Contour Enthusiasts Group Archives Forums Modifications Duratec Performance Keeping the intake charge cooler (re: Jet Hot UIM)

Okay, so I see alot of people are signed up to Jet-Hot coat their UIM. I am skeptical that this will make a significant difference in the intake charge temperature. Why?

Thermodynamics states that heat transfer happens in one of three modalities. In order of efficiency, they are:

1. Conduction (physical contact between surfaces)
2. Convection (air blowing across surface)
3. Radiation (exchange with non-moving air)

So why does the UIM get hot? According to the above, it is more likely that the UIM is heated by the conduction of heat from the engine block than by either the flow of air in the intake or the radiation of hot air under the hood.

If the above thinking is correct, then wouldn't it make sense to block the conduction of heat from the engine block? I am thinking that a good way to do this would be to do something like Jet Hot coat the LIM, as described below:

"Also if you are doing the LIM [Jet Hot] offers an option to coat the bottom side of the LIM between the LIM and the engine block with a BLACK heat barrier to help block/reduce heat coming up off the engine."

now if my assumption is wrong, and the UIM is heated up more by the underhood ambient temperature than by the conduction of heat from the block, then what should really be done is wrapping or coating the exhaust manifolds (i.e. headers), since they are the main source of heat under the hood.

is my thinking on track? if so, people aren't coating the parts that need it the most...

I would have to assume that the manifolds get hot from the heads. Have you felt the manifolds after fully warmed up? There's no way you're going to almost burn your hand on the manifolds strictly from the underhood heat. In effect, you are talking about the phenolic spacer idea for the manifold which has been shot down SO many times by the most knowledgable people of the site. I don't see there being a noticeable improvement from Jet Coating the intake manifolds. Maybe to look better, but not as a performance gain. Especially when our manifolds sit directly on top of the heads, as opposed to say a 4 cylinder Honda IM that sits on the side.

Yeah, you're probably right about the conduction being the #1 cause of the UIM getting hot. No way the ambient temp gets the metal that hot, though it surely doesn't help.

Still, it cant hurt to have the UIM colder than the heads. If nothing else, it'll be a few milliseconds that the intake charge isn't getting super heated.

I am no expert on this but I suspect heat radiating off the heads contributes a good bit of the heat...
1) the surface area of the bottom of the UIM is many times larger than the relatively small LIM/engine contact

2) There are 2 plastic gaskets to reduce convection (above & below LIM) a bit.

I am sure convection transmits a good bit of heat but I think radiation does too.. As "anacdotal" evidence...I have had thermotec heat shielding on the underside of my UIM for over a year. It "seemed" to reduce the touch temp of the manifold to a noticable degree (for only $10 or so)..

interesting! thanks!

so if the heads are the biggest contributor of heat to the intake manifolds, then doesn't it make sense to Jet coat the valve covers to keep the heat inside?

keeping heat in is not always a good thing, if you coat the valve covers then the engine temp will go up and the pcm will start to pull more timing than it already does to compensate and you will end up losing hp

Yeah this has all been debated before.
In fact Im pretty sure Im one the first few CEGers to do this mod.
Thats my engine pictured in the group buy:


I wouldn't disagee with you, but who knows for sure with out actual testing.
I can tell you that (by touch) the heat was noticeably less.
I can actally lay my hand on the UIM after a two hour drive.
Im not gonna tell you I felt a difference in power (butt-dyno). Some people began powdercoating, I figured why not go a step further and ceramic coat it.
Does this help? Sure it does. Is it the best way to go about it? Probably not, Im sure there are cheaper methods as stated above. I was sposored by Jet Hot and had them do this. Along with my cold air intake, Y-pipe, etc.

They do coat the entire UIM, right? Not just the top, right? Just making sure

We're probably not going to feel any kind of power gain, but we're going to have cooler intake charge (well, hopefully ) that'll prevent us from losing hp from said timing pull, etc.

Quote:

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but we're going to have cooler intake charge (well, hopefully ) that'll prevent us from losing hp from said timing pull, etc.

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Derk I usually agree with you, but i'm not seeing how coating the manifold is going to cool the intake charge to a noticeable effect. If every 11 degrees of cooler air is a 1% increase in ouput, I don't even see this cooling the intake charge by 11 degrees. You should do dynos before and after or something, i'm just not seeing how it would really affect the intake charge noticeably.
Ok I just thought about it as you emphasized entire UIM, it's still hard to say, but only testing will prove anything I suppose.

Johnny, I agree. I don't think there'd even be a dyno-able result, unless you dynod, unstrapped, drove around for an hour, then re-dynod.

Coating the UIM means the intake charge has to pass through one less untouchably-hot piece of metal. I think that's the real purpose of this mod.

See what I'm saying?