Coated headers and heat dissipation

[The Veg]

After seeing the brief discussion of coated headers/manifolds in What Did You Do To Your Lotus Today, a more general question occurred to me. If you install one of these coated headers and it dissipates a lot less heat under the bonnet, that heat has to go somewhere else obviously. How much hotter then does the rest of the exhaust system get, since it's conveying heat that ordinarily would have been dissipated farther upstream? Would it be a good idea to add any form of heat-shielding downstream of the header?

[nmauduit]

I have not budgeted a coating (yet) but did a carefull wrap of the header down to past the gearbox, and even though the air flow under the car is much better is does feel hot inside when you slow down...

[alanr]

It was me who has just had the stainless manifold/header ceramic coated by Zircotec in the thread you are talking about.
Whilst I understand where you are coming from with heat dissipation being moved further down the exhaust pipe I don't anticipate a problem having had the 'Y' piece coated as well so any transition of dissipating heat along the pipe I am hoping won't matter that much.(Says he-Famous last words!). I already have a shield for the clutch slave cylinder and also one over the alternator and engine mount. In addition I am also in the process of fixing aluminium heat shield fabric to the the underbonnet sides of the passenger footwell whilst I have access with the manifold off the car.
I am really hoping all this works because I can't really see what else I can do to lower the under bonnet temps and also get a cooler footwell!

Alan.

[Davidb]

I had my headers ceramic coated before installing with the new engine etc 3 years ago. About 10,000 hard miles since and no problem with heat in the foot well (L/h drive). I also put some aluminized material over the fiber glass adjacent to the headers. I do not notice much heat at all off the headers. I dislike header wrap after having a small fire with the stuff on my last car. The exhaust system is slung below the chassis and dissipates the heat.

[TBG]

My passenger - she who must be obeyed - about 30 or more years ago complained about the heat in her footwell. RHD. I covered the front of the bulkhead and down the sides beside the exhaust with something that looks like aluminium bubble wrap and put the insulation that electric cookers use under the floor carpet, front bulkhead and under the trim alongside the gearbox. Sooooooooooooo cooooooooooool !!

When I rang a cooker manufacturer to ask him about the stuff - a sort of fire proof rubber about half an inch thick - he was so amused at my proposed use he sent me a square and a half yard free of charge.

Happy days and it still works wonderfully today, so no expensive ceramic coatings for me.............

[The Veg]

Thanks all, good stuff.

Pipe wrap: I've read that it REALLY smells bad if it gets wet while hot.

Funny about that stuff from cookers- I know a chap who recently retired from being an engineer of dispensing systems for fizzy beverages and he happened on a good-sized sample of Aerogel at work, to be evaluated for use as insulation in a dispensing system. It wound up not being used at work, so he took it home and used it to insulate the footwell next to the exhaust system in his '67 Alfa Spider, and he reports that it works fabulously!

[nmauduit]

Pipe wrap: I've read that it REALLY smells bad if it gets wet while hot.

I wouldn't think it smells significantly : just like when you've installed your exhaust, the oily residue will burn on the first run (or couple runs depending on duration), maybe a bit slower as it'll be trapped in the fiber, but as long as there is no fresh oil dumped into it on a regular basis when it's dry it's fine. It is efficient at insulating (no quantitative measure or comparison, though).

The main problem for me is it's fragile.

[rgh0]

For what its worth my experience:

I have used both ceramic coated headers and wrapped headers in my Elan.

The wrapped headers provided better heat reduction in the engine bay. When I installed the ceramic headers ( coated inside and out) the heat on the panels that saw direct radiation from the exhaust was higher. I fixed this by fitting kevlar backed aluminium insulation onto the footwell and bonnet in the needed areas

The wrapped headers were a pain to not spill oil or other fluids onto as they soaked it up and then smoked and smelt ! and they looked poorly after a couple of year. After about 4 years the wrapping started to loose strength and break if even gently touched. The headers under the wrapping also corroded fairly rapidly due to the carbon steel being at a high temperature and exposure to air (and moisture when cooled down). Also a problem with the thickness of the wrapping where close clearance between a couple of the pipes causing it to get pinched and a braid at these points

The Ceramic coated ones I am using now are over 8 years old and still look new with no corrosion except where the y piece 9 which is also coated) joins and the coating has been scraped off a little in places on the sliding join parts. The coating is a aluminium look metallic finish which does not stain or scratch easily. The matt finish white / grey or coloured style is cheaper but appears to not last as long from what I have seen.

I have used carbon steel headers in both cases as the thinner stainless headers tend to break with vibration especially in race cars and i cant afford titanium ones

In summary I believe metallic finish ceramic carbon steel is the way to go but you probably will need to add some reflective insulation. if I had stainless headers I would probably try them just with reflective insulation on the critical panels on a road car and not bother with ceramic coating at all, at least till i tried them out to see how it works in actual use in the car.

cheers
Rohan

[TBG]

Rohan said...if I had stainless headers I would probably try them just with reflective insulation on the critical panels on a road car and not bother with ceramic coating at all, at least till i tried them out to see how it works in actual use in the car.

Absolutely. Trust me it works amazingly well for very little cost.

Also I have seen chaps cutting holes in the inner wings to aid cooling airflow. I my opinion for a road car in high temperatures - up to 40c odd it is not necessary - especially if your stuck in a traffic jam and have no natural flow...........

[vstibbard]

Here's picture of my 26R engine bay.

The TTR shell is a super lightweight version so very thin and also a very dry layup. You can just see a fine silver line on the inner top edge of the passenger footwell, this is the reflective heat material which is a stiff but malleable aluminium matrix material. The headers are thin wall stainless, no ceramic coating and no wrap as I don't like the stuff, this is the second last of 4 sets I had made, the first set is on an Elan that cover over 35,000miles in 9 years no cracks, the other on race engine, no cracks, and this set, its done dyno time, post rebuild set up time, practice at 2 meetings and a few races so far, no cracking so far. The extractors have bolted slip joints where the 4:2 and again at the 2:1 joint points and good support at gearbox.

The wiring is also contained in heat proof tubing for good measure. clutch mater cylinder is concentric so no heat issue to worry about.

Not sure of the stainless # used but will check, its commonly used on custom race systems that are made for Porsche's current crop of race cars and two stroke expansion chambers, both made by joining two flat panels that are then pumped up to form perfect radiused extractor tubes, I've watched them being drawn up prior to cutting from sheet and being seam welded and pumped up, its a complex piece of craftmanship.

BTW The chap that makes them has also built his own 12 cylinder quad cam 24 valve power boat race engine from scratch!

I've recently had my S2 7 headers and also the original inlet manifolds ceramic coated inside and out and that has made a significant difference to the temperatures of the carburettors. Like Rohan the finish does not mark Silver for headers and black for the manifolds so they remain looking like standard finish.

Cheers

Vaughan