A new cooling discussion

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A new cooling discussion

Post by peter freeman » Thu May 30, 2019 7:06 am

Probably but why put holes in the bonnet - just raise he rear a bit with spacers on the hinges



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Post by TrevorG » Thu May 30, 2019 10:20 am

That's my original idea then, but a differing solution....somehow getting the airflow over the engine and out the tunnel,, after all, there is a dead space trapping air above the engine and as heat rises that's why I think the scuttle area seems the hottest in a se6. Wonder if anyone has tried an air scoop on the bonnet then?

Yet again, many years ago, I was the original builder of 'fart', the highly tuned cox gtm that cars and car conversions later raced and wrote articles about. When I put the twin webers on, I had to modify the hump on the bonnet/boot and soon found that it worked better scooping air and not venting it! Interestingly she is still around.

https://www.bing.com/images/search?view ... 920&sim=11



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Post by Dave 6726 » Thu May 30, 2019 11:42 am

peter freeman wrote:
Thu May 30, 2019 7:06 am
Probably but why put holes in the bonnet - just raise he rear a bit with spacers on the hinges
I was just addressing the theoretical aspect, but was aware that some people did this. Mind, in aesthetic terms, I think neatly installed vents (if you must) is better than having what the iggies might simply call a 'badly aligned' bonnet! :lol:



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Post by Old and Slow » Mon Jun 24, 2019 2:33 pm

At the Bicester "Super-Scramble" yesterday I picked up this fan (for £3), which I will be fitting behind the radiator; I have the standard Reliant fan in front of the radiator; this is not close coupled and tries to push air through (most of the air goes round the outside of the rad!).
Does anyone know which cars used the 3-point mounting on the fan motor? I ask, because the original Reliant fitting on the Sabre Six is the same - does this mean I've bought a Sabre/Coupe fan?
I want to keep as much originality as possible, so adding this as an auxiliary fan suits my aims. The fan blades are aerofoil section and designed to fit in front of a radiator; the blades clamp screw is seized in spite of the Plus-Gas so I won't be fitting it the "right" way round.
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Post by scimjim » Mon Jun 24, 2019 2:45 pm

I think I’d duct the existing fan properly rather than fit another one?

Being a more modern yellow plastic, it’s also totally out of place in a Sabre engine bay :cry:


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Post by Brucky » Mon Jun 24, 2019 6:33 pm

Coupe mechanical fan behind the rad which is ducted. I’ve also an electric auxiliary fan behind the rad which is rarely required.
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Post by Old and Slow » Thu Jun 27, 2019 8:44 pm

Ducting the fan in front of the rad is complicated by the presence of the oil cooler, so for me a non-starter.
I think my '65 Mini had a yellow fan, but I have tins of paint so can possibly satisfy Jim's concerns.
When I bought 660XYB it had a bracket system behind the rad holding the existing motor; to restore some originality I put the motor in front of the rad where it ought to be, which is probably why I've introduced potential cooling issues. I've only boiled over once, when I forgot to turn the fan on. Do I have a problem? I don't really know, as the original arrangement gives the gauges a 30-second inbuilt response delay time; I turn the fan on when the needle starts to climb above the "N" and it takes a while for it to drop. I already have the bracketry and putting an auxiliary fan behind the rad might be "belt and braces" but like insurance, you hope it will never be needed. It will, however give my navigator (SWMBO) peace of mind, and who's worried about an extra 10 amps out of the dynamo (!).


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Post by scimjim » Thu Jun 27, 2019 9:29 pm

Do you have room to fit a modern electric ducted fan to the front of the rad with a temp sensor in the top hose?


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Post by CNHSS1 » Fri Jun 28, 2019 8:27 am

Raising the rear of a bonnet rarely gets the effect one thinks, if you wool tuft the bonnet (4" lengths of wool, sellotaped on) you will see that the flow below the screen at the end of the bonnet actually reverses! The air flows over the bonnet and turns 180deg and down through the engine bay.

Wool stuffing a cheap and simple way of checking where vents/holes/scoops are best mounted, and then testing afterwards to ensure it works.

Randomly found YouTube vid

https://youtu.be/CsREhs9zZTQ


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Post by CNHSS1 » Fri Jun 28, 2019 8:45 am

Great example from one of Sinon McBeaths articles in Racecarengineering, run at MIRAs windtunnel in Leicestershire.

http://carbonweezel.co.uk/testing/testi ... tml#bonnet

You can see the raised rear of the bonnet and reversed flow into the engine bay which stalls rad flow and reduces cooling. They taped the bonnet shut and flow returns through rad, through engine bay and under car


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Post by CNHSS1 » Fri Jun 28, 2019 8:48 am

Another scim related test, anyone with a single skinned lightened bonnet on a small sports but still has hinges at front, if you drive (on a private road of course...) at 70mph without the bonnet clicked shut, the bonnet will actually rise and float about 4" off its stops at the back! Dangerous if you are short as you can see over it lol. Maybe that's why reliant made 'em so bloody heavy??

EDIT
This is due to flow reversion not airflow trying to escape the under bonnet area :)


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Post by Rev Light » Fri Jun 28, 2019 10:28 am

Having read through this discussion, it would seem that a small chin spoiler mounted below the air intake might be the answer to most issues.

I might try that this weekend........Where is my black plastic sheet?

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Post by scimjim » Fri Jun 28, 2019 10:40 am

That’s why the dolomite spoiler was so popular in the 80/90s - Don Pither also made one that looked really nice IIRC.


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Post by Rev Light » Fri Jun 28, 2019 11:25 am

Shouldn't think you easily find one now.


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Post by CNHSS1 » Fri Jun 28, 2019 1:46 pm

Sealing the flow paths makes a huge difference. Wherever the air enters the engine should really be ducted to the rad core, sealed with foam sponge to the end tanks, so that no air car escape, has to go through the core. This alone would cure any over heating issues, although I realise may not look factory or be as practical as original. At speed, the air flow will take path of least resistance, and that means it will move around the core, or even turn back, and just 'churn' in front of the rad, rather than going through it.
If you do decide to duct, another tip is entry aperture for the air should be smaller (rule of thumb 35-40% of rad core area). This allows the air to slow (its expanding to full the greater volume, so has longer (relatively) to pass over the core, allowing the airflow to extract more heat from the rad and its water :)


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RIP Batmobile, await the Rise of Dark Knight 8)
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