[arghx7]

Originally Posted by Homemade WRX

Yes, a turbo engine does have a higher BSFC but what is the point we're arguing for a performance engine?

Under conditions of enrichment it probably will, but if you look at most charts showing BSFC vs BMEP vs RPM the BSFC tends to be less at higher BMEP. But those charts contain isobars so the key is to keep the engine within a particular operating range. When you have to enrich to control exhaust temps and preignition that kind of throws everything out the window. Variable valve timing and direct injection reduces enrichment requirements.

Power gains is on a case by case situation, obviously. Now that you're looking at power from a larger NA engine that has far greater pumping and frictional losses at points other than full throttle, you're going away from all those points that you were hitting on with wasted energy. So now you're taking those trade offs, weight, package size, etc to try and make the same power as the smaller turbo engine.

Frictional losses related to displacement/engine size are one of the main reasons for the downsizing trend.

what pressure is left behind in the cylinder? are you stating that after the exhaust stroke that their is still lots of pressure?

depends on internal EGR rates

Now how are we off on a geeky engine/thermo design debate?

because it is relevant

If you want to see the trends of best BSFC and fuel consumption, looks at the truck diesel industry (as it's usually easier to find data from them than the train or boat world). Their is a reason they run turbos and not 32L NA diesel engines.

There is a lot of truth to that but diesels have their own set of emissions and driveability issues that lead to increased cost versus gas engines in the modern regulator environment.