Turbo Talk

[AndrewBird]

I have a friend with a B6 Audi A4 with the 1.8t engine. We were talking about turbos in general and we couldn't agree on one thing. His stock turbo is tiny and spools very quickly, but runs out of breath pretty quick. We were talking about putting a bigger turbo on it to provide more air at higher RPMs, but what we were disagreeing on was how the power would come on as the turbo spooled.

He was picturing a large turbo having a much more gradual rise in power since it takes longer to spool up, but I was picturing a large delay at first, then a more sudden increase in power when the turbo finally started spooling.

So how would it be? Do larger turbos spool up more gradually, or do they spool quickly, just at a higher RPM?

And I realize I am asking a very general question and there are a lot of factors involved, but as a "rule of thumb" so to speak, what is the answer?

Turbo engines really are hard for me to wrap my head around as they act so differently compared to NA engines that I am more used to.

[iansane]

There are a ridiculous amount of variables that affect spool time but it's much closer to an exponential growth than a linear growth.

[Cambiocorsa]

With an electronic boost controller you can set how boost comes on. I like it to be more gradual (less stress on drivetrain components) but it can come on like a light switch if I want it to. I run a 6262 PTE turbo, as of now you'll feel some torque start building around 3200rpm as it starts making positive pressure, and at about 4200 it hits full boost and HITS.