What is "drive pressure". I keep seeing it in Diesel Power mag. Something about how a lot more drive pressure gauges are popping up and guys are tyriing to achieve the perfect 1:1 ratoio. What does this mean.

 

Basically its the pressure before the turbine section of the turbo, the pressure driving the turbo.

 

ah i see. why is it important to have an equal ratio.

 

Ideally you'd want drive pressure to be less than boost. During valve overlap, when the intake and exhaust valves are both open, if the drive pressure is greater than boost then exhaust will rush back in the cylinder and contaminate the intake charge.

 

Not trying to ruffle feathers here. Ideal back pressure is 1:1, but if you have ever driven a truck that has 1:1, it sucks. Lots of turbo surge and snuffs out on every shift. There is just not enough energy to keep the turbo lit.

The best running trucks I have ever seen run about 10psi more back pressure than boost, at full boost. This helps get things spooled and keep them that way. I just don't see loosing much to valve overlap.

J.D.