Exhaust headers - thermal wrapping

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DamirGTI
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Exhaust headers - thermal wrapping

Post by DamirGTI »

Hi Guy !

Please i need some advice about this product - thermal tape for exhaust headers .

I have read somewhere that mainfold wrapped with this tape holds heat inside which makes exhaust flow faster and can help a little on exhaust scavenging. Is all this true ? Is this of any use on medium modified road car .

Thanks !

Damir
Last edited by DamirGTI on October 22nd, 2007, 8:48 am, edited 1 time in total.
Guy Croft
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Post by Guy Croft »

Exhaust wrap...


I have always been against it because it causes the pipe material to cycle repeatedly thru extremely elevated temperatures as the radiant and convective heat transfer to atmosphere is blocked. Since pipe contains stresses from manufacture and welding and since it is often made from steel or stainless with relatively low strength at high temperature the metal can degrade very badly. This is the effect of thermal stress as it's called. No need to go into the metallurgy.


The only possible benefit - if you are prepared to accept severe deterioration of the pipes themselves is reduced under-bonnet temperatures. The massive flow of heat coming off the exhaust - especially in highly tuned front-wheel-drive installations when not moving at reasonable forward speed - can cause the fuel in the carb to boil, the oil and engine to overheat. The underbonnet temperature can be easily surveyed with an inexpensive hand-held probe from Halfords or other auto shop and will shock anyone who has never done it. Certainly cold air ducting is great when your vehicle is moving but not so effective when it's not. If you must use wrap to reduce underbonnet heat - give the insulating material some stand-off from the pipe to avoid those high metal temperatures.

One must also remember that the heat doesn't just flow outwards radially thru the pipe and down the pipe - it gets into the port, the valve and seat - even piston - region and can cause all sorts of dramas: seats cracking, detonation etc etc. General increases in head temperature are going to degrade the inlet charge density too. And, if, for argument sake, you have a very highly tuned motor and you wrap your exhaust tightly and you're running a cooling system with plain water and no water-wetter or antifreeze your cooling system on the ex side of the head is likely to be totally overloaded due to nucleate boiling = no heat transfer at all to the coolant system - and the first thing you'll know about could well be a blown head gasket, or worse.

Ferriday Engineering (see links) do a special heat-block mica gasket to help inhibit heat flow from header to head - it is well worth consulting with them.

Do you want to wrap ex header/manifold on turbocharged units? No, no way just speculatively, even if it brings a performance gain - unless you know for sure by means of traceable metallurgical data and via accurate thermocouple measurement in the pipes etc that you are not exceeding the maximum rated temperature for the turbine blades and casing and exhaust port/valve region too. Never mind all the nuts and bolts that hold it together. Otherwise you put the whole unit at risk. Remember I was a Chief Engineer with a world-class turbocharger company so I know more than most about the degrading effects of heat on things.

Coatings - though I have no hard test data, I imagine - are an attempt to do the same kind of thing as wrap. I would not use them at all.

I hope this is helpful.

GC
Last edited by Guy Croft on February 23rd, 2007, 6:27 am, edited 3 times in total.
DamirGTI
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Post by DamirGTI »

Great ! Thanks Guy for detail explanation .

Damir
andrew
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Exhaust headers- thermal wrapping

Post by andrew »

Hello Damir,
As a footnote to Guy's answer to your query, I once owned a Lancia Beta Montecarlo that had this thermal wrapping bandage fitted to the brand new tubular manifold. When I bought the car it was newly fitted (within the previous 1000 miles). I can't really comment on how it affected the performance of the car (I doubt if it did at all); however I can comment on the state of the exhaust ten months and 9000 miles later: Two totally separate cracks in tubes 3 and 4, with localized detonation damage in the exhaust valve area too. I did wonder if it was caused by the bandage and after reading Guy's answer I am now more certain it was. And apart from anything else it looked awful too!

Andrew.
DamirGTI
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Post by DamirGTI »

Thanks Andrew !
Already i have cancel this wrapping job , but maybee i make one of mine spare mainfolds this way just for a little experiment .

Damir
Julian
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Post by Julian »

I've been down this route as well for the primary purpose of keeping engine bay temperatures down. My observational notes do not make particularly enthusiastic reading.

Initially in a mid-engined NA car the result was excellent - engine temperatures were slightly elevated but the gains in cooling elsewhere made it all worthwhile but as already pointed out the exhaust manifold life expectancy was massively reduced - typically a new manifold would be needed every 10000 miles. One of the most notable changes was that the normally heatproof paint on the silencer box started to "char". The internal gas temperatures were heating the box beyond the limits of the paint. The internal packing material was being "melted" within 1500 miles of use.

The second experiment - having learned a few lessons from the first attempt was to use just a "turbo blanket" on a similar car with a turbo installation. Damage to the engine from heat and damage to the turbo from overheating made the whole thing a performance and financial disaster. While it did prevent radiant heat damage to other parts of the engine bay (most notably wiring) this was all preventable by rerouting. The final solution was to use a sheet of metal held at about 2 inches from the turbo.

In summary - in the right car the benefits of thermal wrapping are more than worth the decrease in lifespan of the manifold and pipes. Everywhere else it is a liability. More importantly you have to factor in the exhaust wrap in the design and construction. The knock-on effects are far from insignificant.

If you have delicate components that need protecting from heat then wrap those components, not the exhaust.

If the thermal charge from the engine (particularly on forced induction isntallations) is excessive then you need to look at the entire cooling solution not just a quick fix.
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