header wrap


60 replies to this topic
  • Dunlop

Posted June 10, 2005 - 03:20 PM

#21

Do some reading, it will do you good.


From what I read I think Gray has done his reading and knows his stuff. A kid I know had it on his bike but took it off because it stayed wet so long after he washed it and didnt want to casue his header to rust.

  • grayracer513

Posted June 10, 2005 - 04:04 PM

#22

So, I see a dyno chart from the product manufacturer showing a 4.7% increase in power. That would take a 48 hp stock YZ450 to 50 if it were true. Somehow, I find it extremely dubious. A more reliable source would be good. It's a lot like the dyno charts that you find on pipe builders web sites that show fairly realistic figures for bikes with their pipes mounted, but show the stockers at somewhat lower figures than they generate in independent testing.

Plus, you will notice they concede the point that lowering intake temperatures accounts for part of the benefit.

There is a notable lack of good supporting info for these tests, too. How many were done? How many showed these gains? Were these the best two, or were they about average? Was the same system used on before and after coating tests, or two different ones? Was the jetting optimized for either (the trick used by exhaust manufacturers)?

It would also be interesting to see actual before after measurements of the exhaust temperature and velocity to see if there was any real change in it.

I am unconvinced.

  • RC876

Posted June 10, 2005 - 06:13 PM

#23

If maintaining high exhaust velocities were of such importance, why then would modern exhaust systems deliberately feature so many increases in pipe diameter along their length? The first one on a stock YZ250F header is located near the center heat shield bolt. You will have trouble seeing it, but you can feel it by running your fingers along the pipe, and of course, you can measure it easily. The next is typically in the center of the midpipe, and then there is a larger one as the pipe exits into the silencer. Each of these increases in size reduces exhaust velocities. On purpose. .



Although I am in agreement with most of your thoughts on this subject. The step header design has little to do with exhaust gases. Steps are incorporated into header design to help with wave tuning.

Average exhaust gas speed is 350/ft per second. Pressure waves travel at or close to the speed of sound.

Pressure waves respond in an interesting manner when they reach a sudden area change in the pipe. When a pressure wave reaches a larger cross sectional area(step), it will reverse its sign (positive becomes negative, and negative becomes positive) and its direction. For instance, when the exhaust port first opens, a strong positive wave will travel to the end of the pipe, change to a negative wave, and travel back to the exhaust port. This is called a reflection.

Both the positive wave travelling towards the end of the pipe, and the negative wave travelling towards the exhaust port will propel exhaust gasses towards the end of the exhaust system which is exactly where we want them to go. The amount of time that this cycle takes is dependant on the total distance that the wave has to travel.

Obviously when you increase cross sectional area of a primary tube you also decrease velocity. But the benifit of proper pressure wave tuning is much greater than the loss in velocity.

The main reason for any automotive motor sport to use header wrap is to lower underhood temps.

It does work well in motorcycle applications but the added hp due to increased exhaust gas velocity isnt substantial enough to be an issue.

By not allowing the primary tube to release some of the heat that its absorbed it will fatigue the material being used. Obviously mild steel headers are mor succeptable to deterioration than ti or ss headers.

But by having a cooler engine(less temp radiated by the header) the performance gains can be seen for sure.

  • grayracer513

Posted June 10, 2005 - 08:56 PM

#24

Although I am in agreement with most of your thoughts on this subject. The step header design has little to do with exhaust gases. Steps are incorporated into header design to help with wave tuning.

Average exhaust gas speed is 350/ft per second. Pressure waves travel at or close to the speed of sound.

Pressure waves respond in an interesting manner when they reach a sudden area change in the pipe. When a pressure wave reaches a larger cross sectional area(step), it will reverse its sign (positive becomes negative, and negative becomes positive) and its direction. For instance, when the exhaust port first opens, a strong positive wave will travel to the end of the pipe, change to a negative wave, and travel back to the exhaust port. This is called a reflection.

Both the positive wave travelling towards the end of the pipe, and the negative wave travelling towards the exhaust port will propel exhaust gasses towards the end of the exhaust system which is exactly where we want them to go. The amount of time that this cycle takes is dependant on the total distance that the wave has to travel.

Obviously when you increase cross sectional area of a primary tube you also decrease velocity. But the benifit of proper pressure wave tuning is much greater than the loss in velocity.

The main reason for any automotive motor sport to use header wrap is to lower underhood temps.

It does work well in motorcycle applications but the added hp due to increased exhaust gas velocity isnt substantial enough to be an issue.

By not allowing the primary tube to release some of the heat that its absorbed it will fatigue the material being used. Obviously mild steel headers are mor succeptable to deterioration than ti or ss headers.

But by having a cooler engine(less temp radiated by the header) the performance gains can be seen for sure.

All of that is exactly correct, and I don't see where it is that we disagree. The only exception, and a slight one is in the last sentence. A cooler intake results in power gains by increasing charge density. But while it looks good on the surface, and seems logical to say so, keeping the exhaust heat away from the exterior of a liquid cooled engine open to the air is a non-issue at any more than about 10 mph due to the air moving between the pipe and the next nearest component, the radiator included.

The steps in modern exhausts, the divergent cone of an expansion chamber, and the open end of a straight pipe produce pressure reversions just the way you described, and they depend on a loss of velocity in the gas stream to cause it, even though indirectly. Interestingly, pressure waves travel at the speed of sound, but the speed of sound varies with gas density. Cooler, and therefore denser gases carry pressure waves at a higher speed.

And once again, at 350 fps, each gas pulse would spend 14 milliseconds in a 5 foot long exhaust system. It could be moving half that speed and be gone in less than the blink of an eye. The pipe simply does not get a chance to cool the velocity out of the pulse to a significant degree.

  • ONLY4STROKES

Posted June 10, 2005 - 08:59 PM

#25

This sounds like a bad idea...wont tons of dirt get caught on it?

  • YZ250F_Rider

Posted June 11, 2005 - 07:31 AM

#26

I am unconvinced.


No problemo. For those of us that know, it really doesnt matter who doesnt believe. :)

Personally I think the main benefit is the reduced temps put on the shock and the carb. They both went way down in temps after after wrapping the pipes.

  • RC876

Posted June 11, 2005 - 07:52 PM

#27

Thanks Grayracer for the reply.

The only thing I will add is that with on many models the exhaust is close enough to radiate heat to different areas. The radiator, coolant hoses,carb, airbox,etc.This can even happen at higher speeds than 10 mph.

Since the heat being transfered to the radiator is usually very little (depending on model and speeds) we usually wrap the coolant hoses and not the header. Then we place a aluminized heat barrier under the tank and at the airbox by the exhaust.

We have changed out uncoated primary tubes and replaced with ceramic coated and wrapped tubes in the same day. Then measured as good as we could at the time the differnce in heat being radiated to other parts. We have seen good results.

I am also in agreement that there is not a measurable performance gain by increasing velocity via using header wrap.

I manufacture over 1,200 sets of SS headers a year. I have atleast 10 sets of various models ceramic coated inside and out in stock.

I have never ceramic coated a set of headers or wrapped them to help increase velocity. Although I have seen tons of anecdotal data on the subject. I have also seen many dyno charts that show small gains.

Actually if wrapping the primay tude made that much of a difference in velocity. Then if one had a perfectly tuned exhaust system for his model bike and riding style then wrapped the header. It could increase scavenging to the point it would hurt performance .

If there was ever a gain in hp/velocity by the addition of header wrap in an auto use it would be miniscule in comparisson to the increase in hp due to decrease in under hood/air inlet temps.

  • grayracer513

Posted June 11, 2005 - 08:07 PM

#28

Actually if wrapping the primay tude made that much of a difference in velocity. Then if one had a perfectly tuned exhaust system for his model bike and riding style then wrapped the header. It could increase scavenging to the point it would hurt performance .

You make an excellent point. If you build and optimize a system based on a certain set of gas and wave speeds, and then change something that in turn alters those parameters, it could actually cause the system to be sub-optimal as a result.

For heat shielding for the purpose of protecting other parts of the bike, whether for performance or just physical protection, crawling under your car and looking at the exhaust will provide a bunch of good examples. Anyone who has worked around modern cars much at all is only too familiar with heat shields. They're everywhere, and they all have sharp edges. But really, placing a single sheet of aluminum between the heat source and the protected part, with and air gap on both sides is at least as effective as tape.

  • RC876

Posted June 12, 2005 - 05:46 AM

#29

But really, placing a single sheet of aluminum between the heat source and the protected part, with and air gap on both sides is at least as effective as tape.




I agree,

I still forget to quit typing so fast and think out my statements.

What we actually do if we can is use the thermo-sleeve from cool-it/Thermo tec. Thermo tec

We try and use the next larger size then you are sheilding from other heat sources and leaving an air gap.

Since now I am not receiving radiated heat I think with the air gap between the hoses and the thermo-sleeve I am letting the hose breath and radiate heat and cool itself.

  • revolucien

Posted June 12, 2005 - 06:56 AM

#30

I like the idea you guys are talking abut for the radiator hoses.
A couple years ago, I looked into the ceramic tape for my header after buying an FMF without a heat shield. Like many here I burned a couple of my favorite MX pants... not funny at those prices.

The return I got was that the MX pipes were much thinner walled than any auto exaust, and auto exhaust were not prone to objects flying at them. When the pipe gets hot it is more susceptible to damage. Instead of the heat releasing the tape would keep that heat in and weaken the pipe.

After that I bought 3 hose clamps, bent a couple thin strips of metal into a u and mounted the heat shield from the stock pipe and have never had a problem since. :)

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • DigilubeJay

Posted June 12, 2005 - 05:55 PM

#31

I know a dirt bike dad who wraps all of his four stroke headers. He claims that he is seeing HP gains from increased gas scavenging as a result of increased volocity at high revs.
He is also seeing a lower operating temperature at low RPM's.
I'm sure he would provide any sort of information he has to a customer. I never thought to ask if he had Dyno runs to back it up, but knowing this guy and his people, they would'nt be touting the procedure without a good reason.
He did state that the lower low-rev temps are confirmed with a heat gun.
His son has done quite well with his dad as a mentor. Of course when you are Scott Summers dad, you can't do much to slow him down.

To cite Motocross Action as a reference for anything technical is absurd. (it does give some of us a good chuckle though!:) )

I think it's the cynics that should be providing data to the contrary.

  • Guest_RIDE_for_RED_*

Posted June 12, 2005 - 06:24 PM

#32

I've used it, no problameo's.....if anything it aided in low end and same on top. Grass/ dirt is no prob. (does nothing to it) As far as moister: run ur bike after washing it to avoid corrosion.

  • aedwards07

Posted June 12, 2005 - 07:33 PM

#33

RC876,I see that you are a TT sponsor.What company are you with.You seem very knowledgable.Especially with motors.

I have actually learned alot from this thread about the heat wrap stuff.Also I would like to nominate RC876 and GrayRacer513 are the smartest people on thumpertalk by far.

Also where did you guys learn all this stuff.Did you just pick it up from working on bikes or what did you go to college for or where did you learn all this stuff?

  • WheelsUp

Posted June 12, 2005 - 08:32 PM

#34

Send your request to nasa and nascar and NHRA. I'll take their side.

You are the one making the assertion, it is up to you to back it up.

I'm sure you'll agree higher exhaust velocities lead to better scavenging of the cylinder. And that better scavenging leads to higher hp soley due to more room for fresh intake charge. I'm also sure you'll agree that touching the header at the headpoint will be a sure way to get 3rd degree burns if you manage to get your fingers off with any skin at all.

Agreed

Hot gas cooling down also slows down. Keep it hot, and it wont slow down.

This is the point of contention. There is no evidence that keeping gasses hot keeps them from slowing down. Cooling gasses become more dense, which if anything, will reduce backpressure and make more room in the pipe for additional gasses.

NASCAR and NASA may indeed be seeing gains, but for different reasons...

As mentioned above, allowing cooling AT the collector on multicylinder engines can aid scavenging. We don't have multicylinder engines or collectors.

As mentioned above, insulating the header will reduce underhood temperatures, allowing for more consistent tuning of the intake system. We don't have hoods.

NASA? Think about typical NASA equipment. It operates in extreme environments, and it is loaded with sensitive electronic equipment. NASA equipment is also extremely compact, with fuels in close proximity to other equipment. It is in NASA's best interest to keep the heat inside of the exhaust system until it reaches the outside of the equipment. NASA needs to have stable temperatures when and where it is possible.

  • WheelsUp

Posted June 12, 2005 - 08:47 PM

#35

I think it's the cynics that should be providing data to the contrary.

Unfortunately, you can't prove a negative, and that is not how accepted rules of a debate work.

  • xcracer123

Posted June 12, 2005 - 09:09 PM

#36

All I can add here is that Scott Summers has been wrapping the headers on his bikes for years. He makes the same assertions about scavenging. Mostly he did it on the air cooled bikes to eliminate heat from the header from blowing back on to the air cooled head. He still does it on his new 450 so I assume he and his dad see some benefit. Probably to keep heat transfer to the rads and from blowing back on to the engine. No, I do not have any technical info to back this up, if you're going to pop me for my comments. Just what I got from talking to him about it at a race two years ago. Just my 2 cents.

  • WheelsUp

Posted June 12, 2005 - 09:30 PM

#37

I woudn't argue against anyone who makes claims about keeping other areas of the engine cooler. I don't see how anyone could disagree with that.

It's the argument about exhaust velocity being impacted AND it having a favorable impact on performance for that reason where I (we?) are calling BS.

Backyard mechanics have done some pretty impressive accomplishments through trial and error. With trial and error often comes incorrect assumptions as to the REASON for the results.

For a proper, scientific test, one would need to dyno run a single-cylinder bike engine, with the carb and radiators thermally isolated from the header pipe for both before and after tests. Of course, on a dyno, effectively isolating the radiators would not be a problem. The carb could be, but since the object is to test the effectiveness of the heat tape on the header, a custome header could be built that extends at 90 degrees to the engine, or even straight forward, keeping the pipe away from the carb.

Or... do it on a stock bike, then wrap the headers, then unwrap the headers and shield the carb and radiators with an aluminum sheet.
Just for fun, do a third test flowing CO2-chilled water over the header.
Don't forget to monitor exhaust gas temperature and exhaust gas velocity at the entrance to the silencer.

My money is on the wrapped and shielded tests coming out the same.

  • rasta

Posted June 12, 2005 - 10:04 PM

#38

i agree with ride for red, no problems even with mud and dirt, run it after it gets wet

  • YZ250F_Rider

Posted June 13, 2005 - 03:44 AM

#39

You are the one making the assertion, it is up to you to back it up.


I did, I provided the links, read the link of how it works.

It's the argument about exhaust velocity being impacted AND it having a favorable impact on performance for that reason where I (we?) are calling BS.


Hot gases that are moving and then experience a cooling, slow down. The slowing down however improbable to you it may seem directly affects how efficient the scavenging of the cylinder is. The more gas you can remove and the higher the vacuum created doing it to pull fresh charge in during the valve overlap, the more the power it will make. It is why they have valve overlap in the first place.

It's simple physics, and thats what they are trying to capitolize on.

  • WheelsUp

Posted June 13, 2005 - 08:33 AM

#40

I did, I provided the links, read the link of how it works.

Not on OUR engines.
You provided links to data for big-block Chevy engines, and the dyno curves themselves look highly suspect. The HP curves in particular.

As far as the link on how it works, that is more marketing than science, as are the dyno curves. That link is no more convincing and no more "scientific" than the graphs on FMF's page, which show two totally different curves for "stock" for the same engine depending on which FMF pipe is being compared.

It's simple physics, and thats what they are trying to capitolize on.

It's not simple physics. Until a truly controlled test is run, it's merely junk science and marketing.

I'm not saying that it doesn't work, I'm saying that it doesn't work on our single cylinder engines for the reasons stated.
The cooling effect on the carb bowl and radiators is undeniable, and I'd be willing to bet real money that 100% of the gains seen on a dirt bike are from this effect.

IOTW: Run four dyno tests
1 - Stock
2 - Stock with an aluminum shield between the pipe and carb, head, and radiators
3 - Wrapped
4 - Wrapped with an aluminum shield between the pipe and carb, head, and radiators

I'd be willing to bet $100 that the results of tests 2, 3, and 4 will be nearly identical in that they will show comparable gains over #1.





Related Content

Reviews

Yamaha YZ450F 2017 by Chris.GVS


Yamaha YZ450F 2017
  • - - - - -
  • 0 reviews
Forums
Photo

First Hare scramble tips by dhend8


Dirt Bike   General Dirt Bike Forums   General Dirt Bike Discussion
  • Hot  33 replies
Forums
Photo

James Stewart back on a YZ450F by YamaLink


Dirt Bike   Special Interest Forums   Pro Racing
  • Hot  47 replies
Forums
Photo

2016 YZ450 by CaptainKnobby


Dirt Bike   Dirt Bike Technical Forums   Suspension
  • Hot  59 replies
Forums
Photo

Is it worth it? (Cam and High compression piston) by macgi77


Dirt Bike   Make / Model Specific   Honda   CRF 150/230 F/L
  • Hot  36 replies
 
x

Join Our Community!

Even if you don't want to post, registered members get access to tools that make finding & following the good stuff easier.

If you enjoyed reading about "" here in the ThumperTalk archive, you'll LOVE our community. Come join ThumperTalk today!

The views and opinions expressed on this page are strictly those of the author, and have not been reviewed or approved by ThumperTalk.