Just been doing some calculations/simulations in choosing my new turbo and it's thrown up some interesting questions over delta pressures.

Now, delta pressure is the difference between the boost created and the exhaust backpressure, so - for example a delta pressure of 5 would be achieved by having 25psi of boost and 20psi of backpressure in the turbine housing. This is good because it shows efficiency of the turbo.

A delta pressure of -5 is the other way round, so for the same 25psi of boost, there's 30psi of back pressure in the turbine housing.

Now, i'm looking at a delta pressure of -15 at high revs (6000rpm+) on one particular turbo, but the next size up in compatible exhaust housings is a BIG step up, but takes my delta pressure to -4.

So - the question is, what is an 'acceptable' delta pressure and is it worth changing!