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MG Midget and Sprite Technical - Engine bay heat extraction

Hi, off the back of the carb fuel evaporation thread where I mentioned about a heat-shield extension I have also been thinking about getting rid of unwanted heat in the engine bay.

Would it be worth fitting a fan onto the triangular hole that leads from the engine bay into the wheel arch to extract heat from the manifold area and draw it away from the carb.

I realise that the fan would only be approx. 4" in diameter and have to stand up to a lot of heat from the manifold but do you think its worth looking into or would it not extract enough heat?

I thought it could be wired in with the Kenlowe fan stat so would switch on in traffic when it would be needed.

This may have been looked into before but I often have these crazy ideas and call upon the more technically minded to steer me in the right direction!!

Thanks
Mark
Mark Whitmore

Probably not... though ive thought about it

The problem is heat rises does not fall, and the heat still has no where to go once it escapes the triangle hole except back to the engine bay ares

It might be worth looking into drilling out a large hole in the wheel well and venting

The ideal spot is just below the wing curve on the flat side but the whole needs to be a depression, if its just holes drilled into the wing that wont work because the moving air past the holes will act as a shild and hold the heat in... think air plane wings

The next option is a vertical cut and bend out at the A post just before the door

But agian the 3 primary objections....

1 form vs function, does it look good and is it funtional

2. Is it doable... to make it look good is going to take alot of work and craftsman ship and will need to be hand crafted so it could get expensive quick

3. Stamina... how will this perform over time, will it rust out in a year, how funtional will it be and is it worth the cost for the performance, does getting away from orgianlity acceptable, and what about a cold engine bay during the cold weather

I hope that helps...

If I could find those stick fake vents inbthe correct shape and conservitive appearance ive thiught maybe drilling those out and applying

The oval shape I think looks the best

Prop
Prop and the Blackhole Midget

i did some investigation of this about 2 years ago, i actually measured engine bay temps at different places during a typical drive (for me anyway). Search on my thread "science warning" for an exciting read ;). Where i live it rarely falls below 30C ambient and is normally about 34.

I fitted a bonnet vent which is an intercooler scoop from a toyota pickup. This mainly was to give me a bulge to enable me to fit an air filter on top of my downdraught carb, but as you can see from the pic it give a large opening for air to escape.

I also fitted some stick on side vents, behind these is a 5"x 2"hole, i'm not sure how effective these are...
I got these from car builder solutions
http://www.carbuildersolutions.com/uk/self-adhesive-moulded-abs-bonnet-vents-gloss-black
worth while to have a look through their catalogue they have some interesting stuff.

However, from my investigations , when you are actually moving the underbonnet temp is generally ok, its only when you stop then it rises quickly, trouble is the hot air from the radiator fan goes into the engine bay making it hotter.
I tried setting up a switch to reverse the polarity on my electric radiator fan so that then stationary or in heavy traffic the fan would run backwards and push air out of the engine bay throught the radiator and out of the grille.
This had by far the biggest effect on reducing engine bay temps.as it pulls cool air from outside through the engine bay and out through the radiator.

having said all that, i now run with just a large heat shield and the vents and it goes ok...also considering fabricating a cool air pipe to the carb, that should also help keep it cool.



Andy Phillips (frankenfrog)

Andy, I like the reverse fan idea. I'm tempted by side/wing vents just because they look so good but really that's not a reason for doing it. I think what's needed for my 1500 is an air outlet on the bonnet just behind the radiator and another above the exhaust. The main problem is getting them to look right.
Nick Nakorn

If I had a Mkiii sprite/Mkiii midget or newer I would go for the louvred bonnet as can be seen in Daniels book. I have a spare bonnet and my friend has a midget and likes TIG welding and I have a source of ready louvred flat panels......watch this space (but don't hold your breath as it's a long way down a long list!)
Andy Phillips (frankenfrog)

Hi thanks for the replies so far. I don't really want to cut into the body work so kind off stuck with working with what's there already.

Just thinking that if the hot air when stationary gets trapped under the bonnet due to heat rising wouldn't sucking air out (from both sides if necessary) cause more flow of air and keep the engine bay cooler?

"The problem is heat rises does not fall, and the heat still has no where to go once it escapes the triangle hole except back to the engine bay ares"

I appreciate that heat will rise but if its pulled out by a fan then surely its got to help? Also as the air exits through the triangular hole it will be venting into the front wheel arch not back into the engine bay.

My other concern is whether the fan would stand up to the heat of being 6-7 inches from a hot downpipe. The car is a fair weather car so rain shouldn't be too much of a problem.

Thanks
Mark
Mark Whitmore

Mark, I also thought about this sort of solution (and I bet lots of others too ) . The triangle holes are quite low down so sucking air through them unless in large volume wouldn't make much difference to the hot air further up. A better way may be to duct the hot air from the radiator directly to the triangle holes then it stops the hot air going into the engine bay in the first place.
Andy Phillips (frankenfrog)

Technically heat can be transferred in 3 ways, conduction, convection, and radiation. Only convective heat transfer rises due to the hot air being less dense than cold air. Radiation and conduction are omnidirectional.
David Billington

Here is a thought... a stupid easy one, but a thought

Why not 2 bonnets ???

One for the 10 months that we dont need to vent the hot air and another radically modified bonnet for the 2 month we do need to vent the hot air ...ive always thought the reverse hoop scoop is the best way, because it can be vented towards the windshild and it can be designed to create a low depression area to actually suck the hot air out...it would just be a matter of changing the bonnets fir the appropiate condition

For missouri its really just july and augest sometimes its june that are the harshiest times of summer

For the usa... with sissor hinges its easy to un- and re- install the bonnet

Hmmm thats not a bad thought...just have to store the bonnet out of the way

Ive often thought about a 2 rear bonnet set up, one with the luggage rack and one with out

Infact... I could make the heated summer bonnet out of fiberglass for lighter weight and even better heat dispenstaion

Instead of nuts ... I could use wing nuts for easier removal and installation

That would sure be easier and cheaper to make then dealing with a permanent solution to the wings

Prop
Prop and the Blackhole Midget

Following on my last thought....

What about a clear plexy glass lid insert in lay that can be installed into the bonnet that can be hinged.at.the front and open at the back that way you can see into the engine bay without opening the bonnet lid

Prop
Prop and the Blackhole Midget

How about turning the problem on it's head?

Mount the bonnet, UNDER the engine.

Problem sol-ved. As inspector Clouseau might have said.

http://www.youtube.com/watch?v=FfPsULW-wYc Watch from 1 min.40 sec, or better still watch the whole thing. :).

And you might as well watch this too. :)

http://www.youtube.com/watch?v=gF2WO-JZ0WY
Lawrence Slater

The pink panther...haha, classic great stuff

To bad they dont know how to make film like that anymore...those where good days

Prop
Prop and the Blackhole Midget

If you take a look in the MGA archives, there was a lot of work and experimentation with this idea. They used bilge fans. Probably searching with the work "bilge" will get you there.

Charley
C R Huff

I love the look of the big healy 3000 side vents, but good grief there expensive, and to make them your self plus make them look good I havent figured out... but that little triangle in the wing sure looks great

Prop
Prop and the Blackhole Midget

Here is an option ive been kicking around for some time....it should work, but not sure how effective as the vent is in the wrong place

I dont think it would be to hard to do esp with angled aluminum and 2 part epoxy weld



http://www.youtube.com/watch?v=00uhspBYjtE&feature=youtube_gdata_player

Prop
Prop and the Blackhole Midget

Here is an option ive been kicking around for some time....it should work, but not sure how effective as the vent is in the wrong place

I dont think it would be to hard to do esp with angled aluminum and 2 part epoxy weld

Prop
Prop and the Blackhole Midget

interesting site and pictures
http://www.omniautos.force9.co.uk/sprite/m_flip.htm
Andy Phillips (frankenfrog)

Interesting that Andy. Esp' where he comments, ---

Air comes in through the front then through the radiator, it swirls around the engine and exhaust and looks for a way out. ----- "


" ==== Or through the transmission tunnel which is ok but too much and it will end in the cockpit (blowing through the gear stick gatter, ===== "

When I still had the 4 speed g/box, I came to the conclusion that one reason they don't last too long, is that the g/box oil gets way too hot, turns to little more than the consistancy of water, and the gears/bearings can't cope.
Lawrence Slater

This thread was discussed between 19/07/2014 and 21/07/2014

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