engine brake question/idea

[LCAM-01XA]

Has anyone driven a diesel vehicle that had a throttle blade like a gasser? Do you think such a setup would help an IDI w/ engine braking? Since there is nothing really restricting the airflow in an IDI when you let off the throttle while going down a grade the engine speed tends to drop quite slow, if at all - would devising a way to restrict the airflow and thus create vacuum in the intake help bring the engine speed down faster, much like how it happens in a gasser? I'd imagine this will only work on non-turbo engines, and will probably require some reinforcing of the factory airbox or maybe even building a completely new one out of heavier gauge steel, but is the concept sound?

 

[riotwarrior]

Well..
Conceptually it could work...you do choke off runaway engines with a complete block off....

Just don't know for sure...TRY IT...

 

[kc0stp]

You drive an auto or manual? Frankly even without engine brakes no gasser will outdo a diesel in engine braking, we may not restrict the airflow but we have no power pushing the piston back down and it takes more to drive it back up (more drag) do to the compression ratio. However an auto will unlock the TC and essentially put the truck in neutral when you let off the gas. (I think I explained that logiclly at least...)

 

[7.3 powerstrok]

shut down the air but fuel still going ,so when you open it back up by by-by ,on a jake engine brake the have a silinoid on each exhaust valve keeps the valve open ,anytime you foot the clutch ,let off the pedal ,or hit the brakes ,the engine brake responds blAAAAAA or you can hit the switch off to deactivate it ,most have 3 settings hi-lo-off also the enging timing auto retards ,,,

 

[79jasper]

IIRC the old 5.7 diesel had a throttle blade, and I think so others do also.
Another thing, my 7.3idi doesn't even come close to the engine braking on my 6.2 chevy.
If I time it right, it sounds like an old screaming jimmy.

Now back on topic, I like the thought of LCAM. Have it setup to where if you can stop a runaway just in case. I know they're expensive, but what about rigging up a positive air shutoff? Or just copying the design?
You could do the R&D type intake for easier connectivity.

 

[LCAM-01XA]

Al, yah, that's the plan, lol.

kc0stp, I know our diesels generally do better than gassers, however if we can use some gasser tech to enhance the diesel performance that would be nice. Also, dunno why you say we have no power pushing down on the pistons - our injectors fire all the time, combustion at off-throttle may not pack the punch of a WOT one, but it still provides some force down on the pistons. A modern EFI gasser on the other hand can completely shut off its combustion (usually by cutting off the fuel) if programmed to do so... And yeah, you're generally correct that the torque converter will unlock when you let off the throttle, but there are ways around that, and many IDIs don't even have a locking converter to begin with - so technically the type of transmission bears no relevance to what I'm asking here.

7.3 powerstrok, I know how a compression brake works on a heavy-duty engine, however we do not have that technology available to us (heck even the Fummins guys are barely just getting into it). What we have available are exhaust brakes, and possibly what I'm asking about now. Also, you are not correct about what happens when you get back on the throttle again - some Toyota diesels (also IDI setups, just smaller than ours, and inline instead of V8) actually have throttle bodies from the factory, those are linked to the throttle lever on the IP and open and close progressively as you roll into and off the throttle. Also I don't plan on cutting off the air entirely, just restricting its flow to what's normally needed at idle RPMs - this should sustain combustion so fuel is still burned and don't pool into the cylinders in liquid form - which if I understand correctly is what you're concerned about? Really I'm thinking of copying Toyota's idea of matching max available airflow at closed throttle to what's used at regular idle engine speed - Toyota injectors still pump fuel into the cylinders even when throttle blade is closed (just like our IDIs would), but when you snap the throttle shut even at high rpms there are no explosions or misfire or anything when you get on it again after you're done engine-braking... Does that make sense?

Jasper, I'm not going for an emergency shutoff in case of a runaway, if I make the "throttle body" so it can kill airflow completely that's one more thing to think of when operating the TB as engine braking aid while driving - as in, I gotta pay attention to not close it all the way and kill the engine, and power steering and brakes w/ it. However, a "throttle body" will help in shutting down a runaway engine as it will only allow willtle air to flow thru when throttle is closed, it will not completely shut the engine off but it will bring its speed way down and give me plenty of time to pull the intake ducting apart and use the 1/4" thick steel plate I already carry for just those situations.

 

[79jasper]

I knew that's not what you were going for. Just meant it as being an added feature.
Maybe look through a junkyard for some huge single blade throttle bodies and go from there?
I think this would actually be relatively easy to setup. You could go cable operated or use the "drive by wire" type.
But would you have it setup to be moving all the time? Or like on a switch only when needed?

 

[LCAM-01XA]

Not sure what size the 2-stroke Detroit Diesel emergency airflow shutoff blade is, if it's close to 4" it could be adaptable for my purposes. If that's a no-go, I'll just cut a factory air box apart and make my own throttle blade (square in shape) and install it in the section between the round plastic ducting and the air filter's main housing.

As for operation it can go either way, Toyota IDI throttle blades move w/ the throttle (actually the cable from the pedal drives the throttle blade, and that in turn drives the IP lever thru additional linkages), but for my purposes it may be a better idea to control the throttle blade manually and thru a cable so I can vary the airflow (and thus the engine braking) as needed.

 

[Matrix37495]

Maybe I'm wrong but i always thought when you let all the way off the throttle at speed there was no fuel being delivered at all. At least not to the injectors.

My truck has always had excellent engine braking. To the point that in snow it will break traction just by letting off the fuel in first or second.

 

[Dieselcrawler]

Have to run a rdt. Blocking in stake air will pull more threw the cdr if the engine is at high rpm. Also it would have to open back up at idle.

 

[jaluhn83]

Is it possible? Yes.

However, I don't think it's the best idea. Here's why:

1) You'd be subjecting the intake system to a extended high vacuum which it's not designed for. Certainly you'd need to run a RDT, otherwise you stand a good chance of sucking oil out of the crankcase leading to all kinds of problems. It could also cause issues with the intake valve stem seals since I'm not sure how well they seal under vacuum.

2) You're really not accomplishing much....

 

[LCAM-01XA]

Otahyoni, yeah, 1st and 2nd are good here as well, but try going down a 10% or steeper grade at about 40-45 mph loaded to GVW - I'm shooting for having enough engine braking for a controlled descend at speeds higher than those 2nd gear can provide, and I don't wanna wind up my engine to the moon either.

Corey, why do you say it has to open at idle? There ain't that much air our engines use at idle, and if the throttle blade never blocks the entire section of the intake to begin with the (relatively) small amount air needed for idling will pass around it even when it's closed. Yota engines certainly do not open their throttle bodies at idle, they don't need to as they don't shut the airflow all the way so even when they're closed there is still enough air that flows thru them to sustain the idle. But yeah, generally my idea is to run the intake wide open, only restricting it when additional engine braking is needed.

jaluhn83, I dunno about the valve seals either - that's why I'm asking questions before doing anything stupid. From what I've read on the internets the 7.3 IDIs actually have too good of an intake valve seal, apparently it don't let enough oil thru to lubricate the valve stem and guide properly and eventually causes the valve guide to wear out faster than it happens on a 6.9 w/ their older non-positive seals. I'd think if these issues are present, the 7.3 valve seals should hold up quite well under vacuum. But thanks for pointing out this concern, maybe someone more experienced w/ different styles of valve seals can shed some light on this...

Also, excellent points on the RDT - I completely forgot that the Yota IDIs run RDTs and not CDRs or anything like that. I have an adapter to install on the timing cover for that purpose, but I've ran a RDT before and did not much like the smell of it at all - the Yota IDIs and big-truck engines smelled alright, for some reason my IDI just sucked tho. Or maybe I'm just imagining things, and they all stink all the same.

 

[jaluhn83]

I never got a chance to finish the rest of my thought there - actually had to go do work while I'm at work. Weird, huh?

The biggest thing with your idea is that it's not going to really get you much. You'll be pulling a significant vacuum (assuming there's no leakage) but it's not nearly what you'll get with a true exhaust brake. With your idea you're pumping about 10 psi, whereas a typical exhaust brake is 35 psi. So you get ~3 times the effective retardation.

Frankly most gas trucks I've driven don't really hold back much either, so why waste a bunch of time trying to make the diesel slightly better? Do it the right way.

I've got the US Gear setup on my truck and it works quite well. Not as strong as a true Jake, but it's very nice for going downhill. I typically run 14-16K gross with the horse trailer and very rarely will I need to use the service brake to slow down on hills. Cajon Pass for instance I'll cruise down at 50-60 in 4th with the brake on. It's not much help for stopping quickly, but for long down hills it's a dream. I really wish it was more controllable, as it would sometimes be nice to get about 1/2 the retardation instead of cycling it on and off. I've been on a few steep windy roads with the trailer where the exhaust brake in second is so strong it just about stalls out the rig.

Further, the exhaust brake approach is proven and readily available. No having to fabricate, fiddle, adjust, etc, and no worries about it breaking things. The flip side is of course cost, but you can often find them used for a decent price.

Also consider that putting something on the intake side means that anything that breaks is going through the engine.... bad news. Same thing with anything that gets sucked in or comes loose under a high vacuum. Plus you're also adding a restriction (apt slight) to the intake side even with it completely open. The slight restriction on the exhaust side has much less effect on the engine than on the intake.

If you have a turbo you're throttle valve would have to be post turbo - so now you have even more complicated plumbing and pumping losses. And it all has to seal under vacuum and pressure.

Not worth it IMHO.

 

[LCAM-01XA]

Oh, I know how good exhaust brakes can work, got one on my Fummins, thing is godsend. Problem is, as you said, the cost - in comparison I got the materials and skills and time to build a throttle blade, so no out of pocket expenses there. But if it is in fact a silly idea that's more dangerous than it's possibly useful, well then it likely won't happen...

 

[Matrix37495]

Well, if you have the time and materials, could you build it for the exhaust instead? Just an idea...