Boost isn't an air flow measurement. It's a pressure measurement, right? If it's measured near the outlet of the turbo, isn't it "seeing" resistance in the intercooler and piping ahead of it? I'm asking because I was looking at the intercooler and the piping to and from it. It seems so small in diameter for the amount of air moving through it. Or is it?

 

My boost line is plumbed into the side of the eng on the drivers side back towards the rear. There was a plug of some type there. So it would be on the intake somewhere in front of the last or last two cyls and that would be a pressure reading.

 

I'm thinking the whole intake system is pressurized by the turbo.
From one side of the turbo blades, through the intercooler piping, out the other side, into the intake manifold.

All one pressurized circle of life and power.

Therefore, the readings should be the same no matter where they are taken.

Maybe a little lower if taken right before the intake valves, as that is the only place the air gets out.
Well, maybe not lower, but you might see more fluctuation as the valves open and close, the turbo side is more constant.

Unless you "bark" your turbo, then you have some escapage.

phox

 

You really don't have any fluctuation in the gauge as it happens so fast that it is consistent through out the intake and the gauge could not react that fast anyway.

 

I think I want to revise my last hypothesis.<br><br>Think of the turbo system as a drinking straw.<br><br>Your mouth on one end is the turbo, pressurizing the straw. The intake valves the other end of the straw, taking air out of the system.<br><br>In the middle, you pinch the straw together just a bit, this would be the intercooler.<br>(the intercooler has to be at least a little restrictive, doesn't it?)<br><br>Now, blow on one end, with your fingers pinching the middle, just not all the way.<br><br>If you took a pressure measurement by your mouth the pressure would be one reading, rather high.<br><br>If you took a reading on the other end of the &quot;pinch&quot; in the middle, it would be less, as the pinch in the middle is restricting some, and air is leaving the other end.<br><br>So, in theory, the turbo side would have more pressure than the intake side.<br><br>Unless, there is more air leaving on the intake side than is being supplied on the turbo side.<br><br>You have pretty big cylinders wanting to be filled with air, and as the rpm's increase, they want more air per minute.<br><br>The turbo has to be supplying more air than the cylinders are wanting, or the turbo wouldn't be efficient at all.<br><br>So therefore, long story short, a boost guage on the turbo side would read higher than a boost guage on the intake side.<br>At higher rpm anyway, takes a while to build boost.<br><br>It's fun when you get to think out loud.<br><br>phox

 

When working with pressure all parts in relation are under equal pressure. From the turbo outlet to the piston top is all the same pressure. You can take your reading from any where on the intake side. It's a measure of pressure, not airflow. (IE: It's PSI, not CFM)

 

Yup, what Superduty said...<br>And, that's why various turbos/housings have different efficiency maps for different applications. This keeps the boost at max efficiency within the RPM range of the application and also helps to minumize excessive drive pressures which raise charge air temps, and contribute to high EGT's.... um.. I think that's right :<br><br>Bob.

 

OK, so that said, does the size of the plumbing from the outlet of the turbo to the manifold intake have any effect...within reason of course?

 

[quote author=chuck3 link=board=8;threadid=5633;start=0#49638 date=1034043541]<br> My boost line is plumbed into the side of the eng on the drivers side back towards the rear. There was a plug of some type there. So it would be on the intake somewhere in front of the last or last two cyls and that would be a pressure reading. <br>[/quote]<br><br>That's where mine is plumbed as well... <br><br>Tony

 

The size of the plumbing has relation but not a massive amount. The pressure is going to be equal regaurdless of the pipe size. A whole bunch of stuff comes into play with pipe diameter and boost. You can move more air at once with bigger pipe, more surface area = more radiant cooling, less restriction = more pressure (not boost). Like in hydraulics, you lower the pressure of a line by simply making the opening smaller. Like you have a bucket full of water, poke one hole in it and the water slowly drains out the hole, poke 100 holes in the bucket and flow increases at once. More moving mass. Plus.... Bigger is better by a rule of thumb The more packed air you have in a certin size space the more stock you have for demand before having to replenish.

 

What am I missing here? I've been in pneumatics for a lot o'years and I don't see the logic here. First, if this is a static system, ie: no flow, no air moving, then pipe size has no effect on pressure. It will naturally equallize over the full length. But, when air flows, there is resistance to that flow and there is a pressure drop. There are all kinds of charts giving pressure drop per pipe size, per psi, per foot of straight pipe, els, tees, gate valves, etc.

Try this test, make a simple test fixture consisting of a tee, male coupling plug, female coupling, and a gauge. Put the gauge on the leg of the tee, the male plug on one end of the straight through part of the tee and the female on the other. Now hook this to your compressor right after the regulator (you do have a regulator?). Plug your air hose in the other end of the tee and then attach an air tool. Look at the reading, pull the trigger on the airtool and look again. These numbers should be the same (if the regulator is working right). Now remove the gauge fixture from the regulator, re-attach the hose to the regulator, and attach the gauge fixture between the hose and tool. Look at the gauge reading, pull the trigger and look again at the gauge. The third reading (static) should be the same as the first two, but the last reading will be lower.

I have analized systems where the plant engineers, maintenance managers, etc. swore their systems were in great shape. As an example, one had computerized monotoring systems that said they were making at least 100psi at the compressor. They knew they needed 90 psi at the tools. During lunch with absolute minimal air usage in plant we registered 55 psi at a typical tool. Size does matter and there are psi losses everytime pressurized air moves.

My suggestion is to install your pressure transducer in the intake manifold (that's were mine is) or the intake air horn (?).

Sorry, I got carried away.

Gene

 

i have a boost guage hooked up that i did myself. I will take some pics in the light if you would like me to. It takes a couple connectors and a nipple. It is on the driver side of the engint just behind the general area where the lift pump is

 

let me know if you want pics

 

A picture is worth a thousand words.<br><br>phox