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This subject just won't go away. Many Ram owners are successfully using Turbo-Mounted exhaust brakes such as the Pacbrake, Jacobs E-Brake, BD Engine Brake, and Cummins Rambrake. Some trusted Ram experimenters have dyno tested turbo mounted brakes and report no performance loss or measurable restriction. Despite the success of these brakes and the low rate of problems, a few people still claim that the exhaust restriction presented by these brakes is excessive. Here are both sides of those arguments. Read it and decide for yourself.  -Dave

Subject: (no subject)
Date: Wed, 3 Feb 1999 20:50:01 EST
From: RRWOLFJR@aol.com
To: cummins, turbodiesel

I thought that I would pass this along.  This is a letter that my friend wrote to me explaining the restrictions involved with using a direct mount exhaust brake.Let me know what you all think.

Robert,

I have been reading with interest the give and take on this list regarding exhaust brakes over the past few weeks.  Some posts have made me grin while others have made me grimace.

One claim that was made is that if someone had done his homework, they would have discovered that the flow area in the major direct mount exhaust brakes exceeds the flow area of the stock casting on the Ram.  Really?  Flow INCREASE caused by introducing an obstruction two inches from the turbo?

Surprisingly enough, someone  DID do "homework"…ME!. To make the turbo-mounted brake a true bolt-on, it would have to be the same size on the turbo end and the same size on the pipe end and the same shape and the same length as the stock casting.  BUT with one main difference - it would have a divider stuck in the middle of it, a butterfly and a shaft.

I performed flow tests on three units:  a stock housing, and turbo-mounted exhaust brakes from two different manufacturers.  I used a Superflow 1200 machine (at last count there are just seven of these monsters in the country, and I'm responsible for two of them) which can be used to determine the flowing capabilities of various parts so that they can be compared.  The tests were all run with the machine set at 790 cubic feet per minute (CFM) to start as close to 100% flow of the stock casting as possible.  36" of test pressure was used to simulate a high flow, and the ambient temperature was 72 degrees.

I knew at the beginning, that without incurring major expenses, that I couldn't duplicate the actual operating environment of the turbo.  The high-density, 1400 degree, hard swirling exhaust gas commonly found at the exit of the turbo when under power was beyond my flow bench's capability. Instead, I had to use lower-density, cooler, straight-flowing air to test these units.  But all these limitations on the test environment created more favorable conditions for the turbo-mount.

Even with all the testing conditions weighted in favor of the turbo-mounted units, they still fell far short of flowing the same volume of air as the stock casting.  The most restrictive turbo-mount caused a decrease in flow of almost 100 CFM (649.5 CFM versus 748.5 CFM for the stock housing).  The other one did slightly better.  And that's with every bit of the testing conditions in their favor.  And this from a company which claimed its restriction fell within the "manufacturer's tolerance."  It would be interesting to see those Quality Assurance guidelines which permitted a nearly 100 CFM reduction in flow performance.

Maybe the vehicle manufacturer, and the diesel manufacturer, and the turbo maker, and the turbo-mounted exhaust brake supplier all agree that a 100 CFM decrease in flow on a 750 CFM bogey is not restrictive, but to me and the world I have to function in, THAT'S very restrictive!

The above test results led me to believe one of two conclusions - either the turbo-mount brake collaborators didn't feel they needed to do the tests, or they did do the tests and decided to ignore the results.  If they did the testing, the results would have had to have been the same or similar to the ones above because math is math and facts are facts.  And for anyone who was a part of the development group, or anyone on the outside interpreting their information, to claim that there is no flow restriction is the same as saying that the turbo-mounted exhaust brakes have been granted an exception by the laws of physics that apply to the rest of the natural world.

My first inclination is to think they just missed it.  We've all done that. I give them the benefit of the doubt by believing that it just fell through the cracks, rather than thinking they planted a deliberate deception.  Yes, it appears that "homework" wasn't done - the question is, not done by whom?

And the subject of restriction?  Take a look at the manufacturer's own words.  In document PPC #754 dated September 4, 1998, Cummins introduced the release of the E-Brake for the 1998 1/2 and 1999 model years.  One interesting quote: "The internal profile of the brake housing has been designed to ensure that the additional exhaust restriction caused by the installation of the butterfly is minimized and stays within the Chrysler/Cummins specification for exhaust restriction."  Hmm … "additional exhaust restriction."  This would seem to indicate that, despite numerous claims to the contrary; these units do in fact restrict flow.  In fact, one would have to wonder why manufacturers of turbo-mounted exhaust brakes raise such a commotion if anyone suggests that the units restrict flow, especially when their own literature announces it! And, again, the issue of the elusive and slippery "Chrysler/Cummins specification for exhaust restriction" rears its head.

Now, on to a point that everybody seems to be missing.  One statement I read says, "The discussion about turbo heat is misleading as the turbo is hottest when the engine is under power, not braking."  THAT'S exactly the point.  No one should worry about exhaust temperature in a braking situation when the exhaust brake is being used and the butterfly is in a closed position. Obviously, the temperature is going to be substantially less in that case. And as pointed out by everyone, and I have tried to make this point, the exhaust temperature is going to be extreme when you're climbing a long uphill grade and it is precisely there that the questions arise.  It's all the time that the butterfly is in an open position and still restricting flow that is a potential problem.  I didn't need to test the flow on the turbo-mounted units with the butterfly in a closed position - that's when you WANT to have a restriction; that's when ALL exhaust brakes should be restrictive.

When you're climbing a sustained, long mountain incline and the turbo is running at 60,000 to 70,00 RPM and gets so hot you can see through it and it is spewing exhaust gas in a hard swirl, experience shows that any confusion close to the turbine blades causes a reduction in performance.  That is, the turbo doesn't spool up as fast; which means that the vehicle doesn't accelerate as fast.  And acceleration is a major part of towing performance. The last thing you want in that situation is a blade in the middle of the channel two inches from the source forcing the exhaust to try to navigate
the obstruction.  And if flow area and horsepower were actually increased by the butterfly in the turbo-mounted exhaust brake as claimed in one post, then the factory casting would have a non-functional blade sitting right where the butterfly does in a turbo-mounted brake to gain that advantage. But guess what - it doesn't!

I would think that the least you should expect from someone in the diesel PERFORMANCE business who sells large diameter exhaust systems, free-flowing air cleaners, and trick turbine housings on one side of their shop, and sells turbo-mounted exhaust brakes on the other side of their shop is a little honesty.  And, a little honesty would mean that they would tell you that there is one major reason for the popularity of turbo-mounted exhaust brakes-and that reason can be spoken in the universal language: M-O-N-E-Y. It costs less to unbolt that thing and bolt on this thing.

I know that there will always be people who decide on cost when purchasing anything, including an exhaust brake.  But you should make that decision based on all of the facts, not on someone else's fantasy that the turbo-mounted exhaust brake has no effect on the exhaust flow in your vehicle.  The fact is that the turbo-mounted exhaust brake will restrict flow 100% of the time…period.  Facts is facts, physics is physics, "parts is parts", and no amount of wishful thinking can change them.

Regards,
Gene

Dave Fritz's Comments:

Personally, I have not had trouble with my Pacbrake overheating, sticking, or restricting exhaust flow. My EGT stays well below the danger point even with the 230hp/605 ft-lb TST kit. If there was exhaust restriction from the brake, it would appear as elevated EGT. The additional restriction from the butterfly may raise your EGT slightly under heavy loads, but this shouldn't be a problem unless you have *significantly* turned up the engine power.

NOTE: the exhaust pyrometer will not cool below 450 degrees when the brake is engaged, so it's a good idea to idle for a few minutes with the brake disengaged to cool the turbocharger before shutting the engine down.

This was posted to several mailing lists:

Subject:  Re: exhaust brake/long
Date:      Thu, 14 Jan 1999 15:06:50 -0700
From:    "Paul R. Haller" <phaller@uclink4.berkeley.edu>
To:        turbodiesel, DiRT

I have seen and read this article before and it is always associated with the sale of the US gear decelerator because the US gear requires the cutting of the exhaust system for its installation. The one thing this article got right is its reference to not reducing the cross section area of the exhaust flow by the installation of a brake.

 I did some research to determine which exhaust brake does not impede exhaust flow. I found that the Jacobs brake has the smallest cross section followed by the BD and US Gear in that order. Only the Pac brake maintained the original area ,and actually enlarged the area slightly, providing additional braking while not impeding exhaust flow. IMHO, normal aspiration of the truck is paramount to the operation of the brake because the brake only functions less then 1% of all driving time.

 The next step was to determine which brake provides best braking while in operation. The best performer in this category went to BD because of its ability to generate more braking horsepower at 1500 RPM. The lowest RPM range most diesel engines run at while towing at freeway speeds. The other brakes all performed equally well at 2200 RPM.

The third criteria is quality construction ,and as a result, durability. BD clearly lead this category with the Pac a close second followed by US Gear and Jacobs dismally trailing all others. This interested me because Jacobs is the only authorized Cummins product.

The final consideration is price. When doing my comparisons the BD was a little over 1000$, the US Gear was 1150$, the Jacobs 850$, and the Pac 650$.
 
 In the end, it came down to the BD or the Pac. The BD is the best performer but it reduces exhaust flow when installed and it is pricey. The Pac performed reasonably well and performed best when not in operation and its price was substantially lower. For my money... I got the Pac.

 I wish the BD didn't reduce exhaust flow because its variable orifice construction provides the best braking at lower RPM and its construction is very good including replaceable bushings and abundant use of stainless steel. I like the US gears design but the trigger mechanism for the operation of the brake is a solenoid and electrical power and substantial cutting is required for installation. I felt that this made the unit unacceptable to many owners. All other brakes use vacuum as a trigger for operation and despite the articles objection to using vacuum I feel that this method of controlling the brake is warranted. I have a 97 truck and this year does not use vacuum as a booster to the conventional brakes... It uses power steering fluid instead. The vacuum only operates the ventilation controls and other minor operations. The Jacobs brake was a real disappointment both in its construction and its operation.

 On 12 valve motors the exhaust springs will need to be replaced with the heavier 60 psi springs to realize the full potential of any brake. The ISB already includes the 60 PSI springs and the PCM can control any vacuum operated brake in the ISB equipped trucks ,and with a little work, the US gear brake as well. On automatic equipped trucks a converter lock-up switch is a must to take advantage of the brakes ability to slow you and your load down.

 In real world use, I have been pleasantly surprised with the Pacs performance. I now consider its use a necessity when towing. If you don't have an exhaust brake and you tow frequently... get one. You will feel much safer knowing you have help when slowing.

 Happy trailering,      -Paul R. Haller-

This was posted to the Turbodiesel list:

Subject:    Remote Mount Exhaust Brake NOT Best
Date:        Fri, 15 Jan 1999 01:07:05 -0500
From:       Mark Chapple <tstproducts@iquest.net>
To:          TurboDiesel
 
A member of the list has sent to the list a link to a marketing company who markets a product we do NOT recommend.  Our silence might lead to the belief that we agree with this linked product statement thus we feel obligated to give another point of view.  The link was a reference to a remote mount exhaust brake which was claimed to be better because of better durability, better engine performance (direct turbo mount brakes cause a reduction in flow area and a reduction in engine performance), less turbo heat, and was more accepted by the turbo manufacturer.  At best these statements may be misleading.

While at Cummins I had the opportunity to work with the exhaust brake team which released the Cummins Ram Brake (later called EBrake).  Since my retirement I've sold many exhaust brakes, installing several myself, and have continued studying the available products on the market.

The number one requirement of the Cummins exhaust brake team was that the brake mount directly to the turbo for three reason:

1. Get the brake out from under the vehicle where it was splashed with road dirt and salt which had a long history of causing mechanical and electrical failures on brakes so mounted.  (Better durability for the direct turbo mount brake)

2. Keep the brake as close to the engine heat as possible to prevent water in
the exhaust from settling in the brake shaft bores leading to corrosion known to cause brake valving to stick in the open or closed position in the remote mount brakes. (Better durability for the direct turbo mount brake)

3. Installation without cutting or welding as this caused many field installation problems on remote mounts as every dealer installed them a bit differently. (Fewer problems for the direct mount due to more consistent installation plus easier conversion back to stock if one wanted to remove the brake)

The Cummins exhaust brake team also being employed by the engine manufacturer (and turbo manufacturer) had to insure that engine/turbo durability and performance were not compromised.  While the remote mount brake marketer claims a reduction in flow area right at the turbo with the direct mount, had he done his home work he would have found that the flow area of the major direct mount brakes exceeds the flow area of the cast elbow supplied in the Ram.  Cummins engine tested the Ram brake on a 215 hp Ram diesel at all operating points and found about a half horsepower gain with the direct mount brake over the stock cast elbow, not a big gain, but not the loss claimed by someone without the facts.

The discussion about turbo heat is misleading as the turbo is hottest when the engine is under power, not braking.  While the direct mount brake may keep more heat  at the turbo during braking, the temperatures during braking are much lower than under power thus not a concern.  The turbo manufacture is concerned about back pressure on the turbo during braking, but this pressure is similar whether a direct mount or remote mount brake is used.  Design changes were incorporated in the turbo seals 20 some years ago to accommodate the back pressure of exhaust braking.  The turbo manufacturer (Cummins' Holset Division) was included in the design process of direct mount brakes.

The retarding ability of any exhaust brake is based on its ability to create back pressure on the engine during the braking mode.  The maximum back pressure limit is set by the engine manufacturer.  Remote and direct mount brakes can both accomplish similar back pressure levels, but direct mounts are more likely to do this consistently over a long product life, and at a lower total installed cost.

Its your engine, you decide if you want a brake, and what brand based on facts.

Thanks   Mark @ TST