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Focus MK1 Turbo Selection (1.6) – Turbo Kit

GT2052 compressor map with Focus 1.6 Zetec S plots

A quick article going through the process of selection the optimum MK1 Focus 1.6 turbo size.

Key Takeaways

Stock Engine. The GT2052 looks ideal.

Modified Engine. If we put better cams and/or pistons, then the GT2252 looks great.

MK1 Focus Turbo Selection Process

As always, there are three steps to the turbo selection process.

  1. Finding the VE of the engine
  2. Finding the air flow and pressure ratio for our boost targets
  3. Analysing turbo compressor maps


Using the power numbers from this video, we get the following power numbers. And banging in the power numbers in the engine VE calculator, we get the volumetric efficiency of the engine (right column).


Airflow Data

Before we can get our airflow, we need to choose our boost targets. I want 3PSI at 3210RPM, 7PSI at 3890 and 10PSI at 5900RPM.

Why the higher boost at higher RPM. The thinking is the engine efficiency is dropping off at higher RPMs. This suggests the cams are holding the engine back. The cams are holding the engine back because the amount of time the valves are held open per revolution is getting smaller which is not giving the air enough time to fill the cylinder. So by increasing the boost I think we can improve cylinder filling while still keeping peak cylinder pressures around the same as at lower RPMs eg 3890RPM

The boost targets I want are in the table below along with the airflow data. To get the airflow data and PR (Pressure Ratio) we bolt in the boost target, RPM and engine details into the turbo size calculator found here.

RPMBoost Target AbsoluteVElbs/minCFMPR

Comparing Turbos

Now we have the numbers we need to analyse turbo compressor maps.

We could see from the VE charts that the engine is not very efficient, the VE is low. Couple this with the fact that our boost targets are also low we will start looking at small turbos.


Looks perfect

The red dots on the graph are from the table above.

These plots looks to be about perfect, for sure a bigger turbo is not needed. Even if we increase the boost in the future we are still going to be in the sweet spot of this turbo.

The only issue I see is if we were to somehow increase/improve the VE of the engine a lot. That would move all the points to the right which could put us out of the efficiency islands.

Another issue I see with the turbo is the 0.5 A/R (more info on A/R here). This has the potential to offer a real restriction to the exhaust at higher RPMs.

The thing that saves at the moment is the cams. The cams are (probably) the biggest bottleneck, even with the 0.5A/R so while it is a potential issue, with the standard engine I think things would be okay. But again, if we were to get some good gains in VE the 0.5A/R could come into play.

In short, for a stock engine on stock cams, this turbo looks about ideal with these boost targets. It also gives us some headroom if we find we can increase the boost in future.

If this is as far as you want to take it, it looks a great choice. If however you think you will be swapping out cams in the future and perhaps forging the motor, then a may be worth looking at the next size up.

Better VE

Lets bolt in some better VE numbers and see if that last paragraph looks accurate.

RPMBoost Target AbsoluteVElbs/minCFMPR
590029.7 (15PSI boost because of forged internals)0.85 (better cams)222862.0
GT2052 compressor map with Focus 1.6 Zetec SE plots

The combination of improved VE and more boost is too much for this turbo. Couple this with the 0.5A/R, I’d say the GT2052 was a non starter for these mods.


GT2252 compressor map with plots for a Zetec SE as fitted to the Focus MK1
Much better

The GT2252 looks much better. We gain a lot at the top end ie we are at peak efficiency for the turbo.

Bad things. Lower RPM response suffers. The 3PSI target at 3210RPM is probably not going to be met.

7PSI and 3890RPM looks doable. Turbo will be at around 70% efficiency here. Remember we will also have better cams in the engine so perhaps they will start to be an improvement around 3890RPM. If so, the picture at 3890RPM will look even better.

And the GT2252 also has a AR of 0.67 which is even better for engine breathing at the top end and should help the engine not to knock.

Wrap Up – MK1 Focus 1.6 Turbo Kit Selection Turbo Size

Stock Engine. The GT2052 looks ideal.

Modified Engine. If we put better cams and/or pistons, then the GT2252 looks great.

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This page was last modified Oct 25, 2023 @ 4:45 pm

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