I had this wild idea that I would install a solenoid valve in my boost gauge line and measure the exhaust back pressure during the time the brake was actuated. In other words, the gauge would be dual function and be controlled by the exhaust brake solenoid signal from pin-20 of the ECM. My concern is that I have no idea what pressure to expect in the exhaust manifold during deceleration with the exhaust brake engaged. Any ideas?

 

Not sure on your '02 but on earier years the back pressure is limited to 60 psi by the valve springs.

I have a friend you did exactly what you're thinking of, he used an electric solenoid valve that was originally used to switch between two fuel tanks. It was toggled back and forth with the power to the exhaust brake solenoid valve, not the switch in the cab. This way it only reads backpressure when the brake butterfly is closed.

 

I just added another gauge where you over valved boys install fuel pressure gauges.. ..

Rick

 

60 psi "should" be the max pressure developed. DTR member Thumbs has a dedicated backpressure gauge on his truck, you might want to ask him what he's seeing for pressure. I'm not sure why exactly you want to do this, on a PacBrake the pressure rises with RPM, simple as that. Thumbs did it because he wanted to see if the BD Brake works as claimed. The BD brakes use a spring loaded flapper to control backpressure instead of a fixed orifice like the Pacs and Jakes, so the BD is supposed to generate max braking sooner than the competition.

 

'Cause I can

 

That's what I had in mind also.

 

Works for me. Just didn't want you to be disappointed by the somewhat boring and predictable reading on the gauge.

 

Thanks. It's just another case of having the parts and too much time on my hands.

 

Mines set up for 20 psi at idle with the truck fully warmed up. It rarely goes over 40 psi when using the brake in 4th and 5th gear. 6th usually pulls about 30-32 psi.

 

But at least the gauge will be reading something other than the zero boost you would normally have with the brake on.

 

Question: those of you who run backpressure gauges, have you ever pulled the gauge and found black liquid at the gauge connection? Would this be condensation?

brandon.

 

Never found black liquid but have found lot's of soot.

 

The black stuff is soot that travels up the tube to the gauge...The water or condensation is from warm or hot air from the exhaust. I made copper moonshine coils to cool the exhaust down before I connected a boost line tube that runs inside to the gauge. This will work just like it says..moonshine coils.. The hot air will cool and turn to liquid...
I dont see over 30lbs of backpressure as a constant...but it may spike just a little over 30lbs until the wastegate cracks open to bleed off the extra..
When the 60lb springs go on the valve train I will replace the wastegate to the 60lb flavor...

Rick

 

Cool! I kinda hoped that what was happening. My copper tubing runs from the manifold all the way over to the master cylinder/abs module infront of the firewall then it turns into plastic 1/4" line. I guess when I finally hook up the methanol I can actually distill alcohol with my truck.

brandon.