VK56 Turbo Selection (Single, DE) – Finding the Optimal
Find the optimal turbo has three steps and the VK56 turbo selection is no different. First we find the volumetric efficiency of the engine using this calculator, then we choose our boost and RPM targets and bolt them into the turbo calculator along with the VE numbers we just worked out. With the flow and boost numbers from the turbo calculator, we can start to analyse compressor maps.
VK56DE Volumetric Efficiency – Step 1
| CC | RPM | BHP | VE |
| 5552 | 3600 | 260 | 0.9 |
| 5552 | 4500 | 300 | 0.83 |
| 5552 | 6000 | 210 | 0.43 |
Looks like there is a huge restriction somewhere. Lets use another dynograph which has different cams
| CC | RPM | BHP | VE |
| 5552 | 3600 | 270 | 0.94 |
| 5552 | 4500 | 345 | 0.96 |
| 5552 | 5700 | 310 | 0.68 |
VK56DE Dynograph & VE Analysis
Looks like the VK56 is built for torque. With the stock cams there is a huge and unacceptable restriction at the top end. Using the JWT S7 intake cams with S2 exhaust cams helps a lot but there is still a huge restriction from 4500RPM and up. Stock headers look bad but this a conversation for a different article. Using the JWT cams data, lets find the optimal turbo from Garrett.
Turbo Targets
Nivlac has just done a video on turboing the VK56, he had the stock engine making 15PSI with no apparent issues. So for this article, we are also going to use 15PSI as our boost target. He also had the engine running to over 7000RPM, so we’ll add an extra row for that and make an educated guess on the VE.
| RPM | VE | lbs/min | PR | Boost Target PSI | Predicted Power |
| 3000 | 0.94 | 43.32 | 2.02 | 15 | 452 |
| 4500 | 0.96 | 66.36 | 2.02 | 15 | 693 |
| 5700 | 0.68 (0.75 used, good header) | 65.67 | 2.02 | 15 | 685 |
| 7200 | 0.7 (guess) | 77.42 | 2.02 | 15 | 808 |
VK56 Turbo Compressor Maps
Having a quick scan at Garrett compressor maps, the turbo that stands out is the G45-1475 79mm. Because we are making the same pressure ratio over such a wide air flow range 43lbs/min to 77.42lbs/min, it rules out the older tech, namely the GTX Gen II turbos.
The G45-1350 does not leave us much headroom for boost/flow upgrades.
G45-1475 79mm – VK56 Plots
Analysis
First off, at 3000RPM we look in a good place, we could probably even only make 7.5PSI at 3000RPM and not worry about surge.
For the rest of the RPM points we are golden, we could not ask for better.
If we were to make VE improvements to the engine and keep boost the same (move the green dots right) we will still be okay.
And raising boost with the same VE (moving dots up and right) still leaves us in special place.
And if we do both, up the boost and improve VE, we will still be good.
How Much Headroom?
Lets add one more plot point (purple) to the compressor map to illustrate the point.
If we assume we rev the engine to 7500 and we improve the VE to 0.75 at this point, and we raise the boost to 21PSI, where does that leave us?
These are the numbers
| RPM | VE | lbs/min | PR | Boost Target PSI | Predicted Power |
| 7500 | 0.75 | 103.87 | 2.4 | 21 | 1084 |
This is the plot (Purple dot)
Analysis
And confirmed, we are still good with a boost and VE increase. And arguably the turbo still has more to give if we wanted to go further.
VK56 Turbo Selection – Conclusion
I have done a few turbo selection articles now and I have yet to come across a turbo that seems to suit an engine so well. Even at conservative targets (15PSI) the turbo looks happy.
