Boost readings with the exhaust brake on

[JHumphries]

I would like to know what boost pressures you guys are seeing while the exhaust brake is running going down a hill.
I had a '10 a few years ago and noticed the turbo would spin up while the exhaust brake was on.
I currently have an '06 with the BD remote mount exhaust brake.
The '06 doesn't seem to slow as well as the '10.

Since the exhaust brake (VGT Sliding ring) is before the turbine wheel, when the ring shuts to restrict the flow, the velocity of the exhaust is higher which causes the turbo to spin up.
The theory:
An exhaust brake before the turbo is more effective do to the increased airflow into the engine due to the turbo spinning up.

I am trying to verify this by boost readings.
I am asking for the following:
While going down a long-ish hill, look at your boost gauge. Then, turn off the brake and wait a few seconds for the boost to stabilize, and look at the boost again.
If you have an automatic, for consistency’s sake, please lock the transmission in the same gear.
Information at various engine and vehicle speeds would also be appreciated.

 

[Hoefler]

My 08 had gauges, I chose not to install them on my 10. When descending the west side of the Big Horn with my 40' 5ver in tow, locked in 3rd gear, rolling along between 30 and 35 mph, I had a consistant 5-7 psi of boost for the entire descent. I never applied the brakes, just touched the throttle every so often to turn off the exhaust brake to maintain speed.

 

[JHumphries]

Thanks for the info Hoefler.
Any one else?

 

[AH64ID]

The 5. 9 is rated at about 170 retarding hp, and the 6. 7 is around 225 retarding hp. That's the difference you are feeling.

The 6. 7 EB isn't before the turbo, it is the turbo.

One of the reasons it's more effective is the piston size. The exhaust brake is putting up to 60 psi of restriction on 4. 7% more surface area.

 

[JHumphries]

I understand the turbo is the exhaust brake, but since the sliding ring that blocks the exhaust is prior to the turbine wheel, the brake is effectively before the turbo. My thought was that because the exhaust gas velocity goes up, it causes the turbo to spin up, there by putting more air into the engine to be useable for braking.

If it were possible to put a brake before the turbo on a 5. 9, would it work better?

Bore Area Force Force x6 Hp
4. 02 in 12. 69 in2​ 761. 5 lbf 4569. 2 lbf 170 Hp
4. 21 in 13. 92 in2​ 835. 2 lbf 5011. 4 lbf 240 Hp
4. 7% 9. 7% 9. 7% 9. 7% 41%

So how does a 4. 7% increase in area result in 41% more retarding power?

 

[AH64ID]

The sliding ring is at the turbine wheel, and surrounds it. It is certainly not before the turbo. It's internal to the turbo. http://www.youtube.com/watch?v=7EDCKvkQoaE

The boost is from 2 reasons. The main one is the turbo is spinning fast enough to move a bit of air. The seconds is the restriction from the turbo. The airflow that is making 5-7psi would not be enough airflow to make 5-7 psi if there were not an exhaust restriction that is leaving up to 60 psi in the cylinder. Boost is not a measure of flow, but of resistance.

You can still only have 60 psi of back-pressure, and that is what is creating the retarding horsepower.

There are other features, like cam profile, that will effect retarding power as well.

 

[NIsaacs]

I would like to know what boost pressures you guys are seeing while the exhaust brake is running going down a hill.

I had a '10 a few years ago and noticed the turbo would spin up while the exhaust brake was on.

I currently have an '06 with the BD remote mount exhaust brake.

The '06 doesn't seem to slow as well as the '10.



Since the exhaust brake (VGT Sliding ring) is before the turbine wheel, when the ring shuts to restrict the flow, the velocity of the exhaust is higher which causes the turbo to spin up.

The theory:

An exhaust brake before the turbo is more effective do to the increased airflow into the engine due to the turbo spinning up.



I am trying to verify this by boost readings.

I am asking for the following:

While going down a long-ish hill, look at your boost gauge. Then, turn off the brake and wait a few seconds for the boost to stabilize, and look at the boost again.

If you have an automatic, for consistency’s sake, please lock the transmission in the same gear.

Information at various engine and vehicle speeds would also be appreciated.

JH, do you or have you installed a gauge to moniter back pressure? The '06 should work as good as the '10.



Thats interesting, that the VGT has boost on the brake. There is not any with a normal exhaust brake.



AH, how or where have you gotten the 240 HP retarding for the 6. 7? Pac Brakes graft only shows about 170 hp at 3K rpm with VGT. Thanks



Nick

 

[AH64ID]

JH, do you or have you installed a gauge to moniter back pressure? The '06 should work as good as the '10.

Thats interesting, that the VGT has boost on the brake. There is not any with a normal exhaust brake.

AH, how or where have you gotten the 240 HP retarding for the 6. 7? Pac Brakes graft only shows about 170 hp at 3K rpm with VGT. Thanks

Nick

Pac Brake is trying to sell something I have read it in several different places, and saw it on a Cummins/Ram brochure. Let me see if I can find it.

EDIT: I found it. I apologize, it's 225 rwhp.

http://cumminsengines.com/every/applications/dodge_ram/ram67.page

 

[NIsaacs]

AH, thanks for the link. I wonder at what RPM for 225 hp, it would also be interesting to see what it is at lower rpm. I wonder if the boost on the brake is part of the performance like JH says?

Nick

 

[AH64ID]

I would say that's at redline, but the retarding power should come on stronger at lower rpms than the 5. 9, but I haven't seen an OEM graph.

Boost may help some, but you still can only have 60 psi of backpressure.

 

[NIsaacs]

I would say that's at redline, but the retarding power should come on stronger at lower rpms than the 5. 9, but I haven't seen an OEM graph.



Boost may help some, but you still can only have 60 psi of backpressure.

Yes, thats true. I wonder if the boost improves performance at less than 60 psi tho, in the lower rpm as it helps keep the backpressure higher. Humm... I think that is what you already said:-laf



Nick