Exhaust wrap. Good or bad?
 

Well, is it good or bad for efficiency? I want to do a partial grill block and a bely pan and I want to do this to keep my engine bay cool. Is this going to drastically affect mileage or the life of my exhaust system?

I've had wrapping cause premature rusting. You have to make sure its on good and sealed so that moisture, which it will anyways, doesnt get in. The heat makes it more prone to rusting.

No over all effect on anything except ambient temperatures in my case.

good, because I want to use coroplast for my belly pan. I may just use aluminum for the exhaust areas.

If you can get the cat to warm up faster and stay warm longer, that will make up for some of the engine-off and low load conditions where many of our cars operate.

Rust proof coatings before wrapping/insulating will help prevent the rust from forming.

Hotter exhaust piping should keep the exhaust gasses from cooling as much (part of the point of header wrap), which should make exhaust flow stronger, higher velocity, increasing scavenging. It's theory, not practice, that covering the entire exhaust will achieve bigger gains in this department.

At the very least, it will stop parts of the exhaust from cooling as much while the engine is off or at low load, where there is less heat energy in the exhaust.

Faster exhaust heating times will also mean that less moisture gets trapped in the exhaust from short-distance operation.

what rust-proof coating are you talking about? it could stink at high temps.

high-temp ceramics or alumina coatings. They're designed to help prevent rusting.

Here's a little more from a previous thread.

Would the higher temperatures and the absorbed water and salt in the wrap cause 409 stainless to have crevice corrosion or crack welds?

I've used exhaust wrap since the earl 1990's, and I still do. It works very well on stainless. You can use it on mild steel, but it will drastically shorten the life of the metal. Don't bother trying to keep moisture off of it. The exhaust is full of moisture, and besides, it's not the water but the Oxygen and high temp that eats the mild steel. Mild steel will glow red during normal operation and is prone to Oxygen contamination similar to a weld.

Wrap will bring O2 sensors and Cat up to temp quicker, and it drastically increases the life of other under-hood components that would normally be exposed to the radiant heat from the exhaust.

Gains in performance or scavenging are too small to measure even on a 500hp engine, and so should not be the reason for using the wrap.

Keeping O2 and Cat up to temp, and fast O2-switching is measurable.
Less degradation of under-hood components from radiant heat becomes obvious.

Stainless is really a misnomer with 409. Wierd stuff.

I was worried about the salt than just the water alone and sometimes weird things happen at the welds.

I think it will help to not melt the undertray and to keep the underhood temperatures down given the partial grille block.

Thanks for the practical experience and advice.

I assumed i'd remove the clamped metal heat shield on the short pipes between the cats and the engine.

I looked it up and 409 turns red from heat but doesnt rot out like regular steel except when covered with salt water where it will slowly pit.

The exhaust wrap companies sell a high temperature siicone spray paint to seal the wrap up. For extra protection i'm going to use that to seal the pipe first , then wrap and seal the wrap.

What i wonder is if the wrap fibers stick to the pipe or if they rub the metal with the heat and vibration cycles. If they do the latter then the underneath coat would wear away and maybe a high temp coating of antisieze or lubricant would be a better barrier than paint on the inside.

No worries about abrading... I've seen headers that have been used in high-temp applications with wrap for years, and still no noticeable abrasion from the wrap.

There's less chance for dirt and moisture to get stuck in the wrap if you wrap it backwards.. from the rear of the pipe to the front.

My concern wasnt possible abrading of the metal but a soft paint layer on it. I think i'll unwrap part of the pipe a year after to check how its working.

I did a little research last night on how much exhaust wrap can actually help. Your looking at maybe 1 to 1/2 a percent improvement in power. Some of the power gained is because the wrap improves scavenging which allows more fuel to be burned (This doesn't mean that you will burn more fuel).


this link has some useful info and a test done with a graph.
Header Tech - Collector Styles And Coatings - Stock Car Racing Magazine

Probably helps a few more percent with turbocharged engines. If i get a 1% bonus in FE than great!

I want to reduce the temperatures under the hood and underneath the truck. Restricting the grille airflow and putting an undertray under the vehicle would make it even more beneficial.

I've been using exhaust wrap on my TDI for the past couple months and the only noticeable difference is lower under-bonnet temps. I also sprayed my exhaust pipes with Rustoleum high-heat paint to keep the downpipe from rusting. Not sure about the increases in hp though.