Mummy wrap - Wrist Twisters
 
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post #1 of 11 Old 09-22-2008, 12:39 PM Thread Starter
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Mummy wrap

I've seen it on Harleys exhaust but always wondered what it did. Anyone try it? Is it just to protect you from getting burned or does it do more??

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post #2 of 11 Old 09-22-2008, 12:45 PM
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It looks cool and is claimed to increase scavenging of exhaust gases by keeping the gases hotter therefore exiting the tubing faster. You can still burn yourself on it but not as bad as the bare tube. You won't notice any seat of the pants gain of power. see my avatar.

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post #3 of 11 Old 09-22-2008, 12:47 PM
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I've never seen a four cylinder done up in exhaust wrap, the headers get really tight on the niner. It would be interesting to see it on.

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post #4 of 11 Old 09-22-2008, 12:50 PM
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I've seen it used on cars to keep underhood temps down

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post #5 of 11 Old 09-22-2008, 12:54 PM
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It does help under the hood to keep things cooler. You would see better benefits for power in that case compared to a bike.

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post #6 of 11 Old 09-22-2008, 02:06 PM
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I may be wrong but I seem to remember Bucky talking about this or possibly recommending it. Maybe he has it on his drag bike? You may want to PM him or search his posts. He will forget more about this stuff than many of us will ever know!

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post #7 of 11 Old 09-22-2008, 03:00 PM
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First rule ... Never wrap Ti!

It helps keep temps down and as mentioned keeps exit exhaust temps up. Depending on the application it can help, but also hurt. On the RC, I've done it to keep exhaust temps down. I've also done it to the KLR. It's a single cylinder and wanted to improve heat and exhaust.

IMHO, the best route is "ceramic/jet" coating. I usually take this route when time allows.

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post #8 of 11 Old 09-22-2008, 03:09 PM
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Quote:
Originally Posted by RC51_CBRXX View Post
IMHO, the best route is "ceramic/jet" coating. I usually take this route when time allows.
+1
we jetcoat our Turbo header for the reasons mention previously. When spooling a turbocharger, there's energy in heat....or something like that.

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post #9 of 11 Old 09-22-2008, 08:12 PM Thread Starter
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Alright I never claimed to be a mechanic and much of this is new to me but I have a basic question here. How does keeping the exhaust hotter/wrapped/jetcoated gain HP? Based on my rudementary knowledge isn't this a lost leader when in fact the actual combustion has already occured? The piston came up, + fire = power etc. exhaust is a "by product" it can't drive the piston or a wheel, so how does this help??

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post #10 of 11 Old 09-22-2008, 09:08 PM
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Quote:
Originally Posted by Fishfilet300 View Post
Alright I never claimed to be a mechanic and much of this is new to me but I have a basic question here. How does keeping the exhaust hotter/wrapped/jetcoated gain HP? Based on my rudementary knowledge isn't this a lost leader when in fact the actual combustion has already occured? The piston came up, + fire = power etc. exhaust is a "by product" it can't drive the piston or a wheel, so how does this help??
There are varying schools of thought here. I did my thesis on "Boundary Layer Theory and Flow Loss" and have a wee itty bit of knowledge on Heat Transfer and Thermodynamics and still don't totally buy into wrapping wholly.

Note that there are many variables when it comes to engine tune, horsepower, etc. Exhaust heat and removal is only one variable and should be the last variable, IMHO, to focus on. Header wrap on a bike is fairly cheap and a quick do-it-yourselfer. But, also remember that moisture is not a good thing for wrap. You should coat the wrap.

Remember that exhaust scavenging is different than exhaust back pressure.

Here's a brief on what wrap does, stolen from a supplier of wrap. Easier to cut and paste then write it out myself. Wrapping headers creates hotter exhaust gases that exit the system faster thru decreased density. Increased exhaust scavenging is produced, along with lower intake temperatures.

Think of exhaust gases as a piston moving down through the tubular system. As each pulse travels down the system, it creates a vacuum behind itself. The negative pressure behind each is the scavenging effect. As the velocity of the pulse increase, the negative pressures also increase. As you have an increase in velocity, the length of time that you have a negative pressure in the system is increased. The net result of high velocity to assist in scavenging is increased performance of the intake and exhaust system.

Maintaining higher exhaust temperatures throughout the system increases performance in many ways. Think of exhaust gases as a heavy liquid such as an oil additive. If the liquid were traveling down a tubular system in a cold state, it would move very slowly. If you heat the liquid, the density of the fluid changes. The liquid responds to the heat increasing its velocity. Exhaust gases respond in the same manner. Higher temperatures in a system increase the flow of the system. If the liquid is allowed to cool in the system, it slows the flow of the liquid.

Therefore, wrapping the headers maintains exhaust gas heat within the header. This translates into more exhaust flow due to maintaining exhaust temperatures as it flows out of the engine. By improving the scavenging of spent gases, the engine breathes more efficiently. This reduces contamination of gases, thus allowing the engine to develop more power.

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post #11 of 11 Old 09-23-2008, 07:13 AM Thread Starter
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Wow Thanks RC. Talk about "Ask and ye shall receive!" It sure seems like a waste of money for a paultry amount of payback, especially on a Harley.

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