question on load

[marko]

stupid question but anyways lol, would load equal different psi with hybrids ? ie 19ts then stock turbos. for example to get 20 psi on hybrids. load will be lower number then for the same stock turbos ?
thanks

 

[wheela]

Good question, I don't see this discussed much, and I think as a result there is a lot of confusion of what load represents. %load is just the mass air flow (MAF) being consumed by the engine, but expressed as a percentage of cylinder fill. This provides a way to normalize the airflow per rpm, which is really useful for fuel maps, timing maps and others. For reference, here's a little table I made that calculates the MAF associated with each combination of %load and rpm. I don't know the specific assumptions bmw uses in the load calculation so this is an approximation and not 1:1 accurate. That said, it seems to be accurate to my logs within a few g/sec.

Boost pressure is used to get load over 100%. You may get a little more cylinder fill per psi with a bigger turbo since the lower back pressure will help air flow through the engine better. Also the bigger turbos will be more efficient in the high boost/flow areas, so the turbines use less power from the exhaust to compress the charge air, so the engine can send more power to the wheels per psi of boost.

The best way to get more load from the same boost is to increase the volumetric efficiency of the engine, so things like cams, ported head, etc really help this.

 

[marko]

Good question, I don't see this discussed much, and I think as a result there is a lot of confusion of what load represents. %load is just the mass air flow (MAF) being consumed by the engine, but expressed as a percentage of cylinder fill. This provides a way to normalize the airflow per rpm, which is really useful for fuel maps, timing maps and others. For reference, here's a little table I made that calculates the MAF associated with each combination of %load and rpm. I don't know the specific assumptions bmw uses in the load calculation so this is an approximation and not 1:1 accurate. That said, it seems to be accurate to my logs within a few g/sec.

Boost pressure is used to get load over 100%. You may get a little more cylinder fill per psi with a bigger turbo since the lower back pressure will help air flow through the engine better. Also the bigger turbos will be more efficient in the high boost/flow areas, so the turbines use less power from the exhaust to compress the charge air, so the engine can send more power to the wheels per psi of boost.

The best way to get more load from the same boost is to increase the volumetric efficiency of the engine, so things like cams, ported head, etc really help this.

thank you !