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Discussion Starter #1
We all know that headers allow for better breathing. One down side to them is that they increase under hood temp due to heat escaping through a thin wall design. Manifolds on the other hand are thicker and offer more limited breathing but have a decreased under hood temp. My question is with the manifolds, where does the heat go? Would It in fact raise overall engine temp as a result of it not being released under the hood? Thank you in advance for your time.
 

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We all know that headers allow for better breathing. One down side to them is that they increase under hood temp due to heat escaping through a thin wall design. Manifolds on the other hand are thicker and offer more limited breathing but have a decreased under hood temp. My question is with the manifolds, where does the heat go? Would It in fact raise overall engine temp as a result of it not being released under the hood? Thank you in advance for your time.
I'm not directly addressing your question because I believe it's a very complicated answer. Instead, I've tried to offer a little insight to my thought process on the matter. But, I'm not 100% I clearly understand your question though :).

Manifold:
-- Less efficient breathing means more burnt (hot) air/fuel mixture remains in the cylinder. This, in turn, reduces the amount of fresh (cooler) air/fuel mixture into the cylinder and, subsequently, more heat goes through the cylinder walls/cylinder heads and into the anti-freeze. In other words, more heat is actually going into the engine's mass (during this time period in the engine's cycle).

-- The decreased fresh air/fuel charge means the cylinder has less energy (heat) at the end of the power stroke. Therefore, less 'new' heat is produced.

-- On the other hand, the heat retention properties of the exhaust manifold force more heat out of the engine bay and out the exhaust.

Header:
-- Increased cylinder evacuation means a larger charge of fresh (cooler) air/fuel. The larger mass of cooler air will help cool the engine. BUT, the larger mass of cooler air also increased the heat energy inside the cylinder because more air/fuel is burning (vs. the manifold). So, does that, in turn, transfer more or less heat into the engine???

-- The increased flow characteristics of the headers allows the burnt air/fuel charge to flow through the headers more easily. After that hot air/fuel flows through the headers, it goes through the rest of the exhaust.

-- Since the headers allow more heat into the engine bay, most engines probably see an increase in intake air temperatures (IAT). Thereby, increasing the heat transferred into the engine.

So, to find an answer to your question, you would need to run a detailed heat transfer analysis on each of the above scenarios (and probably several more I didn't think to mention). If you done that, you'd figure out which variable was the 'strongest'. I don't know that answer though :).

Have a good day!
Michael
 

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Discussion Starter #3
Damn, that was one hell of a response. It answered my question perfectly and I thank you for it. I did not realize these things were that technical. I guess that’s why you guys get paid the "Big Bucks $$". The more questions I ask the more I know why my title is "Junior Member". My reason for the question was that I am trying to decide between the two (PI Manifolds or Headers) and I am worried as my engine is high compression and I live in a hot climate. Trying to decide which would be cooler so I can cruise with a piece of mind. Thank you again for your time.
 

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Discussion Starter #6
Ok, I guess the headers it is. I just wish they were a little less expensive for my application. $575.00 for plain steel. I was used to the $125.00 351W block huggers. I guess thats the price we pay for Big Block Cool!
 

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One thing not mentioned is the fact that retaining the exhaust gas temp. throughout the system actually helps the exhaust gasses to flow easier. I'm guessing that it has to do with density......
Rob
 

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Years ago an engine builder told me that headers will heat up quicker than manifolds but they will also cool down faster as well.
 

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Call me and I can give you a price on coating your headers,need more info.Mike at M&R Performacecoating 865 933-1478.
 
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