heat shield test

[clive f]

I feel that a few people are a bit concerned about how well the heat shields that I am making, are going to work due to the fact that they are mounted on the exhaust itself,
So I managed to get my hands on a laser temperature meter,so have done a couple of tests this afternoon to see how much heat my heat shields are absorbing from being mounted to the exhaust pipe
I removed one heat shield and wrapped a strip of exhaust heat bandage 2” wide around the pipe, 1 layer thick, and then clamped the shield back over the top of the bandage, the other shield was left fitted directly on the exhaust,I should also note that my exhaust is cam coated.
If we call the shield fitted directly onto the exhaust A, and the shield fitted on topof the exhaust wrap B, then I found that

at tickover, temp gauge at 55dg A was 25 dg, B was 23dg, exhaust was 150dg

took it for a run and let it tick over some more to heat up,readings taken with engine still running, fans off,

temp guage 80dg A was 80dg, B was 58dg exhaust was 260 dg

turned engine off, after 2-3minutes

A was 60dg, B was 45dg and exhaust was 160dg.

Therefor the best thing is to put a strip of exhaust wrap under each clip, as this is the only contact area with the exhaust, and reduces the amount of heat being absorbed by the heat shield.

I should have done this first really, but we live and learn!

Edited by clive f on Wednesday 10th January 19:02

[chris_chim]

Are you sure any of these temperature measurements are valid? If you point an infrared temperature guage at an IR reflective surface then you get the temperature of whatever it is reflecting. So if you have a black body radiator you will be measuring the temperature of it, if you have a perfect IR mirror (glass is pretty good at this) you will get a random reflection of something else and if you have a shiney heat shield you will be probably be somewhere in between but I suspect closer to a mirror.

[hut49]

For clarification, I think the "laser temperature meter" is actually an infrared detector with a laser pointer.

For interest, did you measure the temperature on the exhaust wrap (without the shield)?

If the purpose of the heat shield is to reduce thermal load on components in the vicinity of the exhaust then it is the temperature of these that is important to understanding the efficiency of your product, not the temperature of the product itself.

[clive f]

hut49 said:

If the purpose of the heat shield is to reduce thermal load on components in the vicinity of the exhaust then it is the temperature of these that is important to understanding the efficiency of your product, not the temperature of the product itself.

you have a good point, I will take some readings this evening and let you know of the outcome.

[andy-w]

I think you are going to have trouble proving this.

You have tested before and after temps with good results and now the laser thermometer is being questioned???
I know different surfaces will give slightly different results using these devices but unless you have got access to laboratory equipment/environment then surely this would do as a guideline?

If you have taken the temp of one shield and you got 80 deg consistently then i think it would be safe to assume that you are getting a reasonable accurate reading (unless you are hitting the same spot every time) and if the one on the other side is showing 54 deg then i would think that seeing as they are both made out of the same material then that would be a reasonably accurate reading as well.
Or you could paint a couple black for testing...???

Also TVR did make some heat shields to fit around the swirl pot to stop the otter switch from heating up and protect the lower end of the fan belt.

[victormeldrew]

Just put a black sticker onto the surface and read temps from that, that would avoid reflection issues.

Still think phenolic spacers would be a better option than exhaust wrap, which has been known to cause corrosion.

[andy-w]

victormeldrew said:

black sticker

Ok...a bit easier than painting!!!

[spend]

andy-w said:

Also TVR did make some heat shields to fit around the swirl pot to stop the otter switch from heating up and protect the lower end of the fan belt.

LR also made alternator and starter motor heatshields in later variants.

Dave

[chimune]

As a slight aside, my heatshields have recently been painted black. They were unpainted / silvery before. WRT component protection, is this good, bad or cosmetic only ?

[GreenV8S]

chimune said:

As a slight aside, my heatshields have recently been painted black. They were unpainted / silvery before. WRT component protection, is this good, bad or cosmetic only ?

Being reflective will reduce the emissivity slightly and reduce the amount of radiated heat absorbed by the 'hot' side of the shield and reduce the amount of radiated heat given off by the 'cold' side. Matt paint will have the opposite effect. I don't think the difference is worth losing any sleep over, though.

[chimune]

Ta man. They do look better !
I shall sleep well....

[clive f]

clive f said:

hut49 said:

If the purpose of the heat shield is to reduce thermal load on components in the vicinity of the exhaust then it is the temperature of these that is important to understanding the efficiency of your product, not the temperature of the product itself.

you have a good point, I will take some readings this evening and let you know of the outcome.

I tested this last night, went for a good run, and found that with the coolant temp guage reading 80dg, manifold 260dg, the heat sensor at the bottom of the swirl pot was 96dg.

after dinner, removed exhaust shield, repeated the above and found that the coolant guage 80dg, manifold 260dg and sensor was 116dg.

these give a guidline showing that the heat shield is doing what it is supposed to.
http://cgi.ebay.co.uk/A-pair-of-Exhau

Edited by clive f on Friday 12th January 10:43