Header Wrap

[cooltouch]

XSives,

I know that road racers will do anything they can, within rules limitations of course, to get more fractional horsepower out of their machines, but this same need generally doesn't apply to those of us who use our bikes on the streets. And I know that wrapping headers is one way of extracting just a little more exhaust velocity out of the XS650 motor, which translates into a freer breathing machine, which means more horsepower can be generated. But how much, I guess is what I'm asking.

I suspect a lot of us wrap our headers cuz they like the looks. But I imagine that others here want to get as much out of their engines as they possibly can, just like dedicate road racers. Me, I have mixed feelings about wrapping my bike's exhaust up so's it looks like its got Ace bandages on both sides. Like it's sprained both legs or something

So, those of you who've done it -- does it make a detectable difference -- or did you do it just cuz it looks cool?

 

[PetesPonies]

Its not a seat of the pants change for sure . . keeps the heat in, looks cool, protects etc.

 

[9c1cap]

My opinion is its very practical on short head pipes, especially if yer an all-weather rider....3ft+- of open pipe on an air-cooled(read:HOT) engine in 40* weather concerns me.

...and its good for hiding un-finished welds also!

 

[angus67]

my pipes consist of (1980) stock pipes cutoff after bracket on lower fr;ame tubes, used peices of floor lamp that had stainless sections, welded those on, for a total length of 36 inches, both sides.
I used black wrap to
A: hide the welds
B: started wrap as close to head mount flange to give a look as if the whole pipe is stainless,
C: Gives a wee bit O' warning when I lean against the pipes.
I had heard it improves exhaust velocity, but , really? I know every little bit helps, but.....really? (sarcasm)

 

[kent_in_kc]

Wrap will make your pipes rust. If you want to retain/insulate a little more heat, ceramic coating (inside and out) may be a better, or perhaps cleaner-looking option. But it takes a lot of work to prep old pipes for ceramic so its generally only used on new pipes.

And, before anyone asks, high temp powder coat will burn off. Ceramic will too if you don't cure it (break it in) properly or if your engine is way out of tune and scorches the pipe. For high performance bikes that are run hard, almost no coating, including chrome, ceramic or stainless will withstand the heat without some some stress, discoloration or failure.

Porcelain holds up pretty well but adds $250-$300 to a set of pipes.

Therefore, header wrap is a less costly alternative if you don't mind the way they look and can handle a little rust underneath.

 

[cooltouch]

I had heard it improves exhaust velocity, but , really? I know every little bit helps, but.....really? (sarcasm)

Simple physics . . . really. The header wrap acts as an insulator, which holds the heat into the pipe, thus the exhaust gases don't cool down as quickly. Hot gas is very active -- the molecules are bouncing around like crazy. This molecular activity is what causes an increase in pressure when gases are heated. So if the exhaust gas pressure increases, the gases are gonna push harder down the pipe to get out. Which leads to an increase in velocity of the gases exiting the pipe.

I would expect this to be a bit of a balancing act, though. If there's too much pressure in the pipe (caused perhaps by too narrow or too long of a pipe) then the opening exhaust valve will see excessive back pressure, and it will be more difficult for the exhaust gases to evacuate the combustion chamber. If there's too little pressure (caused perhaps by too large or too short of a pipe), then the engine's torque curve suffers -- at least for practical street use.

Thus it becomes obvious that an optimum size and length for a wrapped pipe, chosen to maintain this balance, will provide an efficient scavenging effect due to the increased exhaust gas velocity, thus improving engine efficiency and ultimately horsepower.

Just bench racing, but I think that's the general idea.

 

[dwyatt]

I'd say the true horsepower gain is in nano-HP, so we really just do it to look cool or cover-up blemishes. I did it to look cool, even though my bike does have two sprained legs.......

My "muffler" is straight through, with some glass packing to take the edge off, not much louder than my Harley. The neighbors love me.

 

[Jonson nike]

I used the stuff on my pipes for my bike because they are very close to my leg....it works great. It is kind of expensive, and I'm not sure about if it is actually bad for the pipes...don't see how it could be though.
_______________________
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Load moving system
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[cooltouch]

Jonson, I believe Kent is right -- it's one of the things I was wondering about in fact. The wrap will trap moisture, and that certainly can lead to an increase in corrosion. As long as short trips in the rain or damp were avoided, though, the problem is likely a minimal one.

Dwyatt, you've got a valid excuse -- your bike is a racer, and in your situation even fractional gains in hp are important. Besides, I actually like your wrap, cuz it's black. So it doesn't look like Ace bandages. I reckon if I decide to wrap my bike's pipes, I'll look for the black stuff too -- mostly just because I think it looks better.

 

[dwyatt]

I didn't like the other colors, and besides, once you get it on, you can get a high temp spray paint that keeps it black and will seal it somewhat.

 

[inxs]

- i wonder about the heat retention in an air-cooled motor

 

[cooltouch]

Well, it's exterior to the motor, isn't it, being that the pipes are wrapped. Michael "Mercury" Morse, owner of 650 Central, is a big proponent of doing whatever it takes to maximize exhaust gas velocity in the XS650 motor, and he races them. So, based on his knowledge and experience, I'm thinking that any heat retained is probably not that much to worry about.

 

[Tech7]

I wrapped mine for 3 reasons. 1st to keep my leg safe, my pipes are kinda high. 2nd to cover the welds. I made my pipes from some Summit J-bends and some original parts. 3rd it was cheap and looks cool. Much cheaper than ceramic coating or chroming. Cost me about 15 bucks from Summit to wrap both pipes.

 

[inxs]

- mostly i see wrapping on standard double-wall headers that may or may not have been shortened...i would have thought that using larger diameter headers aiming for a resonant balance between pipe length and diameter would have more dramatic effects upon exhaust velocity, as would redesigning the exhaust ports and port-pipe transfer for less turbulent flow characteristics...there will also be a trade off between backpressure and exhaust velocity

 

[cooltouch]

I agree with your observations, inxs. But as you well know, horsepower production is a synergistic process. As I stated at the outset, I suspect that wrapping the pipes results in a fractional horsepower improvement, but perhaps this synergistic relationship with the wrap added in helps increase the hp more than it would if the wrap were used alone? I dunno. Maybe next time I order something from 650 Central I'll get a chance to talk to Michael Morse and ask him.

 

[xjwmx]

I was going to do this on my head pipes, still might, to cover bad rust.

Wrap is not cheap. One chain store had it in shorter length rolls than the rest, sorry don't remember which. Seemed cheaper and less wasteful.

 

[angus67]

isnt all this talk about exhaust velocity negated by any baffleing? if so, velocity is slow, unless using unbaffled pipes. too loud for me, thank you. unless it is a racer, like dwyat's bike, it doesnt matter, thats all I was saying when I said really? really?.
This bike is not a commuter, and will deffinately be afraid of rain, mud, roadkill. Thats what my 2003 suzuki is for. commute, rainsqualls, and road kill!
On another point, instaed of some expensive coating to 'seal against rust under the wrap, coulnt you just buy a can of areasol galvination and coat yer pipes, then wrap them? Ive heard of the trapping of mud and water, resulting in rust out.

 

[cooltouch]

I guess it depends on the silencing method, really. Here in Houston, its seems as if most Harley riders are running straight pipes, and they get away with it. But there are other silencing methods that don't appreciably add to back pressure. Case in point, the Peashooters that Norton installed on its bikes. They're straight through, and just have little louvers inside the pipe. I took this design as inspiration and chopped off the baffle in my Mac 2-1 muffler, then welded on a straight piece of exhaust tubing about 8" long that I'd drilled a couple hundred holes in, to the resulting outlet stub. Wrapped this tubing with some fiberglass "cloth" and stuffed it back up into the Mac muffler. It was straight through, louder than the original baffle, but not nearly as loud as the headers with no muffler. Plus, it sounded really, really good.

 

[kent_in_kc]

I don't know if the aerosol galvanization will hold up to the heat... maybe.

If you make some baffles, I'd suggest trying to get some stainless steel wool like this http://www.briwax-online.com/GMTStainless.html rather than fiberglass or regular steel wool. Stainless wool wont burn out, blow out or rust. I've eaten some of my buddies' steel wool (flaming red, btw) as it blew out his tail pipe in front of me. Not fun, really.

 

[cooltouch]

Yeah, but I wanted a glass pack