Exhaust manifold wraps
 

To assist in protecting my distributor from the heat of the adjacent exhaust manifold, I am considering insulating tape wrap or perhaps high temp thermal paint for the exhaust pipes. But some of these products claim HP gains due to hotter exhaust gasses that therefore exit faster and create better scavenging effects. I'm skeptical. Looking for responses on the heat reduction claims as well as the HP claims. If the heat-reductions are real, this seems like a good mod to pair with grill blocks.

HP gains will be there but we're talking a fraction of a HP would be my guess. I'd go with a wrap, not a coating. Before I did either of those I'd try to bend up a piece of scrap metal to go between the two to make a metal heat shield. Its cheaper, easier and will probably even work better.

Wraps are known to rot out exhaust components in a hurry. I'd go with a shield.

Thanks guys. I'll paint if I do anything to the pipes at all. Here's an odd-ball idea too: a small pipe running from the upper grill directly to the distributor to blow ram air onto the distributor during driving. More directed and smaller than a grill opening and therefore maybe more effective in cooling the distributor and less likely to reduce the WAI's effects. Not worth it?

Wrapping does work in the short term. It can even work in the medium-term on stainless steel components. But even those will eventually start to corrode when wrapped.

I am told that ceramic coating makes a very noticeable difference for temperatures, making a header pipe that was formerly second-degree-burn temperature into one that is merely too-hot-to-hold. Coatings on brand-new parts that have been properly prepared can last a long time, but I don't have first-hand experience.

A heat shield can be made from sheet aluminum. Stock ones frequently are, in fact, and they work reasonably well and cheaply. Even when there is a stock shield there, another one can still have some effect.

-soD

Definatly use a heat shield. I have an SS header that is wraped and you can actually grab it and not get burned, however you must release it very quickly because it will be too hot to hold. The wrap definatly works to reduce underhood temps. Will it give you more mpg? probably not. Being winter time, I like the idea of having more underhood heat :) I don't mind runing my underhood temps as high as possible, with out causing damage.

The problem when people wrap pipes they skip a step.
Almost no one seals the wrap. There are silicone sparys that seal oil and water out of the wrap.
I have seen properly wraped piping fail at the flange, where its not coved at all after years of service. The sealed sections on the pipes looked good.

Sealing exhaust wrap/pipes against water
 

I read online one argument that the paint is inferior, claiming that the paint can't contain the heat as well. I have seen folks who polish them up, the paint them with high-heat paint to protect against corrosion, then wrap them. When in such a process would you apply sealant? Only at the end, I guess?

@ Tygen: I painted my heat shield with flat black 1200 degree paint and reinstalled it. Looks nice.

Is the dizzy really getting that hot?

dizzy hot
 

It was, and I made it worse by removing the heat shield thinking I would eventually clean and reinstall it. It being "winter" in California, I think I underestimated the dangers. I developed ignition coil problems that may or may not have been related. The dizzy is right next to the head and above, left of the exhaust manifold. In summer I get too high numbers on the WAI and my grill blocks of course mean more heat in the engine bay. Seems some sort of heat reduction is prudent.

But hey, I just realized I posted in the unicorn corral because of the FE and HP claims associated with the wraps. Maybe those claims are unicorn material, but the heat reduction seems worth while, no?

Maybe reinstalling the heat shield would do it?

Maybe, but maybe not. The heat shield was for a stock set up, but I have grill blocking. The heat conditions I reported above were with the heat shield installed. I am anticipating the return of those conditions when the hot months return. The wrap or paint would be preventative of future failures, though who knows maybe the unicorns will give me an MPG push too. ;) This car is my daily driver, and I need reliability. Even though I have a lifetime warranty on my dizzy, I want to reduce the likelihood of failures that keep "black and green" off the road (or leave me sitting on it waiting for AAA).

Its well proven and measurable on a dyno that insulating an exhaust pipe can improve power through reduction of back pressure. And a reduction in back pressure will translate to a real world savings in fuel. Why would you list it here?

If your going to do a grill block of any kind you will want to reduce under hood temps as much as possible. The following article is a good read.
http://www.engr.iupui.edu/me/courses...stManifold.pdf

PS. don't assume painting a heat shield black is going to make it work better. It may make it work worse.

Because the implied claims I saw for great fuel economy on the Thermo-Tec box in the Autozone seemed misleading. Unicorns often exaggerate plausible results for marketing advantage, like a horse with a horn, or that can sprout wings and fly! But maybe this thread should be moved by moderators. I'd support that.

Agreed. And so, the questions. Thanks.

I didn't. It's about appearance. Only top side is painted. Why worse?

And thanks for the link. The civic has a cover, but I would bet it could be improved.

Black body emissivity is a measurement of how well something absorbs or emits light radiation. If you have a heat shield between something hot and something you want cool and paint it black, it will absorb the IR heat from the hot side and radiate it on the cold side thus heating what your trying to keep cool.

Emissivity - Wikipedia, the free encyclopedia

here is a table of emissivity for different surfaces.

http://www.monarchserver.com/TableofEmissivity.pdf

A bare aluminum heat shield is better than something that is painted. Ideally you would want a heat shield coated in polished silver.

Ugh. I consulted the materials you linked. Thanks. Clearly painting my shield was a mistake as far as the emissivity of the shield goes. But IAT temps are down from when the heat shield was off. So I have to think that an aluminum heat shield painted flat black on the side opposite from heat source (exhaust manifold) is significantly better than none at all. But do you know a good layman's way to estimate the difference between my heatshield painted versus unpainted? If it is significant, I can consider removing the paint, obviously.

I don't think you'll see that much of a difference.

The heat radiated from the black side of the heat shield will be radiated roughly at a normal to the plane of the surface(perpendicular to the plane). The radiated heat will heat up objects that are in this direction. If you don't have objects in this direction that you want to keep cool don't worry about it. If this is the case and your trying to keep air that flows over the heat shield colder you may have done the right thing. If not and you want to keep it for looks just polish up the other side.

calculations like this are very very complex. Things are best solved by experimentation in this case.

As an after thought I did some searching.

For about $25, you could get one of these and put it over your heat shield. It would then add some insulation as well.


JEGS Performance Products 32040 JEGS Heat Shield Panel

are you talking about the heat shield just above the exhaust? if so it may be better to call it a heat absorber / radiator, it stalls the heat to the hood(no paint blister) and a shield so we dont touch the really hot exhaust and ask whats that? dang thats hot! The same heat is generated with or without it

If you want to just paint them even then it seems difficult to get paint to stick to new headers.
Once the headers have been installed and gotten some oil and rust on them you can forget about repainting them and getting the paint to stick around for a long time, unless you sand blast them. If you do sand blast the paint will stick to them and stay there like chewing gum on a cat.

For my diesel I am going to sand blast my turbo manifolds and ceramic coat them inside and out, I dont think the manifolds will be wraped.
The cross over pipe will be wraped with header wrap and covered with my salvaged "silicone sock".

I've done some digging around for more info on manifold and exhaust wrap. It seems very popular with performance modders, and should be very beneficial on turbo engines, adding low rpm torque, while not doing very much for high rpm horsepower.

What is generally advised is to use e special silicone sealant, on the manifold before you apply the wrap, and on the wrap once fitted. This should greatly reduce wear on the manifold.

Other than reducing the temperature under the bonnet, the extra low rev torque would likely increase FE. I might check it out in a couple of months, but it seems like quite a comprehensive mod if you have to take out the manifold to fit the wrap.

kah, a lot of that is anecdotal. I've heard just as many tuners recommend against heat wrap/coatings because it can increase the likelihood of exhaust manifold failure. The primary (really, the only proven) reason to use heat coating is to reduce engine bay temperatures. Doing so prevents the turbo from heating up and passing that extra heat on to the intake air. If anything, according to a lot of people who have been trying to heat their intake air (WAI) for fuel economy, heat wraps might actually HURT fuel economy.

Yes, and no. Reducing engine bay temperatures was a side effect to what powertuners wanted to achieve in the first place, the primary reason for heat wrapping manifolds and exhaust, was to reduce back pressure from the exhaust system for increase in power.
I'm not an expert on motor engineering, but from what I know of warm air intake, the purpose is to decrease the resistance of air when flowing through the throttle, only making it suitable for (non-turbo?) petrol engines.
For turbo diesels, a manifold and exhaust wrap would (theoretically) increase the energy transferred to the turbo, increase scavenging, lead to higher torque figures and improve fuel economy, however i have not been able to find any dyno test that confirm (nor any that refute) this claim, apart from one done by a manufacturer (of wrap)..
As for fatigue and wear on the wrapped parts, I'm pretty convinced that it's true, but a thing to consider is that most people who wrap their manifolds do it for power increase and drive their cars hard, and usually drive petrol engines, and the temperature of exhaust gas of diesel engines is lower than the exhaust gas of petrol engines. How big a difference that makes is impossible to know, but manifold fatigue is definitely a risk to consider.

I'm looking into it for my diesel truck, because anything I can do to lower underhood temps will also reduce the need for cooling air. The factory put so much excess air through there. They designed for a worst-case scenario. When I calibrate the grill louver system, one of the temps I will watch is the area right over the manifold and turbo. A blanket should help greatly.

Yes, I've heard of all of those purposes, but what I was saying is that the only thing that I've seen proven is the decrease in engine bay temperatures. Everything else, including increased exhaust velocity, increased turbo efficiency, etc. is, as you said, unproven. I'm just not sure if it would affect mileage in any way.

The cast iron manifold on my truck has 240,000 miles on it and has grown and warped over the years. I think a blanket my help that problem, since it will normalize the inside and outside temperatures quite a bit.
I do give the engine cool down time before shutdown, if I have been making significant power.
I have a fresh manifold that we are going to port and polish and install soon.
One of the things I have planned is to add pre- and post-aftercooler temperature gauges, and a drive pressure gauge. This will give me information on how tightly I can close down my cooling before it starts affecting inlet temps.

My engine will need a rebuild at some point in the coming years. When I do that, I plan on doing several things.

Friction reducing coatings from Swain tech to reduce frictional losses.

Oil shedding coatings on things like the rods and rockers.

Real 3mil thick ceramic coatings on the piston tops, combustion chambers, valve faces, and exhaust ports. Real 15mil thick ceramic coatings on the header, pipes leading up to the cat, and the entire rest of the exhaust. All from swain tech. They will probably then get wrapped in header wrap, and sealed completely.

Whether or not the increased flow thing makes a difference, i'll be giving it the best chance to work. On top of that, the coolant temp reductions and engine compartment temp reductions are proven, which will allow a smaller radiator and less grill area. Plus, header wrap will also slightly quiet the exhaust note even further.

I have heard from some old-school racers that all of those coatings do help to make power in full-tilt-boogie race motors. Oil shed on the inside of the block (gets oil back to the pan faster), knife-edged crank throws, boat-tailed mains (help with air flow management inside the engine), teflon wrist pin buttons, and so on.

Many of them are only intended to work at high RPMs, which is not where fuel economy is found. It would be interesting to see what good any of them would do for MPGs.

-soD

Yep^, I figure they are in the realm of diminishing returns, but my goal isnt savings, so I figured I would try it.

lots of good info

I'm thinking about wrapping my exhausts.

Reasons? On my petrol ICE the CAT stays too cold during P&G EOC

On my Prius the engine sometimes runs for no apparent reason (like when stopped at a traffic light while fully warmed up). I suspect it could be to do with CAT temps.

On my diesel to help improve DPF regens.

On my turbo ICE to gain a little 'free' energy to spool the turbo at lower RPM.