I was thinking about that engine brake thing for a while. I don't see why they would be hard on the engine at all. The way I understand it they should be a lot easier on the engine.

Exhaust brake works by backing up pressure in the exhaust making the engine compress the same hot air over and over and the heat energy from the truck inertia is turned into heat that the radiator dissipates.

Engine brake cracks the exhaust valves as they pass top dead center so that the stored energy of the compressed air doesn't push the piston back down. No backpressure involved. No compression heating to dissipate through the cooling system either. All the waste heat (much cooler than normal exhaust) from braking goes out the tailpipe.

Maybe I'm missing something?

I kinda doubt that it'll hit the market too. Don't really see why it would only work on the CR considering how the system functions. My guess would be that if they do make it, there will be a way to sneak it on the vp trucks since the valve train is relatively similar.

 

The process of an engine brake which causes stress on the engine is the internal drag created by the loss of compression during the power stroke and then the piston trying move downward without combustion pressure. This is why an engine brake works. If there was no pressure, like removing the spark plugs from an engine, then the process would do nothing. As I mentioned before, I think an engine brake is a great concept which offers tremendous braking power, but its design requires a stout engine. It would be very cool to have one. Gasoline engines simply dont have the strength to even consider an engine brake. And the reason I dont think they'll ever offer one on any light/medium duty diesel is because of the extra head, the added expense, and the added weight. Exhaust brakes work plenty good for the GVWR of our size trucks. But maybe they will.

 

I'm not sure, but I think you might be misunderstanding what I meant.

With engine brake (not exhaust brake) Intake pulls air charge in, piston compresses air on upstroke using energy. This energy normally would push the piston back down, with some being absorbed as heat to the cylinder walls/piston/head.

The engine brake cracks the exhaust valve near TDCf to relieve this pressure so all the energy that was used to compress the air charge, and that would have pushed the piston back down is released out the exhaust. So at this point the piston has no load. Some load may be placed on piston as it draws a slight vacuum on the "power" stroke but I don't see how it could amount to any real loading.

Comparatively the exhaust brake *only* absorbs the heat energy, and *only* the energy that is absorbed by the surfaces exposed to the compression. However it does pick up a little extra from compressing on the exhaust stroke as well due to the restriction.

I'm not entirely clear on *how* they work, but if I'm grasping the concept correctly a hydraulic lattice connects one cylinder's pushrod force to another's valve so that the up pressure of the TDCvo pushrod transfers force to the TDCf exhaust valves to crack them.

 

Personally I'd rather see another type of engine brake. Not sure what they are called, but I saw this setup on an old dump truck many years ago.

It worked a lot like the second intake valves on Honda V-tec systems. The exhaust rockers all had spring loaded lock pins. When you engaged the brake, it pulled on the springs so that when the load on them was off (valves closed) the pins would pop out preventing the rocker from opening the exhaust valves.

Works the same way as an exhaust brake, but with no pressure on the other side of the valve, so no worries of floating valves. And NO leakage out the exhaust, so much more effective braking.

When released, opposing springs pull the pins back into the rockers when closed to make the valves operate as normal.

I doubt we'll see any of this stuff anymore considering how little effort it takes to make VD turbos act as an exhaust brake. Sort of like putting an exhaust brake on a 7.3 powerstroke that already has a brake built in if you just put in a controller (stock warmup valve on the Garrett turbo).

Sorry for the hijack OP.

 

Basic cut and paste info to help make up for hijack:

There are several *types* of exhaust brakes. Full closure, partial closure, pressure and vacuum operated, inline and turbo mounted.

The closer to the turbo the faster it responds. Full closure performs better (a LOT better) at low rpm than partial closure. Systems that run through the pcm are slower, the ones that run through just the tps sensor are faster (really better for stick shifts!!!)

IMO the best for a stick shift is a full closure (BD or Banks) that runs through the tps sensor so you can split shifts. If you don't plan on going over 400hp I say turbo mount for fast performance. Planning on higher, you'll need turbo upgrade, so inline is your only option. The stock turbo can support about 400hp with wastegate mods.

I recommend AGAINST using the brake as a warmup valve since finding that doing so fouled up my AIT sensor which can significantly hurt efficiency. Easy to clean, pain in the butt to have to do regularly.

If in doubt; regardless of type, exhaust brakes are FANTASTIC. You won't know how you did without!
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Oh I fully understand the difference and how they both work but to simplify the conversation, just know that there's obviously some serious internal resistance going in the engine when an engine brake is functioning otherwise they would do nothing. Engine brakes can also vary their resistance by how many cylinders are working. Also, I'm not completely positive but given what you described about that other type of engine brake, I believe you're talking about an engine brake on a 2-stroke Detroit Diesel. Those engines ran under constant positive pressure driven by a blower instead of a turbo.

 

I think the internal resistance with an engine brake is no more than no load though. That air would get compressed regardless of whether the brake dumps it before it can push the piston back down or not. It's a really slick trick if you think about it. I would never think there was so much parasitic energy in the compression cycle. But then again, normally that energy would transfer back to the crank on the downstroke so most the loss (minimal) is from compression heat transferring to the piston and head.

Unlike exhaust brakes which double the amount of compression cycles by backing up pressure through valve overlap not just firing cycle. As well as potentially float valves like in the 12v Cummins (that's why they need the springs).

I don't *think* it was a Detroit, but it's been so long, I can't be sure. It was an inline six with three heads like the Cummins setups. Pretty slick. I wish I would have torn it off in retrospect as it had the valve covers and cab off and was rusting away.

 

Well it clearly sounds like you get the just of it all and yea, I think they're pretty slick too. The only issue I have with exhaust brakes is the fact that they can cause carbon build up and interfere with the IAT sensor. It was such an problem for the 2nd gen trucks years ago that some guys tried to find ways to relocate the IAT sensor somewhere farther from the intake manifold. But apparently most have moved on to 3rd gen trucks and those issues.

 

Yup, I did notice that the time I fouled up the AIT (only once, knock on wood) was when I was using the brake as a warmup valve. I figure if it's idling and still injecting, exhaust soot will foul it up since the cylinder will be under pressure when the intake valves open and it will be sooty from the injectors firing at idle.

Just a guess, but brakes like Pacbrake and older Banks probably are less prone to this problem as they have the little hole in the butterfly. Unlike BD and newer Banks which use the eccentric full closure so the only leakage is through the clearance around the edge of the valve.

I figure the bantering adds clarification. So no harm, right?

 

Actually the older exhaust brakes are the ones more prone to this problem simply because the 2nd gen truck ECM only turns the exhaust brake fully ON or fully OFF. The newer gen trucks allow a partial closure feature during idle and while driving. And they also incorporate features like automatically shutting off the exhaust brake at idle, below certain slow speeds, or below low RPM's. I tried to see if there was anyway I could acquire one or more of those features but apparently the 2nd gen ECM isnt capable and no one makes anything to tie into the exhaust brake wiring to make it possible.

 

That's one reason to not get a brake that operates though the ecm. Mine runs through the tps and flips off quickly. Manually operated, tho. Ecm op is a lot slower. Real bummer for a stick shift. Tps op is so quick I flip it off and back on between shifts.

When I say full closure versus partial closure I'm referring to the butterfly. Before BD made the full closure brake ALL were partial closure. This basically means that they NEVER fully close off the exhaust since there is a hole in the butterfly. The BD is oval shaped with the shaft offset so that dangerous backpressure can overcome the actuator, but up to that point it closes off completely. Banks copied the design, so newer Banks brakes are like this also.

I had thought that the new OE brakes were just partial closure brakes with the hole (?) or computer actuated choking of the variable displacement feature of the turbo.

 

Ya know, I'm not completely sure how the 3rd gen ECM controls the exhaust brake but I hear its far more intricate than the 2nd gen ECM. But as for your comment about "fully closure" or "partial closure"..... My opinion is that all their design differences are all marketing. When you get down to it they all create the same amount of back pressure (about 190 HP) and can go no more otherwise engine damage is possible. But where they do differ is trying to make more back pressure at lower RPM's than others. I personally prefer the ECM controlling the exhaust brake so that I can use the cruise control and the moment I touch the throttle the exhaust brake shuts off. But like I mentioned, I'd also prefer if I could incorporate more 3rd gen features as well.

 

Strangely I had read that my apps controlled brake wouldn't work with cruise, and I drove for YEARS without it before I realized that mine works with cruise. Apps op kicks right off when you touch the throttle, too.

At low rpm you can't hold back 190 no matter what brake you have anyhow, but full closure like BD and Banks are more effective at low rpm. At high rpm, the hole in the butterfly is not really an issue, but at low rpm less air is displaced and more readily sneaks out the small hole. I believe mine only holds back about 150hp, but low rpm performance is STOUT right down to idle.

Ultimately I think it's 90% having some type of engine brake, and 10% choosing the ideal brake for your application. I really do like the type that I bumbled into by chance. My neighbor with a Duramax talked me into it, I wouldn't have otherwise.

Sticker shock mostly, but OMG ABSOLUTELY WORTH IT. Twisty 12% grades pulling a backhoe I used to white knuckle it down, I can now go down without touching the service brakes at all If I take it easy and gear low to work that exhaust brake!

Actually when I drive that road *unloaded* now, most cars smoke their brakes if they try and keep up with me when I'm in a hurry!

 

I second that. Exhaust brakes are so effective that I feel any diesel towing absolutely needs one. I had a couple white knuckle experiences too and after installing my exhaust brake long steep grades are no problem. Far worth the money.

 

I would like to point something out about depending too much on an exhaust brake. I had this happen recently on the Pete I drive part time and that is if the Jake suddenly does not work or not work correctly. My load was over 100,000 gross of crushed cars on an A train and started over the hill when the Jake only wanted to work intermittently. On and off, so I had some Jake and I always try to remain prepared for such an event. I dogged my speed off and dropped at least 2 gears and came down really slow with no trouble other than a car behind me not happy about it. He was less unhappy than I was but he didn't know it.

Just a heads up and something to think about to maybe keep someone out of trouble.