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Wrapping exhaust manifold


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Hi Graham,

in my opinion there is no need to to that.

And if you still use the old cast iron manifold you better don't do it:

it will be hotter than and this is makes it more likely for cracks.

Other options are welcome.

Ciao Marco

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I have a 6-3-1 tubular manifold, and a few years ago I wrapped it.    Some time after that, engine change time and anyway, the wrapping was looking tatty, so I took it off.

Underneath, the metal of the manifold looked most peculiar.   The surface was 'spalling' off in sheets, much worse corrosion than I would expect, and the metal must have been significantly thinned.

No idea why this happened or if it was the usual effect, but I assume that the wrap kept the outer surface anoxic, so that 'hydrogen corrosion' occurred (see https://en.m.wikipedia.org/wiki/Anaerobic_corrosion) with the formation of magnetite, instead of ferrous oxide.

Anyway, the benefits of wrapping, or any other way of insulating the exhaust are marginal and dubious.   As I've said before, the Space Shuttle needed up to six inches of highly effective ceramic insulation, to effect a temperature drop equivalent to what would be useful in the engine bay.  What an eighth of an inch of glass fibre tape can do must be much, much less!

John

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8 minutes ago, john.r.davies said:

I have a 6-3-1 tubular manifold, and a few years ago I wrapped it.    Some time after that, engine change time and anyway, the wrapping was looking tatty, so I took it off.

Underneath, the metal of the manifold looked most peculiar.   The surface was 'spalling' off in sheets, much worse corrosion than I would expect, and the metal must have been significantly thinned.

No idea why this happened or if it was the usual effect, but I assume that the wrap kept the outer surface anoxic, so that 'hydrogen corrosion' occurred (see https://en.m.wikipedia.org/wiki/Anaerobic_corrosion) with the formation of magnetite, instead of ferrous oxide.

Anyway, the benefits of wrapping, or any other way of insulating the exhaust are marginal and dubious.   As I've said before, the Space Shuttle needed up to six inches of highly effective ceramic insulation, to effect a temperature drop equivalent to what would be useful in the engine bay.  What an eighth of an inch of glass fibre tape can do must be much, much less!

John

I have read that exhaust wrapping in Indy cars was prevalent but the sun realised the exhaust would only last a few races owing to the steel super heating itself. 
hmmm. Perhaps of it ain’t broke!!!

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Hi John,

I haven't got the answer to your question but you need to consider the dynamics.

Shuttle re-entry temp 1600'C,  TRaveling at  extremely high speed - constantly

TRiumph engine - temp apprx 800'c  TRaveling at lowish speed - intermittently.

Roger

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5 minutes ago, Graham Baggaley said:

I haven’t fitted it yet but it’sa stainless 4 branch Phoenix

Hi Graham,

 in essence wrapping the manifold is not a bad thing but it does have some serious drawbacks.

It can quickly look very tatty and some folk have reported manifolds getting heat damage.

There is another way - Ceramic coating (not 6" thick).

Zircotec - not cheap - https://www.zircotec.com/?gclid=EAIaIQobChMIzYrvv4__8gIVku7tCh2LlwWEEAAYAiAAEgIc5PD_BwE

Camcoat - slightly cheaper -  https://www.camcoat.com/

I have the Camcoat TRiple system on my 4A in stainless steel finish. 13 years later it still looks clean and tidy.

Does it work!!  Well, nothing in the engine bay has melted yet.

 

Roger

 

 

 

 

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I have mine wrapped with 2” wrapping and when I recently removed and replaced the engine, i renewed it at minimal cost. Underneath the wrapping there was no evidence of the manifold (Phoenix tubular) having suffered. 

whether or not there is a major benefit in terms of reduced engine bay temperatures I couldn’t say, but certainly the exhaust gases at the end of the pipe are very hot.

Rgds Ian

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1 hour ago, trchris said:

Is there a need to wrap ? does the tubular manifold get that much hotter than the original cast one? and half way down the original goes tubular  

Chris

Wrapping was invented in the turbo era, to keep exhaust gas hot and expanded before it entered the turbo. It might decrease under-bonnet tmeperature in a TR a bit at low speeds but a cold-air intake was fitted as standard to the PI- so why wrap?. Changing to carbs and fitting air filters without a cold-air plenum might be a reason for wrapping based upon engineering rather than fashion. Peter

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7 minutes ago, Ian Vincent said:

 

whether or not there is a major benefit in terms of reduced engine bay temperatures I couldn’t say, but certainly the exhaust gases at the end of the pipe are very hot.

Rgds Ian

+1

In changing from the wrap to the ceramic coating i found that the exhaust gas at the til pipe was equally hot.  So the very thin  ceramic catingwas as effective as the thicker external wrap - whether that is good, bad or indifferent I do not know.

But if the exit gas was/is hotter then less heat escaped through the pipe work at the front end.

 

Roger

 

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From a power perspective in non-turbo applications, wrapping the exhaust (keeping heat in the exhaust) reduces power by increasing exhaust back pressure.... its better to allow the exhaust to cool to effectively lower the volume of the exhaust gasses.

Does it matter in a TR engine? I doubt it.

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..well there's some interesting answers to consider, and to be honest I'm surprised by the general bias against.

I don't have definitive answers, but I do plan to wrap my TR4A's manifolds, as indeed I have done so with previous classic cars.     

In answer to Graham’s original question, I use 2” because half of its width overlays the previous wrap, and down a pipe 2" tends to stay neater and needs less ties.  Around a cast manifold with lots of tight corners I might go for 1" wide. 

How long ? ..each wrap of 2" wide goes down the pipe 1” and the length of each wrap can be approximated as ;  pi x D (or to round things off  3 x outside diameter of the pipe).  If there are 4 pipes, each 15” long of 1 ½” diameter, then the maths is simply ; (3 x1½” per wrap) x 1 x 15” x 4 = 270” (7m).  You’ll have to check the outside diameter and lengths of your particular manifolds to determine a more accurate figure, but very likely 10m roll will sort you out.

 

What was the thinking behind wrapping ?  

Contrary to Dave’s summation, the hotter the gas - the lower its viscosity, which therefore it blasts through the exhaust faster.  A performance exhaust such as the 4 branch Phoenix is designed for faster engine speeds & high revs., so that’s fine.   More quickly moving the gasses out of such a pipe reduces back pressure and indeed its inertia (slight vacuum between each pulsation) tends to draws the exhaust from the combustion chamber more quickly.

It also has the benefit of hot gasses reaching the tail-pipe, which soon dries out condensation throughout the exhaust system and lessens sooting up. 

Other benefits include lessening under bonnet temperatures, because if the heat is coming out of the exhaust tail pipe then it cannot also be coming out in the under-bonnet space.  This offers benefits ;

·      less heat to be transmitted through the bulkhead and gearbox tunnel.  

·      If air into the carb is drawn from under-bonnet then it is better for that to be cooler / denser, and therefore more power is produced in combustion.

In addition to the convective heat of under-bonnet-temperatures is radiant heat, which is detrimental to ;

·      the wiring, any rubber (steering column joints for example) and plastic parts, and engine ancillaries (such as the dynamo and starter motor), as well as under bonnet paint and finishes exposed to that heat.

·      the engine block itself is very much less exposed to radiant heat from the manifolds. Whose water jacket is only a few inches away from those pipes.

These things are ever more pertinent when stuck in traffic.

·     manifolds being wrapped might also prevent your getting burnt, and/or some discomfort when working on the engine or when tuning.  

Ceramic coating is likely to be better, particularly on cast manifolds.  It lasts well and looks good.   My old Jaguar 3.8 (six cylinder) had ceramic coated cast-iron manifolds which was standard specification, No problems with those manifolds cracking from that heat.  It was a good job too because the PAS reservoir and pump were within inches of the forward branch, and the space between those manifolds and the straight-six slab-sided engine block was very tight.  

Another benefit, particularly with stainless steel pipes, is that wrapping adds a layer of sound insulation to soften what can otherwise a rather tinny sound from pipes (internal echoes I guess).  I have no experience of corrosion of the pipes, but then I do tend to avoid stainless down-pipes. 

Hope these thoughts help you balance the weight of opinion.

Pete

p.s.  have you asked the exhaust pipe manufacturers what they think about wrapping ? 

 

Edited by Bfg
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13 hours ago, RogerH said:

Hi John,

I haven't got the answer to your question but you need to consider the dynamics.

Shuttle re-entry temp 1600'C,  TRaveling at  extremely high speed - constantly

TRiumph engine - temp apprx 800'c  TRaveling at lowish speed - intermittently.

Roger

Thank you, Tutor Roger, for the correction!

BUT!    The Shuttle's aluminium structure could not be allowed to heat above 175C(!), when some parts were heated by re-entry to 1650C .  So temp differential, lets  say 900C.   That needed six inches of tile.

A ceramic coating on an exhaust pipe is - well, I've see two thou to a millimeter (40thou) quoted.    If the Shuttle needed six inches (150mm), then that thickness could make the inside and outside of your exhaust 240C different.    Mega useful, if you are into F1.    For a road car?

And anyway, the VAST majority of the heat under the bonnet comes from the very thermically inefficient internal combustion engine, that only converts about 40% of fuel into motion, at best.    The rest goes into noise, vibration and HEAT!    Which is chucked out into the radiator, so that expensive ceramic coating will make no difference at all to the under bonnet temp!

John

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A cool air intake is needed for optimum max power. But for best fuel economy, best mpg, a warmer intake and inlet manifold is desirable. The closer the mixture can be made to a gas rather than a mist of droplets the more consistently it burns cycle-to-cycle, the leaner the mixture can be set and the more the spark advanced. Wrapping seems to me to be going against the CC-GW agenda, if only in a minor way.  Peter

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5 hours ago, john.r.davies said:

Thank you, Tutor Roger, for the correction!

BUT!    The Shuttle's aluminium structure could not be allowed to heat above 175C(!), when some parts were heated by re-entry to 1650C .  So temp differential, lets  say 900C.   That needed six inches of tile.

A ceramic coating on an exhaust pipe is - well, I've see two thou to a millimeter (40thou) quoted.    If the Shuttle needed six inches (150mm), then that thickness could make the inside and outside of your exhaust 240C different.    Mega useful, if you are into F1.    For a road car?

And anyway, the VAST majority of the heat under the bonnet comes from the very thermically inefficient internal combustion engine, that only converts about 40% of fuel into motion, at best.    The rest goes into noise, vibration and HEAT!    Which is chucked out into the radiator, so that expensive ceramic coating will make no difference at all to the under bonnet temp!

John

Hi John,

I wouldn;t put my hand on my ceramic coated manifold BUT!!!  it has retained its looks (more or less)..

 

Roger

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My exhaust has been wrapped since 2000.  Keeps a lot of heat away from the carbs.  Still holds in place but looks tatty now.

It is wrapped in foil face asbestos strips from the aircraft world.

 We used fit a long sleeve of the stuff over pipe work near the turbine/jet pipe of turbine engines to stop those pipes cooking.   I merely cut the stitching, flattened the tube to a long sheet and wound it round the stainless manifold pipes, retaining with stainless locking wire.

Peter W

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I use wrap on several cars with stainless manifolds, most notably a TVR Cerbera V8 which had a serious under bonnet heat problem. I use 2" wrap and a wide stainless steel tie wrap every 8-12". It's not pretty after 10 years but when I had cause to rewrap one side of the engine recently there was no sign of any damage to the steel and this particular car has done some time on track besides normal road use. Ceramic coating is IMHO good only for aesthetics. It has little, if any, effect on under bonnet temperatures. This usually causes a squawk from people who have spent hundreds on it for the wrong reasons, but the tests of the theory are simple. Pull up with a hot engine, lift the bonnet and grab a good hold of a wrapped manifold and you will be fine, do the same with a coated one and you're going to the hospital. Hold your hand near a coated one and feel the radiated heat, do the same with a wrapped one and it's hugely reduced. There are only two ways heat gets from the manifold to the air, conduction and radiation, both easily tested without any expensive kit.

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20 hours ago, RogerH said:

Hi John,

I wouldn;t put my hand on my ceramic coated manifold BUT!!!  it has retained its looks (more or less)..

 

Roger

It depends how fussy you are about how it looks like under the bonnet. Personally, as long as it is reasonably clean and tidy, I’m not that bothered.

Rgds Ian 

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I have to say I’m with you Ian on this one. 
 

but I am impressed with those like Mike (ie Brenda) who does some serious mileage and the car is immaculate.

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