Heatwrapping exhaust manifolds

[tomson]

Any opinions on this guys?

Will it really keep engine bay temperatures down that much, which is my reason for wanting to do it?
Pro's and con's of doing it also and how much is needed for a 6 branch and how far down the manifold should I wrap it? Are there different grades of the stuff and where is best to buy it from ?

[DanThe]

I did mine and just standing over the engine bay you can instantly feel how much cooler it is, also now they are wrapped my engine mount wont melt again! I wrapped both front pipes which was a mistake as any speed hump scrapes just pulls it off.
20 metres will be plenty to do a pair of 6 branch manifolds, mine came from ebay £20 odd for 30 metres

[E30BeemerLad]

how much fun is it doing this with the manifold fitted? The heat off my manifold is insane and it would help to quieten it down a bit, but I sure as hell ain't taking the damn thing off

[DanThe]

Impossible

[march109]

Has anyone got any pics? Where does the heat go? It always worries me with my a level physics brain that the heat will take the quickest route out which would clearly be through the head in my mind at least.

I've no doubt its not detrimental to the engine, but I'd like a scientific reason why.

[fowler]

now the heat sould technally find its way down under the car as my turbo downpipe is wrapped but the maifold is not as it PITA HTH
cheers Ben

[jaistanley]

The heat stays in the gas, which A level physics will tell you (well, possibly degree level thermofluids) keeps the velocity of the gas higher...

Jai

[DaveD]

Impossible

there is this stuff

http://rallynuts.com/motorsport/DEI_Com ... s_5314.asp

a might expensive but a LOT cheaper in the States
http://www.hrpworld.com/index.cfm?tpc=D ... on=product

[tomson]

I did mine and just standing over the engine bay you can instantly feel how much cooler it is, also now they are wrapped my engine mount wont melt again! I wrapped both front pipes which was a mistake as any speed hump scrapes just pulls it off.
20 metres will be plenty to do a pair of 6 branch manifolds, mine came from ebay £20 odd for 30 metres

Nice one Dan. Have you got a link to the stuff you bought on ebay?

[GeoffBob]

Has anyone got any pics? Where does the heat go? It always worries me with my a level physics brain that the heat will take the quickest route out which would clearly be through the head in my mind at least.

I've no doubt its not detrimental to the engine, but I'd like a scientific reason why.

Ah yes, the physics of this little problem.

Two basic laws apply. Heat always flows from hot to cold, and the greater the difference in temperature between two objects (in this case parts of the exhaust system) the faster heat will flow between the two.

BTW, Heat is not temperature - they are not the same thing. Heat is just one manifestation of energy. Temperature is just a physical quantity that we use to measure the effect of heating various objects.

Now thats the basics out of the way. To the question:

By wrapping the manifold (in a thermally insulating wrap) the manifold will get hotter (simply because its heat cannot escape). Because it runs hotter (under the wrap) the heat of the manifold flows faster away to the cooler parts of the exhaust (that is to say, down towards the rest of the exhaust system) and the whole thing falls into thermal equilibrium, with most of the heat transferred through the now hotter running manifold down to the cooler bits.

Heat will however be transferred to any other part of the engine in which it is in contact that is cooler than the manifold (since, as above, heat flows from hot to cold). In other words, the head will run slightly hotter due to increased heat transfer to the head. This is also why your exhaust manifold gasket is made from a thermally insulating material, usually sandwiched between two bits of metal foil (to minimise heat transfer from the exhaust to the head), so never run without a proper exhaust gasket!

BTW, wrapping the manifold of a turbo car is done for totally other reasons than minimising heat transfer to the engine bay. But I won't go into the physics of that problem since that wasn't the question asked.

[march109]

Cool beans, nice answer. So as I thought the head will run hotter.

[tomson]

Has anyone got any pics? Where does the heat go? It always worries me with my a level physics brain that the heat will take the quickest route out which would clearly be through the head in my mind at least.

I've no doubt its not detrimental to the engine, but I'd like a scientific reason why.

Ah yes, the physics of this little problem.

Two basic laws apply. Heat always flows from hot to cold, and the greater the difference in temperature between two objects (in this case parts of the exhaust system) the faster heat will flow between the two.

BTW, Heat is not temperature - they are not the same thing. Heat is just one manifestation of energy. Temperature is just a physical quantity that we use to measure the effect of heating various objects.

Now thats the basics out of the way. To the question:

By wrapping the manifold (in a thermally insulating wrap) the manifold will get hotter (simply because its heat cannot escape). Because it runs hotter (under the wrap) the heat of the manifold flows faster away to the cooler parts of the exhaust (that is to say, down towards the rest of the exhaust system) and the whole thing falls into thermal equilibrium, with most of the heat transferred through the now hotter running manifold down to the cooler bits.

Heat will however be transferred to any other part of the engine in which it is in contact that is cooler than the manifold (since, as above, heat flows from hot to cold). In other words, the head will run slightly hotter due to increased heat transfer to the head. This is also why your exhaust manifold gasket is made from a thermally insulating material, usually sandwiched between two bits of metal foil (to minimise heat transfer from the exhaust to the head), so never run without a proper exhaust gasket!

BTW, wrapping the manifold of a turbo car is done for totally other reasons than minimising heat transfer to the engine bay. But I won't go into the physics of that problem since that wasn't the question asked.

Hi Geoff, I understand your above post. My question is will heat wrapping the manifold make the engine run hotter than without wrapping? I am not so bothered about engine bay temperatures, my aim in doing this was to make the engine temperature lower while running, but your post as I understand it now makes me think the opposite...

Tom

[e30_singh]

my aim in doing this was to make the engine temperature lower while running

If I wanted to reduce engine temp whilst running, I would use heat wrap on the manifold and I would arrange for some extra ducting to the engine bay, increase the air flow so air can easily pass around the engine, by this I mean lift the bonnet with spacers. Fit a larger radiator, larger cooling fan etc.

[e301988325i]

There is also a supposed power benefit, with the manifold insulated the exhaust gas keeps the heat energy and therefore maintains a higher volume (things expand with heat), this extra volume flowing down the exhaust translates to a faster speed (bigger volume same area), this increases the syphon effect of the exhaust gases getting more air/fuel mix into the engine and better evacuation of exhaust gases.

[GeoffBob]

Hi Geoff, I understand your above post. My question is will heat wrapping the manifold make the engine run hotter than without wrapping? I am not so bothered about engine bay temperatures, my aim in doing this was to make the engine temperature lower while running, but your post as I understand it now makes me think the opposite...

Tom

Hi Tom,

Sorry, hadn't been keeping up with this thread so missed your post.

Just to be clear on this, wrapping any part of an engine in an insulating material doesn't make it cooler, it makes it hotter because it prevents the heat contained in the engine from escaping. Same principle as putting a jumper on in the winter time, it helps you retain your internally generated heat.

So, heat wrapping your manifold will not make your engine run cooler. Your engine bay will be cooler, but your engine will run hotter, but typically by only a few degrees or so.

Following the basics laws of physics, heat flow between two objects is proportional to the temperature difference between the two. By wrapping (lagging) the manifold the heat flow from the manifold to the engine bay is reduced, raising the temperature of the manifold. Thus, as the manifold gets hotter the heat flow from the exhaust gas to the manifold is likewise reduced and thus more heat is now retained in the exhaust gas itself (exactly as Jai said a few posts above). If you don't have a proper gasket between your head and manifold you could dramatically raise the temperarture of the head by wrapping the manifold. However, with the correct gasket I doubt you will see a dramatic rise in head temperature.

[GeoffBob]

There is also a supposed power benefit, with the manifold insulated the exhaust gas keeps the heat energy and therefore maintains a higher volume (things expand with heat), this extra volume flowing down the exhaust translates to a faster speed (bigger volume same area), this increases the syphon effect of the exhaust gases getting more air/fuel mix into the engine and better evacuation of exhaust gases.

Yip. Most noticable on turbo engines since it is the momentum of the exhaust gas which drives the turbine.

The momentum of an object is the product of its mass and velocity (which is why a heavy truck can do so much damage in the event of an accident, even when going slowly.

To the point, regardless of the temperature of the exhaust gas the mass of gas passing through the engine is purely a function of the mass of air inducted into the engine. However, the hotter the gas the higher its velocity, and thus the higher the momentum of the gas, and thus the better job it does spinning the turbine. It's always a good idea to lag (heat wrap) a manifold on a turbo engine.