Note: All the numbers in this article are hypothetical and assume other parts are installed to match the turbo size. Use this as a very rough guide only.
The calculators used in this article can be found here > Calculators.
The turbo compressor maps from Garrett can be found here.
RS3 Turbo Upgrade – The Short Answer
Out of the three turbos used as examples in this article…..
For 500bhp at around 25PSI the choice turbo looks to be the G25-660
For 600bhp at around 30PSI the choice turbo looks to be the G30-770
First we need to find the VE of the engine, then, from the VE numbers, find the pressure ratio and airflow numbers for our boost targets. Then we can plot these points onto turbo compressor maps.
First step is to find the volumetric efficiency of the RS3 engine. To do this we need dyno graphs that show horsepower, RPM and boost pressure. These are not easy to find so I had to settle on using two different sources, one for boost the other for power. Both graphs are on stock cars so there shouldn’t be big issue combining the numbers.
Boost pressure vs RPM for a 2016 RS3 is listed on this page
Horsepower vs RPM for an RS3 8V is listed on this page
Putting these numbers into a table and using the engine volumetric efficiency calculator we get the engine VE in the right column
RS3 VE Observations
Generally good. Does taper off at the top, this could hint at the turbo becoming a restriction
Turbo Selection – Finding the airflow numbers
Now we know the VE of the engine we can move on to find the air flow numbers. We choose the same RPM points as above. We choose our boost target at these same RPMs.
In the numbers/boost targets below I have chosen to give up some low RPM power to gain power at high RPM. Bolting the numbers into the turbo size calculator we get these numbers
|RPM||Desired Boost Relative||VE||PR (Pressure Ratio)||CFM||lbs/min||BHP (Predicted)|
The last two rows show two VE numbers and two boost targets. The second VE number 0.87 is a hypothetical VE for the improved breathing a bigger turbo will give then engine. And the higher boost target will give us some numbers so we can “future proof” our turbo if we decide to turn up the boost at a later date.
Turbo Compressor Maps – RS3 Turbo Upgrade
Now we have all the numbers we need to start analysing turbo compressor maps
We are going to choose turbos from Garrett because they give the most comprehensive and easy to read compressor maps IMO.
Plotting the lbs/min and PR number onto the compressor maps we get this:
The G30-770 is a little big at 2500rpm, arguably a little big at higher RPM as well but for our hypothetical 30PSI boost target and improved VE (blue plot) the turbo is right in its sweet spot.
Let’s try a smaller size
The smaller G25-660 is superior to the G30-770 everywhere except 30PSI (blue plot) where it gets a bit marginal.
Going smaller again
The G25-550 is too small. Probably an improvement over the stock turbo at high RPM but not as good as the other two turbos. Good mid range though but is that really why we are getting a big turbo?
RS3 Turbo Upgrade – Conclusion
Up to around 30-32 PSI the G30-770 looks to be the choice turbo but some compromise on boost pressure below 3500rpm will have to be made. Max power at 30psi could be around 580bhp
For people who are happy with 25-27psi, the G25-660 looks to be the choice & from around 2500rpm and onwards it should give stock turbo like power. Max power at 25psi could be around 500bhp
I couldn’t find any videos of an 8V with the G25-660 but here is an 8P RS3 with a G25-660