Well, It looks like it is back to turbo selection time for me. Hence I have pulled out some of my old 3sgte airflow predictions on turbo compressor maps.
I will try and formalise this over time so if anyone has any comments on engine VE or the basic method I used for airflow predictions please feel free to comment. If there are any particular turbos that I have missed let em know and I will try and add to the list.
There are some quite major items I have previously ignored in order to get a rough idea:-
1) Compressor efficiencies - these vary for each turbo - between 75% to 80% and will effect charge temps.
2) Turbine side efficiency and matching - trying to cross reference between the shaft speeds etc started to make my head hurt.
3) Engien VE varies over RPM/Boost -
4) Intercooling efficiency
I have seen some really nice calc sheets about that try and take into account most of the above but unfortunately I have never found one that actually produces realistic figures!
In order to understand a compressor map this diagram is posted by Garrett:-
This graph comes from an MR2 forum and provides soem guidance on what figures are actually achieved on a Dyno Dynamics rolling road:-
As a guide you will need circa 30 lbs/min (430cfm) or air for 300bhp, 40 lbs/min (575 cfm) of air for 400bhp and so on.
Starting off with smaller turbos for the 3sgte first:-
Garrett TO4E 46 trim - this is used in the ATS racing CT27 and smaller ct26 based hybrids
this turbo looks like it would hold 1.6 bar to the redline, should make circa 1 bar by 3400rpm and provide a maximum HP potential of circa 380bhp. A good match for the 3sgte. You can see that asking it to provide 1 bar earlier than 3400 rpm ish may result in crossing the surge line/falling off the compressor map and hence it is likely to surge under these conditions.
Garrett TO4E 54 Trim - this is used in quite a few large hybrid ct26s - Turbo Dynamics MD117 for example.
this turbo looks liek it will hold 1.7 bar to the red line, should provide a maximum HP potential of circa 420 bhp and will not make 1 bar until after 4K rpm! You can also see that the surge line does not correspond to a 3sgte very well and is likely to surge if asked to provide high boost at low/mid RPM - in fact this turbo could surge up to 5K rpm if asked for high boost. My own experience of this compressor wheel located in a CT26 hybrid was that it was a poor match, and surged a lot if I asked for 1 bar .
Garrett T34/T35 - This is loosely what a Turbo Technics S148 hybrid is based on. Apologies for the quality of the compressor map - I understand this was reverse engineered.
This turbo also looks like it will hold 1.7 bar to the red line and should have a maximum HP potential of circa 400bhp. The surge line is a good match for the 3sgte and it is unlikely to surge even if you ask for high boost around 3K rpm. I was very impressed with my T35 based hybrid and I had boost earlier and without any surge in comparison to my TO4E 54 trim hybrid.
It should be noted that the above compressor maps are for compressor wheel in matching compressor housing - they will not work as effectively if you try and strap them in to a CT26 housing as it is not designed for teh job.
Garrett GT28RS - "Disco Potato"
This turbo looks like it will spool earlier than a standard CT26 or CT20b (full boost at 2700rpm), hold 1.4 bar to the redline and have potential for circa 330-340bhp. This turbo is a perfect match for a limited BHP car and will provide the widest power band of any turbo looked at to date.
This turbo is a very similar size to the GT28RS. Will make slightly less power - 310-320bhp predicted and should hold 1.3 - 1.4 bar to the red line and make 1 bar around 2700rpm. Similar in size and performance to a CT20b I suspect.
The large version of the TD05-16G has a greater HP potential at circa 360-380bhp and should hold 1.5 bar to the red line. 1 bar should be achievable just after 3000rpm. This looks like a good match for a 3sgte in place of a hybrid CT26 based turbo.
The TD06-20G is quite popular in the 3sgte world. Whilst it appears to make 0.8-1 bar around 3K rpm it takes until 5K rpm to get up to 1.5 bar. At the top end of the rpm range it appears to be a good match for a high boost 3sgte and should hold 1.7-1.8 bar to the redline, teh turbo is normally sold with a 270 degree thrust bearing and IMHO is not therefore suited to prolonged high boost applicatiosn without rebuilds. max bhp potential is estimated to be around 420-430bhp.
The smaller of the Gt2871R turbos should make 1 bar by around 2800rpm and rapidly rise to 1.5 bar around 3300rpm and hold it until the red line. Max Hp Potential should be 370-380bhp. Unfotunately the turbine is known to be restrictive on this turbo and the compressor wheel is lareg compared to the turbine wheel which results in a loss of efficiency - in practice thsi turbo rarely performs as well as the compressor map only would suggest.
The larger GT2871R should make 1 bar by 3300rpm and quickly rise to 1.5 bar by 4K rpm. It shows taht it can hold 1.7-1.8 bar to the red line and has a mximum HP potential of approx 440bhp. Again thsi still has a small T28 turbine setup which chokes the turbo and is a poor match for the large compressor wheel. As such it is unlikely to make much more power in practice than the smaller Gt2871R
The Gt3071R is reported to have been designed for a high boost 2.0 litre application. 1 bar is predicted at just after 3K rpm and it should hold 2.2 bar until the normal redline at a predicted 480bhp. Thsi turbo has a good compressor to turbine wheel size match is thus quite efficient. In practice it spools later than my predictions (which I assume is due to a free flowing turbine section). Care shodul be taken in selecting a GT3071R as numerous options have appeared that use internal wastegates in T28 & t3/T4 turbine housings without using the GT3071R turbine wheel and hence will not perform as orginally intended. In order to use teh best and most efficient GT3071R an external wastegate is required IMHO. I have however datalogged an internally gated GT3071R that made 0.8 bar by 3K rpm and pulled very very hard making circa 380bhp at 5K rpm and 1.6-1.7 bar of boost until a problem was identified and the dyno run terminated.
This is the turbo of my choice for a high boost 3sgte if run with an external wastegate.
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