Heat management advice

[Butters]

I have a cefiro with a g35-1050 on a 6b00ber. It is a black car with ABS and aircon still in place.

I drive the car on the street and sit in traffic.   I am having really high underbay temps , so hot you can't even touch the strut tower even on a winters day. 

 

Everything is ceramic coated(inside and out), turbo has a nappy and the dump pipe(made in stainless) is also heat wrapped. 

 

I have another car that is similar, ceramic coated and it seems to work MUCH better than this car, both done by the same place but some years apart.  

It works so well i can touch the dump pipe while the car is running, it is not even heat wrapped, nor does the turbo have a nappy. 

The only difference between the two cars the the one that works well is a mild steel dump, ceramic coated. 

 

Things I am considering and would be interested in advice on :

1> Swapping to a mild steel dump

2> trying the inconel heat shielding on the 6boost and dump

3> Titanium dump ? 

4> Carbon bonnet with vents above turbo

5> other suggestions ?

 

When the car run twins it was very hot on the hot side but the heat didn't bleed into the body like it does now. 

#waits to hear how this is all my fault

[GTSBoy]

On 12/29/2021 at 12:26 PM, Butters said:

1> Swapping to a mild steel dump

Cannot see how this could make a (positive) difference. The thermal conductivity of stainless is less than of mild, so if anything SS should be better than mild WRT this problem.

On 12/29/2021 at 12:26 PM, Butters said:

2> trying the inconel heat shielding on the 6boost and dump

What is this? A sheetmetal shield? If so, doesn't need to be inconel, because any shield that is stood off from the hot surface will never be anywhere near as hot as it would justify inconel over some other SS or similar (and cheaper) alloy.

Further, I am a great advocate of radiation heat shields, but you must always remember that when you need one, then the source of the heat is bloody hot, and with a radiation shield between it and some other heatsink (in this case the strut tower, etc) then the heat source will radiate less heat away and will run at an even higher temperature. So, if this then means that more heat is pumped into the air flow around it, then you're just moving the problem from one place to another. And the hot air flow can move the heat from one place to another also.

On 12/29/2021 at 12:26 PM, Butters said:

3> Titanium dump ?

Again, not sure if it will help. Ti's conductivity is not drastically different to typical SSs anyway.

On 12/29/2021 at 12:26 PM, Butters said:

4> Carbon bonnet with vents above turbo

CF not required for the purpose. Vents could well be helpful regardless of CF or metal bonnet. Obviously chopping up a metal bonnet is unlikely to be palatable, so understand the drive towards CF.

Additionally, this thing about venting harks back to the question about convective heat transfer. If you put in any extra heat shielding, such that hot surfaces get hotter and move more heat into the air, then you really need to find a way to get rid of the heat. Now, a vent on the bonnet directly over the turbo will work as a short chimney to allow hot air to rise out whenever the car is stationary. When moving, who knows what the aerodynamic effect of the vent will be wrt all the other aerodynamic effects in play? It could be good or it might do nothing or it might even impede the "cooling" available without it.

That last point is probably where the difference between your two cars (unless they are both Ceffies). The airflow in the engine bay is probably the main difference, notwithstanding the possible influence of the black paint on this car being better at receiving radiant heat from the exhaust. Maybe the airflow is better in one because of an undertray difference, or bodykit difference where the air can escape under the car better in one than the other. Maybe the radiator/intercooler/etc sealing and ducting on this black car is better than the other car and the heat shed into the air stream is better (more of it) and that is making the starting temperature in the engine bay higher, before you start adding heat from the exhaust. This is the same argument as having balanced fans on a computer case. There's no point having 10x90mm fans blowing into a case if there's only 1x90mm fan's worth of exit area. You'd be better off switching a few fans to exhaust and get more airflow and lower temperatures. In the case of the car, having a great system for getting the coolers at the front working isn't necessarily great if that heat gets stuck in the engine bay.

What is really required is some form of low pressure zone somewhere down low in/behind the engine bay to encourage the hot air to escape. If there is a high pressure zone down there between the floorpan and the road, then there's an obstacle for the engine bay air to escape. I'd be willing to bet that any number of cars have a relatively higher pressure under the front floor than they do in the engine bay. Or at least, not sufficiently lower than the engine bay to allow the air out. How to change that situation on a street car is possibly a tough answer to come up with and likely to be quite different between chassis/setups also.

 

On 12/29/2021 at 12:26 PM, Butters said:

#waits to hear how this is all my fault

It probably is all your fault. 😛

I think a CF bonnet with a means to exhaust the air from the radiator out in the front centre is a logical thing to want. Cause suction behind the coolers and further improve their performance without putting much of their heat contribution into the engine bay. Then the other vents on the bonnet would be arranged such that you have some scoopy things towards the front on the sides to get some cool air in and some vents with negative pressure arrangement further back to allow it to escape and take some heat out with it. Stay away from the cowl region as it will provide inconsistent results (possibly an exhaust at low speed and possibly an inlet at higher speed when the pressure rises at the base of the windscreen).

There might even be an argument for a small, high speed axial or barrel fan to draw cool air from a brake vent or similar and duct it to the hot spot so that you're starting with the coldest air available rather than general hot engine bay air. Obviously this will require an escape route afterwards, because otherwise you're back near square one again.

[Butters]

This is what i mean in regards to inconel shielding 

 

[Butters]

With changing to mild / Ti , I tend to agree hence asking the question. I don't know or can find enough about the heat properties of the materials to understand. 

 

The bonnet vents make a lot of sense and what you say about creating a flow does too. 

I said carbon bonnet, as i don't want to cut my factory one, these things are getting rare.