Exhaust wrap?

[nickodemon]

What's the point in exhaust wrap? I have seen it fitted to a few bikes and never worked out what it does

[mickvp]

It's about exhaust scavenging is it not? Something to do with hot gasses being less dense?

[nickodemon]

Here is a pic of it fitted to an fzs600? Is it really required on a 600?

[celticdog]

I take it the Steampunk image is 'in' at the moment 

[BBROWN1664]

Looks like exhaust bandage to stop an exhaust leak.
If the collector is a bit holy, wrap the whole system to fool the MOT tester into thinking you have modified your bike rather than just patched a dodgy exhaust?

From the look of the brake pedal in the picture above though, I think a leaky exhaust is probably only a minor issue for that bike.

[Gnasher]

It was used to act as a heat shield to protect close fitting firings on race bikes.

Customisers discovered it's excellent for covering mild steal painted or non painted exhaust systems to hide rust.  As we all know just about every painted system rusts it's just a matter of time remember the black systems of the 70/80's trail bikes, or the black chrome of the Gpz of the same era!   

[nickodemon]

In the advert for the bike the guy says it has stainless downpipes?

[joebloggs]

I thought it was developed for car racing to keep the under bonnet temperature down

[pilninggas]

When I was at Uni, a mate of mine did some research around this for his dissertation. The aim is keep the walls of the exhaust hot so that when the exhaust gases contact the boundary layer they don't cool rapidly and lose kinetic energy/drag (and that change in pressure due to contraction doesn't adversely affect gasflow). I know he did his research primarily around a single cylinder engine, but measurable gains (on an old school dynamometer) were made by reducing the heat losses in the walls. There may have been other pressure wave effects also, but fluid mechanics is not my strength.....

[Gnasher]

In the advert for the bike the guy says it has stainless downpipes?

Yes, it's now become a styling things you see it a lot on American retro customs and cafe racer with old Jap engines.

[mickvp]

When I was at Uni, a mate of mine did some research around this for his dissertation. The aim is keep the walls of the exhaust hot so that when the exhaust gases contact the boundary layer they don't cool rapidly and lose kinetic energy/drag (and that change in pressure due to contraction doesn't adversely affect gasflow). I know he did his research primarily around a single cylinder engine, but measurable gains (on an old school dynamometer) were made by reducing the heat losses in the walls. There may have been other pressure wave effects also, but fluid mechanics is not my strength.....

Sort of my understanding as well. By reducing resistance and keeping the density down it allows the exhaust gasses to move faster. I believe there is a risk of it leaning out the mixture though so sometimes re-jetting is necessary.

That said I know a lot of people do it purely for cosmetic reasons. Not a fan of it myself though

[fazersharp]

Looks like he has also had snapped studs to deal with, I like those stainless (looking) header clamps, the rest looks crap though

[nickodemon]

I think it looks terrible... I wonder if anyone on here has dyno readings before and after fitting the wrap to see if it's worthwhile or not. It would need to be a good gain to make it worthwhile making the bike ugly! (any model of bike)

[Gnasher]

I thought it was developed for car racing to keep the under bonnet temperature down

It's been used in many applications for well over a century.  It's really just lagging which was used on steam engines to keep heat in the transfer pipes and to protect people form touching hot pipe work while working.  It's been used on aircraft exhausts to protect fabric fuselages or to stop heat transfer in engine bays still used my mates plane engine has it.  Yes it's been used in cars and most likely before bikes, to my knowledge it started being used on bike exhaust systems in the early 50's when full firings began to appear on speed record and racing bikes.

My earlier statement was just referring to it's application on bikes.       

[mark g]

I hate the look of it, never would do that to any of my bikes