Just a clarification, the specific reason I pursued re-use of the OE SS gasket, was I wanted to maximize heat transfer from head to header (just as did the OE manifold). I have a couple reasons for wanting that, but neither is in any sense critical for an aftermarket header. Roller_Toaster is clearly pleased with the performance boost gained from installing the header with the supplied gasket, and I'm definitely not suggesting there's anything amiss with his install !

 

Thanks everyone for clearing this up for me...I have this on my "mod list" of things to do..

 

I did have one or two dots of slag on the mating surface that I filed off.

Since I was in a bit of a rush to get it put on, I used the supplied gasket (due to it being thicker than the oem metal gasket) to reduce the chance that I would get a leak if the mating surface was not completely straight. No leaks so far, but TrevorS is correct about the original gasket transferring more head TO the header, and not retaining it as much as the gasket I used.

 

Somehow I think the 1700F exhaust gasses transfer a lot more heat to the header than the gasket material between the MUCH cooler head and header. As long as your gasket doesn't leak, it's as good as any.

 

Sure it does, but heat transfer from the head proper to the header is one of its cooling mechanisms. I disagree that leakage is the only measure.

 

Another interesting theory.

 

So you think the more expensive OE stainless steel super thin gasket was for grins? Maximizing head cooling makes much more sense to me. They're already taking a hit on the intake side due to use of a plastic manifold. Doubt they intended to take a hit on the exhaust side too, especially given that SS OE gasket.

 

I thought they used a thin MLS gasket for it's superior sealing, heat and chemical resistance and extremely long service life.

In order for the header to act as a heat sink for the head, the surface temp of the head (outside the water jacket) would have to be higher than the surface temp of the header, correct?

I propose a test. Take a rubber valve cover gasket and attach it to your header pipes and see how long it lasts.

 

But you've already said an aftermarket gasket is just as good as the SS if there's no leak! Plus, different portions of the head are at different temperatures (I've never run into a rubber intake manifold gasket either, though they have to be doing something special to permit a plastic intake manifold with these engines). Don't know about you, but I haven't heard of or experienced an exhaust manifold gasket failing (presuming properly torqued). So, as already indicated, I'm not dis'ing the provided gasket, I just don't consider it optimal.

As far as head temperature, the heat delivered to the head is maximal (no gas release during ignition and power stroke) and the close coolant passage design is critical and I'm not questioning its adequacy, but does that mean the heat transfer to the exhaust manifold flange isn't intentional? Whatever, it's definitely not worth arguing over. The reason is the reason and I've yet to come across a Toyota design engineer to shed any light on these specifics !

 

It's a gasket! If it seals the mating surface irregularities forming a leak-free union, it's doing it's only job as well as any other.

Any engineer that would even contemplate using the intake manifold as a heatsink to assist in cooling a water cooled engine should be fired! A plastic intake manifold with a thermally insulating gasket is a very good design. Why would anyone want to heat the air charge and fuel injectors all the time?

Since the header flange is hotter than the mating surface on the head, the only heat transfer taking place at that junction is from header to head to engine coolant.

I've seen several exhaust manifold and header gaskets fail. The graphite paper gaskets blow out and are single-use. SS MLS is probably the best overall although some people swear by copper.

 

The plastic intake manifold is an evolution in engine design, not that long ago it was iron. Obviously, plastic is preferable in terms of keeping the fuel mixture cool.

True, that would be the question, how does the head exhaust face temperature compare to that of the header flange? The OE manifold flange is thin and will be radiating only modest heat from the small contact surface area of the four pipes passing through it, and that was what the OE SS gasket was spec'd for use with. The aftermarket flange is thicker and has a larger pipe contact surface area and will reach a somewhat higher temperature. You say you know both will have a resulting temperature that exceeds the head exhaust flange surface. Well, I don't know that and I'm not clear how you know that, so once again, I fail to see the reason for prolonging this!

 

Look at the big picture, not just the thin MLS gasket. The head is a big chunk of aluminum with water cooling passages inside. AL is the 4th best element for thermal conductance behind gold, silver and copper. Heat moves quickly throughout the AL head to the coolant passages, minimizing hot spots. Cast iron, Mild and SS all have poor thermal conductance, hold heat and make terrible heatsinks.

I'm not trying to argue, merely inform.

 

Well, I simply can't be sure of the direction of heat flow, so I'm forced to leave it at that. I do know from reading there can be dramatic differences in temperature between one part of an aluminum head and another (measured in multiple thousands of degrees), but I have no conclusive information one way or the other regarding the issue I raised.

 

If you search a little for "external cylinder head temperatures" you'll find that head surface temps usually run between 250-400F at the hottest point. This includes air-cooled engines. Combustion chamber temps are obviously a lot higher than that. The next time I'm near Harbor Freight I may pick up an infrared thermometer and measure my head and manifold temps. I've wanted one for a long time anyway and for only $30, why not?

BTW, I forgot to mention previously that our engines are also oil-cooled to an extent.

 

http://www.iiis.org/CDs2010/CD2010IM...df/FB075TI.pdf

 

Link is to a blank pdf?

 

Strange, it was anything but blank when I linked it -- a pretty large file at that containing internal head temperature maps and example cooling modifications.

Trouble is, my system picked up a serious virus a couple days ago and I'm still trying to recover. Just reinstalled Adobe Reader, but I'm not able to read anything PDF off the web right now -- like I've a plug-in problem.

 

Ahhh! Finally got my Adobe Reader plug-in function working properly again and no, the file is definitely not blank.

Here's the URL again: http://www.iiis.org/CDs2010/CD2010IM...df/FB075TI.pdf

 

Sorry to hear about your PC virus. I hope it didn't cause too much damage or trouble. The link is working now and contains some very interesting, if overly technical info.

Admittedly I didn't read it all, just scanned through it, but I didn't see any mention of external surface cylinder head temps or additional air-cooling of the cylinder head via intake or exhaust manifolds. It appears to be focused on reducing detonation on turbo-charged engines through the use of better optimized water cooling passages, water/meth injection and more effective intake air charge intercoolers.

 

No, I haven't seen anything regarding non-waterjacket cooling, that wasn't the reason I linked the article. It was because it provides example measured temperatures within a head, and they can get quite high (knock being a concern for N/A as well as F/I engines). In any case, as far as I'm concerned, it's a conclude what you choose situation, which is what I was trying to say a few posts back.

PS. My original link also works for me now. I just needed to get my browser setup properly.