Why do would you heat wrap your downpipe? - Toyota Tacoma Forum
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#1 (permalink) Old 05-18-2011, 01:01 PM
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Why do would you heat wrap your downpipe?

So cold air is denser, i get it. When you heat that air up (like adding fuel and a spark!), the volume of that same air increases significantly. This is how turbos turn thermal expansion into extra power. The turbine has a larger volume of air flowing into it than what went into the engine that revolution, this drives a compressor that forces some proportional volume of air into the engine for the next revolution, this is where the compression comes from.
Ideally you want the air to go thru the turbine of the turbo at the highest temp, giving you the highest volume of air possible. This being the reason for ceramic coated manifolds and thermal jackets over the turbine housings, to keep the air from cooling (condensing) until the turbo is done with it.
But as soon as the turbo has used those exhaust gasses, wouldn't you want to cool them as quickly as possible? If you wrap your DP that keeps the expanded gasses trapped in the pipe. higher volume (hot air) inside of a fixed volume container (exhaust system)=pressure in the container (back-pressure). I understand that part of the reasoning is to keep the temps under the hood down, that makes sense, but wouldn't it be more effective to build a heat shield around your DP to keep the heat in and then force cool air thru the gap between the two to cool the DP, condensing the air, and making it flow through the pipe with less resistance? If you ran cool air in from the front, like brake ducts and other things are cooled, plumbed it to the top of the heat shield, and had the opening at the bottom under the truck and away from the "underhood" area, you could keep the engine bay cool AND reduce back-pressure.
Why doesn't anyone do this?
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#2 (permalink) Old 05-18-2011, 03:01 PM
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Re: Why do would you heat wrap your downpipe?

Quote:
Originally Posted by arr4u2nv View Post
So cold air is denser, i get it. When you heat that air up (like adding fuel and a spark!), the volume of that same air increases significantly. This is how turbos turn thermal expansion into extra power. The turbine has a larger volume of air flowing into it than what went into the engine that revolution, this drives a compressor that forces some proportional volume of air into the engine for the next revolution, this is where the compression comes from.
Ideally you want the air to go thru the turbine of the turbo at the highest temp, giving you the highest volume of air possible. This being the reason for ceramic coated manifolds and thermal jackets over the turbine housings, to keep the air from cooling (condensing) until the turbo is done with it.
But as soon as the turbo has used those exhaust gasses, wouldn't you want to cool them as quickly as possible? If you wrap your DP that keeps the expanded gasses trapped in the pipe. higher volume (hot air) inside of a fixed volume container (exhaust system)=pressure in the container (back-pressure). I understand that part of the reasoning is to keep the temps under the hood down, that makes sense, but wouldn't it be more effective to build a heat shield around your DP to keep the heat in and then force cool air thru the gap between the two to cool the DP, condensing the air, and making it flow through the pipe with less resistance? If you ran cool air in from the front, like brake ducts and other things are cooled, plumbed it to the top of the heat shield, and had the opening at the bottom under the truck and away from the "underhood" area, you could keep the engine bay cool AND reduce back-pressure.
Why doesn't anyone do this?
Probably due to the complexity of it. I honestly dont think there would be much of a measureable difference in your power, plus that DP can get orange hot with or without the wrap on it so without the wrap that temp wont change a great deal, I see what you are talking about, but after the wrap in the exhaust system it will cool considerably at that point and this can cause a scavenging affect under normal (unboosted) conditions reguardless of wrap or not. Also with turbo systems the exhaust is usually a much larger size (compared to NA vehicles) in order to keep the exhaust from creating the "backpressure" you speak of.

Just my "theory"..

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#3 (permalink) Old 05-18-2011, 03:31 PM
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Re: Why do would you heat wrap your downpipe?

I wrapped mine, but that was just to try to keep the heat in the exhaust rather than under my hood, and away from the wiring. I don't see a lot of scavenging going on at lower power levels. I would assume that the back pressure needed for out of boost performance would be accomplished by having a turbo in place.

Mostly its about what works best for your application.

and things move faster when they are hot.


Last edited by 2rzfun4me; 05-18-2011 at 03:35 PM.
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#4 (permalink) Old 05-18-2011, 07:50 PM
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Re: Why do would you heat wrap your downpipe?

Quote:
Originally Posted by arr4u2nv View Post
So cold air is denser, i get it. When you heat that air up (like adding fuel and a spark!), the volume of that same air increases significantly. This is how turbos turn thermal expansion into extra power. The turbine has a larger volume of air flowing into it than what went into the engine that revolution, this drives a compressor that forces some proportional volume of air into the engine for the next revolution, this is where the compression comes from.
Ideally you want the air to go thru the turbine of the turbo at the highest temp, giving you the highest volume of air possible. This being the reason for ceramic coated manifolds and thermal jackets over the turbine housings, to keep the air from cooling (condensing) until the turbo is done with it.
But as soon as the turbo has used those exhaust gasses, wouldn't you want to cool them as quickly as possible? If you wrap your DP that keeps the expanded gasses trapped in the pipe. higher volume (hot air) inside of a fixed volume container (exhaust system)=pressure in the container (back-pressure). I understand that part of the reasoning is to keep the temps under the hood down, that makes sense, but wouldn't it be more effective to build a heat shield around your DP to keep the heat in and then force cool air thru the gap between the two to cool the DP, condensing the air, and making it flow through the pipe with less resistance? If you ran cool air in from the front, like brake ducts and other things are cooled, plumbed it to the top of the heat shield, and had the opening at the bottom under the truck and away from the "underhood" area, you could keep the engine bay cool AND reduce back-pressure.
Why doesn't anyone do this?
I never wraped my downpipe just for this reason.

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#5 (permalink) Old 05-18-2011, 10:28 PM
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Re: Why do would you heat wrap your downpipe?

Because race car!


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#6 (permalink) Old 05-19-2011, 03:43 AM
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Re: Why do would you heat wrap your downpipe?

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Because race car!
^

I wrapped mine, but not over the welds. It might crack.
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#7 (permalink) Old 05-19-2011, 09:59 AM
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Re: Why do would you heat wrap your downpipe?

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Originally Posted by toycoma98 View Post
^

I wrapped mine, but not over the welds. It might crack.
You can wrap the welds, I did it on mine and I ran the piss out of it, never heard of the welds cracking unless it wasnt welded properly, wrap that sucka!

Race cars, lol..

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#8 (permalink) Old 05-19-2011, 10:38 AM
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Re: Why do would you heat wrap your downpipe?

Thermal coatings like Jet Hot are much better than wrap.

Heard too many horror stories about wrapping exhausts.
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#9 (permalink) Old 05-19-2011, 12:09 PM
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Re: Why do would you heat wrap your downpipe?

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Originally Posted by Greg_Canada View Post
Thermal coatings like Jet Hot are much better than wrap.

Heard too many horror stories about wrapping exhausts.
The only bad things I have heard is running a wrap on mild steel piping that gets wet a lot, then it can rust like mad..havent seen issues with stainless or non-ferous metals, but thats not to say that it doesnt have them.

I run a wrap on my Desert race bike and never had an issue, it has a stainless exhaust, also ran it on my Truck for 2 years and removed the wrap after that and it looked new still (except for discoloration), so I have had good luck with it so far. I have personally never seen any problems first hand with wrap and I have wrapped tons of exhausts in various vehicles I have had in the past as well and no problems.

BOOST BRIGADE I fabricate custom parts: HEIM STYLE STRUT RODS, FORWARD FACING INTAKE MANIFOLDS, and TRACTION BARS (5 LUG) contact me for more info @ www.Speed-freek.com or just PM me here THANKS!
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#10 (permalink) Old 05-19-2011, 06:59 PM
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Re: Why do would you heat wrap your downpipe?



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