Estimating Compressor Maps
Turbo Mini Forums

I have been looking for a compressor map for my GT2056V to see if it will suit my BMW M40B18 @ 0.8 bar.

I measured the compressor exducer and inducer diameters (which I can't remember off hand) and got a compressor trim of 50. The compressor housing has an A/R of 0.45.

I cannot find a map for this turbo so it seems like I will have to assume a map based on other available maps. So how do I estimate a map? Do I need to find a map where both A/R and trim are proportionally scaled? i.e. finding a map with an A/R of 0.5 and trim of 55 (10% increase in both figures). Then I could simply increase my calculated airflow by 10% and read that off the map?

Also, can I estimate a map based on only changing one figure? I have found GT2056 maps with a 50 trim but a different A/R. If so, how does a change in A/R (or trim) effect the pressure ratio and air flow figures on a map? From what I have read, trim is directly related to the airflow capability of the compressor and the performance is relatively insensitive to changes in A/R. Should I concentrate on finding as close a trim as possible and working from that map?

Would it be safe to say that I would not need to change any airflow or pressure scales if the base map is also a GT2056?

Lastly, I cannot see any A/R markings on the turbine housing. Is "A" measured at the flange or the circular section of the housing before it changes to the shape of the flange?

Thanks for bearing with me on such a long post

On 12th Nov, 2009 Paul S said:

I think Gary OS has taken over my role as the forum smart arse

I would have thought calculating a comp map for a variable vane turbo would be pretty complex?

Would it even be similar to a solid state turbo?

That was a whole different area I didn't want to start thinking about yet . From my (very limited) understanding, wouldn't VNT be equivelent to a variable turbine A/R though. Would it really have any effect on the compressor side as all we check with the compressor map is peak efficiency at peak boost?

On 12th Nov, 2009 Paul S said:

I think Gary OS has taken over my role as the forum smart arse

isnt the point of a vane turbo that you can have a variable peak efficency due to the variable ar?

could be talking out my ass here but that was my understanding as they spool low but can open up when the need arises.

garrys correct, tthe vnt only affects the turbine side,

I think your scaling thery stands up garry, iirc paulS did a similar thying with the gt17 to estimate its performance at higher rpm.

this calculator may be of use to, saves a bit of calculator work


http://www.motorgeek.com/index.php?page=6

Thanks Joe. It's good to know I'm finally getting something right! I'll put that link into favorites. It should keep me busy in work if things stay as slow as they have been

On 12th Nov, 2009 Paul S said:

I think Gary OS has taken over my role as the forum smart arse

Ah of course, i need to stay away giving my opinion when hung over, its a bloody wednesday! A meal and a drink was the plan....

lol,

Ah, don't worry James. The only reason I am managing to make any progress and/or sense is because for a couple of weeks a year I get a spurt of enthusiasm, stop drinking, get the hampster turning on that wheel and attempt to justify the life changing amount of money that I have wasted on both cars so far.

Anyway, that calculator is great Joe! I'll just have to find a suitable map that I can scale

On 12th Nov, 2009 Paul S said:

I think Gary OS has taken over my role as the forum smart arse

OK, I have found a GT2056 compressor map with a trim of 55 and an A/R of 0.53. That is ~10% increase in trim and A/R in both figures. Working with that and increasing pressure ratio and air flow figures by 10% gives me a spot just inside the peak efficiency island.

Obviously, it's by no means accurate and I've no idea how innaccurate it is but it is a good indication that it isn't a million miles off. I would imagine that trim has a fairly linear relationship with the air flow scale but I just guessed at increasing the pressure ratio and I don't know what effect A/R actually has on the map. I might think a little harder about that one.

Time to start making a manifold :)

On 12th Nov, 2009 Paul S said:

I think Gary OS has taken over my role as the forum smart arse