Shit, lost post...
Anyways, long story short
Heat is energy
Heat in exhaust is what MAKES velocity
Hence this stupid thermodynamic equation, the gas law
PV=nRT
p=pressure v=volume n=the weight of gas in moles
r=the molar gas constant t=temperature

What this equation should immediatly show you is the relationship between pressure, volume, temp and weight.
Take a given amount of gas(in an exhaust pipe), then n and R stay constant, and that breaks down to PV/T=constant

This shows that in a given amount of gas, increasing the pressure and keeping the volume the same will increase temp, and so on
Increasing temp with constant volume will create more pressure
So if header wrap increases temp in the pipe, it creates more pressure. High pressure has quite the affinity for low pressure. End of the tailpipe and atmosphere is nice and cool, and lower pressure. Bam, more velocity.
If you want to understand what I was talking about earlier how stepped headers work, I can write up a summary for everyone when I have time.
Sorry for being a dick, I just was told I was clueless.

 

Stepped headers for the win! Heatwrap for the lose! I have ceramic coated, stepped headers on my bike. Fuckers keep a lot of heat trapped and exhast velocity is very good for a non-baffled setup.

 

dragula- In no way was I disagreeing with the increase of temperature resulting in an increase of exhaust velocity. What I was getting at was the increase in tubing temperature increasing exhaust port temperature. Ideally the primaries would travel upwards (such as the case of top fuel dragsters), but unfortunately the primaries in most street cars flow down, which allows the heat of the tubing to go right back up to the exhaust ports.

 

NERD!!

 

I just run a aluminum air duct hose from the front, and run it pointing at the turbo.
Car moves, turbo cools.

Didn't NASCAR stop using heat wraps a long time ago because it was cracking their manifolds?

 

thanks for shareing that..so we are both right then..stepped tube headers and a ceramic coated header will both speed up the exh gasses..

but yeah nascar,prostock cars and so on dont run them anymore..the all ceramic coat there shit..
below is a link to rick jones ihra mountain motor for sale..
Sonny's 816 Chevrolet HEMI - Rick Jones - Free Classifieds Powered By Racingjunk.com
ceramic coating is the way to go

 

A happy medium is once again restored

I can agree on the movement to cermic coating in the big leagues, probably alot more now than when I was at the track every weekend(2yrs)
But the principle is the same, achieved by different methods. I mispoke when I said every car, that I admit. Im a poor fucker, so wrap it is...

 

+1 wear gloves or you will be rashed up

i have it on my mani and downpipe. Bought it black but turned white after a couple months. I guess it brought down the temp a little. Mine also cleaned up mani by covering up the tarneshed metal look.