Exhaust manifold wrapping + Precats in or out ?
Discussion
Have the exhaust manifolds off at the moment (gaskets leaking again). While they are off I am tempted to wrap them as an attempt at reducing under bonnet temperatures, another option is to have them ceramic coated but not quite got to gips with that process yet. Have heard that wrapping is quite difficult to do well and quite delicate when done. Seem to think I have also heard of a treatment that you can spray on at home and then bake in the oven, anybody done that ?
As a supplementary point, what are the pros and cons of taking out the PreCats ? Plainly they generate a lot of heat and allegedly they have little effect on emissions for MOT, although plainly they must do something. The oxygen sensors are downstream of them which seems interesting. I am told taking them out “changes” the engine noise and you may gain perhaps 2-3 bhp. Apparently hacking them out is quite a task.
Advice please
As a supplementary point, what are the pros and cons of taking out the PreCats ? Plainly they generate a lot of heat and allegedly they have little effect on emissions for MOT, although plainly they must do something. The oxygen sensors are downstream of them which seems interesting. I am told taking them out “changes” the engine noise and you may gain perhaps 2-3 bhp. Apparently hacking them out is quite a task.
Advice please
Precat removal is a no brainer IMHO, less to go wrong, better flow in the exhaust, less heat.
Best way to remove is by cut & shut with a welder, and have the 4/1 joint tickled up at the same time.
Ceramic coating inside & outside is way the best performing & looking treatment IMHO. Never seen 'mummified' F1 cars, have you
ACT used to do an exchange service IIRC, send them your old manifolds and they return decatted & coated versions. If you wanted the lot doing by someone else that would probably work out cheaper overall.
Best way to remove is by cut & shut with a welder, and have the 4/1 joint tickled up at the same time.
Ceramic coating inside & outside is way the best performing & looking treatment IMHO. Never seen 'mummified' F1 cars, have you
ACT used to do an exchange service IIRC, send them your old manifolds and they return decatted & coated versions. If you wanted the lot doing by someone else that would probably work out cheaper overall.
I've used 'Black Satin' diy ceramic paint on the outside of mine. Although it can be baked on, I didn't do that. I figure the exhaust heat will take care of that. 
The thing with this is that it is only a few microns thick and nowhere near enough to give any substantial insulating effect. It helps a bit though, and does look a bit smarter than the original manky corroding exhausts.
Maybe the cermachrome style ceramic coating is more effective, but given that it costs ten times as much it would have to be *very* effective indeed to be worth the money imo.
Thermal bandage wrapping is a very effective way to keep the heat in. This has a reputation for causing corrosion problems in mild steel exhausts (didn't have that problem with mine) and can also encourage stress cracking around the collectors (to be fair this can be a problem for unwrapped exhausts too). The main disadvantages are that it muffles the exhaust note a lot, and it physically quite fragile and will tend to break up after a year or so. It's not particularly difficult to apply but at around £50 for the tape you might not be happy to keep replacing it.
The thing with this is that it is only a few microns thick and nowhere near enough to give any substantial insulating effect. It helps a bit though, and does look a bit smarter than the original manky corroding exhausts.
Maybe the cermachrome style ceramic coating is more effective, but given that it costs ten times as much it would have to be *very* effective indeed to be worth the money imo.
Thermal bandage wrapping is a very effective way to keep the heat in. This has a reputation for causing corrosion problems in mild steel exhausts (didn't have that problem with mine) and can also encourage stress cracking around the collectors (to be fair this can be a problem for unwrapped exhausts too). The main disadvantages are that it muffles the exhaust note a lot, and it physically quite fragile and will tend to break up after a year or so. It's not particularly difficult to apply but at around £50 for the tape you might not be happy to keep replacing it.
GreenV8S said:
I've used 'Black Satin' diy ceramic paint on the outside of mine. Although it can be baked on, I didn't do that. I figure the exhaust heat will take care of that.
Hmmmm... I'm rather surprised that you didn't exactly follow the manufacturers instructions? I understood the process to be something like:
degrease
blast with 120grit ally oxide
clean off
spray on (20secs visc cup is pretty thin as well)
air dry
bake at 400C for 1 hour.
..and they do state that only one coat is necessary, it should just look 'wet'. This has always surprised me a bit, I'm sure the nice chap at cam-u-coat said they applied the cermakrome/coloured stuff over the black satin?
I am certainly planning to use some of their other barrier & dispersal products
luckily they don't need curing at such high temps 
I too are thinking of removing my pre-cats. I currently have a sleeved silencer and love the sound my car makes. Im not trying to make it sound like a pre-cat, but improve flow and reduce heat build up. However im worried that removing the pre-cats will alter my exhaust sound to a sound I don't like as much as it is now. I would love to hear a Griff before and after pre-cat removal (with main cat and sleaved silencer!!!). does anyone have videos of before and after and how much does it alter the exhaust note. Ive heard systems which are straight through with no cat and they sound tinny like an empty baked bean can!!!!
Yep , the previous owner of my Griff had it's pre-cats out, I only realised this by going through all the receipts which had not all come with car at the time of purchase( Rob Ingelby had sourced it so was not worried), but cutting to the chase: my car sounds rich and fruity, not a hint of tinnyness so I too would say go for it!
GreenV8S said:
The thing with this is that it is only a few microns thick and nowhere near enough to give any substantial insulating effect.
As I understand it "k / x" determines the heat transfer, so decreasing k or increasing x will improve the insulation.If k is small enough then x can be reduced accordingly.
You will also actually double the insulation provided if you coat internally, I can't see that being disputed? This doesn't take into account the added advantages provided by preventing heat soak and conduction internally within the steel pipes themselves?
As I understand the material properties, thermal expansion is not at all related thermal conduction. The expansion will cause a thick substrate to crack & peel very quickly - I would assume that is why they are a specific about using a very thin layer when applying.
On reflection I guess the Cermakrome overcoats are modified in terms of expansion with this in mind. Blinkin clever these chemists if you ask me, but we can always screw up their ideas
spend said:
If k is small enough then x can be reduced accordingly.
I assume k is thermal conductivity and x is thickness.k is low compared to steel etc but the ceramic paint does still conduct heat, and x is absolutely minute. The end result is a small amount of insulation, any insulation helps but this is not enough to make any huge difference. It's far less, for example, than the effect of insulating bandage. This is based on my experience with Black Satin DIY ceramic paint; maybe the professionally applied cermachrome stuff is much thicker and works better. The problem is that no matter how good an insulator the material is, when it's only a millionth of an inch thick you're still going to see a lot of conduction.
If the k value is extremely minute so the thickness can be extremely thin, its only simple maths I would like to think that the manufacturers got the 2 in the right ball-park, and I guess that since so many advanced engines (F1, Indy, powerboats...) use the coating over bandages that it is does work.
As I mentioned before, I believe the Cermakrome finishes are applied over the 'satin black'. I have certainly come to the conclusion that they offer better durability than plain black from my own experiences, and would certainly put the Cermakrome/colour? on top of black if doing it again in my own case. The black is however all that you can coat the manifolds with internally as I understand it. I certainly can see it has worn off inside my manifolds where the gas hits the first bend in the primaries.
I plan to do a fair bit of DIY coating myself this year, but you can be assured if it doesn't work I will put it down to my own technique not Techline/CamUCoat products Eek! that could be tempting fate :bugger: 
One thing is quite certain, on our cars every mm around the manifolds counts, whether air gap or finger gap - they are always very close to the inner wings
I would like to think that the manufacturers got the 2 in the right ball-park, and I guess that since so many advanced engines (F1, Indy, powerboats...) use the coating over bandages that it is does work.As I mentioned before, I believe the Cermakrome finishes are applied over the 'satin black'. I have certainly come to the conclusion that they offer better durability than plain black from my own experiences, and would certainly put the Cermakrome/colour? on top of black if doing it again in my own case. The black is however all that you can coat the manifolds with internally as I understand it. I certainly can see it has worn off inside my manifolds where the gas hits the first bend in the primaries.
I plan to do a fair bit of DIY coating myself this year, but you can be assured if it doesn't work I will put it down to my own technique not Techline/CamUCoat products
Eek! that could be tempting fate :bugger: One thing is quite certain, on our cars every mm around the manifolds counts, whether air gap or finger gap - they are always very close to the inner wings
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