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Tobyforlife

Head pipe

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Just curious to find out if anybody is using header wrap in lieu of the guard, stock or aftermarket. I am already aware of the benefits, or the lack thereof, but was wondering if dirt and grime after it gets onto the wrap, makes the whole thing look like a basket case? Thanks

Jeff

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I don't use it. But yes, it gets a bit scruffy looking over time, and dirt also gets under it, which lets it scratch up the pipe finish.

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wait. what is there to be aware of with a exhaust wrap?

Hey Kurt, On automotive applications (which header pipe is design specifically for), it is designed to either discipate heat from contacting or 'warming' other components (protect)...and or maintain exhaust temp (insulate) for various reasons, bla bla bla. Were you serious in your question or just razzing?:censored:

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On certain Header types, I could see it being used to keep the heat away from the radiator and gas tank, but I havent heard of any mjor problem with not doing it. If anything, Id think it would keep the pipe itself hotter, because You wouldnt get any air flow to the header itself.

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Does the higher temperature of the exhaust gases effect the way the bike runs in any way? In the summer would the wrap help keep the radiator a noticeable amount of degrees cooler? Does a cooler running bike produce more power?

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In theory yes, hotter exhaust gases make more power. The hotter gases maintain velocity in the pipe and therefore should scavenge the cylinder better. MAX power is usually achieved at or near max cylinder temp before detonation occurs. That point is different with every motor and with a dirt bike your riding style will have a ton more to do with your lap time than the negligble power increase from cooling the motor more or keeping the exhaust moving at max velocity. That being said, there is more to be gained from keeping the intake charge cooler than fron keeping the exhaust gases hotter/faster.

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Does the higher temperature of the exhaust gases effect the way the bike runs in any way? In the summer would the wrap help keep the radiator a noticeable amount of degrees cooler? Does a cooler running bike produce more power?
No, No, and not necessarily.

The oft stated theory is that keeping the heat high keeps the velocity high, which is somehow supposed to aid the performance of the exhaust system. It does none of these things because:

> The individual exhaust pulse doesn't remain in the pipe long enough to be affected significantly by the insulation or lack of it one way or other.

> The exhaust system doesn't work that way. If the designers wanted the velocity to stay high, they wouldn't keep increasing the cross sectional size in so many steps along the system.

No one I have ever seen has produced what I consider a sound, scientifically conducted series of dyno runs that establishes that there's any gain in power either way. If we were discussing a full bodied car, then there could be benefits, but they would result from the reduction of under hood temperatures and their effect on the fuel system.

Furthermore, the exhaust cannot appreciably heat circulating coolant in the radiator across the at least 1/4" air gap (usually larger) between the two parts quickly enough to be measurable, even at a near standstill, much less when underway, with air blowing through the space.

As to the question of whether cooler engines produce more power, the answer basically is no. The function of an internal combustion engine is to extract energy from fuel in the form of heat, and convert that heat to mechanical force. The heat used to heat water in the cooling system is a total and complete waste, albeit a necessary one. Because engines are made from metals, all of which have thermal limitations, temperatures must be kept below the point where damage to the engine parts occurs, and also below the point where the combustion process gets out of control. Cooling the engine below that point reduces power, rather than raising it. Keeping the intake air as cool as possible does increase power by increasing the air density in the intake.

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A friend of mine who has an 06 CRF250R has had a ton of problems with the right intake valve stretching. That is the only valve that has given him problems and he has to shim it after a hard day of riding.

After repacing the valves, he just put on some header wrap to see if it will increase the time between shimming by reducing the heat coming off the header and attacking the head on the right side.

I know that isn't much help, but when I saw this thread I just had to mention it.

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No, No, and not necessarily.

The oft stated theory is that keeping the heat high keeps the velocity high, which is somehow supposed to aid the performance of the exhaust system. It does none of these things because:

> The individual exhaust pulse doesn't remain in the pipe long enough to be affected significantly by the insulation or lack of it one way or other.

> The exhaust system doesn't work that way. If the designers wanted the velocity to stay high, they wouldn't keep increasing the cross sectional size in so many steps along the system.

No one I have ever seen has produced what I consider a sound, scientifically conducted series of dyno runs that establishes that there's any gain in power either way. If we were discussing a full bodied car, then there could be benefits, but they would result from the reduction of under hood temperatures and their effect on the fuel system.

Furthermore, the exhaust cannot appreciably heat circulating coolant in the radiator across the at least 1/4" air gap (usually larger) between the two parts quickly enough to be measurable, even at a near standstill, much less when underway, with air blowing through the space.

As to the question of whether cooler engines produce more power, the answer basically is no. The function of an internal combustion engine is to extract energy from fuel in the form of heat, and convert that heat to mechanical force. The heat used to heat water in the cooling system is a total and complete waste, albeit a necessary one. Because engines are made from metals, all of which have thermal limitations, temperatures must be kept below the point where damage to the engine parts occurs, and also below the point where the combustion process gets out of control. Cooling the engine below that point reduces power, rather than raising it. Keeping the intake air as cool as possible does increase power by increasing the air density in the intake.

The expanding cross section is necessary because exhaust gases are rapidly expanding as they exit the cylinder and continue to do so as they travel down the header pipe, therefore the introduction of stepped headers in various types of racing. The combination of pipe size and velocity is critical

to an efficient exhaust system as cooling gases in a restricted pipe will cause inefficient cylinder scavenging and therefore reversion of exhaust gases back into the cylinder during the valve overlap period causing a dilution of the incoming charge and a measurable loss in power.

As for no one performing scientificly based dyno pulls to prove or disprove the many theories about exhaust gas control, look into either F1 engine designs or the world of Prostock drag racing and you will be surprised.

And lastly as for the head pipe heating the radiator where it is in close proximity, I to feel that there is enough air flow at speed that the heat is probably negligble. But while sitting still it definetly puts heat into the radiator. Just picture the induction harding process where steel is heated to very high temperatures in just seconds by being exposed to a heated coil with a space usually larger than 1/4 inch seperating the coil and the item being heated. Now start your bike at night and notice the red glow from the pipe in the area near the radiator or try to hold your hand a 1/4 inch away from the pipe and you will see or feel the heat that would be transfered to the lower part of the right radiator.

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The expanding cross section is necessary because exhaust gases are rapidly expanding as they exit the cylinder and continue to do so as they travel down the header pipe, therefore the introduction of stepped headers in various types of racing. The combination of pipe size and velocity is critical

to an efficient exhaust system as cooling gases in a restricted pipe will cause inefficient cylinder scavenging and therefore reversion of exhaust gases back into the cylinder during the valve overlap period causing a dilution of the incoming charge and a measurable loss in power.

As for no one performing scientificly based dyno pulls to prove or disprove the many theories about exhaust gas control, look into either F1 engine designs or the world of Prostock drag racing and you will be surprised.

And lastly as for the head pipe heating the radiator where it is in close proximity, I to feel that there is enough air flow at speed that the heat is probably negligble. But while sitting still it definetly puts heat into the radiator. Just picture the induction harding process where steel is heated to very high temperatures in just seconds by being exposed to a heated coil with a space usually larger than 1/4 inch seperating the coil and the item being heated. Now start your bike at night and notice the red glow from the pipe in the area near the radiator or try to hold your hand a 1/4 inch away from the pipe and you will see or feel the heat that would be transfered to the lower part of the right radiator.

No, No, and not necessarily.

The oft stated theory is that keeping the heat high keeps the velocity high, which is somehow supposed to aid the performance of the exhaust system. It does none of these things because:

> The individual exhaust pulse doesn't remain in the pipe long enough to be affected significantly by the insulation or lack of it one way or other.

> The exhaust system doesn't work that way. If the designers wanted the velocity to stay high, they wouldn't keep increasing the cross sectional size in so many steps along the system.

No one I have ever seen has produced what I consider a sound, scientifically conducted series of dyno runs that establishes that there's any gain in power either way. If we were discussing a full bodied car, then there could be benefits, but they would result from the reduction of under hood temperatures and their effect on the fuel system.

Furthermore, the exhaust cannot appreciably heat circulating coolant in the radiator across the at least 1/4" air gap (usually larger) between the two parts quickly enough to be measurable, even at a near standstill, much less when underway, with air blowing through the space.

As to the question of whether cooler engines produce more power, the answer basically is no. The function of an internal combustion engine is to extract energy from fuel in the form of heat, and convert that heat to mechanical force. The heat used to heat water in the cooling system is a total and complete waste, albeit a necessary one. Because engines are made from metals, all of which have thermal limitations, temperatures must be kept below the point where damage to the engine parts occurs, and also below the point where the combustion process gets out of control. Cooling the engine below that point reduces power, rather than raising it. Keeping the intake air as cool as possible does increase power by increasing the air density in the intake.

Completely impressed by you two. Look foward to you both, opening a MX engine performance, and engineering & consulting business, preferably near my home! Very informative.

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Header wrap has some negitive results that I experianced. Once you wrap a header and heat cycle it it becomes deeply stained or tatoo'd by the patern of the cloth . Ugly . Sanding doesn't help on steel . I do not know about titanium. The other thing that I didn't care for is Gas (FUELING) or any other flammables (CLEANERS)that may fall on the wrap ignites when the header gets hot (SUPRISE)and will not extinguish till the header is cooled . I did see a bike wrapped and though it was a job well done it did now look like a asthetic improvement.

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Just curious to find out if anybody is using header wrap in lieu of the guard, stock or aftermarket.

When you say in lieu of, are you also trying to find a gaurd for an aftermarket header? I ran into that problem with my replacement FMF header and finally found a good replacement gaurd at BonsiaBrothers Racing. They have a website and I've got pics of one on my YZ if you're interested.

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When you say in lieu of, are you also trying to find a gaurd for an aftermarket header? I ran into that problem with my replacement FMF header and finally found a good replacement gaurd at BonsiaBrothers Racing. They have a website and I've got pics of one on my YZ if you're interested.

No, I actually saw a pipe wrapped, and it looked kind of interesting, thanks though.

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The expanding cross section is necessary because exhaust gases are rapidly expanding as they exit the cylinder and continue to do so as they travel down the header pipe, therefore the introduction of stepped headers in various types of racing.
Interesting, then that stepped headers are not currently used on the F1 cars you cited as cutting edge (which, of course, they are). Nor header wrap either, for that matter.

Stepping the pipe up in cross section suddenly creates a sudden drop in the pressure of the gases in the pipe at that point. This is done with current muffled MX exhausts to achieve pressure wave effects within the pipe. The behavior of pressure waves in open exhaust systems, and timing them through controlling the length of the exhaust is old technology, long understood, and little changed for many years where open exhausts are used. F1 systems make use of this, as well as other pressure effects that can only be harnessed in multi-cylinder engines. Unfortunately, mufflers play havoc with the implementation in the traditional manner, and other things have to be done to make the system more than just a non-restrictive outlet for waste gases. The system must be "fooled" into thinking there is no muffler damping the pressure waves and interfering with their activities. Stepping the pipe is one method that's been developed recently with some success.

... cooling gases in a restricted pipe will cause inefficient cylinder scavenging...
I categorically disagree. The pressure waves (both positive and negative) travel up and down the pipe at the speed of sound regardless of the speed of the exiting gases. Besides, the act that the exhaust is stepped up in size once again argues against that, since every increase in section causes a drop in pressure, which in turn causes an associated drop in temperature as well. If what you contend is true, such steps would cause a loss of power in and of themselves.

As for no one performing scientificly based dyno pulls to prove or disprove the many theories about exhaust gas control, look into either F1 engine designs or the world of Prostock drag racing and you will be surprised.
Not asking for validation of pressure wave extraction or any of the similar principals that have been employed for years and are well understood. The only one I don't see is solid evidence that insulating the exhaust creates any gain in power at all. If it's so effective, why is it not used on the most sophisticated engines in motor sports?

engine3.jpg

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