Stock Boost Pressure - GTI

[JonP01]

It is interesting to compare turbo performance over the generations. Perhaps I am showing my age here, but back when I was learning to drive, the very first "cheap" (i.e generally affordable) turbo cars had just come onto the market (Pulsar ET and Daihatsu Charade, which both came out in 1984). As opposed to the curent Polo which is designated as a "low pressure" turbo for efficiency purposes (with 6 psi boost as mentioned), the Pulsar ET was of course marketed as an outright performance car for the era and ran 7 psi boost in stock form. It certainly had vastly superior performance to all the atmospheric competition at the time.

The comparison between the current 77TSI Comfortline and that original Pulsar ET is particularly interesting. Both cars in stock form outright have almost identical performance, though perhaps with the nod going to the Polo, mostly due to it's superior torque and the width of that torque band. But both cars, despite the quarter-of-a-century age gap, are almost exactly the same dimensions, have exactly the same quoted official power figure and are surprisingly not too far apart even in weight when considering the Polo has vastly more gadgets and safety features on board.

But VW achieve this same performance level with less boost and 20% less engine capacity. Obviously it can equal the power of that original Pulsar with other improvements and enginering know-how, especially things like direct injection, less internal friction, etc.

Interesting too, to see that the DNA tune I linked to above is probably more commensurate with the type of "performance" tuning that those old "performance" turbo cars came with back in the 80s in stock form. The boost on that stage 1 DNA tune likely isn't really more aggressive than that used on the original stock Pulsar and Charade Turbo - in which case the dramatic improvements in power and torque (100kw and 225 nm) are even more impressive, even allowing for the expected improvements from a quarter of a century difference in engineering know-how.

Actually, given that the increase in boost is quite modest in that tune, I tend to feel we stock Polo drivers are short-changed and the stock tune and boost are (understandably in one sense) an extreme case of lowest-common-denominator tune for worst-case driving scenarios in worst case conditions with worst case fuels. I think in this country at least they could have given us something closer to the DNA tune as stock, and given us 7 psi instead of 6 psi I think the factory could easily have given us, say 85 kw and 200 nm @ 7 psi, with absolutely no difference whatsoever to engine durability or driveability. That way we would not have to have worried about the possible "modification" aspects of ECU re-tunes, since we would have gotton what the engine was easily capable of - with a good "safety" margin - straight from the factory.

[JonP01]

The ECU does include ambient pressure in it's output so that needs to be subtracted.

That explains nomad38x's "impossible" boost figure of 22 psi - something more akin to what those fire-breathing Group A Cosworth Sierras were running on the racetracks back in early 1987!!

I actually think adding atmospheric pressure in any quoted figure is misleading in one sense, since atmospheric pressure is always changing. Pilots of course have to know all about this because it effects a nunber of flight parameters, not least of which is the altimeter setting. Those ECU readouts would read less on bad day where a low pressure weather front exists and vice versa. Though of course in another sense it does relate more accurately to the outright performance level the engine is acheiving on any particular day in any given weather conditions.

[RMayzu]

Do the europeans have a funny way of measuring boost where they include atmospheric pressure (14.7psi) in the boost figure?

So you should subtract 1 BAR or 14.7psi from the figures given.

i was going to reply but you have already figured it out VW quoted boost for the 1.4l tsi motor is 2.5 bar (absolute) which is not including atmospheric pressure of 14.7psi approx.

They make peak boost approx 21psi at 2000rpm majority of which is supplied by the supercharger and at full load and an engine speed of 5,500 rpm 1.8 bar (absolute) equating to 11.4 psi at sea level, now this all changes depending on where you live, climb up to the top of a mountain and you wont be achieving that boost level.