Manifolds - Wrap or Ceramic anyone interested in a comparison?

[Spit_2.5PI]

The problem is, you wrap your exhaust manifold to lower under-bonnet temperatures and improve the charge density as the cylinders fill ... but the wrapped exhaust doesn't loose as much heat, so the exhaust gasses don't contract as much, so the cylinders don't empty as much, so less of the denser inlet charge is drawn in. Do you still win? or loose? or end up about where you were before the wrap??? Maybe you need one of those "Rolling Road" apps for your smart-telephone!

 

I know that the temperature at the back of the Spit's engine bay (near metering unit) rises significantly after enthusiastic application of the loud pedal - about 15' ~ 20'C or more on the open road. (Even more in traffic queues!) Would probably be more still if I wasn't on public roads.

 

Cheers, Richard

[Steve T]

I know its a modern car, but when I had my 2001 Vectra rolling road tuned, the tuner suggested I wrap the manifold. I had 182bhp before wrapping and 196bhp an hour later after Id applied 2 rolls of glass tape type in their workshop. Obviously this is all well and good in the confines of a workshop with a static car revving to full chat and probably helps around town, but out on the road, there more than likely wouldnt be a huge improvement.

Edited November 14, 2017 by Steve T

[Peter Cobbold]

The problem is, you wrap your exhaust manifold to lower under-bonnet temperatures and improve the charge density as the cylinders fill ... but the wrapped exhaust doesn't loose as much heat, so the exhaust gasses don't contract as much, so the cylinders don't empty as much, so less of the denser inlet charge is drawn in. Do you still win? or loose? or end up about where you were before the wrap???

 

Cheers, Richard

Richard, Thats very difficult to fathom. If the exhaust-back pressure is say 0.3atm above atmos and the intake is at atmos then (for 9.5 comp rat) the volumetric efficiency will be lowered by about 3% compared with no back pressure.** Dropping the intake temp from 50C to 20C adds about 8% more power and also 8% more heat to the exhaust That will raise the exhaust temperature hence back-pressure. By how much ?

8% more heat will raise exhaust gas at say 800C to roughly 860C which raise its pressure by a factor of 1133/1073. Which gives 5.5 % more back pressure. So our 0.3atm rises to 0.315atm. That drops the volumetric efficiency by a negligible amount.

In short the intake air temperature is paramount. Wrapping the exhaust keep the gas hotter will make very little difference to cylinder filling., fora given exhaust design. Wrapping is only useful to keep the mixture intake cooler. Except for turbo engines when losing heat before the turbo is bad.

Peter

** John B Heywood fig 6-4

Edited November 15, 2017 by Peter Cobbold

[RogerH]

Hi Folks,

having read all the pro's and con's,

all the gumph on intake temp and air density,

all the jolly stuff on exhaust back pressure,

all the myths busted and dreams washed away

 

I'm glad I got my pipes ceramic coated because it is a pretty silvery colour - hmmmm

 

Roger

[Ben Freer]

 

I'm glad I got my pipes ceramic coated because it is a pretty silvery colour - hmmmm

 

Roger

+1????

[Hamish]

Hi Folks,

...........

I'm glad I got my pipes ceramic coated because it is a pretty silvery colour - hmmmm

 

Roger

Roger wins the award for cutting to the core of the important technical factors as usual

????????????????????????????

[oldtuckunder]

OK run a whole bunch of measurement on my wrapped headers this morning, I'll post a picture and results later today

 

 

Very interesting Rob. Looks to me that wrapping will win, easily. Peter

 

As with all things one needs to check the source, that paper was produced for NAIMA the organisation in the US that represents Insulation manufacturers, so they have a vested interest in Insulation being best, not saying tests results are rigged, just............

 

 

We can all appreciate a lower underbonnet temp is usually a good thing but I'm still struggling to find any evidence that insulating the manifold offers any performance benefit?

 

I think the performance benefit is via cooler carbs and cooler air charge, although (and I could be wrong) if I understand correctly hot gas is lighter than cool gas so it takes less effort energy to shove it out the way i.e. start pushing it down the exhaust system so delaying the cooling in the manifold theoretically does have a benefit.

 

 

 

As far as I can tell the cooler the air into the carbs the denser it is thus more power available.

Very hot air is a bit like loosing power due to altitude over the mountains due to thin air.

And why many sporting or race version of cars had air intakes like the TR4 and healey 3000 rally cars. That have them in the wings.

But Im open to correction.

 

I think most of the wing vents you see on Healey, TR, Spitfires etc are normally to get hot air out from under the bonnet i.e. promote flow and thus cooling under the bonnet.

 

 

Only way to know is to measure the carb air intake temperature without/with insulation, and allow for ambient changes,driving/stationary etc

Inlet valve mixture temp is much more difficult, impossible if wet fuel is present.

Peter

 

All I know is that with heat wrap, a huge amount of heat shielding to keep most under bonnet air away from the carbs and also ensure that the carbs only breath ducted air from the front of the car, and also extra insulation between carbs and inlet manifold, that my carb body temps are normally about 15-20C lower than other cars I measure.

 

Again its only anecdotal but I did have a problem earlier in the year when I sat in a long queue at Shelsley on a hot day, when a couple of hold ups with cars earlier in the batch meant I sat with the engine idling for around 15 mins, the start and first 1/4 mile were awful, felt like 40% less power and spluttering. Next run an hour or so later I made sure that the oil was up to temp with the bonnet open, and then didn't idle the car at all or as little as possible in the queue, and had zero problems.

 

I suspect that we have a whole bunch of issues that affect people differently, for me that 30 secs of degradation is bad, in a normal road car if you sat in a traffic queue for 15/20 mins and it splutters a tiny bit, or seems a bit hesitant for the first 30 seconds until you get going but then behaves perfectly as you swoop along the B roads, it would be an incident that hardly registers.

 

Alan

[Peter Cobbold]

 

 

Again its only anecdotal but I did have a problem earlier in the year when I sat in a long queue at Shelsley on a hot day, when a couple of hold ups with cars earlier in the batch meant I sat with the engine idling for around 15 mins, the start and first 1/4 mile were awful, felt like 40% less power and spluttering. Next run an hour or so later I made sure that the oil was up to temp with the bonnet open, and then didn't idle the car at all or as little as possible in the queue, and had zero problems.

 

I suspect that we have a whole bunch of issues that affect people differently, for me that 30 secs of degradation is bad, in a normal road car if you sat in a traffic queue for 15/20 mins and it splutters a tiny bit, or seems a bit hesitant for the first 30 seconds until you get going but then behaves perfectly as you swoop along the B roads, it would be an incident that hardly registers.

 

Alan

Fuel evaporating off the intake manifold walls will cool them. My blower intake , fed by an SU, drips water after a run on a humid day. At tickover the heat removed from the manifold by evaporation will be small as the fuel flow is very small. That means any source of heat even condcution from head will heat up the wall and that heat gets transferred to the air intake and the mixture density falls, effective compression drops, and the engine stutters. So wrapping the exhaust to keep the iinlet cold is right thig to do,as you have found.

When at cruise the load ( hp) and hence fuel flow and evaporative cooling is much higher so the wall stays cool and the mxiture density is fine.

Peter

Edited November 15, 2017 by Peter Cobbold

[Peter Cobbold]

 

 

 

 

I think the performance benefit is via cooler carbs and cooler air charge, although (and I could be wrong) if I understand correctly hot gas is lighter than cool gas so it takes less effort energy to shove it out the way i.e. start pushing it down the exhaust system so delaying the cooling in the manifold theoretically does have a benef

 

Alan

==========

Hmmmmm...'fraid not, its the other way about, keeping it hot is theoretically bad.

The mass of gas going down the exhaust is exactly the same as the mass of air plus fuel going into the carbs.

Hotter gas is less dense, not 'lighter', and will in a given volume of pipe exert more pressure:more back pressure. But as I showed earlier the effect on VE hence power is tiny. A negligible efect compared with keeping the intake cool.

 

All ic engine textbooks cover gas flows in considerable depth. I find Heywood's is the most comprehensive.

 

Peter

[MikeF]

Interesting stuff, with some informed comment, but all the stuff about airflow seems to be about getting cold air in, then what? Don't you need similar improvements to get it out again to get any benefit?

 

Mike

[Peter Cobbold]

Interesting stuff, with some informed comment, but all the stuff about airflow seems to be about getting cold air in, then what? Don't you need similar improvements to get it out again to get any benefit?

 

Mike

Mike, Yes indeed. But this thread is about insulating an existing exhaust system.

Exhaust pipe design is crucial for making best use of the impetus of the departing gas to create a depression above the piston that pulls in extra mixture when both valves are open at the same time.

Its not something I get involved in - for a supercharged engine valve overlap is a no-no, and six short exhaust stubs would do the job best, but a bit loud.

A Graham Bell book on 4 Stroke Performance Tuning is useful .

Peter

Edited November 15, 2017 by Peter Cobbold

[oldtuckunder]

Interesting stuff, with some informed comment, but all the stuff about airflow seems to be about getting cold air in, then what? Don't you need similar improvements to get it out again to get any benefit?

 

Mike

 

Actually no. The difference is that on inlet there is not much helping it, at best you have slightly higher than atmospheric pressure pulling/sucking (however you want to describe it) air/fuel mixture into a cylinder as the piston descends, a bit of exhaust scavenging may assist this, but also you have all the losses in the inlet manifold, carbs, filters etc, so a reasonable engine might only be at 80% VE, a good engine 90% and a good race engine 100%+ a tad. Whilst the exhaust gas is one compressed so want to rush out and is also pushed by the piston as it rises using the power of the other cylinders.

 

Its why Turbo and Supercharged engines don't really need (or only marginally) bigger exhausts, i.e. the extra power is achieved by getting more air/fuel in (under pressure).

 

Also explains why there has been a cycle in exhaust valve sizes, there was a tuning tendency in the 60/70 to also increase exhaust valve size as well as inlet, but now it is realised that it achieves virtually nothing (enough is enough) and all it does is add weight into the valve train.

 

Alan

[oldtuckunder]

OK here are my results.

I left the engine running for around 20 mins until nice and warm, not just coolant warm.

Set the engine at 1Krpm idle and took most measurements, then took up to 2Krpm and took a few more.

Also took a couple of additional temp readings for fun.

NB. The "A" readings were taken of the bare black metal flange of the headers where they bolt to the head (i.e. not under wrap)

"B" readings are about 2" down from the flange and under wrap.

I put some big White Splodges on to see what difference it made to recorded readings with Wrap.

The complete system back to and beyond E1 is wrapped.

E1 is just before the collector where the two pipes join (interesting temp drop between D & E)

NB The A2,A3,B2,B3 reading are higher because two pipes are sandwiched.

 

 

Covering: Wrap (a good one 1/4" overlap 2" wide)

Colour: Black

1K rpm

A1 220

A2 240

A3 240

A4 220

B1 200

B2 210

B3 210

B4 200

C1 280 & 250 (Dropped to 250 almost instantly fan cuts in, and then jumps back to 280 when it stops)

C2 280 & 250 (No difference between readings on Black or White area)

D1 235 (Out of direct air from fan)

D2 235 (Same Black or White area)

E1 180

2K rpm

A1 245

A2 300

A3 300

A4 245

B1 225

B2 250

B3 250

B4 225

 

Cylinder Head 110

Top of Block 90

Water Pump 90

Rad 95

 

[Peter Cobbold]

Alan,

Not a lot of difference. Surprising .

What I think it means is the heat transfer to air is slow compared with the heat flux through the insulation.

That has allowed the temperature of the wrap to almost equilibrate with the steel.

The fan's effect supports that.

 

The wrap thickness can be increased to reduce the heat flux. That should produce a bigger temp drop,

Doulbing the thickness of an insulatng layer will halve heat flow:

https://www.engineeringtoolbox.com/conductive-heat-transfer-d_428.html

But that will only drop the surface temp by 40 rather than20C

 

In a nutshell, the wrap is doing very little.

I'd try a sample of that Aerogel under the wrap. Or put a layer of reflective ali foil between two wrap layers.

 

Peter

[oldtuckunder]

Alan,

Not a lot of difference. Surprising .

 

But that will only drop the surface temp by 40 rather than 20C

 

In a nutshell, the wrap is doing very little.

 

 

Funny I read it differently, I thought a 10% drop within 2" was fairly good, especially as its probably more as the "A" measurement points aren't really directly in the gas flow and are being cooled by contact with the head.

 

So what we need now is someone to measure a Ceramic Coated manifold!

 

The Fan was the interesting thing. Now assuming that the IR Thermometer wasn't confused by cooler air passing between it and the target measurement point (maybe a big assumption I don't know) What it means is that a large amount of heat was suddenly transferred to the under bonnet space rather than going out the exhaust, and as the car isn't moving that hot air isn't going to be going far. Making me think about an extra bit of heat shielding to direct/duct the air coming backwards from the fan down and past the manifold pipes rather than blowing over them.

 

Alan

Edited November 15, 2017 by oldtuckunder

[Peter Cobbold]

 

Funny I read it differently, I thought a 10% drop within 2" was fairly good, especially as its probably more as the "A" measurement points aren't really directly in the gas flow and are being cooled by contact with the head.

 

So what we need now is someone to measure a Ceramic Coated manifold!

 

The Fan was the interesting thing. Now assuming that the IR Thermometer wasn't confused by cooler air passing between it and the target measurement point (maybe a big assumption I don't know) What it means is that a large amount of heat was suddenly transferred to the under bonnet space rather than going out the exhaust, and as the car isn't moving that hot air isn't going to be going far. Making me think about an extra bit of heat shielding to direct/duct the air coming backwards from the fan down and past the manifold pipes rather than blowing over them.

 

Alan

Alan, I was disappointed and expected a much bigger drop.10% wont help much when the exh gas comes out at 700C+ at full chat and the bare pipe heats up to that !

If the exh is at 700C then the wrap surface will rise to close to 700C. I think we have to use degreesK (ie absolute temps).to estimate it. For example, taking A4 =290 and B4=200. The % drop is 493 to 473 working in deg K ( abs zero is -273deg),. That's only 6% drop. So at exh gas at 700C = 973K the wrap surface will be at 915K , which is 642C. Toasty !!

 

I think you have shown convincingly that the fan is cooling the surface of the wrap.Whcih means the underbonnet air will heat up unless blown away- - directing air down below the heat shield sounds good to me.

 

It may sound crazy but for a sprint or h/c could you also wrap the intake manifold in wet sponge ? use evaporative cooling ! Or maybe dry ice

Peter

.

[ed_h]

Too cold a manifold is not a good idea either, is it? Not sure if it can happen in a car, but in some carburetted aircraft there is a control in the cockpit to duct heat to the carb/manifold so the venturi dosent ice up.

 

A racing friend of mine routed his fuel line through a coil in a canister filled with dry ice.

 

Ed

Edited November 16, 2017 by ed_h

[RobH]

Alan's measurement really doesn't show anything surprising. As Peter points out, if there is no mechanism for removal of surface heat there will be no temperature drop. The electrical analogy of this test is trying to measure a voltage through a high value resistance. If the meter is high impedance, the voltage will hardly be affected but try a light bulb as a load and the voltage will reduce dramatically.

 

The thermal resistance of the insulation can only drop the temperature if there is heat flowing through it. Under still-air conditions the heat flow is minimal because the air in contact with the surface heats up until flow almost ceases. Only by continually replacing the warmed air can there be sufficient heat flow for the insulation to be seen to be working. Convection (and radiation) will do that a bit but the fan does it a whole lot better. Even though the replacement air is probably already approaching 70 degrees it will still be a lot cooler than the air at the surface.

 

A more meaningful test, though difficult to achieve, would be to measure the under-bonnet temperature under real conditions with and without the different laggings. It is likely that would show only a small reduction for idling while stopped in traffic.

Probably the main benefit would be seen when the engine is working harder with the exhaust pipes hotter, and there is more air flow to take away the surface heat. What the lagging will do then is to dramatically reduce radiated heat over that from a bare pipe.

[BlueTR3A-5EKT]

The OP question was about which is better for reducing radiated heat from the manifolds - wrapping or coating. I am enjoying the info that is coming forward.

Has anyone yet checked the surface temp of a coated manifold - by hand or IR thermometer?

As a simple real life guide. At idle tickover after a run - My wrapped manifolds can be touched without melting my fingers, brother's unwrapped manifolds start to glow a visible dull red. (about 400 - 500 c I think) Same manifold type and engine specs on both cars.

 

To add my bit what about producing manifolds from thermally non conductive material? PS or are we seeking a glass hammer?

http://www.tech-ceramics.co.uk/Tube&pipe.htm

Then all that hot gas can go out the back, blue the bumper/overider (as it has on my car) singe pedestrians and small dogs, deform plastic bumpers of close following 'soft roaders' & crisp up motorcycle tyres....

 

Peter W

Edited November 16, 2017 by BlueTR3A-5EKT

[oldtuckunder]

Alan's measurement really doesn't show anything surprising. As Peter points out, if there is no mechanism for removal of surface heat there will be no temperature drop. The electrical analogy of this test is trying to measure a voltage through a high value resistance. If the meter is high impedance, the voltage will hardly be affected but try a light bulb as a load and the voltage will reduce dramatically.

 

A more meaningful test, though difficult to achieve, would be to measure the under-bonnet temperature under real conditions with and without the different laggings. It is likely that would show only a small reduction for idling while stopped in traffic.

Probably the main benefit would be seen when the engine is working harder with the exhaust pipes hotter, and there is more air flow to take away the surface heat. What the lagging will do then is to dramatically reduce radiated heat over that from a bare pipe.

 

I too was pondering this overnight, and realised that we are looking at multiple issues as though they are one problem.

 

I know racers that claim that their in cockpit temperatures have dropped noticeably when they have switched from wrap to ceramic coating, part of me always said "well you would say that having spent a few hundred pounds/dollars having it done" But I think I'm starting to pull a few threads together.

 

Not sure of my science but a few other like Rob/Peter may be able to add light to my ponderings.

 

One of the differences between a wrapped pipe and a ceramic coated pipe is surface area, I'll make a bet that with wrap the knobbly bumpy surface that is already of a bigger circumference than a plain or coated pipe, is probably twice the surface area. So as Rob says put them both in a cooler air flow and I'm betting that the wrap convects (have I got the correct term) way more heat away than a coated pipe, thus under bonnet air temps and probably the cockpit are going to be higher with wrap, however whilst hotter and probably to a human noticeably so, to most stuff under the bonnet its probably a marginal rise and as we are running at competition speeds there is an awful lot of air flowing through the under bonnet area, so things like carbs aren't going to get much hotter as a result of convected air temperature rise (even if the driver does). What will affect carbs in these conditions is I believe radiated heat.

 

So the question for protracted running (with carbs, as injection doesn't suffer this problem) is which radiates the least, wrap or a smooth coated surface, and does colour make a difference. Why are central heating radiators white not black?

 

To some extent I'm looking at a similar but different problem. I'm not running long enough hard enough for the high speed running convected or radiated heat to be much of a problem (although as an aside I have commented to a few people that I was going to have to check the heater control valve over the winter as I had noticed that on a few longer road journeys (like more than 30 mins) with the hood up, that it felt like the heater was stuck on full), If my carbs and induction are cool (at the correct temperature) at the start of a run, the exhaust pipes could get to red hot almost instantly and the amount of heat that would transfer to the inlet manifold or carbs in 60 secs is minimal. They may bake when I stop as there is nothing to take the heat away and the under bonnet area turns into an oven!

 

So my problem is keeping them cool whilst idling before a run. So what I need to know is does wrap convect more heat to the air than coating ( I suspect it now does if the fan is blowing over it) and is the difference significant, and does wrap radiate more heat than coating, I suspect but don't know that in this case I think coating is worse.

 

And then we have the problem of what temperature range we are operating in. High Speed running and the header pipes are going to be in the 7/800C range with lots of air passing over them, Idling they are as I have measured in the 2/300C range with very little air. Does this make any difference to the efficiency in both convected and radiated forms of wrap and coating?

 

And then we have the does keeping the gasses hot inside the pipe help performance or not issue.

 

Just found this short paper from the CamCoat manufacturers about a test, without Rose Tinted Glasses on it makes interesting reading, and Peter might be interested in some of their comments in the summary.

 

https://techlinecoatings.com/wp-content/uploads/BHK-Comp-Cams-Test.pdf

 

Alan

[john.r.davies]

"Disappointingly little effect from wrap"

What about Ceramic?

 

One word - Shuttle!

 

John

[Peter Cobbold]

 

As a simple real life guide. At idle tickover after a run - My wrapped manifolds can be touched without melting my fingers, brother's unwrapped manifolds start to glow a visible dull red. (about 400 - 500 c I think) Same manifold type and engine spec

 

Peter W

Peter,

Nothing beats an experiment ! That does indcate that the wrap is considerably recducing the heat flux into your finger. The wrap is acting as an insulator. It means that Alan would need a lot less air flwo to cool the wrap surface compared with the bare steel. The wrap is working well.

How well?

Alan's temp measurements coud be extended to give an idea of the heat flux - which would be current in Rob's electrical analogy. By measuring the rate of temperature rise of a lump of metal after sudden attachment to either bare exhaust or the wrap....maybe a magnet could be used. The larger the 'current' the faster the temp will rise.

 

Peter

[oldtuckunder]

Peter,

Nothing beats an experiment ! That does indcate that the wrap is considerably recducing the heat flux into your finger. The wrap is acting as an insulator. It means that Alan would need a lot less air flwo to cool the wrap surface compared with the bare steel. The wrap is working well.

How well?

Alan's temp measurements coud be extended to give an idea of the heat flux - which would be current in Rob's electrical analogy. By measuring the rate of temperature rise of a lump of metal after sudden attachment to either bare exhaust or the wrap....maybe a magnet could be used. The larger the 'current' the faster the temp will rise.

 

Peter

 

Not sure I'm trying to cool the wrap surface under the bonnet, under the car in air flow maybe!

I also can attest to having touchd my fingers/hands against hot wrap, and gone HOT! rather than BLISTER!

I have to start stripping the head etc this weekend, but could just squeeze in one more test on the wrap, if it proves anything. I do have a magnet that would grip through the wrap, I could putt on hot wrap and measure surface temp rise with a probe, and then repeat with it direct on bare pipe at the same spot, what will it show, or do we need someone to do the same on a coated surface to find out anything?

Alan

[Peter Cobbold]

Radiant heat is governed by Stefan Bolzmann Law. Two main points

1.Doubling the surface temperature iscreases the heat radiated by 16 times. As Waldi said earlier it is a fourth power law. Note you have to use degree absolute ( Kelvin, K) so add 273 to every degC and then calculate the radiation.
2. At the same temperature a black surface will radiate more heat than white or polished surface. The ability to radiate is called emmissivity and is set at 1 for a notional perfect black body. All other surfaces will rediate less.

https://www.engineeringtoolbox.com/radiation-heat-transfer-d_431.html

 

 

So the wrap must insulate, which it does ,as Pete's brave fingering showed. To reduce radiation it is best either painted white** or wrapped in shiny foil, either will reduce emmissivity hugely.

Take your pick of emmssivities:

https://www.engineeringtoolbox.com/emissivity-coefficients-d_447.html

A second wrap of shiny heat resistant ali foil might be quickest.

 

For the same reason a polished or white ** surface reflects radiant heat best. Whcih is why Vizard's tuning tweaks, for Minis IIRC, polished the intake manifold exterior.

 

I have no idea why Tech LIne think a black coating was desirable.. That goes against the S-B Law, and that is cast-in-stone physics.

 

Peter

 

** no, see Rob's post #77 and Ed's #78

Edited November 16, 2017 by Peter Cobbold

[Peter Cobbold]

 

Not sure I'm trying to cool the wrap surface under the bonnet, under the car in air flow maybe!

I also can attest to having touchd my fingers/hands against hot wrap, and gone HOT! rather than BLISTER!

I have to start stripping the head etc this weekend, but could just squeeze in one more test on the wrap, if it proves anything. I do have a magnet that would grip through the wrap, I could putt on hot wrap and measure surface temp rise with a probe, and then repeat with it direct on bare pipe at the same spot, what will it show, or do we need someone to do the same on a coated surface to find out anything?

Alan

Alan,

The magnet experiment is to measure the rate of temp rise after it is suddenly clamped on. Take reading every 5sec or so and plot out. That will give an idea of insulation.

 

Try shiny ali foil wrap, that will have a big effect on radiant heat- see SB Law above.

To measure radiant heat replicate the TechLine setup with the temp probe 1" off pipe.

Peter

Edited November 16, 2017 by Peter Cobbold