Exhaust Manifold Temperature And Turbo Efficiency

[Gav]

I've got a bee in my bonnet over a common belief (from some very well respected members included) that coating/wrapping/insulating the exhaust manifold to keep the heat in makes a marked difference to turbo efficiency.

Sorry guys, I just cant subscribe to this theory. Sure, the basic gas law principles apply (i.e. the hotter the gas the higher the pressure and therefore the faster the exhaust turbine spins), but really, what is the temperature difference going to be between an insulated and uninsulated manifold.

There is a huge gas flow (even more than on the inlet side) and the surface area is relatively small. I would therefore sugest that for a given volume of gas, the temperature drop of the exhaust gas is relatively small as a fraction of the total temperature.

Lets consider a drop of 5C in the exhaust temp. This relates to a percentage drop in temperature of 0.5% assuming an exhaust temperature of 1000 Kelvin (remembering we need to work in absolute temperatures). As there is a direct relationship between temperature and pressure, this equates to a similar drop of 0.5% in pressure applied to the exhaust turbine.

OK - perhaps some may argue that there is a larger difference in temperature between insulated and uninsulated manifolds? I personally just can see it as really even a tubular, thin walled manifold is a pretty inefficient heat exchanger in size and design.

However, I certainly agree that the exhaust components in and near the engine bay should be insulated to stop the engine bay temperatures from rising. I also spent a lot of money on ceramic coating turbo exhaust housings, manifolds, dumps, from pipes etc. I did this from the point of view of lower inlet temperatures and avoiding heat damage to hoses, abs, wiring etc near this area.

In conclusion - I am far from convinced that there is enough heat loss to markedly affect turbo efficiency. If someone can show me otherwise - I have an open mind, however

[Sydneykid]

I've got a bee in my bonnet over a common belief (from some very well respected members included) that coating/wrapping/insulating the exhaust manifold to keep the heat in makes a marked difference to turbo efficiency.

Sorry guys, I just cant subscribe to this theory. Sure, the basic gas law principles apply (i.e. the hotter the gas the higher the pressure and therefore the faster the exhaust turbine spins), but really, what is the temperature difference going to be between an insulated and uninsulated manifold.

There is a huge gas flow (even more than on the inlet side) and the surface area is relatively small. I would therefore sugest that for a given volume of gas, the temperature drop of the exhaust gas is relatively small as a fraction of the total temperature.

Lets consider a drop of 5C in the exhaust temp. This relates to a percentage drop in temperature of 0.5% assuming an exhaust temperature of 1000 Kelvin (remembering we need to work in absolute temperatures). As there is a direct relationship between temperature and pressure, this equates to a similar drop of 0.5% in pressure applied to the exhaust turbine.

OK - perhaps some may argue that there is a larger difference in temperature between insulated and uninsulated manifolds? I personally just can see it as really even a tubular, thin walled manifold is a pretty inefficient heat exchanger in size and design.

However, I certainly agree that the exhaust components in and near the engine bay should be insulated to stop the engine bay temperatures from rising. I also spent a lot of money on ceramic coating turbo exhaust housings, manifolds, dumps, from pipes etc. I did this from the point of view of lower inlet temperatures and avoiding heat damage to hoses, abs, wiring etc near this area.

In conclusion - I am far from convinced that there is enough heat loss to markedly affect turbo efficiency. If someone can show me otherwise - I have an open mind, however

I wrap the primary pipes to keep the heat out of the engine bay. Any heat kept in is a bonus.

cheers

[HRthirtyone]

that sounded like milhouse, then bart

[The Dan]

It is dyno proven that the more heat you can keep inside the manifold, the more efficient the results will be. You will not only spool faster but reach full boost quicker as the pressure difference is somewhere around 30% not 0.5%.

That is why most people complain about power loss after swapping their cast manifold for a custom stainless one, because cast holds the heat in for longer whereas the stainless will dissipate it more quickly.

As you already know, it is heat that drives the turbine....so the more you can get into the housing...the better.

[Busky2k]

The more heat in the gas and the less in the surrounding components etc the better.

Hotter gas through insulation would theoretically help spool up as well. Same goes with wrapping the dump pipe for faster exhaust velocity.

[Gav]

It is dyno proven that the more heat you can keep inside the manifold, the more efficient the results will be. You will not only spool faster but reach full boost quicker as the pressure difference is somewhere around 30% not 0.5%.

That is why most people complain about power loss after swapping their cast manifold for a custom stainless one, because cast holds the heat in for longer whereas the stainless will dissipate it more quickly.

As you already know, it is heat that drives the turbine....so the more you can get into the housing...the better.

We agree with the concept - the amount of loss is where we differ. You claim 30% pressure difference due to heat loss? This means that 30% the exhaust gas must be 30% cooler due to the tubular manifold (i.e. from 1000k to 700k - or from 727C to 427C) - it just can't be so - sorry.

Edited May 31, 2006 by Gav

[The Dan]

We agree with the concept - the amount of loss is where we differ. You claim 30% pressure difference due to heat loss? This means that 30% the exhaust gas must be 30% cooler due to the tubular manifold (i.e. from 1000k to 700k - or from 727C to 427C) - it just can't be so - sorry.

It's not due to tubular manifold....I was using that as a seperate example.

The heat wrapping or coating will hold 30% more heat than an unwrapped/coated system

[Color_Of_Green]

Heh, so if Gav is correct we might as well take the ceramic tiles off the space shuttle and see how it goes through reentry

[Gav]

Heh, so if Gav is correct we might as well take the ceramic tiles off the space shuttle and see how it goes through reentry

Nah - Space Shuttle is "Old Skool" and uses plain old Chemical Accelerant (liquid oxygen) - no turbos on those Bad Boys

[discopotato03]

You'd find your turbo / manifold / dump burning up on re entry as well .

What Bart said .

[saliya]

I wrap the primary pipes to keep the heat out of the engine bay. Any heat kept in is a bonus.

cheers

Hey,

Does wrapping have a downside (accelerated primary pipe wear,

"too hot" for the primary pipes/turbo, other?)

Regards,

Saliya

[R33S2]

because cast holds the heat in for longer whereas the stainless will dissipate it more quickly.

This is why the standard dump is cast as well.

[Color_Of_Green]

In theory we see a gain, in practice it would very much depend on the materials used to the degree of gain. At the very least we're reducing the heat transfer into the engine bay by keeping it in the pipe and we're reducing the heat transfer from the gas to the metal pipe itself...

I've ordered a 6boost low mount turbo manifold for the GTST which is HPC coated for my 2835ProS. I will post before and after dyno sheets when this is fitted [ may be a few weeks ].

While I dont expect huge gains in rwkw I would expect small gains and slightly better curve.

Keeping an open mind. We'll soon see.

[Busky2k]

I'd be keen to see the results, please post them when you can!

[Gav]

It's interesting that the material of choice for aftermarket manifolds seems to be stainless steel. This expands/contracts much more than plain old mild steel and tends to crack at the welds more often. Cosmetically there is bugger all difference if you are going to coat/wrap them anyway as well!

[saliya]

In theory we see a gain, in practice it would very much depend on the materials used to the degree of gain. At the very least we're reducing the heat transfer into the engine bay by keeping it in the pipe and we're reducing the heat transfer from the gas to the metal pipe itself...

I've ordered a 6boost low mount turbo manifold for the GTST which is HPC coated for my 2835ProS. I will post before and after dyno sheets when this is fitted [ may be a few weeks ].

Hey,

Keep in mind, unless you dyno the _same manifold_ before/after coating, these dyno sheets won't

shed any light on what's being questioned in this thread. If you receive your manifold already coated,

the results are from manifold + coating change, not just the coating. And from all accounts the 6boost

manifolds flow excellently.

I've _just_ received my 6boost manifold (workmanship is nice; the timeframe estimate was way off )

and I'm still tossing up whether to coat it or not. I'd really prefer the coating to be on inside and out if I

was going to get it done... but nobody seems to want to guarantee the coating against flaking off and

destroying my turbine.

Can I be a%&ed fitting it up, dynoing it, then pulling the entire manifold off _again_, sending it

away for coating, refitting, dynoing again, retuning (if needed) and dynoing for a third time? Probably not.

If the coating is worth all that much in terms of HP gain you'd expect that one of the coating vendors

would have done a controlled test to document the gains their product provides. A quick look around

doesn't exactly provide lots of graph evidence one way or another regarding exhaust manifold coating.

Those dyno results I did find related to ceramic coating engine internals, not manifolds.

Most of the vendors say something like "there is a noticeable drop in under-bonnet temperature"

before/after. You should be able to rely on this. As for a noticeable HP change - still looking for graphs

Regards,

Saliya

[Sydneykid]

Can I be a%&ed fitting it up, dynoing it, then pulling the entire manifold off _again_, sending it away for coating, refitting, dynoing again, retuning (if needed) and dynoing for a third time? Probably not.

Exactly why it isn’t done, very time consuming and difficult to duplicate the exact conditions. Also difficult to isolate the under bonnet temperature reduction (horsepower improvement) from the increase exhaust gas velocity (horsepower improvement).

What I can say is I have wrapped the primary pipes and collector on an N/A V8 and it picked up 18 bhp, that was on the engine dyno. The principle is basically the same, maintaining the exhaust velocity to give better scavenging.

cheers

[djr81]

Hey,

Keep in mind, unless you dyno the _same manifold_ before/after coating, these dyno sheets won't

shed any light on what's being questioned in this thread. If you receive your manifold already coated,

the results are from manifold + coating change, not just the coating. And from all accounts the 6boost

manifolds flow excellently.

I've _just_ received my 6boost manifold (workmanship is nice; the timeframe estimate was way off )

and I'm still tossing up whether to coat it or not. I'd really prefer the coating to be on inside and out if I

was going to get it done... but nobody seems to want to guarantee the coating against flaking off and

destroying my turbine.

Can I be a%&ed fitting it up, dynoing it, then pulling the entire manifold off _again_, sending it

away for coating, refitting, dynoing again, retuning (if needed) and dynoing for a third time? Probably not.

If the coating is worth all that much in terms of HP gain you'd expect that one of the coating vendors

would have done a controlled test to document the gains their product provides. A quick look around

doesn't exactly provide lots of graph evidence one way or another regarding exhaust manifold coating.

Those dyno results I did find related to ceramic coating engine internals, not manifolds.

Most of the vendors say something like "there is a noticeable drop in under-bonnet temperature"

before/after. You should be able to rely on this. As for a noticeable HP change - still looking for graphs

Regards,

Saliya

There is another way. You can take an infra red photgraph of the exhaust manifold section that has been coated. If (& only if) the coating works you will see a significantly lower temperature on the exhaust manifold section that is coated. If it doesn't work you won;t see any real difference between the coated & uncoated sections. Do a search - you should find it.

[Sydneykid]

There is another way. You can take an infra red photgraph of the exhaust manifold section that has been coated. If (& only if) the coating works you will see a significantly lower temperature on the exhaust manifold section that is coated. If it doesn't work you won;t see any real difference between the coated & uncoated sections. Do a search - you should find it.

You can actually measure it with an infra red pyrometer.

We do that to check individual cylinder tune.

Cheers

[The Dan]

Took this snippet from the HPC site

Benefits of using HiPerCoat Extreme™

On-tracking testing has shown as much as a 35% reduction in under hood ambient temperature and more than 50% reduction in component skin temperature. HiPerCoat Extreme's™ superior insulation qualities mean increased horsepower for your race or turbo-charged engine. HPC’s HiPerCoat Extreme™ helps to maintain exhaust gas temperatures, increasing flow velocity, aiding in cylinder scavenging and decreasing turbo spool-up time.

An additional benefit is the reduction of underhood temperatures, preventing damage to hoses, belts and wiring harnesses. Independent testing of a turbo charged Mazda engine has shown a 5% increase in horsepower when HiPerCoat Extreme™ was used on the exhaust manifold, turbo and downpipe.