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# Golf R MK8 Turbo Upgrade – Best Turbo Size

In this article we are going to be looking at Golf R MK8 turbo upgrades and specifically, which Garrett turbo would be suitable as a big turbo upgrade.

## Key Takeaways

Up to 30PSI the G25-550 looks to be the choice MK8 Golf R turbo upgrade from Garrett

30-35PSI the G30-660 looks to be the pick.

At 25PSI with a G25-550 turbo we could see 398BHP at the flywheel at 6500RPM

At 2500RPM and 7PSI with a G25-550 we could be down 61BHP vs the stock turbo

At 3000RPM and 20PSI with a G25-550, power could be the same as the stock turbo

At 4000RPM and 25PSI with a G25-550 power could be 61BHP more than the stock turbo

Get Garrett compressor maps here

I made assumptions about the stock boost pressure vs RPM, check the article for more details

## The Turbo Selection Process

To analyse turbo compressor maps we need to know the lbs/min air flow and PR (Pressure Ratio) at our boost and RPM targets.

First step in the process is to calculate the approximate VE (volumetric efficiency) of the engine at some RPM points

Step Two – Once we have the VE numbers, we can plug them into the turbo size calculator along with our boost targets and the calculator will spit out our lbs/min and PR numbers that we need to plot on turbo compressor maps.

## Golf R MK8 Engine VE

To use the VE calculator we need a dyno graph which shows power against RPM and boost.

The best graphs I found were here by UGP

Overlaying the boost graph onto the dyno graph we get this

By converting KW to BHP and..

Converting wheel BHP to flywheel BHP (I’ll use 1.15 as the multiplier) and..

Converting millibar to PSI

..and bolting the numbers in the volumetric efficiency calculator

We get the numbers in the table below

NOTE: I am presuming the airflow/boost graph is for the same car, the Facebook post is not clear. The same company did this video with FullBoost and they say the stock car is making 21PSI stock which is less than shown on the graph above.

### Boost & Dyno Numbers from the Graph

 MK8 Golf R Stock RPM Power KW wheels Power BHP Fly Boost Millibar Boost PSI (relative) VE 2500 90 139 2800 26.3 0.7 4000 170 262 2850 26.6 0.82 6500 195 300 2730 24.9 0.6

So looking at the VE results, they are lower than I would expect. The airflow/boost chart we have is probably for the tuned car (red line on the dyno graph above)

So let’s do the VE calcs again using the 21PSI number (35.7PSI absolute) that UGP give in the video above.

We are giving up a bit of accuracy here because we don’t know what boost the car was making at what RPM, but given the boost curve is pretty flat on the graph we do have, I am going to assume it’s the same at 21PSI

 MK8 Golf R Stock RPM BHP Fly Boost PSI Relative Boost PSI Absolute VE 2500 139 21 35.7 0.8 4000 262 21 35.7 0.95 6500 300 21 35.7 0.66

Now the VE numbers look more as I would expect.

**These are the VE numbers I will be using for the rest of this article.

You can follow the process with different VE numbers if you want to. The principles are the same.

### Observations

Out of the VE calculations, the big thing that sticks out is at high RPM, the stock MK8 Golf R turbo looks to be a big restriction, efficiency goes off the metaphorical cliff.

## Boost & RPM Target

The next step in the process is choosing our boost and RPM targets so we can bolt them (along with the VE numbers from above) into the turbo size calculator.

The Golf R MK8 runs 21PSI stock from the factory. Logically speaking we want our MK8 Golf R turbo upgrade to run more boost, lets say 25PSI max.

I’m happy to give up a bit of boost low down for more power at the top. My hypothetical boost targets for this article are

 RPM Boost Target PSI VE Predicted BHP 2500 7 0.8 83 4000 25 0.95 291 6500 25 0.8** 398

**I have increased the VE here. The stock engine was 0.66 and I’m going to assume this is down to the stock turbo. With our MK8 Golf R turbo upgrade I am going to assume we will increase the efficiency of the engine breathing at the top end by a lot. I have chosen a conservative improvement of 0.14 which makes our assumed VE with our MK8 Golf R turbo upgrade to be 0.8 VE at 6500RPM.

## Turbo Size Calculator

Bolting the numbers into the turbo size calculator we get the PR and lbs/min numbers we need to start analysing turbo compressor maps.

 RPM VE Boost Target PR lbs/min CFM 2500 0.8 7 1.5 8 104 4000 0.95 25 2.7 28 362 6500 0.8** 25 2.7 38 495 6500 0.66 24 2.7 31 409

## Analysing Turbos

For a two litre engine, the go-to turbo is usually the GT3076R but because the boost target we are going for is higher than we usually go for in these articles, I’m going to start with the G30-770.

Note: The blue plots on the compressor graphs are if we have 0.66 VE at 6500RPM

### G30-770

The G30-770 looks to be too big, I believe we are too close to the surge line on the left and we are leaving a lot of efficiency unused (to the right of our plots). Let’s look at a smaller turbo.

### G30-660

The G30-660 is better at high RPMs but I think maybe we can do better low down and still be okay at the top end. Lets look at the next size down.

### G25-660

To me it looks like the G30-660 and the G25-660 are identical for compressor maps. Lets go smaller, again….

### G25-550

The G25-550 looks much better. Better at low RPM and in the sweet spot at 4000RPM plus. And if we want to add say another couple of PSI of boost later, we can do it.

That’s the smallest G-Series turbo available. Lets look at the GTX range and see if we can improve the bottom end response without compromising the top end.

Worse at low RPM

### GTX2867R

Limited/no room to increase boost at high RPM, low RPM not as good as G25-550. But it should be a good turbo all the same.

### GTX3071R

Worse than the G25-550 at low RPM but it does have a bit of scope to increase boost by 5PSI at the top end.

## In Conclusion – MK8 Golf R Turbo Upgrade

We are asking a lot to get 7PSI of boost at 2500RPM and get good efficiency at 6500RPM with 25PSI of boost.

Out of the turbos in this article, using the calculators on StrikeEngine.com, the G25-550 looks to be the choice turbo for 25-30PSI. It should do the job at low RPM & it’s in the sweet spot at 4000RPM plus.

If we think we might want to go to 30-35PSI in the future, the G30-660 looks to be the choice turbo.

Generally the G-Series turbos look to be superior to the GTX turbos.

I said we are asking a lot to get 7PSI at 2500RPM and 25PSI at 6500RPM and it looks like the G-Series turbos are the only turbos that can do it efficiently, at least from Garrett.

Up to 30PSI the G25-550 looks like it could be the best

30-35PSI the G30-660 looks like it could be the pick.

#### Honourable mentions

For max 25PSI the GTX2867R also looks a good turbo, not as good as the G25-550 and it doesn’t have much room around it (it’s at the limit for low RPM efficiency and high RPM efficiency). However, I think its a bit of a tight fit performance wise for the Golf R so I personally would not use it.

From the GT series of turbos for max 25-28PSI the GT2871R looks the most suited but again, its at/beyond the limit to get 7PSI at 2.5K but for 25PSI up top it looks good. Having said that,personally I would not be considering this turbo over the G-Series turbos because of the low speed performance hit vs the G-Series turbos.

In short, I’d be going for the G-Series turbos as a MK8 Golf R turbo upgrade.

## Assumptions/Provisos

I mentioned towards the start of this article, there are some question marks about the boost the stock engine is running. If you have a dyno graph of a MK8 Golf R which has boost and power, feel free to bolt those numbers into the calculators and do your own analysis.