boost sensor location - does it matter? (1 Viewer)

[kgrove]

Does it make much difference where the sensor for a boost gauge is mounted? Or is the pressure pretty much the same all the way from the turbo to the intake ports? I thought it might be possible there is at least a few psi loss of pressure after the throttle body, especially when the throttle is not wide open.

I installed a pressure gauge on my 1kz-te and have been a little surprised how high the boost is. I mounted my pressure sensor on the crossover pipe just before it actually crosses over the valve cover (so on the angled section before the crossover pipe crosses over) because it was the easiest location for me to insert the sensor without interfering with anything else, and in my head at the time I was thinking the pressure should be about the same throughout the intake system with minimal head loss. I'm seeing pressure readings (and assuming they're accurate) that get as high as 13psi and I think I saw 14psi once, but briefly.

I know the engine's boost sensor uses a small tube on the intake manifold furthest away from the throttle body, and from what I read, it starts limiting fuel from the IP at around 14 or 15psi. Since I had read 9-10psi was typical for the stock version of the 1kz, I had been planning on increasing the boost a few lbs to see if I could get my EGT down or if I could tell any performance difference, but if I'm already near that, it doesn't make any sense to mess with it. On the other hand, if there is a material difference in boost pressure after the throttle body, then I could still see some improvement (decline) in EGT if add a boost controller because the 13 psi I'm currently seeing in the crossover pipe could be well below what the engine is actually seeing.

I assume somebody has already seen this? I didn't see it in any searches. Tons of stuff about the correct location for EGT probes, but none for a boost sensor.

 

[stevebradford]

Also applies to gasses.

The only difference of pressure you might see briefly in your intake system is after an Intercooler if it’s restrictive.

 

[kgrove]

View attachment 3791652

Also applies to gasses.

The only difference of pressure you might see briefly in your intake system is after an Intercooler if it’s restrictive.

Yes... pressure in a fluid is the same throughout the fluid. Complications to the simplified statement are gravity (not relevant here due to small size and low density of air) and head loss due to friction or restrictions. Intercoolers could create a restriction resulting in a pressure drop... but by definition, doesn't the throttle also cause a restriction and therefore a pressure drop? So wouldn't a pressure sensor mounted on the crossover pipe (before the throttle body) always read higher than a sensor in the intake manifold like the sensor connected to the ECU that controls the injector pump?

I assume if there is a pressure drop across the throttle, the drop is most substantial when the throttle is the most closed... so in other words, when I'm not pressing the engine hard and am maybe not that concerned with boosting pressure anyway, maybe it doesn't matter that I'm reading pressure in front of the throttle instead of behind the throttle like the ECU is doing. On the other hand, when I'm most interested in increasing boost, like while climbing a hill, the throttle is probably less restricted to begin with, so the 13psi I'm reading right now in front of the throttle might be very close to what the ECU is seeing. If I were to add a boost controller, I might not gain much because any more than 1-2psi more pressure and it would start rationing fuel to the engine anyway.

 

[mudgudgeon]

Does the 1kz-te have a throttle plate?

Many diesels do not

 

[kgrove]

I believe this is the throttle body... not mine, just a quick google search for 1kz throttle body but it looks the same as mine. The bigger valve is controlled by the throttle cable - the pulley on the left side of the photo. The tiny butterfly valve I believe is related with the EGR system - not relevant here.

So my interpretation / assumption -- at low throttle pedal positions, the throttle will be restricted and there might be a material pressure drop from the crossover pipe to the intake manifold due to the throttle restriction. At higher pedal depressions, that throttle valve would be wider open and less restrictive, so there may be little or no pressure difference between the crossover pipe and intake manifold.