Experimental exhaust brake

[sk66]

I bought this EVC 60mm exhaust controller valve off of Ebay... I chose it because I was hoping I could just slip it inline on my DelicaWorks SS exhaust. It also looks to be heavy duty and well built... at least comparatively. I also wanted it to be electric switch control as that's just easier.

Well, it mates right up but the extra inch of length is too much; causes the exhaust hangers to line up poorly and the tailpiece to hit the leafspring perch. So it looks like I'm going to have to get the tailpiece shortened and one of the new flanges welded onto it.

I might also need to make a larger plate for it so it creates a bit more of a complete blockage... In my quick test I didn't feel much braking force; but I was also just coasting along a neighborhood street at 35mph and not going down a 14% grade. I'm hoping to test that tomorrow.

 

[Growlerbearnz]

That's a good price if it works! I looked at exhaust brakes but haven't done anything about it as the commercial units are very expensive. Let us know how it goes on a longer, faster grade.

Just beware of creating too much blockage: if the pressure in the exhaust becomes higher than the pressure in the cylinders, it can force the exhaust valves open. Exhaust brakes usually have a calibrated orifice or spring-loaded valve to limit backpressure and prevent valve float.

 

[sk66]

I looked at exhaust brakes but haven't done anything about it as the commercial units are very expensive. Let us know how it goes on a longer, faster grade.

Expensive and huge...
You wouldn't know of any specifics regarding the lockup characteristics of the AW72L would you? I know it's a 4th gear only function and probably why I didn't feel any notable benefit on side streets.

 

[DustAngel]

I looked at the banks kit for a 7.3 diesel years ago and I remember that it came with a module for torque converter lock up control. Maybe you can theorize their system and make your own?

 

[sk66]

I looked at the banks kit for a 7.3 diesel years ago and I remember that it came with a module for torque converter lock up control. Maybe you can theorize their system and make your own?

Pretty sure that's only possible with electrically controlled valves...

 

[sk66]

 

[Growlerbearnz]

Expensive and huge...
You wouldn't know of any specifics regarding the lockup characteristics of the AW72L would you? I know it's a 4th gear only function and probably why I didn't feel any notable benefit on side streets.

Correct. It locks up in 4th gear, above 65kph, at half throttle or less (Diesel L300).

I couldn't find an easy way to manually control lockup. The lockup control valve compares pressure from the governor (varies with road speed) and the 3-4 shift valve (varies with throttle position, but only pressurised when in 4th gear). If the conditions are right, the valve operates and reverses the flow direction of the fluid going through the torque converter, which (somehow) makes it lock up.

I'd still expect to feel some difference though, the torque converter isn't *that* loose.

 

[sk66]

I'd still expect to feel some difference though, the torque converter isn't *that* loose.

The effect with it unlocked is similar to downshifting... i.e. you can feel it, but it is inadequate to prevent the vehicle from accelerating on a grade of any real significance. But you definitely know it's closed if you try to accelerate with the gas pedal.

I've been afraid to really test it fully yet; I want to make sure it doesn't generate too high of a back pressure w/o risking breaking a rocker. I ordered a compression tester and plan to temporarily install it in place of my EGT sensor. I know the valve springs are 61lb, so I'm thinking no more than 50lb. I'm guessing it can't even generate that much as it is... but I really don't know.

I didn't even think to check the inlet pressure... guess I should look at that too?

Correct. It locks up in 4th gear, above 65kph, at half throttle or less (Diesel L300). I couldn't find an easy way to manually control lockup.

The reference I have for the 72L has lockup at 85kph (52mph); 65kph (40mph) would be much better. Around here, most of the steeper descents also have slow speed curves (≤ 35mph), which is what makes it kinda scary and harder to manage the brakes adequately. Theoretically I could replace the signal valve spring with something a lot weaker, then it would lockup anytime it was in 4th gear (~40kph/25mph)... but I have zero experience/knowledge working on transmission internals.

 

[Growlerbearnz]

I know the valve springs are 61lb, so I'm thinking no more than 50lb.

The springs are 61lb, but the backpressure is operating on a valve face that's 1.4 square inches (34mm diameter valve).
So backpressure of 43psi (61lb/1.4in2) is enough to unseat the valves. I also doubt the exhaust can make that pressure, but I'm super curious to find out.

I wouldn't expect exhaust backpressure to have any effect on the intake pressure, apart from maybe the turbo dropping off a bit quicker.

The reference I have for the 72L has lockup at 85kph (52mph); 65kph (40mph) would be much better. ...

Theoretically I could replace the signal valve spring with something a lot weaker, then it would lockup anytime it was in 4th gear (~40kph/25mph)... but I have zero experience/knowledge working on transmission internals.

I got my numbers from the workshop manual shift chart.




Replacing that signal valve spring might work. The valve body is intimidating, but I've met the lightly-trained gorilla who rebuilt my transmission so how hard can it be?
...though my transmission did explode shortly afterwards, so maybe it's trickier than it looks.

 

[sk66]

So backpressure of 43psi (61lb/1.4in2) is enough to unseat the valves. I also doubt the exhaust can make that pressure, but I'm super curious to find out.

Thanks for that.

I wouldn't expect exhaust backpressure to have any effect on the intake pressure, apart from maybe the turbo dropping off a bit quicker.

I was thinking that any residual pressure that can't get out on the exhaust stroke would exit the chamber when the intake valve opened... except that the chamber is expanding negating the pressure inside

I've got the 4.875 gear ratio which looks even more promising; like 4th gear is always locked up at reduced throttle.