Fuel Economy ?

[LNDYCHT]

New to the group, thought I would share a theory.

My coach has a 475 8V92 with a wrapped exhaust system. It surprises me that more coaches do not have insulated exhaust. A wrapped exhaust has many advantages, one of which should be improved fuel economy. A hot exhaust manifold increases the velocity in the manifold scavenging the cylinders of exhaust gases more effectively. The increased velocity should result in higher turbo boost at any given engine speed. The exhaust heat is concentrated in the pipe reducing the temperature of turbo housing reducing intake temperature and increasing charge density. Engine compartment temperatures are reduced extending the life of surrounding rubber components. Engine noise is reduced, noise is converted to heat and expelled through the tail pipe.

Although I am not an engineer, it makes sense. This should apply to all engines, and may be worth the investment to those who do not have a insulated exhaust system.

[Darrell and Linda]

It makes total sense. There are quite few, in both the "92" and series 60 that have exhaust blankets but below is a source for the turbo also.

Some my forget about their generators. If I had a blanket on my generator exhaust, my sound proofing in the compartment would be in better shape than what is is today.

see this link: http://www.pittsburghpower.com/produ...roducts_id=171

[Jon Wehrenberg]

I wonder if anyone has ever documented the impact of doing this as compared with an uninsulated exhaust.

We often are blessed on this site with opinions, but not often hard facts. As fuel prices go up it would be advantageous to know the things that enable us to stretch fuel dollars. I have recorded every gallon of fuel I ever put into my coaches since we bought our first coach in 1990. I not only record the fuel purchase, but the mileage, location, fuel cost, and if I was towing.

I annually would compile the numbers for tax purposes so I was looking at long term averages and not single tank numbers.

From my not so scientific data I have lifetime averages for a 41,000 pound 8V92 powered coach of 5.6 MPG. It was geared 3.73 and towed almost 100% of the time.

My 46,600 pound Series 60 powered coach has averaged 7.6 MPG also towing a similar amount. I don't know the gearing but it is turning a much lower RPM in top gear than the first coach.

My conclusions relating to mileage, apart from a more efficient engine and transmission combination are that the biggest impacts are speed (headwind), hilly or mountainous terrain, weight (towing extracts a penalty and the heavier the toad the greater the impact), and air conditioning.

The difference in MPG when driving 70 MPH versus 60 MPH is almost 1 MPG, and driving 60 MPH into a strong wind over 10 MPH is the same.

Winter driving uses more fuel than summer driving. While the engine is getting a denser air charge the fuel burn is proportional and the headwinds into more dense air requires more power. I think different DDEC programs also impact fuel consumption so direct comparisons have to be made on coaches with the same version of DDEC set up the same.

Bottom line.......I drive in a manner that suits me, mostly at a speed that allows almost complete use of the cruise control without the need to vary speeds when overtaking cars and having to pass. Or if I am in a hurry I can hammer down, but those times are rare. I think we all drive at what is a workable speed for us and accept whatever MPG we get. After all, fuel is one of our smallest costs of operation, with depreciation overshadowing everything else.

[Darrell and Linda]

Jon, we have the same driving habits. Typically the enjoyment of cruising down the hyway, taking it all in, in comfort, is the things I can't get enough of. Now, I may hammer it down when coming up behind a plastic, but again it all about the shear enjoyment of operating our magnificant crusers and leaving them in my dust with a big smile.

I think the most important thing regarding this thread is about the efficiency that these blankets / wraps will give in maintaining the health of our engines.

[stevet903]

Here's my two cents:

There's definitely a benefit to reducing the heat in the engine compartment - less heat in the coach, longer life of the rubber and electrical components, etc. There's a drawback to exhaust blankets though, they tend to trap moisture and corrode the manifolds faster than a bare manifold.

As to the efficiency, a hotter exhaust increases the flow rate per unit time. However, that higher flow, in the same sized pipe, actually increases the backpressure, which may or may not increase fuel economy (most cases not).

Ceramic coatings have been developed to do the same thing as exhaust blankets, without the corrosion disadvantages. They work pretty well, as long as the inside and outside are coated. Here is a review of some Jet Hot coated headers. They were dyno tested on the same engine, same dyno, and same headers with and without coating. There was a 250 to 300 degree decrease in temperature with the coated headers, but no significant difference in power or torque between the coated and uncoated headers. I know this is not apples to apples with an 8v92 or Series 60 but it looks like it would not make an big economy difference. Here's the article: http://www.carcraft.com/techarticles...ngs/index.html

Steve

[phorner]

Thanks for the info Steve.

You make a good point. The ceramic coated headers I had on my 1970 Challenger T/A had absolutely nothing to do with fuel economy.....

[stevet903]

Most of the cars I have had with headers on them really needed a wrap for the sound- they were definitely louder than the cast iron manifolds they replaced. The thin wall tubing seemed to have kind of a ring to it that the cast iron damped out. On the 8v92, There's a funny bend at the end of the passenger side exhaust manifold that does a 90 and looks like it restricts down the ID of the manifold - I wonder if anyone has looked at it and came up with a better flowing exhaust?

Steve

[Jon Wehrenberg]

Based on the number of years Detroit produced the 8V92 and that entire family of engines I would bet the engineers refined that engine with the knowledge and tools they had available to them at the time. That's not to say they couldn't have done better, but that they were limited in the development of that engine because a lot of the technology we take for granted wasn't yet available.

Further, unlike the 4 stroke Series 60 the two stroke 8V92 was an inherently less efficient design, and the addition of DDEC was simply that, an addition, whereas the Series 60 was designed from the start to be a DDEC engine. To show the pace of engine technology, the Series 60 is no longer capable of meeting today's standards. Of course I wonder how much of the obsolescence is due to unreasonable regulations as opposed to engine technology. My bet is with regulations because mileage seems to have gone backwards.

[truk4u]

Brian did both to my Liberty, ceramic and blankets, sure did run good!

IMG_3338_1..JPG

[antioch01]

Lee,
I have been looking for a quality wrap for my exhaust and turbo. do you know the manufacturer of yours ?

Robert Johnson
92' Liberty 8V92