How To: Read Compressor Maps

[EEEEeeee36]

problem. . .i cant download any of those spreadsheets


is there a certain guideline you could base spool up on for changes in a/r. say something like for every ______ change in a/r, boost is delayed _____rpms?

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!

[highboostingm3]

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!

email me too please camh@cox.net

[luv4myE36]

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!

awesome. . .ur the man jesse

[M Fan]

I would also like a copy please, desijigga786 at yahoo dot com.

Thanks!

[kaliE36]

great thread ..
@def: i'm wonder if the "turbocalc" excel spreadsheet is apllicable for an supecharged (centrifugal) application.

[EEEEeeee36]

I would also like a copy please, desijigga786 at yahoo dot com.

Thanks!

I just saw this post! Sorry it took me so long - email sent!

[kaliE36]

great thread ..
@def: i'm wonder if the "turbocalc" excel spreadsheet is apllicable for an supecharged (centrifugal) application.

i try to approximate what it will happend will s/c thermal efficiency when i'll change the pulley ratio;
so, can help me enyone with a approx way to calculate boost/ airflow on rpm range for an centrifugal supercharger ? - taking into consideration rpm/ engine displacement/max boost.
thank you,

[Def]

i try to approximate what it will happend will s/c thermal efficiency when i'll change the pulley ratio;
so, can help me enyone with a approx way to calculate boost/ airflow on rpm range for an centrifugal supercharger ? - taking into consideration rpm/ engine displacement/max boost.
thank you,

Airflow requirements will be roughly the same at a given boost pressure. A CF SC will be pretty easy to plot on the compressor map of it given that you should be able to calculate the speed its turning and the airflow of the engine at each speed. Just gotta find the map and do some simple math.

[kaliE36]

thank you,
i estimated the boost/ airflow delivered by the cf s/c using the principle that the boost at half of max rev is square root of the boost delivered at max rev.
after my calculations the s/c will be ok even if i will rise the max boost to 0.9bar (from 0.55bar now).
i also make an .xls with this calculations but i can't upload-it (it is a way to do this?)

[EEEEeeee36]

thank you,
i estimated the boost/ airflow delivered by the cf s/c using the principle that the boost at half of max rev is square root of the boost delivered at max rev.
after my calculations the s/c will be ok even if i will rise the max boost to 0.9bar (from 0.55bar now).
i also make an .xls with this calculations but i can't upload-it (it is a way to do this?)

No there isn't unfortunately. They took the ability to post .zip files away. You would have to email it to others, or host it yourself.

[kaliE36]

ok, if someone want to see my calculations - can post the email adress ..
the excel calculate PR vs airflow (cf/m and m3/s) for an centrifugal supercharger and have 2 warnings about knock (one based on TECR and fuel octane .. very imprecise, and other based on temp increase calculation .. a bit conservatory)
inputs are : existing power, desired power, engine displacement, CR, engine redline, VE, fuel octane.
the main assumptions: 90F degrees ambiental temp, at least 70% compressor thermal efficiency, at least 75% intercooler efficiency, 11.5 - 13.5 afr<AFR p <13.5<>

[NTSOS]

If you find a turbo or a set of turbo's that place most of your motors operating range in a high efficient area of their compressor map, what is the big deal about programming either an electronic exhaust waste gate controller or a manifold excess pressure control valve to follow just inside of the surge line until the compressor is out of trouble....especially if the motor can indeed spool up the compressor/turbine at low rpm to get the compressor (s) into surge trouble?

John

[Def]

Most compressors that are large enough to surge on your engine won't be paired to a turbine that really allows it to spool soon enough to get into that region.

In the event you do have that problem, then sure, an EBC with PWM control vs. RPM vs. gear could be used to keep it from surging.

[NTSOS]

Would you happen to have a suggestion for a good reliable EBC with PWM control? This one sounds interesting from Haltech....

One of the latest features is also the implementation of closed loop boost control where all that needs to be done is tell the ECU exactly what boost to run at each RPM and the computer computes the opening duty cycle of the boost control solenoid automatically - this feature accounts for changes in air temperature, barometric pressure, intercooler heatsoak and any other unexpected factors that may effect inlet air temperature and pressures.

Thanks!

John

[Def]

Almost all EBCs now use a closed loop control system, some are just better than others. They almost all use PWM(Pulse Width Modulation - a way to alter the duty cycle of something like a solenoid that is used to control pressure going to the wastegate).

I know the Apex'i AVR-C or whatever it's called does boost vs. gear, but not sure if it can do it versus RPM as well. I think the AEM EMS can do more complicated things like having a boost map that can be linked to things like gear choice or engine RPM.

[M Fan]

Apexi AVC-R can do gear based and rpm based boost control.

AEM EMS cannot do either of those, but can do speed based boost control.

John, I have an HKS EVC V for sale if you are interested in an excellent EBC.

[NTSOS]

Def,

Ok...how about this. Instead of using an EBC to control an exhaust wastegate to limit turbine speed/compressor speed whilst trying to keep the compressor out of surge at low rpm as discussed previously.....how about using a wastegate device on the compressor outlet, controlled by an EBC to vent pressure until the compressor is out of trouble.....therefore circumventing the need to limit the turbine speed? Thanks!

M Fan,

I appreciate the offer, but I'm probably 2 years away from needing an EBC. Thanks!
John

[Def]

Why double the complexity and most likely triple the cost by doing something with the compressor versus just using the existing control loop you've got(i.e. turbine bypass/wastegate control).

[NTSOS]

Why double the complexity and most likely triple the cost by doing something with the compressor versus just using the existing control loop you've got(i.e. turbine bypass/wastegate control).
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Wastegate control is fine for overall boost control.....just thinking out loud that perhaps venting the compressor discharge initially to control low rpm surge would allow the turbine to continue to spool up as opposed to limiting turbine/compressor speed via the exhaust wastegate.

Thanks!

John

[Def]

It sounds easy to implement, but in practice I think it'd be pretty hard to implement and not have it leak.

[EEEEeeee36]

Wastegate control is fine for overall boost control.....just thinking out loud that perhaps venting the compressor discharge initially to control low rpm surge would allow the turbine to continue to spool up as opposed to limiting turbine/compressor speed via the exhaust wastegate.

Thanks!

John

If you are worried about low rpm surge, why don't you get a variable geometry turbo? They work awesome on turbo deisel cars because deisel engines flow exhaust gasses at lower speeds; variable geometry turbos are able to use lower exhaust velocities at low rpm and then as rpms rise the vains increase and keep the turbo within it's effeciency range at higher rpms. I know that gasoline IC engines don't have 'slow' exhaust speeds by comparison, but the concept would be the same for using a turbo that is larger than what you would typically use for your engine size.

[EEEEeeee36]

It sounds easy to implement, but in practice I think it'd be pretty hard to implement and not have it leak.

Jacob,

What do you think about this new twin-turbo 335i? I am confused as to why two turbos are more efficient than one: why couldn't they use 1 medium size ball-bearing turbo to achieve the same results? You could still have full boost by 1400-5800 and achieve the same effeciency...

To put it in perspective...isn't that why a lot of tuners go to one single turbo on a TT Supra? A BB turbo can be just as efficient and spool as quick (if not quicker) but also produce more power...

[Def]

It's just another way to do it. Twin turbos usually do cut down on the total rotating inertia on OEM sized turbos, but it's a small difference. Another big reason why OEMs love two small little turbos is - it sounds cool, and it's easier to package two little tiny turbos that can be moved all over the place versus one fairly large turbo. Just look at what some of the guys do here to try to fit reasonably sized turbos up against their I6's and still have them drain, get an intake pipe to them etc. It's a lot easier when by design you can put the turbo up a few inches higher, closer to the block AND run a dinky little 2" intake pipe to each and be fine.

[EEEEeeee36]

It's just another way to do it. Twin turbos usually do cut down on the total rotating inertia on OEM sized turbos, but it's a small difference. Another big reason why OEMs love two small little turbos is - it sounds cool, and it's easier to package two little tiny turbos that can be moved all over the place versus one fairly large turbo. Just look at what some of the guys do here to try to fit reasonably sized turbos up against their I6's and still have them drain, get an intake pipe to them etc. It's a lot easier when by design you can put the turbo up a few inches higher, closer to the block AND run a dinky little 2" intake pipe to each and be fine.

Good point...for OE it's sometimes all in the packaging. I bet it will sound cool! I am seriously contemplating buying this car as a birthday present! September Birthday ftw!

[NTSOS]

If you are worried about low rpm surge, why don't you get a variable geometry turbo?

I'm not sure how a VGT would help solve low rpm surge unless they come with an extremely wide map. It would be interesting to take a look at the new turbo porche's VGT compressor maps.

John