Thread: Turbo Output
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      12-17-2012, 03:21 AM   #16
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Drives: 340i M-sport AT
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Originally Posted by mikew2069 View Post
The new Kia Optima 2.0T runs 17.5psi stock....
BMW N20 18.9 psi.

Smaller displacement engines have to have very high stock boost pressure to achieve that type of power, as they have 33% less displacement compared to the N55's 3.0 liters.
The N55 can run lower boost pressure as it makes more displacement power.
1.0 liters more and 2 more pistons.

In simplest terms adding appx 15psi (normal atmosphere is 14.7 psi) of boost is like doubling the engines combustion chamber volume. For example, a 2.0 liter with 15psi of boost is like a 4.0 NA engine.
N20 2.0 at 19psi is like a let's call it 4.5.
N55 3.0 at 15psi is like a 6.0 NA.
But, the N55 has average boost a bit over 10psi, not quite double, 2/3's, or 2.0 liters more. 5.0 NA.

Even with a modest 5psi increase over stock, the N55 would then have 15psi of boost, doubling NA displacement to 6.0

The N20 would need 30psi total boost to make it like a 6.0 NA.
N55 with 30psi would be a 9.0!

That's why a larger displacement engine can run with less boost and create more power.
It also shows why the N20 is as powerful as it is compared to the N55.
This simple example shows a 4.5 vs 5.0 NA power.

This is just for fun, I'm not promoting this as exact as there are many variables.
The N54 is also a 3.0 running close to 9psi yet developed the same power as the N55.
But, that's a twin turbo vs a single twin scroll. It's one of those variables.

Last edited by RPM90; 12-17-2012 at 03:26 AM.