Header heat wrapped?


29 replies to this topic
  • Yz400Flyer

Posted June 28, 2007 - 07:30 PM

#1

I always wondered if you wrap up your header pipe on a 400/426 from the header to close to the silencer. I know in cars and such it helps with heat control which keeps the rest of the engine a bit cooler.
Do you think wrapping it up would be bad due to the lack of air cooling or it is something that would be fine to do? (thinking about blue heat wrap)

Arno

  • jimbo1143

Posted June 28, 2007 - 07:52 PM

#2

Actually wraping the header & silencer pipe you would benefit greatly by creating a siphon effect when the exhaust gets up to temperature & thus keeping the external temps down around the exhaust while on the bike & on the trail but you might have to rejet depending on how your bike reacts. So wrap the complete header thick & tight espically around the complete radius at least an 1/2" thick & then on normal with each wrap overlaping an 1/2" for the rest of the header to get the results I'm talking about .

  • grayracer513

Posted June 28, 2007 - 07:53 PM

#3

The only thing you can accomplish on a dirt bike by using header wrap is to prevent contact burns on your pants, etc. In a full bodied car, you get some boost from keeping the heat away from the fuel system, but with the entire engine in the open the way it is on a bike, that advantage doesn't exist.

Before anyone says otherwise, there is also no gain from insulating the exhaust.

Oops, too late. The myth has been repeated.

  • jimbo1143

Posted June 28, 2007 - 08:01 PM

#4

I use the 1" wrap for the bends & 2" wrap for the straight sections to get tighter more effective coverage. when I rough wrap I use zip ty's & once I've got everything ran neat & I'm happy with it then I use stainless safty wire with safty pliers to secure the ends of the sections & then cut off the zip ty's afterwards. Patience is the key here.

  • Yz400Flyer

Posted June 28, 2007 - 08:05 PM

#5

I use the 1" wrap for the bends & 2" wrap for the straight sections to get tighter more effective coverage. when I rough wrap I use zip ty's & once I've got everything ran neat & I'm happy with it then I use stainless safty wire with safty pliers to secure the ends of the sections & then cut off the zip ty's afterwards. Patience is the key here.


Excellent, that sounds good. Thanks for the advice. It might not change performance much or at all but I think it looks cool and like the other poster said, you won't burn your pants :thumbsup:

Thanks much.

btw, where are you in IL Jimbo? I'm in the St. Charles, Geneva, area

  • GixRider

Posted June 28, 2007 - 09:04 PM

#6

Before anyone says otherwise, there is also no gain from insulating the exhaust.


What about keeping heat from soaking into the shock? :thumbsup:

  • millwright

Posted June 29, 2007 - 01:31 AM

#7

Wade Summers, who has earned a name as a top 4cycle tuner of our industry, will tell you that from extensive testing he and his son Scott have done, that wrapping the pipe not only protects from burns, but it also helps with keeping the temps down at idle (easily proven/disproven with a temp gun), as well as providing quite a bit of help with scavenging back the exhaust gasses to be reburnt at high RPM.

When a person claims that there is no gain by wrapping the header pipe, perhaps they should show a bit more than simply stating opinion?
Especially when there is contradictory evidence.
Have you tested this modification, and can you show us evidence that backs up your claim to mythage?

I think that Wade would be glad to show us his testing and results.

  • 642MX

Posted June 29, 2007 - 04:27 AM

#8

From what I understand the exhaust wrap keeps too much heat in the pipe itself and can cause the exhaust to crack around the welds.

  • 642MX

Posted June 29, 2007 - 04:29 AM

#9

When a person claims that there is no gain by wrapping the header pipe, perhaps they should show a bit more than simply stating opinion?
Especially when there is contradictory evidence.
Have you tested this modification, and can you show us evidence that backs up your claim to mythage?

I think that Wade would be glad to show us his testing and results.




Didn't you just make a claim without backing it up with hard evidence, dyno sheets, pyrometer results, ect....? :thumbsup:

  • millwright

Posted June 29, 2007 - 04:56 AM

#10

I referenced my source.
And my information, albeit anecdotal, came from the mouth of a person who has actually tested and markets the technology and product concerning this issue.
I read that his product and technology was myth, and I was merely debating a contradictory stance.

642MX, can you tell us just where you got your information? Experience, testing, learned it from a competent professional?

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  • grayracer513

Posted June 29, 2007 - 08:05 AM

#11

What about keeping heat from soaking into the shock? :thumbsup:

The air gap between these parts is adequate to prevent any significant heating of the shock if the bike moves much over 10 mph. In any case, the part that's closest is the gas reservoir, and nitrogen doesn't expand much with heat (which is why it's used in the first place).

Wade Summers, who has earned a name as a top 4cycle tuner of our industry, will tell you that from extensive testing he and his son Scott have done, that wrapping the pipe ...helps with keeping the temps down at idle ..., as well as providing quite a bit of help with scavenging back the exhaust gasses to be reburnt at high RPM.

When a person claims that there is no gain by wrapping the header pipe, perhaps they should show a bit more than simply stating opinion?
Especially when there is contradictory evidence.
Have you tested this modification, and can you show us evidence that backs up your claim to mythage?

I think that Wade would be glad to show us his testing and results.

I'd love to see ANY credible evidence of a significant gain of any kind by this little trick on an open engine vehicle. In 40+ years, no one has produced it.

The statement:

(insulating the exhaust helps) with scavenging back the exhaust gasses to be reburnt at high RPM.

Shows a clear misunderstanding of what actually happens in an exhaust system in operation.

Proponents claim that insulating the exhaust system increases the exhaust temperature, which in turn increases the velocity of the gas stream, which is somehow supposed to improve "scavenging". Ask yourself then, why, if higher exhaust velocity is good, are virtually all header/midpipe systems designed to reduce the pressure and velocity of the gas stream through increases in cross section over the length of the pipe?

As to the contention that the temperature of the exhaust stream itself is raised, consider that each individual exhaust pulse at any speed above about 4000 rpm spends less than 40 milliseconds inside the exhaust system. That doesn't give the hotter tubing of the exhaust much time to impart any of the extra heat to the exhaust gas, does it? The only thing that could really happen anyway is for the gases to cool less (the exhaust is the source of the heat in the first place) as they traverse the system, but there again, the system is designed to reduce pressure in several steps through increases in section, and the exhaust will be cooled to some degree by each of these steps.

One of the projects I helped a friend work on some time ago was an EFI Twin Turbo 302 cubic inch Chevy in a '69 Camaro (and yes, it was ferocious). We had often heard that insulating the exhaust would increase the speed of the turbine, and thus increase the boost level. However, after doing so, we saw no increase in boost. At the time, we had access to a heavy duty diesel shop, and we fitted the car with a pyrometer (measures exhaust temps), and an exhaust manifold pressure gauge. We first tested with the insulation in place, then removed it. The hood was off of the car during the teats to eliminate the effects of radiant heat on the results, and the car drew cold outside air into the intake from behind the grill in any case.

We found no significant or consistent difference it the exhaust heat, or the boost levels either way, although with the hood on, the car did perform better with the exhaust insulated, especially in traffic.

One of the misconceptions in terms of scavenging is that people tend to think of the exhaust as a steady stream, when in fact, it's a series of individual events. To simplify, the valve opens, and a pressure wave starts down the pipe at the speed of sound (about 1000 fps, depending on temp and pressure). When the pressure wave reaches the end of the pipe, or any significant increase in cross section, the gas in the pressure wave suddenly expands, which causes a negative pressure wave (a wave of lower than ambient pressure, like a partial vacuum) to be "reflected" back down the pipe toward the exhaust port. As it moves up the pipe, it accelerates the exiting gases. If this wave arrives at the port just before the exhaust valve closes, and is still strong enough, it can actually help draw more air fuel mix into the combustion chamber while both sets of valves are open during the overlap period. At 10,000 rpm, this is repeated 83 times a second.

So, anyway, if Mr. Summers has any concrete data to override my own experiences, please produce it. It would be a first. In the meantime, I will remain "skeptical", to put it kindly. Feel free to disagree if you like, and don't let me stop you from running header wrap if that's what you really want to do.

  • jimbo1143

Posted June 29, 2007 - 04:13 PM

#12

When I did this on my 98 WR400 I had to go up 3 mainjet sizes to compensate for the modification. Meaning when it is scavenging from your exhaust that much more you must provide that much more fuel to compensate or you will run too lean & will have a very serious dead spot in your throttle response which is not the case. My throttle response is actually snappier then before the mod. Besides, this is not a car we are talking about, but a bike & how can you even try to compare a car engine wedged between the fenders & under the hood of a car compared to a bike that is yeah open to more air but what does that have to do with wraping your exhaust !! Nothing to compare between the two. That is like trying to compare an apple to an orange! Just because they're both a fruit doesn't mean that they are the actual same fruit. Go talk chevy talk on super chevy .com & leave the bike chat to actual bikers who have experienced this mod with great results.

  • King_Air

Posted June 29, 2007 - 04:33 PM

#13

Oh boy this is a fun thread!

  • grayracer513

Posted June 29, 2007 - 04:46 PM

#14

When I did this on my 98 WR400 I had to go up 3 mainjet sizes to compensate for the modification. Meaning when it is scavenging from your exhaust that much more you must provide that much more fuel to compensate or you will run too lean & will have a very serious dead spot in your throttle response which is not the case. My throttle response is actually snappier then before the mod.

In the first place, it's a flawed assumption that a more open exhaust, that is, one in which the exhaust can escape more efficiently, will require an increase in mainjet size. The fact is that it often works just the opposite of that, since the improved throughput results in an increased vacuum level over the spray bar. This can require a reduction in jet size, even though it results in an increase in power. Try bolting a WB R4 on a YZ250F without dropping the pilot and main jet, if you don't believe it.

Secondly, I usually find that such claims result when a modification of some kind is made just prior to the first serious attempt to jet an engine optimally. Thirdly, you can normally go up 10% on a correctly jetted engine without much adverse effect that most people are capable of noticing, and lastly, the main jet is not really responsible for "throttle response".

Besides, this is not a car we are talking about, but a bike & how can you even try to compare a car engine wedged between the fenders & under the hood of a car compared to a bike that is yeah open to more air but what does that have to do with wraping your exhaust !!

I went over that already. Most people who can actually show an increase in power as a result of insulating the exhaust have full bodied cars, and the gains came from reducing radiant heat absorption by the fuel system and intake. We eliminated that in our tests by removing the hood.

Nothing to compare between the two. That is like trying to compare an apple to an orange! Just because they're both a fruit doesn't mean that they are the actual same fruit. Go talk chevy talk on super chevy .com & leave the bike chat to actual bikers who have experienced this mod with great results.

A four-stroke engine of any size and configuration runs on and conforms to the same principals. I'm really sorry that you can't see the connection. The only reason I gave the example of the Z28 is that there had been a definitive test run on the engine that spoke directly to this issue as it pertains to claims of power gains from exhaust heat and velocity. In some testing we once did on one of our 70 hp Norton half mile bikes, we did try this. The results were simply...nothing. :thumbsup:

And please don't make the mistake of telling me or any other member here what they can or cannot talk about, or what forum they should be on. It might be considered discourteous.

  • 642MX

Posted June 29, 2007 - 07:38 PM

#15

642MX, can you tell us just where you got your information? Experience, testing, learned it from a competent professional?


competent professional :thumbsup:






Where is Summer's results?

  • Wiz636

Posted June 29, 2007 - 09:18 PM

#16

I have no technical data, references, or experience with this however it seems rather simple to me: If wrapping the header provided any real benefit why don't the factory race teams do it?

  • millwright

Posted June 30, 2007 - 01:55 AM

#17

It is easy to see that a wrapped header is going to contain some of the heat within the pipe, that would have normally started to dissapate more at the pipe/engine connection with an unwrapped header. This containment of heat is what increases the exhaust temp, which in turn creates more exhaust gas velocity/volume.

Btw...the exhaust is not the source of the heat as you stated, grayracer513. The exhaust is simply a means of guiding the gasses and heat away from the actual source, the engines combustion chamber.

And by insulating the heat removal apparatus in the vicinity of the cooling unit (radiator), it only makes logical sense that the lesser heat going to the rads will improve their ability of overall function.
And if the heat wrap can keep the exhaust heat from buring your leg as bad...it can also help to keep the radiators cooler than they would be without the heat barrier. This alone takes the wrapping past the "no benefit" zone that you seemed to have placed this mod in.
And I would really like to see you debate the "air gap" theory of heat protection with a thermal engineer, grayracer513. His information may "shock" you.

And after looking back into what I had heard from Wade himself, and what he has posted on the web, I think that I may have misunderstood the help with scavanging that the wrapping can provide.
Apparently the part where the scavenging of exhaust gases is helped is also at low RPM's. An unwrapped header, that is producing cooler exhaust gas temps, can actually allow scavenging during the intake stroke at low RPM's, which can be detrimental to engine performance. The wrapping again increases the exhaust gas temps thereby helping to eleminate the scavenging that can occur with the cooler/lower volume/velocity exhaust gas in the unwrapped pipe at lower RPM's.

Wiz636,
Scott Summers has been riding with this wrap for a few years now.
Wade told me that he wraps ALL 4 stroke bike headers till just past the engine.
And maybe there aren't that many factory teams running this mod, but how many of them also have 9 national championships and a few ISDE gold medals?
Wade sure isn't getting rich from the sale of header wrap. It is simply another modification his company offers. He is making way more money (getting rich) from the sale of his Tire Balls invention.
How many factory teams run those?

This is a simple modification that has merit in both theory and real world application. To state that there is no benefit from doing it is, well, simply just an opinion. One with little backing, other than an experiment with an unrelated engine set-up, and no controls relating to the modification in question.
Just how close are the headers of a 302 to the radiator? Wait..I know that answer, because I used to race a 302 engine.

642MX,
You may want your competent professional friend to find another source for his welding applications. And perhaps you could site your source for us, so we know just who we are dealing with here?

  • NavyNuke

Posted June 30, 2007 - 02:13 AM

#18

I wrapped the headpipe on my 06WR because with the oversize tank it would boil the gas in the tank. wrap the pipe, and whammo, no more boiling gas. not a performance gain I could measure with my seat of pants. just no more bubbling gas

  • Polar_Bus

Posted June 30, 2007 - 03:59 AM

#19

I wrapped the headpipe on my 06WR because with the oversize tank it would boil the gas in the tank. wrap the pipe, and whammo, no more boiling gas. not a performance gain I could measure with my seat of pants. just no more bubbling gas


Many racers wrap exhausts to contain excessive engine compartment heat, which minimises the possibility of fuel system vapor lock. It's a big issue with drag, and oval cars, but I really never heard of vapor lock being an issue on bikes.

Wrapping the expansion chamber on 2 stroke racing snowmobiles is widely done, as racers want to keep heat IN the pipe. Hot exhaust gasses flow much faster than cold gasses, which faster flowing gasses makes for better exhaust scavenging, and more consistant power.

  • 642MX

Posted June 30, 2007 - 04:53 AM

#20

And maybe there aren't that many factory teams running this mod, but how many of them also have 9 national championships and a few ISDE gold medals?


I agree that Summers can ride, but when he won all the championships there really wasn't the competition out there that there is today. The sport wasn't as mainstream then as it is today. At Summers prime there was 3-4 guys that where considered 'fast'. Currently there are 10+ guys that could win at any event.

I'm not discrediting the guy, but he racked up the championships in the same fashion that Richard Petty won his.





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