Reading Turbine Maps

[BHDave]

Has anyone found any documents or equations in their travels that allows you to accurately gauge the effect of the turbine map on the compressor map?

Other than the obligitory big A/R = poor response, small A/R = good response.

The problem i have, is we can all figure whether the comp wheel will be able to flow enough for our power goals and then plot a few intermediate points through the map using fairly readily available formulas but it all falls apart in real terms because you are only looking at half the picture.

And it really falls on it's arse if you choose the wrong turbine or turbine housing for your application.

What i'm trying to figure out, is if i move from my prefered .63 housings (yes i like response and am willing to for go top end for it) and picked up a .8x housing will i then be looking at say 300 rpm more til the boost threshold but gain 25rwkw for example which would be acceptable or would i add 700 rpm and only gain 30?

And how is my choice of .63 housing skewing the comp map by causing a huge restiction in the exhaust and so limiting flow potential?

Anyone? :

[StockyMcStock]

too many variables. the best way to judge it is from other people's experiences with similar setups to yours.

going from 0.63 to 0.8something will *generally* add between 300 and 500 more RPM to full boost. again, lots of variables.

i'm not sure what you're talking about with that last question, but the reason the 0.63 housing restricts power compared to the larger housing is mostly in the back pressure changes in the manifold. bigger housing = less back pressure = less pumping loss of energy = more power.

[BHDave]

It's the backpressure issue i'm getting at. You can get the turbine map as well as the compressor map but the turb one is generally ignored and it's just a general statement that smaller for response, bigger for power.

There has to be some way of using that turbine information combined with the compressor map to get a more accurate idea of how the turbo will perform on a given engine.

I dont disagree about finding others with the same setup, I'd just like to look at it more critically is all in an attempt to improve my own understanding.

[discopotato03]

Will get back to you on this one tomorrow - stay tuned .

Cheers A .

[StockyMcStock]

i looked more at the turbine map for my turbo than the compressor map, but then again i had a very specific purpose behind my choice.

it is possible to figure out the amount of airflow needed to make XXX amount of power, then you can find that point on your turbine map and get some idea of whether or not it's close to peak efficiency.

other than that, i'm not too sure. disco might know a bit more about this than me i would guess.

[nuffin_werks]

This may help you some , i don't know, but maybe.

I knocked it up ages ago by colating info from various web sites and magazines.

Selecting a Turbo

cheers

Ron

[discopotato03]

BHDave , as a start we really need to know which turbo you are talking about because many different ones can use a .63AR turbine housing - must know compressor and cover as well .

When you look at turbine housing area radius ratio its not simply a case of small = good response and large = poor response . Small AR housings will give higher gas velocity through the turbine blades than larger AR ones given the same exhaust gas heat/flow . A small AR housing is NOT the way to make a large turbocharger responsive . The theoretical perfect turbo uses mid trim wheels and housing AR's BUT it all hinges around what is trying to be achieved .

Turbine maps are usually a two dimensional graph of exhaust flow in corrected pounds per minute vs the pressure ratio of the gas . What it tells you is that once a certain flow rate in lbs/min is reached increased turbine inlet pressure (TIP) wont make it pass any more . Note changing the turbine housing AR will increase or decrease the flow rating for larger and smaller ratio housings . The balancing act with gas turbines is tuning the turbines trim and housing ratio to get adequate shaft power vs low gas flow restriction . Looking at the turbine/housing combination purely from a flow rate perspective wont tell you the full story either . You could have a small diametre large trim turbine flow the same amount of gas as a larger diametre small trim turbine so they both do the same thing right ? wrong . What generally changes is turbine shaft torque or twisting energy to drive the compressor with . The larger diametre turbine makes more shaft torque in that situation for the same turbine gas flow rate .

The compressor wheel has a large say in how the turbine performs eg throw a huge high trim compressor on your typical turbine and it just cannot power it properly . Turbine lag city .

Someone in the States once came up with the 15% rule of thumb meaning the OD of the turbine should be 85% or greater of the compressor OD . This was from the days of bush bearing turbos so it can probably slip another 5% or so and still be a reasonable theory . The people that get the best results have it closer to ~10-12% where possible . So that gets you basic turbine to compressor dimensions .

If you look at lots of turbo specs and maps you start to see a pattern forming of maximum exhaust gas flow in pounds versus compressor flow in pounds and its easy to work a ratio of one to the other . You start to see the extremes such as Garretts GT2540R and GT3040R where turbine size and flow is lower that the norm in relation to compressor flow . This alone should make you think hang on thats not what it should be . It can go the other way with turbos like eg the GT3071R where the turbine size went up a family and the compressor did not . This should make you think hmmm - more exhaust gas flow and turbine torque for the same compressor that a GT2871R has so less restriction and more power to zip up the compressor .

Out of time more later .

Cheers A .

[BHDave]

I'm thinking seriously about a hks 3037 in a non gated housing but the issue is that hks skip the t3 flanged inlet in their ex gate turbos so i was going to be looking at a custom garrett based equivalent.

the hks turbo runs 52 trim comp 55/76.2 inducer/exducer and .6 cover with an 84 trim 60/55 turbine. hks offer a variety of 5 housings from memory starting around .6 up to 1.xx, where as the closest garret, the 3076R only offers 3 different housings. the 3076r has a 56 trim comp aswell where i would prefer to keep the 52 trim based on some of your earlier posts regarding the difference in response due to the change in trim, and hence the custom jobbie.

I want to remove some of the guess work from the selection of the exhaust housing size, as i will be getting the new turbo to make more power obviously (and better transient response due to bb core as opposed to my current bush core).

If I was to select a .6 odd housing for example, would i be choking the turbine side and not making the most of the bigger compressor and ultimately have a setup that is laggier than a 2835 based turbo but makes the same max power, say 275-300rwkw roughly, which is around what i'm chasing.

What i'm trying to figure is what is the best combo that can give me around 280rwkw with minimal lag and best transient response but has a bit of headromm to just crack 300rwkw if i decide i want to go further. I'm not after a specifc number but i want to find the best compromise between power and response and decide from there.

That and i like having formulas to work shit out

Edited April 9, 2006 by BHDave

[discopotato03]

BHDave , I would talk to Brett at GCG turbos because he knows what alternative compressors are available and although popular opinion is that these ball bearing cartridges can't be altered or rebuilt its not the case . You would be surprised what custom combinations are floating around out there for those who go to the extra trouble and effort to improve upon whats available off the shelf . Its often not as expensive as High Kost Spec turbos .

Something in the GT30 turbine family should be on the money , either a GT3071R CHRA no 700177-0023 or a GT3076 52T equal to CHRA no 700177-0006 would be pretty close . Maybe GCG's BB Hi Flow would do if your using all the original fixings .

I am not keen on the .63AR turbine housing on a GT30R/GT3037 particularly in 56T compressor . It would probably be ok on the GT3071R because its a cartridge with a little more turbine bias than most . The 76mm (GT37) compressor versions seem to do better with an 82 turbine housing .

Also with GT3071R's from Garrett the -23 cartridge is the one to have , their other two versions are more like HKS GT2835's in 56T and not too brilliant in my book . No T3 flanged turbine housings available for them from Garrett either .

Cheers A .

[BHDave]

Thanks mate, you're a wealth of information as usual.

I think i'm going to have to do a bit of reading to try and improve my general understanding and will definatley be having a chat to gcg before making a final decision.