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Go Back   TDIClub Forums > VW TDI Discussion Areas > Upgrades (non TDI Engine related)

Upgrades (non TDI Engine related) The place of handling, lighting and other upgrades that do not relate to the performance or economy of the TDI engine. In other words upgrades to your TDI that don't fit into TDI Fuel Economy & TDI Engine Enhancements.Please note the Performance Disclaimer

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Old June 15th, 2019, 11:34   #31
Typrus
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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.
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Old June 15th, 2019, 17:48   #32
[486]
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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.
nope, the overwhelming portion of the braking from a compression release brake is the 300 psi of pressure compression makes being released before it can push the piston back down on the power stroke (though that seems like the name of the stroke could cause confusion, as there is no fuel being injected on overrun, nevertheless that's what it's called even when it is a net-neutral stroke)

the 14 psiA of air pushing up on the underside of the piston on what would have been the power stroke is nothing in comparison
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Old June 18th, 2019, 05:11   #33
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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.
A lot of people forget about this part, but I get it. It's not always about money. I think a lot of people just want that big turbo whooshing-compressor-spooling whistle and the brapapapapapa when they let off, like on a big rig.
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Old June 18th, 2019, 05:44   #34
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and the brapapapapapa when they let off, like on a big rig.
I know I put about 40 hours of machining into a compression release brake, got about 3/4 of the way through putting together a single cylinder one before I realized that it was more work than it was worth

just wanted the dakka
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Old June 18th, 2019, 06:29   #35
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I know I put about 40 hours of machining into a compression release brake, got about 3/4 of the way through putting together a single cylinder one before I realized that it was more work than it was worth

just wanted the dakka
Yeah, I don't imagine it's easy, fast or cheap to make it for a smaller passenger car diesel. Also, i don't think it would sound as impressive as a Peteterbuilt or something. It would probably sound like a kid blowing raspberries into a metal pipe instead of that deep rumble noise.
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Old June 18th, 2019, 10:42   #36
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Originally Posted by Votblindub View Post
Yeah, I don't imagine it's easy, fast or cheap to make it for a smaller passenger car diesel. Also, i don't think it would sound as impressive as a Peteterbuilt or something. It would probably sound like a kid blowing raspberries into a metal pipe instead of that deep rumble noise.
I just about spit my coffee all over the monitor reading this one.

Made me remember the Swiss Army chain saw....

Jason

PS: I have thought about a way to adapt an engine brake for several of the long grades I have towed down.
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Old June 18th, 2019, 17:50   #37
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Originally Posted by Votblindub View Post
Yeah, I don't imagine it's easy, fast or cheap to make it for a smaller passenger car diesel. Also, i don't think it would sound as impressive as a Peteterbuilt or something. It would probably sound like a kid blowing raspberries into a metal pipe instead of that deep rumble noise.
getting at the bucket tappets past the camshaft while avoiding the lobe was the hardest part of it

if it were a pushrod motor it'd be so much easier
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Old June 20th, 2019, 05:13   #38
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getting at the bucket tappets past the camshaft while avoiding the lobe was the hardest part of it
if it were a pushrod motor it'd be so much easier
See, you're to a point where it's more for just proof of concept, rather than making it practical, economical, reliable, easily accessible and anything a daily car would have. It's still awesome and I wish I could hang out with engineers and machinists and see this custom stuff get made. Maybe even learn a thing or two.
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