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Author Topic: Thoughts on engine bay heat  (Read 1416 times)

RhysN

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Thoughts on engine bay heat
« on: 21 January 2021, 09:04:38 am »
Our engines with all the attendant ancillaries can generate quite a bit of heat. Much of this comes from exhaust heat, a smaller amount from the actual cooling of the engine, and some from brakes and drive train.
The outcome of the heat can be that the engine is trying to breathe in warm air through the carburettor, which leads to a loss of power. A secondary effect can be that the fuel in the tank becomes warm, which causes loss of volatility in the fuel. Thirdly, the engine bay is so warm that there can be concern for the materials the body is made from causing troubles.
Let’s deal with this in a logical manner and draw on lessons learned in much hotter environments where cyclekarts are used, and owners have dealt with this without resorting to compromising the looks by removing the engine cover. It’s an absolute fact that these “vehicles” are commonly run in temperatures over 40 degrees Celsius. In some of those places the organisers insist on fully clad vehicles, so it’s not over difficult to resolve this.
To help inlet breathing, draw the air from outside the engine bay, at least then the inlet is at ambient temperature. Making an extension through the side of the body might not visually appeal, but it’s a definite help especially with a pod type air filter.
If fuel heat is an issue, relocate the tank, be it the original or something else to somewhere away from heat or find a way to shield it. Again, I believe exhaust heat is the biggest contributor. A secondary benefit is that it makes the engine substantially smaller to fit in. Do you really need that full size tank anyway?
The only ways I can think of to deal with concern over the heat affecting the body materials are twofold. First, get the heat out, and secondly put a heat reflective material inside the body where there is concern. http://www.textiletechnologies.co.uk/reflective-heat-shield-sheets.html is an option.
By having scoops or such to draw air from the outside there is an initial benefit, however it’s even more important to encourage the air to exit the engine bay more freely, so the area of exit must be greater than the inlet, of course heat rises, so exits at the top is going to help more.
If you are using one of the aftermarket exhausts, they can readily be “wrapped” with the material made for the job. This has a beneficial effect of increased power, at least in theory, probably that’s very small in our cars. Somehow you need to get the exhaust out of the engine bay, there are two reasons, the fumes coming out don’t do a lot for good clean oxygenated air for the inlet, and of course it’s a source (the major one in my opinion) of heat, so get it outside the car.
I have checked with the tuners of these engines to see if what they call a “top plate” is to help air from the fan, they say not, it’s purely cosmetic or to mount a diaphragm pump on for low mounted or remote tanks, so you don’t need that.
Brake heat. If you have read Stefan’s article you will have some data which clearly shows heat rise from the brake (s). How to deal with that? Scoops to direct air to the disc is standard motorsport practice, again that needs to get away too.
By the time you are having this issue to deal with, it’s probably too late to think that choosing an inspiration car with perhaps a tonneau cover over the back for display, and taking it off for heat issues might be of benefit, perhaps the next car?  You may have seen a US car with what looks like a “dicky seat” opened when running, that’s one way to get a large opening, aero drag might cause you to wonder, I suspect our own bodies would contribute more.?

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Marek.Z.N

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Re: Thoughts on engine bay heat
« Reply #1 on: 21 January 2021, 11:16:09 am »
Interesting points there Rhys. scooping cool air to the breaks doesn't have to effect aesthetics either. A scoop below the CK tub or even routed from the radiator grill are subtle ways of getting cool air to the break or air intake or even fan on the engine (obviously making sure to use a filter to block contaminants from the track from getting on the brake disks or into the air intake. equally with exhausts, they can be subtle by pointing down out the lower back end of the CK like on Adrians Renault or Dad's Bugatti (or any others i have forgotten). for venting air out the top, fake fuel caps to take off when driving, mesh painted the same colour as the body and louvres are subtle ideas for achieving this heat release without compromising looks. All really good points from you Rhys as they do look much better driving around with tails on!

Marek

Chris Brown

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Re: Thoughts on engine bay heat
« Reply #2 on: 21 January 2021, 04:28:40 pm »
That covers things very well Rhys, prompted me to think in terms of venturi extraction systems. I'll think a bit more about it before I go into detail.

sjc56

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Re: Thoughts on engine bay heat
« Reply #3 on: 21 January 2021, 07:13:07 pm »
This is all interesting stuff, it’s something I have been thinking about for my build.

synthpunk

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Re: Thoughts on engine bay heat
« Reply #4 on: 21 January 2021, 10:32:19 pm »
Id been planning to hide scoops behind the back wheels so you cant see them from side on, and using painted mesh for the engine cover.
Something i was pondering about but havent really devoted many brain processing cycles to was installing a fan run via a belt / pulleys/ layshaft driven off the engine itself. It would probably need a power takeoff from the engine itself rather than off the axle to avoid running too slow or overheating whilst idling?

One other thing i thought about was installing an actual air cooled radiator at the front, and wrapping some copper (3/16ths) brake pipe round the cylinder between the air cooling fins and using an electric (or maybe belt driven)pump to run water round the system, as a water cooling system. A fairly basic water jacket basically. Im somewhat keen on having an electric start on the engine, which will mean a battery anyways, so well see.

Marek.Z.N

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Re: Thoughts on engine bay heat
« Reply #5 on: 22 January 2021, 09:36:14 am »
With my build the cooling issues will be quite different because i chose to mount the brakes outside of the body meaning that their heat will be a much smaller issue which helps engine bay temps and keeping the brakes cool and therefore more effective. Also the electric motor should generate little heat and the battery will be mounted at the front with a fan cooling system so the only main temperature thing for me is the battery.

sjc56

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Re: Thoughts on engine bay heat
« Reply #6 on: 22 January 2021, 01:44:42 pm »
I’m thinking, to relocate the tank, this would free up more space for fresh air flow directed over the engine. Possibly some form of heatsink plates mounted on the cylinder of the engine. Also mount the motor on a magnesium mount and use a vented brake disc on a magnesium carrier.

magnesium helps dissipate heat from parts although the heat would still be in the confines of the engine bay, but good air flow would help get rid of it. If you were able to run the engine slightly rich, that would help but to the detriment of power. I think the key is good air flow with a good exit for hot air.

Adrian

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Re: Thoughts on engine bay heat
« Reply #7 on: 25 January 2021, 02:30:21 pm »
Direct the exhaust out to the back end of the car. Ensure the air intake is taking in fresh air and no exhaust fumes and make sure the engine area is well ventilated, (there's usually a big hole underneath anyway) and heat will never be an issue.
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sylvaman

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Re: Thoughts on engine bay heat
« Reply #8 on: 27 January 2021, 06:02:38 pm »
So going back to moving the fuel tank.  if using an alternative design , what capacity has been used ?

  Bearing in mind that the original GX tank is 3 litre ?   Do you need that size / capacity ? Or would you be constantly topping up with a smaller tank.

Average run time at Stretton..... 15 mins ?

As there are plenty of smaller mower tanks out there 1 to 2 litre . Seems to be a quite jump up to next size of 5 litres , then need to find more space to fit.

Chris L

RhysN

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Re: Thoughts on engine bay heat
« Reply #9 on: 24 February 2021, 04:05:47 am »
Adrian's one is 1 litre on the Renault, possibly a bit small. Kim was to have had something similar, I ran out of time, to do it, but there are plenty of various racing kart tanks out on the interwebby thing.

Chris Brown

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Marek.Z.N

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Re: Thoughts on engine bay heat
« Reply #11 on: 24 February 2021, 11:46:32 am »
could a fuel tank be made out of fibreglass to fit the body shape somewhere to make more efficient use of what can be very precious leg space? and then epoxy in a filling cap and fuel output?.

crozier5

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Re: Thoughts on engine bay heat
« Reply #12 on: 24 February 2021, 12:28:21 pm »
Marek,
Fibre-glass petrol tanks went out of fashion some years ago because of fractures in the skin.
Not sure of what current regs are regarding their use.
You could fab a fancy tank from allow but at what cost.
Billy

Marek.Z.N

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Re: Thoughts on engine bay heat
« Reply #13 on: 24 February 2021, 06:22:22 pm »
ahh i see. someone with access to vacuum forming like adrian could possible make a custom shape one in 2 halves and then bond it but as you say that is probably more effort than it is worth

RhysN

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Re: Thoughts on engine bay heat
« Reply #14 on: 24 February 2021, 06:27:05 pm »
The greatest issue is the constituents of current fuel attacking the tank material.
That's one of the major factors which lead to the demise of fibreglass tanks, both for karts and motorbikes like Montessa and the like.
There are so many varieties of kart tanks, chainsaws, lawnmowers, lawn tractors and the like, for me it's a bit like re-inventing wheels. Please don't take this the wrong way, I just think it's spending time and effort where it's not needed.