Where to place probe for exhaust backpressure

[RSchwarzli]

Where is the correct place to pick up exhaust back pressure on a twin turbo system with in line exhaust brake?



Do I go right off the E brake housing or does it need to be in the manifold? Maybe inbetween the turbos? Any thoughts?



Thanks!



Robert

 

[dpuckett]

Since we are normally concerned with backpressure on the engine (i. e. dont float the valves), I'd put the gauge in the manifold, either right next to the pyro probe, or on the front half of the manifold.



Daniel

 

[JLEONARD]

FWIW in a marine application, exhaust backpressure is measured after the turbocharger and is supposed to be measured in each installation. I will have to look it up, but I believe that spec for all 6BTs is 4 in hg which converts to 2 psi.



EDIT: Correction..... the spec is 3 in hg or 1. 5 psi.

 

[Joseph Donnelly]

Since you are trying to measure backpressure caused by the exhaust brake, put the port just in front of the brake. You will then measure the difference in backpressure with the brake on vs. off to determine the efficiency of the brake.

 

[HPetrat]

JLeonard is correct in measuring the exhaust "system" back pressure, but as J. Donnelly has stated, if you are measuring the exhaust brake performance the probe should be just infront of the exhaust brake.



I mounted mine in the pyro hole on my BD turbo mount exhaust brake (pyro is mounted pre-turbo in the manifold) and it works very well there.



HP

 

[Woodenhead]

I installed one to measure drive pressure in the exhaust manifold. I had to flip my ATS manifold to install the twins so I drilled a new hole in the top (which was the bottom) to install the pyro. Then I used the old hole that was on top but now on the bottom and installed the fitting for my drive pressure.



You could just drill and tap a hole in the manifold just like you would for a Pyro. You'll get both turbo drive pressure and back pressure created by the brake.

 

[LarryB]

One thing I did that works well. I use a A-B solenoid valve, connected to the E-brake curcuit. When the ebrake is inactive the boost gauge reads turbo booste as usual. When the ebrake is activated then the solenoid valve switches the gauge air line from the intake manifold to a line going to my ebrake. This way the boost gauge reads the ebrake back pressure. This saves having to have a seperate gauge for the ebrake.

 

[RSchwarzli]

Thanks for all the responses!



Larry - May have to consider that idea to switch back and forth between system backpressure and E brake back pressure as I am running a separate boost guage for backpressure.



Is there much of a differance between the readings of having the back pressure measured pre turbo and aft turbo? Makes sence that there is a big differance as the turbo compresor wheel is holding back air, just wondering how much.



Basically is it worth doing the Larry setup so I can see both system and e brake backpressure? I already have the hole as I flipped my manifold upside down for the twins and I tapped a new hole.....



Robert

 

[JLEONARD]

I think where you take your measurement depends on what you hope to accomplish.

Maybe you need to drill and tap several locations and make a chart of your findings.

 

[AH64ID]

I have mine in the manifold. . as shown below. It does both drive pressure and exhaust brake pressure.

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[HPetrat]

If you want the system back pressure, install a port directly after the turbo charger and temporarily route a gauge to the cab. Take the truck for a run and have some one monitor the gauge to record max back pressure under loaded (ideally full load) conditions.



Afterwards remove everything and install a plug into the port. Once the readings have been taken they will never change, unless you change the exhaust or change turbo(s) to something radically different.



In other words, there is not much point to continuously monitoring the systems' back pressure as it will remain unchanged from the max. reading.



HP

 

[JLEONARD]

I pretty much agree with HP. You might be surprised however if you find the max back pressure is at something less than WOT that might depend on load.

I say this based on what I saw on my boat when we measured backpressure... . it was highest just above idle speed... it was 2. 5 in hg at approx 1100 rpm.

Once the turbo started pushing some air thru the enigne it dropped off to basically 0 right on up thru WOT. But I was still not overloaded that might be why. I was at 2650 rpm, zero black smoke, EGT at about 900 F post turbo (which is est 1200 ish pre turbo).

 

[RSchwarzli]

Thanks guys! That is the info I need!



Robert