Exhaust Brake Adaptability

[vanscottbuilders]

I've been talking with PAC about building an exhaust brake for my B-67 with a 673P diesel.

They have told me that, although they do not offer a brake for that particular engine, they could easily build me one, if I knew the amount of back pressure the engine would handle.

Does anyone have any idea?

Or, does anyone have any ideas where I might go to find out?

Exhaust brakes were, at one time, a fairly popular accesssory. So I am certain that information is out there someplace.

Along the same line - PAC says that Jacobs always built the exhaust brakes for Mack products. I have learned that Jacobs still makes exhaust brakes for motorhomes and the "big three" pickup diesels, but nothing for Class 8 trucks.

Does anyone know of another manufacturer that might offer a stock product for the 673? Williams or TEC? or?

I am interested in this exhaust brake idea. An engine brake for a 2 valve Mack head does not fit under the firewall on a B-67 easily.

I would have to shim the cab and fenders up about 1" to make it work. That puts the steering wheel pretty close to the top of the dashboard - looks like a knuckle buster to me.

Thanks,

Paul Van Scott

[Packer]

Paul.

The truck I first drove was my fathers 1957 B-63.

When Williams came out with their compression brake, the 'B' got one.

As I remember, the brake put 30 lbs. of back pressure on the engine.

After the brake had been in place a while, the engine started swallowing valves.

The thoughts, at the time, was that the pressure held the exaust valve open just long enough that the piston tapped the valve, popped it up high enough to allow the keepers to drop off then the valve followed the piston down.

That was not a bad thing.

When the piston came back up on compression, it pushed the valve with it, and THAT was a BAD thing!

After 3-4 times of that, the compression brake was no longer used, and the valve thing went away.

This all happened in the late 50's and/or early 60's

And don't give up on the B-61 cab, I got pictures but I'm still working on getting them down loaded and sent.

Packer

[b61fred]

I have read some paper work on the williams brake for cummins engines, It read that heavier valve springs were recommended and new valve keepers. I would assume that it would hold true on the mack engines as well. I would see how much spring load could be put on the cam without wiping a lobe off of the cam. I have 2 cummins engines with exhaust brakes and HAD one cat (1673 in a pete) and all were on the original line sheets for the trucks. I would look over the Peterbilt I sold to your uncle and see how the bolt patteren matches up to the mack.

Later

Fred

[vanscottbuilders]

Thanks Garth,

I don't have any idea how much back pressure would be tolerated by one of these fifty year old engines and their tired valve trains. Probably not as much as when they were new.

My understanding from PAC is that many of the early exhaust brakes did not calibrate the back pressure very accurately, and as a result many engines had trouble. An over pressure condition could conceivably cause a multitude of problems.

I think the pressure used today on the Dodge/Cummins, Ford/International and GM Duramax pick-up truck diesels is down around 14 psi. I assume that it is a low enough pressure to keep from driving the exhaust valves back against the springs from an open position.

It would seem to me that almost any added back pressure in the exhaust system would have a braking effect on deceleration. It should fill the cylinder with exhaust air on deceleration, making the piston work harder to come back up.

This could be way off the mark - but I'm thinking that a 10# wastegate would do the trick.

Thanks for the input.

We are hoping to load shortly for Portland Or., and load home with Morgan's Peterbilt and a GMC project. I'm not sure if I'm getting stiffed out of my B-61 cab delivery or not. There may not be room on the trailer for it. I'll keep you posted.

Thanks,

Paul VS

[vanscottbuilders]

I need to correct myself - I said that the exhaust brake back pressure for the newer "pickup" diesels was low at 14 psi.

It is not - actually it is around 40 psi.

And, apparently, the Mack diesels of the fifties and sixties (not including the newer Maxidynes) were rated at a maximum back pressure of 40 psi also. And Garth is correct in that the original Williams exhaust brake did supply 30 psi max pressure for the Mack engines.

My idea of 10 psi for less engine stress is okay for the engine, but not enough pressure to do any braking. Apparently much less than 25 psi is not very effective.

Morgan's comment about heavier valve springs has been brought to my attention by a local Caterpillar wizard. And Cat even offers a retro-fit kit that allows 70 psi back pressure in the 3406 and 3408 engines! Must stand the truck right on its nose when you lift the throttle.

I have contacted three manufacturers of these units, and I am waiting for a reply. I will keep you all posted. My general initial feeling is that putting the old engine at risk is probably not worth it. And I don't know if stiffer valve springs are even available. It's just my nature to be curious and always looking for better efficiency and better performance.

For those who might be interested in an exhaust brake - I have learned that a little maintenance is pretty critical. Lubrication and cleaning of the moving parts needs to be done frequently and with the correct high temp lube. I have been cautioned by one of the manufacturers to be sure that all operating parts are located within easy reach for service.

If the butterfly valve sticks and remains closed, which can happen, it is either time for an immediate shut-down or good-bye motor. And it could be spectacular!

Paul VS

[vanscottbuilders]

I have received a reply by phone from US Gear, manufacturer of the D-Celerator exhaust brake. They say there is no undue or added stress on the engine with a properly sized and properly operating exhaust brake. quote:"An exhaust brake is basically a throttle plate, similar to any gasoline engine, albeit with the throttle on the exhaust side of the engine rather than on the intake side. The exhaust brake causes positive pressure in the engine, which slows the piston in the diesel, rather than a vacuum which slows the piston in a gas engine when the throttle is closed."

The comment was that the valve failure, which indeed does happen, is caused by the pressure overcoming the valve spring strength and slowing the exhaust valve closing, which in turn affects the rocker arm and the followers', or lifters' ability to follow the cam. After a short while, valve, or as Morgan pointed out, camshaft damage occurs. Over pressure is most commonly caused by the butterfly valve sticking closed, or by orfices in the butterfly becoming "coked up" from exhaust deposits. Both scenarios can cause severe over pressurization. (The Williams brake unit used small orfices in the butterfly to limit the amount of back pressure a brake would allow)

The US Gear unit, which appears to have better control over the back pressure by using a second smaller "waste gate" valve for active pressure control, is designed for a maximum of 33 psi back pressure. In a 40 psi rated engine like the 673 or 711 Mack with healthy, stock valve springs there should be ample braking assistance and no pre-mature valve failure.

At about $1,295.00, it is a bit less than a new TEC engine brake, but more important, the exhaust brake does not require a shimming plate beneath the valve cover. In my B-67 there does not appear to any room for the raised valve cover where the engine comes thru the firewall.

Interesting Stuff!

Paul VS

[theakerstwo]

I have received a reply by phone from US Gear, manufacturer of the D-Celerator exhaust brake. They say there is no undue or added stress on the engine with a properly sized and properly operating exhaust brake. quote:"An exhaust brake is basically a throttle plate, similar to any gasoline engine, albeit with the throttle on the exhaust side of the engine rather than on the intake side. The exhaust brake causes positive pressure in the engine, which slows the piston in the diesel, rather than a vacuum which slows the piston in a gas engine when the throttle is closed."

The comment was that the valve failure, which indeed does happen, is caused by the pressure overcoming the valve spring strength and slowing the exhaust valve closing, which in turn affects the rocker arm and the followers', or lifters' ability to follow the cam. After a short while, valve, or as Morgan pointed out, camshaft damage occurs. Over pressure is most commonly caused by the butterfly valve sticking closed, or by orfices in the butterfly becoming "coked up" from exhaust deposits. Both scenarios can cause severe over pressurization. (The Williams brake unit used small orfices in the butterfly to limit the amount of back pressure a brake would allow)

The US Gear unit, which appears to have better control over the back pressure by using a second smaller "waste gate" valve for active pressure control, is designed for a maximum of 33 psi back pressure. In a 40 psi rated engine like the 673 or 711 Mack with healthy, stock valve springs there should be ample braking assistance and no pre-mature valve failure.

At about $1,295.00, it is a bit less than a new TEC engine brake, but more important, the exhaust brake does not require a shimming plate beneath the valve cover. In my B-67 there does not appear to any room for the raised valve cover where the engine comes thru the firewall.

Interesting Stuff!

Paul VS

When i used to keep certified on cummins i had to go to school at cummins at Arlington and he told us on the 5.9 and 8.3 that the springs had to be replaced to a 65 lb spring to keep the valve off of the piston and i got him to tell me what he knew about that and it came clear to me what was going on. On a normal engine the compression and combustion holds the valve tight as well as the spring up to the seat.That pressure is on the valve when the piston is traveling up to the top untill the cam opens the valve. There is little pressure on the exhaust after it passes out into the manifold. Now then if you put a butterfly valve on the manifold and hold a 50lb back presure on the manifold and no more than that on the top of the piston because there is no combustion and very little compression there is only the valve sping pressure holding the valve closed and when the piston starts up from the bottom and the exhaust is closed there is no pressure on top of the piston to hold the valve closed when there may be 50lbs of back pressure in the manifoild and it is trying to push back against the back side of valve and open it and once it opens it will stay open until the piston comes up and hits it. I have seen the blue ox brake installed on DD and it is not uncommon to pull the head and see where the valve have been hiting the pistons but have not dropprd one yet. It is scarry to think about.Old mecedels engine had that brake system from the fractory but there valve sping were heavy and it did not do much good. I think the exhast brake may help but to me it would not be worth much to me on a mack because you dont have but a 673 cc engine any way. The guys that i have talked to that have the exhaust brake on dodge trucks say they work good at 2500 to 3000 rpm but no good below that and i can beleive that. I have a jake brake on a 315 in a b61 and it does pretty good but only keeps you off of the service brake on small hills but not as good as a 60 DD or a cummins. If you could get both doors open and hold them open i think it would be better than a jake brake on a mack. Hope that all makes sense maybe not exspaining it right. glenn

[vanscottbuilders]

I was hoping you would chime in here.

That's what I wanted to hear Glenn, Thanks.

The exhaust brake manufacturers tell me that, because of the low RPM on the Mack, more back pressure is better for braking.

But everything I know about pressurizing the exhaust system with no cylinder compression says that the valves will float, or close slower than normal.

I don't think I am going to go further with this idea, unless someone can really convince me that there won't be valve problems.

I do own a new TEC engine brake. As I have said, it doesn't look like there is clearance under the firewall for it. But I should really measure it to be sure.

And I was hoping to keep the TEC brake for a future 285hp project I have up my sleeve.

Probably the best research I could do right now is to find the best performance brake lining to get the most effective braking from the service brakes. The old truck won't be used for revenue anymore, and I'll never wear the brakes out. So a softer material might work out well. Do you know anything about what might be available?

All I remember about driving the B models thirty five years ago was how many times I thought I was not going to stop! I'm way too old for that now.

Thanks,

Paul Van Scott

[theakerstwo]

I have read some paper work on the williams brake for cummins engines, It read that heavier valve springs were recommended and new valve keepers. I would assume that it would hold true on the mack engines as well. I would see how much spring load could be put on the cam without wiping a lobe off of the cam. I have 2 cummins engines with exhaust brakes and HAD one cat (1673 in a pete) and all were on the original line sheets for the trucks. I would look over the Peterbilt I sold to your uncle and see how the bolt patteren matches up to the mack.

Later

Fred

that 1673 is a old engine , not many around any more or people that remember them, that was the forunner for the 3305. glenn

[b61fred]

Paul,

If you wanted heavier valve springs for your 673, any camshaft grinder, (comp cams, isky, engle,ect...) could make valve springs in any configuration you desire. The info they would require is installed hight, diameter(i.d and o.d.), and seat presure desired. It would be very inexpensive. I plan on new valve springs for my engine, they are weak from years of working and then sitting( with a few compressed for who know how long while it sit)

Morgan

[theakerstwo]

that 1673 is a old engine , not many around any more or people that remember them, that was the forunner for the 3305. glenn

3306 i should say glenn

[vanscottbuilders]

Hey Morgan,

Do you know the original spec for the springs?

And, if you were to guess, how much stiffer would they want to be before there was a potential for excess valve train and camshaft wear from trying to overcome the added spring strength?

Thanks,

Paul VS

[Packer]

Paul,

Back in the "Good Ol Days" a Jake was said to put out at (or near) rated horse power.

170 hp, 170 brake hp

300hp, 300 brake hp.

A 673 without a wind machine on the side is worth about 170 hp for stopping.

Not much!

Packer

[Freightrain]

I remember way back in maybe early 90's when Two guys garage(was Shadetree Mechanic) was a useful show to watch, Sam Memmollo put an exhaust brake on his Cummins pickup. I remember him talking about also switching exh springs to help keep them from floating.

I put an exhaust brake on my Ford F350 powerstroke in 2000. Since Ford put a Exhaust back pressure valve in the system to help with warm up anyway, a company came out with a controller to actuate it for braking purpose. It worked slicker than snot and I could practically stop the truck just downshifting it(6 spd). I had the turbo go out at 9k miles and replaced under warranty, the service manager reamed me a good one about how that exh brake was NOT allowed and would void my warranty. Since I had spent near $100K in the last few years on trucks, they let me go but had to promise to remove it. They claimed it was the cause of failure(ya, right), though it was a common issue with them back then to have bearing failures due to oiling issues. I got 50K miles out of it before selling truck.

The Ford EBV had a hole in it to protect it from over pressurizing, as it had hydraulic lifters and valve float was VERY possible.