Exhaust manifold wrap?

[chuckm]

According to Corolland's website, a "cheap exhaust trick" is to wrap the exhaust manifold with exhaust wrap. The gases maintain higher temperatures, which translates into lower density, greater volume and thus higher velocities. They claim, with out backup, that this increases fuel economy.
My initial reaction is mixed. Yes, the density will be lower and so forth. But the dynamic viscosity of a gas increases with temperature. Anybody have any experience here?

[cfg83]

chuckm -

At first I thought you mean wrapping the whole exhaust pipe. I have read that you risk melting your catalytic converter when you do that.

But, I have seen wrapping of the exhaust manifold for HP-only reasons. Hrmmmm, where did I see this recently ... Here it is :

Pegasus -Header Wrap, 2" wide x 1/16" thick - 50 foot Roll

Header wrap will result in a cooler engine compartment. Not only will this help to prevent burns but it can also result in power gain by lowering intake air temperature. It can also help lower oil and water temperatures. Our 1/16 inch thick material will not degrade the header pipes nearly as fast as 1/8 inch thick material. (All header wraps contribute to shorter header life due to the intense heat within the wrap.) A 50 foot roll of header wrap is enough to cover most 4 cylinder headers. Does not contain asbestos.

Pegasus - High Velocity Thermal Exhaust Jackets

The quick-wrap High Velocity Exhaust Jacket kit from Thermo Tec is an innovative way to insulate and block radiant heat. The jackets cover the header tubes vertically instead of wrapping around the tubes like header wrap. High Velocity Exhaust Jackets can be applied with the headers already on the vehicle, saving time and hassle. The "relaxed" fit allows room for the header to expand without restriction, extending header life, and the air space between the header and the jacket provides added insulation. Fits all headers with 2 inch diameter or smaller primary tubes. Kits are sized to cover approximately 22 inches of each primary tube.

Assuming it works, it sounds like you have to be careful with the application.

CarloSW2

[Duffman]

Header wrap will turn to sh*t on a street driven car that is regularly exposed to the elements. It will never be cost effective even if you do get a FE boost.

[eco_generator]

Header wrap would be great if you have a bunch of extra headers laying around and it's super easy to replace them.

After a while... the wrap essentially becomes the header. Try to take it off and the whole thing will crumble. Race teams do not have to worry about this, they usually don't put 100k miles on their car with the same exhaust components on it.

[chuckm]

Yeah, if my header dies, then this would not be a wallet friendly mod no matter what my FE boost was.

[gascort]

I've used it in my mustang - helps around spark plug wires and starters. Definitely does cool the engine compartment, which is a good thing in a sports car. Don't know about the mpg claims though.

[Bullockracing]

As exhaust gas cools, it contracts, effectively reducing the volume of the exhaust pulse as it cools and moves towards the exit of the exhaust system. A hot, fast-moving exhaust pulse is adversely affected by restriction in the exhaust system, thus why headers and oversize exhaust pipes are used in high performance exhaust systems.

The primary function of the exhaust wrap is to prevent heat soak of the engine compartment in high performance vehicles. A use for FE purposes could be to improve thermal efficiency of a conventional ICE. To effectively do this (you will lose th cost battle, tho) you have to take advantage of the improved thermal efficiency, i.e. reduce cooling capacity, slow water pump drive, change timing/fuel delivery map, etc.

Scientifically, the more thermal efficiency you have, the more "calories" you convert to motion versus losing as heat. Sounds like a costly experiment, but it would be interesting...