Pumpgas Tuning: 1g head vs 2g head

[danl]

Lots of people do things to help the motor take more timing when in fact they should be doing things to decrease the amount of timing the motor needs. At least this is what many OEM's have been doing for 20-30 years.

 

[donniekak]

The largest factors i have found to have an effect on my timing curve are, compression, valve timing(cams), and hotside of the turbo. This is on the same fuel, same boost level.

Higher compression always takes less timing to get mbt.

Cams change ve at different points of the rpm range, making some changes in the map a good idea.

The hotside of the turbo has a huge effect also. A 6, or 7cm td05h hotside is making almost 2x the boost pressue in the exhaust manifold at decent boost levels. This seriously dilutes the charge in the cylinder with inert exhaust gasses. A larger exhaust housing/turbine allow for less back pressure, increasing ve, and lowering the need for timing advance.

It's not really the efficiency of the compressor that makes the big difference. A good intercooler makes up for the differences in compressor efficiency. However, a really inefficient compressor takes more exhaust energy to produce boost, causing higher exhaust backpressure at the same boost level.