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Author Topic: exhaust wrap  (Read 8001 times)
Sojourner
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« Reply #30 on: February 01, 2008, 08:54:16 PM »

Gus….yes what you said is correct in regard to the fact that the exhaust coming out is greater force than cooler exhaust (un-insulated) because back pressure is greater.
However read further to under stand what is happening.
Back pressure affects engine efficiency to breathe in more or less (oxygen+) intake air. The lower the back pressures the better.
Other word exhausts pulses are working harder to escape due to higher volume of expanded (heated) gases within given size pipe. Cooling to shrink the volume.

So by cooling somewhat will be freer & takes less forces to come out of exhaust opening to a point of softer pulses.

Do your self a favor…make an inexpensive & hook up water manometer gauge to compare results.
Such this link but use clear Tygon tubing instead of glass “U” bends, that can be purchase at any major hardware store for your “U” tube meter.
http://www.rverscorner.com/manometer.html
http://www.dwyer-inst.com/htdocs/pressure/ManometerIntroduction.cfm
I do not know the factory spec. back pressure number on your bus. I suggest trying at least 30”or more of water to start.
Tap in exhaust steel tubing nearest to turbo's outlet flange. Use 1/4 “metal tubing at least 30” or longer to isolate heat and slide on Tygon over it. Fasten metal tubing onto engine wherever to keep it from vibrating & breaking off.

Manometer is one of the most over look tools to determine differential pressure or vacuum points. At work I use it almost every day of testing & diagnostic.

Thank Gus for bring up your point.

FWIW

Sojourn for Christ, Jerry
« Last Edit: February 02, 2008, 08:30:36 AM by Sojourner » Logged
skipn
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« Reply #31 on: February 02, 2008, 07:07:16 AM »


 Jerry,

   I hope you are talking about putting the manometer after the turbo not between the turbo and head
 exhaust pipe.............

   If you are running 20# of intake boost pressure you will be running that or more between the turbo
 and the exhaust head. turbo efficiencies are the measurements between exhaust pressure and intake
 pressures. The intake impeller creates the pressure that the exhaust impeller must over come inorder
 for the gases to escape.

   Just my personal opinion Smiley

 Skip
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TomC
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« Reply #32 on: February 02, 2008, 08:22:29 AM »

If wrapping the exhaust manifold and turbo is such a great thing to do, why don't any of the OEM's do it on their engines?  We have new trucks in with the particulate trap and NONE are wrapped between the exhaust manifold and the turbo.  The exhaust pipe from the turbo to the particulate trap is wrapped to retain as much heat as possible to facilitate the maximum chance of the particulate traps catalytic converter to produce its' own heat to burn the soot down into ash.

I have my generator exhaust manifold and exhaust pipe through to the outside custom wrapped to reduce the heat in the generator compartment since the compartment is very tight. 

Personally- if you have a turbo engine, wrapping the exhaust manifold and exhaust pipe might get you a little more boost on the turbo.  Otherwise, I'd only wrap them if you want to control heat. Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
Ray D
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« Reply #33 on: February 02, 2008, 09:47:50 AM »

Just because OEM does not do it, does not make it right or wrong most of the times.  So where is the trade off, are we better with reduced back flow in the exhaust pipe or lower engine compartment & turbo intake heat?Huh?

Ray D
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Sojourner
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« Reply #34 on: February 02, 2008, 09:51:02 AM »

Skipn….Thanks for pointing my incorrect stating “manifold” instead turbo.
So sorry to confuse anyone….I try to my best to give my experience facts of results from working at General Motor test lab running dyno, from rotary, gasoline and diesel as well chassis dyno. I never post any post anything that I cannot prove and/or have no experience about the subject.
I corrected that post.

I appreciates your responds…I never want to miss lead anyone.

TomC….This only pertain V-6, V-8 with long pipe to turbo. Only reason I can think of that it not worth extra production cost to keep sale prices within competitor’s market. Turbo equips with automatic transmission will be most benefit from it. Quicker responding time from stand still into motion and passing performance.

I appreciate your update about the today world in class 8 engines and transmission….I look for your post when I can.

FWIW

Sojourn for Christ, Jerry
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skipn
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« Reply #35 on: February 02, 2008, 10:15:07 AM »

Jerry,

   I was more confused trying to make sure I could picture what you were saying....I was not doubting
 your knowledge.

   I think we sometimes major in the minors..... If one looks at it from the 30K feet level the question
 should be what part of this system has the greatest chance of being effected by higher temps?

   To me the most affected side is the intake. Usually longer piping in an already warm (hot) environment.
  Inline engines a lot of times have a heat deflector between exhaust side and intake side.
  V style engines tend to have long exposed pipes from the heads to the turbo.  Heat is always the enemy Smiley

   The back pressure from the turbo through the muffler can(does) affect turbo operation but heating up
 intake air can be the greater issue.

  Just a thought or two or none Smiley
   Skip
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luvrbus
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« Reply #36 on: February 02, 2008, 10:26:09 AM »

RayD, it is OEM for heavy Equipment and if you are going to buy from ATP (advanced thermal products) sit down first my 3 pc wrap was 700.00 8 years ago
« Last Edit: February 02, 2008, 10:38:18 AM by luvrbus » Logged
Ray D
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« Reply #37 on: February 02, 2008, 10:58:16 AM »

$700.00 ouch!! Now I have to think again, was it worth that much??

Ray D
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buswarrior
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« Reply #38 on: February 02, 2008, 01:47:06 PM »

Hello.

The transits are overwhelmingly being equipped with exhaust coverings from the factory now, and many over the road coaches being spec'd too.

As Jim points out, engine room temperatures, and engine room fires from leaking ignitables being the motivator.

Lots and lots of engine room fire suppression systems being spec'd from the factory as well.

Too many new buses catching fire.

If for-profit companies as well as government transit agencies are protecting their equipment with fire suppression, maybe we should be thinking about the cost benefit? We don't have the resources some of those others do to deal with the after effects of a fire....

My motivation to wrap the exhaust on the 8V71 would be lower the engine room temp, and reduce the heat soaking of the air filter cannister (incoming air temp being heated), and help the air-cooled alternator live a little longer.

happy coaching!
buswarrior
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gus
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« Reply #39 on: February 02, 2008, 06:11:23 PM »

Ray,

I doubt that EHP would be more than $300 to cover the turbo, probably less. I think I covered all my gen exhaust system for less than $100 including the muffler.

The exhaust pipe cost of course depends on what size and how long.

It won't cost anything to call or email and find out.
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PD4107-152
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Ash Flat, AR
JackConrad
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« Reply #40 on: February 03, 2008, 05:03:22 AM »

We have Jim Shepherd's Fire Detection and Suppression system on our MC-8 8V71 NA. We have no exhaust wraps in the engine compartment (completely OEM). Normal engine compartment temperature (recorded by a thermistor directly above the engine, approx. 1" below top of compartment, and out of blower fans discharge area) run about 145-155 with ambient temps in the 80's-low 90's. The hottest we have seen was 171 last summer climbing a hill eastbound on I-20 coming out of Birmingham, AL. Outside air temp was 103.  Jack
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« Reply #41 on: February 03, 2008, 01:53:17 PM »

I think Jack has made the case...in spades.  Using his numbers if I were climbing out of El Centro going west and it was one of their common 117-120 degree days I could expect to see 190 ish temps in Jacks bus.   Another MCI equipped with a 8V92 making another 125 HP might get temps approaching 210 or so.  All this is by guess and by golly but the inescapable point is that 171 at 90 ambient is pointing to some scary stuff ahead, especially if his engine temp goes up or air flow diminishes or exhaust gas temp goes up for any reason.

Think about the alternator and all the rubber stuff in there that thinks you hate it.  Thimk abut et.

How much of a discount could we get with a MASSIVE buy of that wrap?  Lets see....1,600 members at .....

ALL THE TRANSITS are coming with the stuff standard equip?   How did we miss this?

Time to buy stock in EHP.

John
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gus
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« Reply #42 on: February 03, 2008, 03:41:47 PM »

I don't know what Jim Shepherd's Fire Detection and Suppression system is but 170* is certainly nothing to worry about in an engine compartment. I would guess that most autos run hotter than that.

Consider that your coollant is 180*+ and any exhaust manifold is bound to be 400*+.

That makes a good argument against heat wrap but he doesn't mention a turbo which is another situation altogether, turbos get hot.
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PD4107-152
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orfunauto/Darrell
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« Reply #43 on: February 03, 2008, 05:59:34 PM »

JMHO, at the previously stated 170*, (I'm guessing mine was near that also) the bottom of my bed was getting very hot after a days drive.  It was very uncomfortable to sleep in the middle of the summer with all that radiant heat.  After wrapping the exhaust cross over on my 8-71NA, the radiant heat was gone.  I bought my Thermo-Tec header wrap from Speedway Motors.  To cover the cross over I ordered the 2" X 50', ($37.99) and I have enough left over to wrap my generator exhaust.  No scientific data to report, just my comfort level while sleeping was much improved.  Also, I can put my hand on the pipe wrap just after shut-down.....
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74 MCI 8
LaGrange, NC
Sojourner
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« Reply #44 on: February 03, 2008, 07:34:35 PM »

There no need to wrap natural aspirate engine unless you don't have much air cooling around the compartment.

Turbo exhaust inlet & outlet temp is much higher than natural aspirated engine. It can get to 1200°F+ under full load.

Use tape that is rated 1200°F continuous.

FWIW

Sojourn for Christ, Jerry
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