Typrus
Veteran Member
Oh man...
This thread could legally drive now haha
I love all of the misconceptions with engine braking. I love them because I used to have them.
Just like several have stated- when you compress the air in the cylinder, it will want to return to an uncompressed state- it will push the piston back down. A true engine compression brake (Jake Brake colloquially) pops the exhaust valves open just after TDC to blow all of the compressed air, then snaps them shut so you actually have a partial vacuum by the time the cylinder hits BDC- that's where the braking comes from, from the partial vacuum and having to defeat friction to turn the engine.
In an exhaust brake, the braking doesn't come from "more compression", it comes from the 35-70psi of exhaust backpressure fighting the pistons as they attempt to evacuate, then being relieved as the intake opens and the charge moves back and forth to a point- it isn't as effective as a true engine brake though.
On an engine like the ALH, it is perfectly happy to fill over at 3500RPM while on a downgrade. It will contribute to your braking, but you will still need to feather the brakes at times. You won't hurt it doing this.
For years of living in the CO mountains, that's exactly what we did, with the 96 Passat, with Dads 11 Jetta and 14 Passat. No harm done. Also with their 99.5 F250 7.3L and 02 Excursion 7.3L. The Ex has over 250k miles, of which over 150k is towing and they downshift the auto of grades to help with speed all the time. No worse for wear, and no exhaust brake.
I get the appeal though and understand your concerns.
If you wanted to try to install a quality EB, get one with a spring bypass, not an orifice. You will also need an air compressor to actuate it. Also, you will need to make sure the pressure produced does not tend to float the exhaust valves. In addition, you will need to find a good place to mount it and to adapt it. For a quality brake kit and all the other good stuff, you may be in it for 2 grand.
Or, you could buy a lot of brakes for 2 grand.
This thread could legally drive now haha
I love all of the misconceptions with engine braking. I love them because I used to have them.
Just like several have stated- when you compress the air in the cylinder, it will want to return to an uncompressed state- it will push the piston back down. A true engine compression brake (Jake Brake colloquially) pops the exhaust valves open just after TDC to blow all of the compressed air, then snaps them shut so you actually have a partial vacuum by the time the cylinder hits BDC- that's where the braking comes from, from the partial vacuum and having to defeat friction to turn the engine.
In an exhaust brake, the braking doesn't come from "more compression", it comes from the 35-70psi of exhaust backpressure fighting the pistons as they attempt to evacuate, then being relieved as the intake opens and the charge moves back and forth to a point- it isn't as effective as a true engine brake though.
On an engine like the ALH, it is perfectly happy to fill over at 3500RPM while on a downgrade. It will contribute to your braking, but you will still need to feather the brakes at times. You won't hurt it doing this.
For years of living in the CO mountains, that's exactly what we did, with the 96 Passat, with Dads 11 Jetta and 14 Passat. No harm done. Also with their 99.5 F250 7.3L and 02 Excursion 7.3L. The Ex has over 250k miles, of which over 150k is towing and they downshift the auto of grades to help with speed all the time. No worse for wear, and no exhaust brake.
I get the appeal though and understand your concerns.
If you wanted to try to install a quality EB, get one with a spring bypass, not an orifice. You will also need an air compressor to actuate it. Also, you will need to make sure the pressure produced does not tend to float the exhaust valves. In addition, you will need to find a good place to mount it and to adapt it. For a quality brake kit and all the other good stuff, you may be in it for 2 grand.
Or, you could buy a lot of brakes for 2 grand.