Odd you should say that today. Some time ago I mentioned a magazine I'd seen that did a test of coated vs non-coated headers. Today I found it and actually have it laying right beside me trying to figure out how to capture the info in it w/o getting in too much trouble. And, while I was thinking of placing the info in some place a bit more accessible than hidden in a thread like this, here goes nonetheless.

Basically, they found no difference in power, meaning torque or HP, with or without the ceramic coating. However, the surface temps of the headers were a whole 'nuther thing:

• Full load on dyno
  • With coating: 258° dropping to 195° one minute after shutdown
  • Without coating: 870°, dropping to 520° after one minute
• 60 ft-lb load on dyno simulating cruise
  • 288°
  • 850°

I think I'll have mine coated.

 

Wow that's a huge difference. I would have never guessed it would be that much. With that much difference I would think it would make a difference in power because of having less heat in the engine bay warming up the fuel and air going in. I bet it does make a difference in the truck just not on a dyno. Just my guess though.

 

I should have quoted the Engine Masters magazine, and the Winter 2014 issue.

Cole - That's pretty much what they said as well. Imagine the heat under the hood and people that insist on running headers with an open-element air cleaner. Ever wonder why many of the really go-fast cars in the 60's had cold air inlets? There's your reason. And, Ford provided the same for our trucks and we take it off and stick a cute little round air cleaner on to suck up all that hot air.

This guy claims "a 7.2 degree change in air temperature causes a 1% horsepower change". Not sure that's the right #, but there is a significant improvement. So think about how much help the original air cleaner can give, both in cold weather with hot air from the exhaust and in hot weather with cool air from the radiator support. And then you'll see why I'm creating a dual snorkel air cleaner for my "stroked 351M".

 

I never thought of it that way. I always figured the heat created under the hood wouldn't be enough to affect much anyways, but it seems Ford disagrees.

 

That's very interesting! So that is truly a myth that coated headers run hotter. I would have never thought that. I would have assumed that the coating acts like insulation and would slow the heat transfer down vs painted or bare metal.

Another myth I would like to bust open here is the BBQ paint on headers. I have heard that it lasts a good while. Here is my personal experience. The Bronco has about 2 hrs of run time on it since we painted the headers. Gary, you remember the prep we went through. I put them in the blast cabinet and stripped them . You applied liberal amounts of brake cleaner and then completely soaked them down with BBQ Grill paint. IMO the prep was more than adequate as well as the application of the paint. The small amount of run time mine have on them has burned off half of the paint and gone back to naked metal.

 

Angelo - A carb is a wonderfully complex device that is dumb. A thick as two planks they would say in the UK. It can't sense air temp. But, the amount of oxygen in a given cubic foot of air varies dramatically with the temp of that air. So the air/fuel ratio effectively changes with changing temp.

Given that, the only way to hold the air/fuel ratio fairly constant is to feed the carb air at a fairly constant temp. And you'll never do that with an open element air cleaner. You will have terribly cold air in the winter that leans the mix out to the point you need the choke a long time, and even then you can easily have carb icing, as several on here have had this winter. And in the summer the mix will go quite rich with the HOT underhood air and the fuel mileage will go away.

Bruno - Jet Hot is in OKC, so I'm planning to visit them at some point. I wonder if we should have a GTG there? As for the BBQ paint, we prep'd the goodie out of those headers, so if the paint is going away after 2 hours it is not worth it to use that paint. Simply a waste of time and money.

 

So, at cruise there would be a 562 degree difference in temperature. Assuming that 1/10(total guess) of the heat from the headers is transferred to the air in the engine bay that would be a 56.2 degree difference in intake air temp, which according to that number would be a 7.8% hp change... So if your motor puts out say 200hp with normal headers it would put out 215hp with coated ones.

 

Cole - I haven't bought into the 7.2 degree change making 1% difference in power. That's just one guy's # and I haven't found it substantiated. Others have said 10 degrees equals 1% change, but I've not found even that cast in stone.

In any event, the fact remains that there is less oxygen in hot air as opposed to cold air. So there is some reduction in power potential as the air inlet temp warms up. Given that your calculations are going in the right direction. I just don't know the magnitude of the answer, but I do know the sign. Does that make sense?

 

Yeah, and my guess of 1/10th the header temp going to the air is way off I'm sure so it's not accurate at all anyway. And doesn't cold air have the same amount of oxygen as hot air? I thought that the density just changed and there was still the same proportions of the contents in the air. So you just have to use more volume to get the same amount of oxygen because the hot air is less dense. Which is why boost is good for making power, it makes the air more dense which puts more oxygen(and everything else in air) in less volume, correct?

 

Actually, I've been saying it incorrectly. Charles' Law states that "A gas occupies 1/273.15 more space for each 1° C. rise in temperature." So as the temperature rises there is less everything in a cubic foot - less oxygen, less nitrogen, less everything. However, for an engine all we are concerned with the the oxygen as it is all that will burn. In other words, the chemical makeup of air doesn't change as there is still as my oxygen as a percentage of everything else. But, there's just less of everything. So the result is the same - there is less oxygen to burn when the temp goes up.

And, you are right, you have to have more volume to get the same amount of oxygen. However, since the carb dispenses on the cubic feet of air that passes through, regardless of the amount of oxygen, if the temp increases we have more fuel than we want with the oxygen that is coming through. So the mix goes rich and the gas mileage and power suffer.

 

Yeah, and that only applies for ideal gases right? That's what I was getting at is the amount of oxygen in proportion to the rest of the air doesn't change, there's just less of everything in hotter air because it's less dense.

So according to Charles' Law if it applies to everything in air(I don't think everything in air is an ideal gas but can't remember) then 1/273.15 per C would be a 0.00366099 increase in volume for every C it is heated. So converting 562F to C you get 294.4C, 0.00366099 x 294.4 = 1.07796. So in our 200hp example 200hp x 1.07796 = 215.6hp. And I just realized I didn't factor in the fact that header temp doesn't equal air temp but I'm not doing the calculations again haha...

 

I have a degree in both math and physics - and I think I followed that. Well done!

Yes, ideal gas. But what we are dealing with is close enough. And, you are right about the header temp not equalling air inlet temp. I realized that earlier but there were enough other things to discuss I didn't see it as a big issue.

 

??? The engine is creating the same amount of heat out of the exhaust I would think. If their detector detected less heat around the headers while it was running, then the ceramic coating would be a insulator wouldn't it? Blocking the heat from escaping the header pipes.


BBQ paint is what they put on them from the factory. I do not know that for a fact, but it acts the same way. That expensive VHT paint you can get in the store will stay on them. It will discolor a little bit, but it will not burn off, I tried it like I said in my previous post. So it would be worth painting them with that.

 

All this temperature theory is true, but then you have what the factory was trying to achieve. They want a STABLE air intake temperature. Their ultimate goal is tuniing for power to beat Chevy and Dodge, and tuning for emissions to get the Gov off their back and meet emissions. It's very difficult to tune a carb to the best air to fuel ratio for power and emissions when the temperature of the air entering the carb varies over a wide temperature difference. Like was mentioned, the oxygen content varies greatly, so that affects the tune of the carb, and I think it was also mentioned a carb cannot compensate for temperature differences.

When you realize this, then you get the jist of what all that aircleaner stuff is about. Drawing air from the grill area and from the exhaust heat stove, with a sensor that modulates a door that can mix both air sources to keep the temperature constant. Then they can tune the carb to that. I seem to remember reading somewhere that either Chevy or Ford tried to keep their air intake temp at a constant 100 degrees(that is what the sensor was set for). Not ideal for max power, but good enough for decent power and to tune the carb for emissions.

That's why I like aftermarket non-emissions carbs on a engine that has been modified. If all this other stuff is not right or has been taken off, the original carb doesn't run as well as a aftermarket carb does.

 

Hey! That's my song!

Absolutely. The factory had what, 800+ "calibration codes" which were all the bits that added up to air/fuel ratio and spark advance. Those were to zero in on the exact AFR the engine needed to meet the emissions requirements and still try to deliver power and economy. And the only way to accomplish that was with keeping the inlet air temp as constant as possible.