FDNewbie

iTrader: (10)

I'm reviving Tyler's comment from another thread (https://www.rx7club.com/3rd-generation-specific-1993-2002-16/need-some-ideas-engine-bay-dress-up-202358/) because yesterday I was talking w/ an FD old timer (used to mess around w/ FDs back in the old days...like 1998, time of the PFS Gold Computer..etc... and he saw how I had everything polished minus the UIM, and told me "Smart thing for you not to polish the UIM." When I asked him why (because I actually planned on doing it) he said "See all the little bumps on it, how the surface is so coarse? That peice is cast iron and left like that to increase surface area, allowing for greater heat dissipation. When you polish the UIM, you get rid of all the grainy surface bumps, smoothing it out, effectively decreasing your surface area for heat dissipation. What you want to do is powedercoat it a thin light coat, maybe even a chrome powdercoat, then they can put a a thin color latex on it, so it still has the chrome appearance, but in a different color, plus the latex paint will protect the chrome from oxidizing. That way it's still bling while maintaining the increased surface area for heat dissipation."

Anyone have any comments on this?

Riccardo

iTrader: (1)

I think the guy ios right !!!!
attention to detail !
I would have never though of it in a mn years

Maxthe7man

I think someone is dreaming in technicolour....

FDNewbie

iTrader: (10)

I think the theory behind it is def. 100% correct and true, but what I'm wondering is the magnitude of the effect...if it's substantial or negligible? But then again, I think as FD owners, nothing that potentially makes our cars run cooler is seen as negligible

DaleClark

iTrader: (55)

First, the upper intake manifold is cast aluminum, not cast iron. Second, the reason the factory doesn't polish the cast Al pieces is because it's expensive to do in a production run - it's much cheaper to put the cast part on the car, which really doesn't look *bad*.

In theory, removing the roughness from casting COULD decrease heat dissipation, but I doubt you'd ever notice any difference. It's likely such a tiny difference in heat dissipation that it would be hard to measure. Even if there is a difference, are you going to get any performance gain or loss? Not really.

I'll wait for the mechanical engineer crowd to step in here .

Dale

ptrhahn

iTrader: (9)

I remember Brad Barber saying specifically that he left his manifold raw for heat dissapation. Surface area is surface area.

I've actually wondered about this as well in relation to ceramic coatings. Does one want to "seal in" the air, or "seal it out", and does the ceramic coating impede dissapation?

On a downpipe, it's obvious, you want to prevent the ultra-hot exhaust heat from disapating though the DP, and subsequently heating the engine bay... but on intake parts, it isn't so clear.

Mahjik

iTrader: (1)

IMO, I would worry more about heat absorption rather than dissipation.

If you are that worried about it, have it ceramic coated to reduce the amount of heat absorbed. That will probably get you a better benefit (i.e. stopping/slowing down the problem at the root rather than at the end).

Kento

It does impede heat dissipation, because ceramic is an insulator. It's the reason why true ceramic coatings on pistons only coat the areas exposed to the combustion chamber. Otherwise, the piston would gradually retain enough heat to suffer metal fatigue or even failure.

I doubt you'll see any intake temp differences between a polished and non-polished UIM.

jimlab

At high rpm (or even at idle, for that matter), how much time do you think the air charge actually spends in the intake before being pulled into the engine? How much heat could it absorb between the intercooler and being burned? Not a hell of a lot.

Anyone worrying over whether or not polishing the casting will decrease its potential to dissipate heat has far too much free time on their hands, if you ask me. The upper intake manifold is going to heat soak eventually whether it's polished or left as-cast. If you're truly worried about it, have it thermal barrier coated inside and out.

Ramy, why do I get the feeling that you're going to reach 10,000 posts and still not really know anything substantial about your car?

jeremyb

Putting a ceramic coat would still allow you to put paint on top of it right?

Jeremy

moehler

iTrader: (12)

This is a VERY rough estimate as i'm on my lunch break with no real measurements in front of me. Since people usually only polish the top of the UIM, assume the UIM is a rectangle with a top surface is 27 cm X 21 cm (rough guess ). So, this is a surface area is 27X21 = 567 cm^2.

Now assume that the bubbles are 1/2 spheres with a 1mm radius. That would give us approximately 56,700 little bumps on the top of the UIM. This would be a total surface are of 56,700 *4*pi*(0.5)^2/2 = 89,064.0 mm^2 = 890.06 cm^2.

So just from looking at the top surface of this fake UIM there would be approximately 50% increase in surface area over the top of our fictitious UIM. If the rest of the UIM was not polished this would probably reduce by roughly 1/3 to be 16% more surface area over the OUTSIDE of the UIM. Thus maybe 5% or so over the entire (outside and inside) UIM.

Considering all of the other factors with air flowing though it, heat absorption, etc... I would think that this has a negligible impact overall.

Kento

RX 4 Speed

I agree... the effects are probably negligible. But if you really need to know, why not just take a temp reading before and after on the UIM? You could probably use an infrared temp gun... it wouldn't be 100% accurate, but close enough...

CrispyRX7

iTrader: (139)

I'll agree with Jim. The time the intake air spends in the UIM is so short that any temperature difference in the UIM itself will result in negligable increase in intake air charge temp.

Addiitonal point, although not really relavant as the UIM will heat soak eventually, is that a polished surface will reflect radiant heat energy better (like a mirror) and absorb less. Likewise once hot , that surface will not emit as much heat due to the polished surface. A rough cast surface however will absorb more heat energy (less like a mirror) but will also be a better emitter of the energy. Like I said, once heat soaked, it comes out a wash so is relatively inconsequential what surface finish the UIM has. One must also consider conduction and convection.
Engin-nerds refer to the Stefan-Boltzmann law. Incorporate an emissivity value for varying surface and you can determine radiation energy emitted from the surface.
I don't have exact values for AL but polished surfaces typically have emissivity values about half an order of magnitude less than metals with "unfinished" surfaces.

FWIW,
Crispy
- with polished UIM

Herblenny

iTrader: (13)

GEEZ!!! what else people going to worry about next..
Ramy, Get a bigger IC and don't worry about some dimples that increase surface area.. by what.. 20-30%?? Also don't forget that its pretty freaking thick! Like others said, Mazda and most auto companies, when they cast, its cheaper not to get it nice and smooth.. you'll also see some cast marking around to seperate from the mold.. Is this guy calling that cooling fins?? That mazda put there for purpose..

dgeesaman

iTrader: (7)

It's not a dumb question, first of all. The ability to ask meaningful questions (this one is based on sound ideas) isn't appreciated enough.

IMO it's probably negligible. In theory, the decrease in surface area and bulk mass changes the way the UIM absorbs/passes on/soaks heat, I just dont' think it will affect the air much.

Maybe a test would show a measureable difference, but I will bet my new wiring harness that I can still find 5 other things are more effective at changing the charge temps. (intercooler, I/C ducting, CAI).

Dave

DaleClark

iTrader: (55)

Also, I think a key factor as far as heat dissipation is the *mass* of the item, not the surface area. Polishing takes only a fraction of the mass away.

Jim's got it dead right - most people don't realize how VERY fast air moves through the engine. When I talked to Corky Bell years back, he was saying he had seen air speeds in intercooler pipes in the HUNDREDS of miles an hour. You have to have a turbulator of some kind - ie, the cooling fins in an intercooler - to make the air slow down enough to give up some of the heat energy.

Dale

DaveW

One thing nobody has mentioned here is that the air is not always at maximum velocity. Whenever you lift off the throttle (I assume that everyone has to do that sometime...) the air mostly stops moving and heat soaks (assuming that the CAI, IC, etc. was providing air that was cooler than the engine compartment). Then, when you open the throttle, you have hotter air for at least the first moments after throttle opening, at the very least, slowing throttle response.

iluvmy3rdgen

Just run a chemical like liquid nitrogen but to a lesser degree through veins in a pre-fabber LIM/ and UIIM and make some intercooler pipes that have some tubes of a chilling chemical. The colder the chemical can be, when nothing is moving will make for substantial throttle response, maybe too much?

iluvmy3rdgen

Wow, I just spoke like a drunk. I apologize for the grammer and punctuation.

turbojeff

iTrader: (30)

Because there are WAY to many variable to any meaningful data that way. Outside temp, driving conditions, location(s) measured, etc, etc.

I think the surface finish has more to do with heat radiation (into or out of the system) than the surface area change in convection heat transfer (HA(deltaT). Radiation heat transfer only happens in "line of sight". Since the manifold can't "see" anything hot I don't think it matters much.

If your going to worry about anything worry about polished, thin walled aluminum intake pipes right above the turbos and IC pipes...

dgeesaman

iTrader: (7)

That's true - the solenoids and vacuum lines soak up all the engine block heat

jxl914

ok guys let me throw my 2 cents in here, I have built several intakes for formula style cars and here are my thoughts

-the intake is rough because it is probably a sand casting and its a cheap way of doing things although it has a crappy surface finish. All other ideas aside, this is probably the reason for the rough texture.

-the increase in surface area will increase the heat transfer rate but the effects will be negligible and I highly doubt that this was the designers intention.

-ok, now on to my idea. In the past we have intentionally roughed surfaces before the injectors to act as turbulence promoters. While turbulent air is generally bad, it's random nature has the benefit of mixing and creating a more homogeneous charge to the engine. If the surface was roughed intentionally, then this is probably the reason for it.

just my opinion.

mad_7tist

they will prob heat up and cool down at different rates. but so what? if you want to compare take 2 throw them in the oven and hit the surface with an infared thermometer. see which gets hot faster. then see which gets cool faster. it is all silly as jim said after any amout of driving it will reach a threshold temp for a given driving style/time. throw a bag of ice on it like all the auto X guys do between runs

poss

iTrader: (5)

Not necessarily directly on topic, but aluminum has very low emissivity. Unless it's molten state, do you ever see it glow red? There is very little heat lost to radiation, it's mostly through convection.

I agree with most every one else here, the difference is going to be negligible.

Another reason against the factory polishing it is the maintenance issue. Stock, a good wash down and and it looks like new vs. repolishing it every couple months.