wimwerf

like subject....


how do i understand/read something like this...

i have no idea...

thanks...

GARETH T

the map is used too first see if the intended turbo is the right selection for the application, and if the airflow/pressure ratio falls within the graph it is used too calculate how much heat is going too be added into the compressor outlet air!

enigne capacity in litres X rpm X VE X pressure ratio
-------------------------------------------------------------------------= air flow (in cfm) (multiply by 0.07 for lb/min)
5660

boost press X atmopheric pressure (1.013bar)
-----------------------------------------------------------------=pressure ratio
atmopheric pressure


you plot your engines characteristics (airflow/pressure ratio) at a couple of points and see how much heat is being added,, you want really to aim for the highest efficiency possible (this is the % on the graph)

any good too you?

GARETH T

wimwerf

thanks....but i dont understand it...

what is pressure ratio...is that boost or something

why does a turbo surge at 1.5bar boost with 10lb/min and not at 1.5bar with 30lb/min...(in graphic) if i understand it right..

OMG i feel stupid if i see a graph like this..

GARETH T

pressure ratio is just the unit used for boost, the amount of times we are over atmopheric pressure

one bar of boost has a pressure ratio of 2
1 + 1
--------------=pressure ratio
1

2 bar of boost has a pressure ratio of 3
1 + 2
-------------prssure ratio
1

the reason why they dont just write a boost figure on there charts is because not all people use there turbo at atmopheric pressure (hill climbers-pikes peak and shit)

sorry i shouldnt of wrote "surge line" this is the surge limit, the turbo just becomes unstable at this point! you can get surge at any point in the compressor map, have you read stus surge topic?

people only know what they know,, you shouldnt feel stupid mate,, they are dawnting too look at mate! willing to leanr is far from being silly

mattbibs

dont feel stupid mate - im in the same boat!

always good to learn - think i half understand it but will read again when fully awake!

wimwerf

ok thanks...

so if i read it right....pressure ratio of 2 (1bar boost) gives surge at 15lb/min...but....at the same pressure ratio at 30lb/min it doenst surge...

but why does it give surge at 15lb/min air flow and at 30lb/min not...

how can a turbo give that much difference at such boost...where does it depends on...

how can i see this turbo is good for my engine...is this graph enough to see its good for the engine..mmmm..this is to technical in english i guess...

GARETH T

the word surge is used on the compressor map just too show the compressor is unstable at this(and below) this point!

i dont understand what you mean

TBH you cant really tell if this turbo is suitable for an engine, (well not without fitting it and testing it, then using the compressor map) as the formula used to work out air flow includes VE, and as VE changes as turbine changes (pumping losses)

trail and error is the only real way or specing turbos

Rs Gus

iTrader: (2)

at a guess id say its because engines are generally more efficant at higher rpm than lower

GARETH T

buy this book mate

http://www.amazon.co.uk/exec/obidos/...361845-6403838

it will help you alot too understanding!

i gotta be honest im not the best person too try and help on any matter,, is im dyslexic and find it hard to type what im thinking

wimwerf

i mean difference in air flow with the same pressure...

GARETH T

you gotta think what pressure really is,,,

its just unwanted (maybe unloved) flow

wimwerf

mmm...this part is hard to understand in english for me...maybe in dutch i would understand..

GARETH T

the compressor is producing air,, the engine is consuming air
any air which the engine does not consume gets built up as pressure