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Old 05-04-2013, 06:42 PM   #29
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So many Rocket Scientists, not enough Rockets.
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Old 05-04-2013, 06:53 PM   #30
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Is there a standard measure of pounds per hp? Not sure where I read the statistic but it works out to be 100lbs per 1hp. Is that a better standard than 10 hp per ft? Any comments?
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Old 05-04-2013, 07:01 PM   #31
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I'll only add one comment to all that has been said so far and that is, if you haven't driven with a true compression brake you can't appreciate how incredible that device is when you're going down steep mountain grades. According to CAT and Jacobs, the compression brake on my C-12 can develop over 300 HP that is applied to slowing down the MH. Essentially, the power of the engine gets "turned around" so it is helping you maintain a safe speed during your descent. As another post noted, with the Jake engaged I can take a 6% descent without ever touching my service brakes.

I recognize that only CAT C-12/13 or ISL/ISX engines will have compression brakes, but, based on my experience, I would rather buy an older MH with one of these engines than a newer one without it. Guess what? That's what I did.
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Old 05-04-2013, 07:06 PM   #32
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I agree as I have a PAC brake on my 330 kitty 3126e and my next rig will have a real compression brake as we drive in mountains quite a bit. I also want more hp and torque. Love my Dutchie but have my eye on an Essex or a Country Coach Intrigue 530. Can't wait to get my foot on some real torque and hp!
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Old 05-04-2013, 08:01 PM   #33
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[QUOTE="docj;1555996"]I'll only add one comment to all that has been said so far and that is, if you haven't driven with a true compression brake you can't appreciate how incredible that device is when you're going down steep mountain grades. According to CAT and Jacobs, the compression brake on my C-12 can develop over 300 HP that is applied to slowing down the MH. Essentially, the power of the engine gets "turned around" so it is helping you maintain a safe speed during your descent. As another post noted, with the Jake engaged I can take a 6% descent without ever touching my service brakes.

I recognize that only CAT C-12/13 or ISL/ISX engines will have compression brakes, but, based on my experience, I would rather buy an older MH with one of these engines than a newer one without it. Guess what? That's what I did.[/

Some ISLs have exhaust brakes based on the VG turbo so look carefully but most do have Jakes. ISMs were used until the 2010 emissions requirements and they all have Jakes. There are some Detroit Diesels around & they have Jakes.
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Old 05-04-2013, 08:43 PM   #34
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Steve,
How to you feel about the VG turbo brake? I have one and think it has about half the stopping power of my prior RV with a compression brake. I honestly rarely used the "high" setting on the compression brake so I am not sure it matters but I miss the high/low option.
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Old 05-04-2013, 09:32 PM   #35
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Steve,
How to you feel about the VG turbo brake? I have one and think it has about half the stopping power of my prior RV with a compression brake. I honestly rarely used the "high" setting on the compression brake so I am not sure it matters but I miss the high/low option.
I've never driven a coach with the VG turbo brake. I like the idea that its integrated into an engine system rather than being a separate add on. I really think the perceived effectiveness of the brake systems is very dependent on coach weight. When you get up in the over 40k weight range then the 2 or 3 stage Jake is needed.
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Old 05-08-2013, 01:28 AM   #36
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Thanks again for your replies. One more "related" question...

Is "variable engine braking" the same as a Jake brake?
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Old 05-08-2013, 03:38 AM   #37
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Jake brake is a brand (Jacobs) and they make along with other manufacturers engine brakes which can be variable. An exhaust brake is fixed and not as aggressive.
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Old 05-08-2013, 05:29 AM   #38
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Thanks again for your replies. One more "related" question...

Is "variable engine braking" the same as a Jake brake?
The fact that they use that particular terminology probably means no. More than likely its an exhaust brake utilizing the variable geometry turbo. If it was a Jake they would be quick to point it out.
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Old 05-08-2013, 06:17 AM   #39
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Steve is correct. The Jake break changes the valve openings to increase the pressure inside the engine to make it work like an air compressor (with no fuel in it). It can be set to "low" to shut down three cylinders or "high" to shut down six cylinders.

The turbo brake is using the air from the back of the turbo to "push back" on the exhaust to slow down the engine. (It is a little different than the exhaust brake in that it is not a "paddle" inside the exhaust system.) The exhaust brake and turbo brakes on either on or off and work best when the rpm is higher.

They all will hold back your motor home coming down a step grade but the Jake brake has a little more braking power when set to six cylinders. On my old motorhome I had a Jack and just left it on low all the time (on high it was just too aggressive). Now, I have a turbo and just leave it on.
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Old 05-08-2013, 08:51 PM   #40
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Regarding the three engines you referenced : The difference , in performance , would be a factor of the coach weight ( weight divided by hp ) . In real life you would not feel any appreciable difference . Unless one of those coaches you are looking at is
24,000 lbs with the 400 hp cummins.. The're all good
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Old 05-09-2013, 06:56 AM   #41
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Torque is the factor that gets you up the hill, hp is misleading as an ISB 6.7 l is rated at 350hp but only about 700 lb ft torque. ISC is the same hp but over 1000 lb ft of torque. Get a ISC 8.3 l minimum for a 40 ft mh is my opinion.
That is going to be 5-6 MPG , a ISX will be 7-8 MPG I almost got 10 with my ISB the coaches were different sized and weights but still were all pretty close - but the power seemed silmiliar with all of the them
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Old 05-09-2013, 07:02 AM   #42
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A Jake Brake (so called because it was built by the Jacobs Co) is internal to the engine. It's also called a compression brake. When it is active, it changes the valve timing and turns the engine into a big air pump. The Jake will have a on/off switch and a high/low switch. A few have 3 positions. This switch controls how many cylinders are involved. A Jake is more effective and is generally in heavier coaches.

An exhaust brake is a valve placed in the exhaust just after the turbo which, when activated, blocks the exhaust flow and creates back pressure in the cylinders which slows the coach. The exhaust brake only has an on/off switch. Some Cummins engines utilize the VG turbo as an exhaust brake by using its electronic control to restrict the exhaust flow.

In the Cummins engine lineup, the ISL and above are equipped with a Jake. The ISL can be equipped either way. The ISB and ISC have an exhaust brake.
Cat C7 & C9 are exhaust brake equipped and C13 a Jake.
There are other engines but these cover about 95% of coaches.

Hope that helps.
Some ISC do have a Jake brake , JFYI
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