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Barra Turbo Selection – Finding the Best Size 20-30PSI

Barra turbo selection. Airflow points plotted

In this article we are going to use the calculators on StrikeEngine to find the optimum Barra turbo upgrade size (using an XR6 Turbo in our example) for 20PSI and 30PSI. We’ll follow the standard turbo selection process.

Barra Turbo Selection – Key Takeaways

The Garrett G30-770 looks to be an ideal fit for motors running 20PSI and the turbo leaves headroom for running up to 30 PSI of boost and has headroom for breathing improvements to the engine (The Barra looks to be a bit inefficient from the factory).

In short good for 20PSI and future proofed.

Turbo Selection Process

Step 1

Step 1 is to find the volumetric efficiency of the engine. We’ll use the StrikeEngine engine VE calculator and the data points from this dyno graph from a 2010 XR6 Turbo.

ccBHPRPMVEBoost PSI
390032753900.6125.7
390033538300.7431
390020125000.7214
Comments – Very low volumetric efficiency. I wonder what the compression ratio the engine has. And generally how the plumbing is set up, exhaust manifold, intake, intercooler, stock turbo size etc.

Actually scratch that.

I used the tuned numbers from that dyno graph. Let’s use the stock numbers and see what that gets us.

ccBHPRPMVEBoost PSI
390030053900.677
390025438300.768
390016725000.778
Using the stock dyno numbers from the same graph things look a bit better. Again, it looks like there is a restriction in the system somewhere. Is it the turbo? I don’t know the stock size.

Step 2

Step 2 is to bolt the VE numbers into the StrikeEngine turbo size calculator with our boost target. For this article we want
20 PSI at 3830 RPM and 5390 RPM &
10 PSI at 2500 RPM.
I am also going to presume the stock turbo is a bit of a restriction. So for 5390 RPM I’m going increase our stock number VE number to 0.7

Bolting our numbers into the turbo calculator we get these flow and pressure ratio numbers.

PRCFMlbs/minBoostRPMPower Predicted @ Fly
2.3661347205390492
2.3647336203830380
1.6822217102500179
Now we have out PR and lbs/ft flow numbers we can bolt them onto turbo compressor maps to find a suitable turbo. In this case we are looking at Garrett G-Series turbos. The Green plots on the graphs below are our numbers for the Barra.

You can use these numbers to do your own research. Get a compressor map for a turbo and plot the PR (Pressure Ratio) and lbs/min onto the map.

Which Size Barra Turbo Upgrade? – The Contenders

G30-900

The G30-990 seems a bit big for the Barra at 20PSI and 10 PSI at 2500 RPM is close to the surge line.

G25-660

G25-660 looks good for a Barra at 20PSI but the turbo is at the limit. There is little headroom for improvements to the engine breathing or for turning up the boost. If you are spending this much money to fit a turbo, I think I’d probably go for something with more future proofing. But the G25 is nice low down. Maybe it would make a bit more than 10PSI at 2500RPM.

G30-770

The G30-770 looks like it could be perfect for the Barra. We can probably have 10 PSI at 2500RPM. And we are right in the sweet spot at 20 PSI to redline. We have space to the right of the plots for breathing improvements to the engine and we have space above if we want to turn up the boost in future.

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This page was last modified Oct 15, 2024 @ 9:10 pm

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