Mitsubishi Canter 3 inch Exhaust Brake and System

[SkiFreak]

Correct me if I am wrong here, but the butterfly assembly is a round disk that pivots through the mid plane.
There should be equal pressure on both sides of the pivot, so 50% of the pressure would be trying to push the butterfly open and the other 50% would be trying to push it closed, meaning that the vacuum assembly would only serve to give the butterfly valve movement.
As I see it, the vacuum assembly only needs enough force to overcome the return spring pressure, plus maybe a bit more for a positive action. The butterfly valve does not create a 100% seal against the walls of the retarder assembly either. There is a small gap at the top and bottom, according to the specifications in the workshop manual.
Am I missing something here?

 

[Amesz00]

That pretty much was my thinking (Dan). The fighter I scavenged mine from had an air system, so the actuator was an air cylinder. To make it vacuum it had to swivel the other way so I pulled it apart and swapped it. Either the vac actuator couldn't hold it closed or for some reason turning the butterfly caused it to not seal.
It also didn't have a hole in it vs the stock one that did, at 1st I was concerned it would build too much pressure so I backed the stop off so it wouldn't quite close (only by a tiny bit) but it did literally nothing.

My original plan for the 84 is to run a full time air system then just run a pneumatic actuator

I know in theory there should be equal pressure but would have thought it might have a fail safe in case the actuator mechanism stuffs up?

 

[steve4wdaus]

My take on this (lack of exhaust brake) is that the vacuum chamber is not strong enough to hold it closed. A way to find out if this is the case is set up a video camera to watch what is going on when you engage the exhaust brake. This is the same problem with Candy's Canter. I have been looking for a larger diameter chamber but they all seem to use the same one. I will keep looking otherwise I will modify an air brake chamber to try on mine when I get that far.

The spring only holds the butterfly open so increasing pressure on this will make it worse.

Dan.

Dan have you ever looked into the lever system the vacuum operates. Could it be possible to give the vacuum switch more leverage, without affecting its ability to closed the butterfly 100%?

 

[SkiFreak]

Another thing to take into account here is that a 3" exhaust system has twice the volume of the standard 2 1/4" system (Pi x Radius Squared and all that). This should mean that the exhaust gas speed is halved in a 3" system.
Having said that, pressure is caused by resistance, so the pressure between the manifold and the closed exhaust brake butterfly should be the same, no matter what diameter exhaust you have. It would just take twice as long to get to the same pressure in a 3" system, than it would in a 2 1/4" system.
No idea if that has any relevance, but I thought that I would mention it anyway.

 

[Amesz00]

Another way of looking at it is the possibility for pressure leak as based on length of joint between butterfly plate and pipe wall, ie pipe circumference. 3" has 33% longer circumference than 2.25" pipe.
Just a thought.

 

[Aussie Iron]

Dan have you ever looked into the lever system the vacuum operates. Could it be possible to give the vacuum switch more leverage, without affecting its ability to closed the butterfly 100%?

No. When I converted Candy's there is no extra length in the movement of the cylinder to be able to change leverage point and it is adjusted to fully close.

Correct me if I am wrong here, but the butterfly assembly is a round disk that pivots through the mid plane.
There should be equal pressure on both sides of the pivot, so 50% of the pressure would be trying to push the butterfly open and the other 50% would be trying to push it closed, meaning that the vacuum assembly would only serve to give the butterfly valve movement.
As I see it, the vacuum assembly only needs enough force to overcome the return spring pressure, plus maybe a bit more for a positive action. The butterfly valve does not create a 100% seal against the walls of the retarder assembly either. There is a small gap at the top and bottom, according to the specifications in the workshop manual.
Am I missing something here?

You could be right but my take is that there is no pressure on the other side of the butterfly (actually possibly vacuum) and this is helping opening it up. A video camera will tell when I can get to it. Right now not a priority but I will be looking at it as I really like the exhaust brake when we are 4WDing and going down a steep climb. It is unbelievable how much braking you can get when it is working as in standard form.

Dan.

 

[steve4wdaus]

Interesting reading here
http://pacbrake.com/supplemental-brakes/prxb-exhaust-brakes/

 

[SkiFreak]

You could be right but my take is that there is no pressure on the other side of the butterfly (actually possibly vacuum) and this is helping opening it up.

The leading edge of the butterfly should be pressurised and the trailing edge should produce a low pressure area behind it (basic venturi logic), so I still think that it should have a pretty neutral balance.
But, as has been said, fitting a video camera in a position where you can see what the actuator is actually doing is probably the simplest way to prove/disprove things. If you do get the time to do this, can I suggest putting a marker on the actuator linkage and something like a 6" rule in a position where you can measure movement.
I don't have a video camera, or I would do this myself. This topic has peaked my interest, given that I have a 3" butterfly assembly fitted to my truck.

 

[yabanja]

I am glad this thread came up, I am on the verge of doing this mod myself, but the exhaust brake is more important than a power increase. Particularly when descending off road in low gear.

Allan

 

[westyss]

Is the upgrade to the three inch pipe for future other upgrades or do you guys find an increase in power from only the increased diameter of pipe?

 

[SkiFreak]

For me, the original OEM exhaust had to be replaced because my camper design required that. The price difference between 2 1/4" and 3" was negligible, so it just seemed logical to use 3".

 

[Aussie Iron]

While we are on this my thinking today is I wonder if the angle of the butterfly is what may be a problem. Creating not equal pressure on both halves !.

We will find out,
Dan.

 

[steve4wdaus]

3,000 km report. As we pull into Alice Springs, home of the Finke Desert race, completing about 3,000kms with the new exhaust, I am very happy with this mode.

Truck feels great and is pulling up the hills much better than previously. It just seems to have an edge it didn't have before. Fuel economy has slipped a little but I think that's due to extra weight and the higher speed we have been travelling at. Economy across plenty highway and 4wd down Binns track has averaged about 19.2l / 100kms.
Cheers
Steve

 

[dezatec]

i have problem with my truck too how can i chek volt on exhaust brake what value it must have?

 

[Aussie Iron]

Old Thread I know. Testing exhaust brake difference.
I have worked out how this can be tested. In my chase for a better Turbo for on my Canter I have fitted a Drive Pressure Gauge (it just measures exhaust pressure in the exhaust manifold before turbo). When you take your foot of the accelerator and the exhaust brake comes on we get a rapid increase in drive pressure. The highest I've seen to date is 45.6Psi , now all we need to do is find a standard Canter and fit the gauge too and get ourselves a reading. If someone had one local to me I would certainly be interested to fit one for testing. Because of the heat from the manifold you have to actually use a piece of tubing to get the sender further away from the manifold to cool the gas some and not melt the sender.

Dan.