How much heat does the Fiat engine generate?

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How much heat does the Fiat engine generate?

Postby EmlynC » Mon Jan 14, 2019 8:15 am

I was talking to Alan Docking about radiators at the show. The conversation went something like, "how large do I need to make the radiator?" to which the answer was, "how much heat is being generated at full revs?"

As I don't know the answer, I was wondering if anyone has this data after using a rolling road?

One interesting thing he said was that the efficiency of the radiator reduces with its depth. I had never thought about is, by Alan explained that the air passing through the radiator core is getting hotter, so therefore there is less potential to remove heat at the back of a thick radiator. His suggestion was to go for a thinner but larger radiator.

The other thing he talked about was making sure that the ducting out of the radiator is larger than the inlet – I'm now thinking I will duct some of the hot air out through the outlet I have in the top of the body, but will also let some go down the sides of the car.

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Re: How much heat does the Fiat engine generate?

Postby F1300Tony » Mon Jan 14, 2019 10:36 am

The capacity of a radiator totally depends on the amount of air going through it, and the amount of water.
I based radiator size on the standard 1.1 Punto rad. You can then use a rad of the same area and depth. The total volume is a good guide but greater depth tends to block flow. The old VW Golf ali rad is good as it is shallow and the pipes come out the right way. That has more capacity than the Punto. The standard Punto rad is a bit small.
Based on WW2 aircraft research and in one of Carroll Smith books it says (from memory) the inlet opening can be down to 25% of the rad area and the outlet should be not less than 40%. The figure of 25% is pushing it a bit. In the last few years I have learnt that the ducting expansion should expand in area no more than a round pipe with an 8 degree included angle. It seems OK to run the rad at extreme angle to the direction of flow. And a long duct will reduce flow.
One of the rad supplier's sites has details of the sizes and diagrams showing the mounting, connections, etc. You often need to make a threaded plug, and that includes both rads mentioned.
Talking to a friend of mine 'who knows' water is the best heat transfer medium.
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Re: How much heat does the Fiat engine generate?

Postby F1300Tony » Mon Jan 14, 2019 10:53 am

I should have said the 25% inlet area will only work if the inlet is facing straight into clean air. It does surprise me how some rads get enough air, but they obviously do, inlet in a high pressure region, outlet in low, and there is nowhere at lower pressure than the rear of the car.
For a very, very rough figure for the waste heat generated I would guess at 30% of the engine power.
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Re: How much heat does the Fiat engine generate?

Postby F1300Tony » Mon Jan 14, 2019 7:37 pm

I just asked someone who really knows and the waste heat energy to the radiator is more like 60-70% of the output power energy.
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Re: How much heat does the Fiat engine generate?

Postby Martin Kemp » Mon Jan 14, 2019 9:35 pm

It is the thermal efficiency of a petrol engine that is about 30% (it depends a lot on the compression ratio) so the heat wasted is about 70% of the fuel value or nearly 3 times the flywheel power output.
I don't think you can get any of that information from a rolling road unless you also measure the fuel consumption as well and do some complex calculations. However the rolling road will tell you how much heat is generated in the transmission.

The waste heat from the engine is dumped in 3 main ways, down the exhaust pipe, airflow around the engine, and airflow through the radiator.

If your exhaust system is inside the bodywork then the hot exhaust pipes will retain some of the exhaust heat in the engine bay and the exhaust is a lot hotter than the rest of the engine. If there is no airflow through the engine bay then the only engine cooling will be the radiator. Getting a good airflow through the engine bay can make a big difference and dump a lot of heat. It is also a good idea to allow the engine bay to vent when the car is stationary and the engine off. A lot of cars cook themselves during red flag incidents.

If this seem to be getting complicated, the good news is that a VW Golf or Polo radiator should work fine provided the ducting follows Tony's guidelines above and provided the inlet is in a high pressure zone and the outlet is in a low pressure zone. Another good radiator if you have room for it is the Ford Ka which is very thin and can be run at a very low angle with a very low airspeed.

Martin Kemp
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Re: How much heat does the Fiat engine generate?

Postby suebmick » Tue Jan 15, 2019 11:25 am

I still use the Mini twin-core rad that I used in Reliant days. As it's located in the nose it gets the full brunt of air flow, and there's a 10ins square gap in the side panel to allow that air to pass over/past the engine & out of the sidepod through a duct. Originally there was no hole in the sidepod & I thought the air would be carried out via the exhaust hole, but she ran very hot. At Cadwell, Dick gave me a saw & said "cut a hole in the pod". I added a "lip" to the front edge of said hole & she then, & now, tends to run at a steady 80deg water & 90deg oil temp. Even in really hot weather. When it's really cold, I add a piece of duct tape to the rad. Or even 2 tapes if its snowing

When we went to Fiat, I also had to drill some large holes in the bonnet to get the air flowing over the engine more than with the Reliant

It's all a question of flow, outside temp & weather, & what circuit you're at. Got to get out there & see what happens, with a contingency plan to alter it if conditions change. It can all work perfectly in the garage, but not on track. Suck it & see
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