Legal and beneficial to coat outside of 16V intake?

[GTIspirit]

Question for those in ITA running a 16V, or anyone else who can offer feedback. Legal and beneficial to coat the outside of the intake manifold?

GCR 9.1.3.D.1.q


The application and/or use of any painting, coating, plating, or impregnating substance (i.e. anti-friction, thermal barrier....) to any internal engine surface, including intake manifold internal surface, is prohibited.

So does this mean it's legal to coat the outside of the intake manifold? Reason I'm asking is because I've noticed that my 1.8L 16V intake manifold gets awfully hot, and that can't be good for intake air temps. Would coating the outside with the recommended Swaintech coating be beneficial for reducing intake air temps?
http://www.improvedtouring.com/forums/showthread.php?t=18081&highlight=thermal

For the same reason I was thinking of getting my header coated, and it's quite clear that is legal.
GCR 9.1.3.D.1.g

Any exhaust header and exhaust system may be used....

[Gary L]

I can't scientifically address the benefits of coating the outside of an intake manifold... I'll let the HP gurus take that on. But according to the rules, parts may, in fact, be "...coated, painted, or plated" (9.1.3.C).

But be careful, because if the blanket rule above were not extant, your assumption - if it is illegal to coat the inside of a particular part, it is therefore legal to coat the outside - would be dead wrong. IMO, this sort of interpretation would eventually put you at risk of ending up with illegal parts. Remember the overriding rule in Improved Touring is "IIDSYCYC"... If it doesn't say you can, you can't. This is in it's vernacular form, the actual quote from the ITCS being:

"Other than those specifically allowed by these rules, no component or part normally found on a stock example of a given vehicle may be disabled, altered, or removed for the purpose of obtaining any competitive advantage."

[m glassburner]

I agree !!! :blink:

[shwah]

I think you would get more benefit by coating the heat source - the header. 1. because this item is completely open in the rules - no grey area, and 2. because this helps prevent heat soak to several items - head, coil, intake.

I am kicking myself now for not doing this when I had the motor out last, and will do it at the next opportunity.

[JamesB]

On the 16V the header is not the complete source of heat on the intake manifold, but coating the exhaust would likely reduce some of the heat in that area of the engine bay and the upper part of the intake. Otherwise, the fact that the intake wraps around the head you will never be able to completely stop the heat soak since the radiant heat of the head will still transfar to the intake.

[Andy Bettencourt]

An interesting topic. I have wanted to repaint my valve cover for a while now and have thought about it. I think the best thing to do wrt horsepower is to limit the radiant heat getting TO it (by developing a proper exhaust heat shield and intake shield) but also letting the heat get OUT of the manifiold by NOT coating or painting it. If you trap the heat inside the intake manifild, in my mind you are losing power. The opposite of the exhaust manifold.

[mbuskuhl]

In reading the rule, I would say coating the outside of the intake manifold is legal. If the rule was meant to prohibit coating the outside, there would be no reason to have added internal in saying "intake manifiold internal surface". Clearly the adding of internal was done for a specific reason.


Here is a good read on coating intakes, a thermal barrier is applied to the underside and a thermal dispersant to the top.

http://www.engineceramics.com/coating_a_manifold.htm

Andy was right not to paint his valve cover, paint would reduce the ability of the cover to dissipate heat. Coating it with a dispersant would be the way to go, also doing the oil pan is an option.

http://www.engineceramics.com/coating_the_oil_pan.htm

[GTIspirit]

....but also letting the heat get OUT of the manifiold by NOT coating or painting it. If you trap the heat inside the intake manifild, in my mind you are losing power. The opposite of the exhaust manifold.

Hmmm, a good point to ponder. My thought is that intake air, ambient air, is always cooler than the intake manifold itself. Heat flows from hot to cold, if I remember my thermodynamics correctly (not a class I did so well in:( So the hot intake manifold is heating the cooler ambient air flowing through the intake manifold. So my thought was to keep the intake manifold cooler, it shouldn't absorb heat from the engine bay. If the radiant heat could be 100% reflected by the intake manifold, it would always be at ambient air temperature, except for the conduction effects from where the intake manifold contacts the head. (And I've seen some power gasket products sold for turbo manifolds to supposedly address this to increase power.)

I'm thinking this probably isn't something cheap enough for me to just experiment with, so probably best to just start out with coating the header....

[shwah]

You are probably near 50/50 in terms of the manifold surface 'seeing' hot or cold surfaces to have radiant heat transfer with. You will have a fair amount of conductive heat transfer from the head to the manifold. A barrier on the bottom surfaces and dissipator on the top surfaces makes good sense, or heat sheilds and a dissipator everywhere.

[evanwebb]

OK, so I'll speculate on a few things here based on what I have learned from building spacecraft that depend ENTIRELY on conducting heat to radiators that look at cold space to maintain their desired temperatures. This is speculation, though, and we would need to do some careful testing to verify.

First keep in mind that your whole engine is pretty much a big chunk of heat conductive metal, generally iron or aluminum. There are a few "heat breaks" in the system, basically intake/exhaust/head gaskets. The manifold gaskets are pretty thin (plus some have metal cores anyway), so probably (would have to test to know for sure) they don't provide much of a thermal barrier. Good thermal conductors (most metals, the exceptions being most stainless steels and alloys of titanium) in general don't tend to allow much in the way of temperature gradients: even with the forced air (preheated by the water radiator, oil cooler, etc.) going through the engine compartment I doubt you get any more than several degrees F gradient between spots near the top of the block or head (excluding the manifolds which are a special case). I assume that a thick head gasket might be somewhat effective in allowing a gradient across the head-block interface, maybe 10 degrees or so?

The hottest area is the exhaust manifold, so reducing the surface temps of that by a thermal barrier coating to reduce its radiative heat transfer to the surroundings makes sense. Assuming a non-crossflow head, the situation with the intake manifold is different. The intake is bolted to the head, and after the engine is up to operating temps the head is going to be a fairly constant temp except for local hotspots in the combustion chamber and exhaust port. Hence, since the head and the intake are good conductors and they are bolted together then the intake is probably going to be more or less the same temp as the head, which will likely have a bulk temperature somewhere between your water temp and your oil temp.

I think it's likely that the best thing to do with the intake is to coat it on the exterior with a heat-dissipative (high emissivity) coating to try to reject as much heat as possible via radiation. The downside is that unless you spend DOD- or NASA-type money on the coating, it might be a wash because many high emissivity coatings tend to also be high absorptivity as well, which would tend to absorb more heat from the exhaust manifold. (see discussion of A vs E below...)

Surface finish and coatings can have a huge effect on the emissivity of a surface. Polished metal is pretty bad at radiating, so one possibility for the header rather than coating is to use a stainless header and shine it up real nice.

For the intake, rough surfaces radiate better so if you accept the philosophy of trying to radiate heat out of the intake, then an as-cast surface or a glass beaded surface combined with a light coat of flat black paint (remember we are trying to get it to be a blackbody radiator) would be the best solution short of an expensive aerospace high-emissivity coating. You definitely don't want to use a header coating that has low emissivity.

Coatings (including paint) can be categorized in their radiative thermal properties by stating the absorptivity (or A) and their emissivity (or E). A and E are dimensionless parameters bet ween 0 and 1. The ratio of A/E tells you whether the coating preferentially absorbs or radiates heat. Keep in mind that the actual amount of heat transfer is dependent on the temperatures of the objects that the coated surface can "see".

Someone mentioned not painting a valve cover so it would radiate better? Why would you want your valve cover to be a radiator anyway? But anyway, if you do, then the same suggestion as I mentioned for the intake manifold is what you want.

[evanwebb]

But then again, I'm an electrical engineer, so that all might have been total BS anyway...