 66.6/ 1,814/ 2,223
16G/ 60.1/ 1,830/ 2,365
16G/ 50.0/ 1,892/ 2,680
16T/ 60.4/ 1,713/ 2,205
17G/ 53.6/ 1,744/ 2,382
17G/ 53.6/ 1,744/ 2,382
18A/ 50.3/ 1,900/ 2,680
18G/ 55.2/ 1,970/ 2,652
18G/ 55.2/ 1,992/ 2,680

Cheers
Jordan

P.S: the calculator link works fine for me, the button you need is at the bottom right of the page that opens.

[Sam_Q]

wow thanks, when it turns up I will check it out

[chris davey]

If anybody wants some good tech shit, download it! Jordan has made an AWESOME spreadsheet! Most of it goes over my head though

One thing I did notice is that when you change the boost levels it only calculates it in increments of 5psi. So it seems that if you run 15psi is the same as 19psi. Is there any reason for this besides it taking longer or more space? I was going to add a few more in between 15 and 20psi (hoping it is linear) so that I could work out the difference between calcs, dyno and trap speeds

Once again, highly recommend downloading this!

[jfallen]

change the green fields to a more appropreate scale (negative values also work) if need be

if you look in the grey fields you'll understand why I've limited it to 8 boost levels. got feed up writing 'if' statments.

Cheers
Jordan

note: a readme is comming soon

[chris davey]

shit, didn't realise I could do that. Won't have to add any more if statements then.

Thanks mate.

Can't wait for the readme as there is seriously a shitload of stuff calculating.

[The Witzl]

thread dig.

does anyone have the spreadsheet Jordan links to in the first post of this thread.
The link is dead.
I'll host it back up again.

[woggin]

man, i have seen them comp maps all over the place, and yet, i am still unable to read them

i=epic fail,

u=awesomeness,
=rep yo! (yo as if in v-tec yo!)

wog

[trdee]

simple method woggin, draw line horizontally at your max boost (represented as pressure ratio on this map) draw vertical line at your engine's max air flow (need a calculator for this)

and then where they intersect see which efficiency band the turbo is in by seeing which two sets of curved lines the intersection sits between. this will tell you how efficient your turbo is at the boost pressures/hp you are trying to achieve (if im right then this turbo is at about 67% efficiency at 2.4PR and 14.9m3/min, cant see how fast it's spinning but it's prob there somewhere, otherwise you could calculate it anyways

man i need to revise all my old pumping shit again, i dont remember what any of those other lines represent anymore other than the, efficiency ones lol

edit; +1 for wanting a linky to that calculator

[The Witzl]

well here is the spreadsheet... now hosted at the awesome 18rg.com.au

http://www.18rg.com.au/tech/JAs_turbo_sizing.xls

[MS-75]

Have a squiz here too.

Very useful for those learning turbo engineering in general.