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MG Midget and Sprite Technical - Air scoop

Hi Lads, in a previous thread on overheating I postulated the use of an "air scoop/dam" to force more air through,voile, here it is. OK its somewhat agricultural but it is experimental after all. Haven't had a hot enough day to test it yet, keep you posted. Cheers Rod

R W Bowers

Hi Rod, i think it looks quite good.
I'm very interested, let me know how it goes

Andy Phillips (frankenfrog)

Nice... that should do the job, and it looks great

Any ideas on how to get the hot air OUT of the engine bay and make it look good doing it?

Prop and the Blackhole Midget

How about this?

I'll just go and put my coat on :)


Peter Burgess Tuning

Hi Rod,

I'm sure that scoop will help as it's in an area where a lot of cooling air can get in

I don't know but I would have thought that the scoop would be even more effective with the back edge following the bottom of the aperture by either having a straight bottom or the back edge being straight and the front edge flared out perhaps

I also wonder about turbulence with some of the air getting through the apertures cleanly whilst some might be rebounding off the metal(?)

perhaps bringing the bottom edge up in the middle to create a stretched w shape would help with airflow and (minutely) drag on car (or perhaps I'm over thinking this)

you seem to have a lot of set screw fixings at the top what are they holding?
Nigel Atkins

took me a good few seconds to see the driver
Nigel Atkins

Wish I could get my 1500 warm enough to heat my cabin this winter. I blame the system flushing advice Nigel gave me ;-)
Dave Squire 1500

perhaps I should have supervised you with a cattle prod to make sure you didn't stray from advice
Nigel Atkins

Aerodynamics is certainly a strange art. Things that look like they will work, don't, and unlikely shapes can be very streamlined.

Rod, I think you now need to do some airflow testing. You lie facing forward on the bonnet, head hanging over the front bumper, cigar ready lit. Then blow smoke infront of the scoop whist a trusted friend drives the car at various speeds, 20, 40, 60 and scream speed.
Guy W

good point about speed, you probably want it to work well below about 40mph and above about (?70) 80 mph

it could work differently at different speeds

aerodynamics are very complicated as seen on Speed with Guy Martin where he cycled at 112 mph with the help of being close to an adapted lorry that benefited from two days of computer calculating the aerodynamics required for speed and safety

my car developed a whistle and the only difference I can think of is an uprated ARB
Nigel Atkins

I thought it's the lack of hot air getting out, not the cold air getting in that's the problem. Surely airflow won't increase much unless it can get out as easily. Much the same as the inlet/exhaust balance. Bigger carbs need a more freely flowing exhaust.
Lawrence Slater

That's why overheating just isn't a problem in "Gaps"

G Lazarus

I think Rod is just dealing with getting cooling air to the rad at the moment, at lower speeds and stationary if the car is too warm he might need or want to look at getting the warm air out by putting holes in
Nigel Atkins

just reread my last post

I wasn't suggesting that holes are the same as gaps just that on Rod's car he can't get the same gaps as Gary's car
Nigel Atkins

Lawrence makes the very point I would make, only he made it first (on this thread...).

A midget owner who works at an F1 team, designed and made some very neat, and I guess extremly efficient, vents to let air out of the engine bay. He did this I guess, because he correctly identified plenty of air/enough air gets into the engine bay but not enough can leave fast enough, and even then under pressure (via the transmission tunnel).

Daniel Stapleton

to get the hot air out of your engine compartment you could use the bonnet louvres as fitted to the old Astra GTE.And the would look good,However living in Australia I would just remove the bonnet.

Sorry danial and lawerance....

Im the 1st to mention heat excavation... I just said it very nicely

#### Nice... that should do the job, and it looks great

Any ideas on how to get the hot air OUT of the engine bay and make it look good doing it? ####

NOW bow before me you saxon dogs and worship me


Prop and the Blackhole Midget

All kidding and stroking my ego aside

I saw some of those oval shaped faux stick on heat vents but over sized and look nice with the correct aero disign seriously considering cutting out the fake screen, converting to some loose mesh and installing them along the top.side of the wing...theres 3 per side (6 vents in total) and looks like a hole of 2 - 3 sq inches so we are talking 12 to 18 inches of venting out the wings

Ive got a photo somewhere...give me a bit to look it up


Prop and the Blackhole Midget

Ive got a fast photo in one of my mg movies... the photo is on my laptop I fear

But look at the blue midget at around can just make them out on the upper sides of the wing

Yepp... I made the film, im in the blacket helment at the beginning loosing control in the green that was a long time ago

Prop and the Blackhole Midget

I'd suggest you move your number plate up vertically to get rid of the overhanging lip below the bumper. On the inlet side of the radiator you need to encourage laminar flow and minimise turbulence.
I've always fancied encouraging air out the engine bay through the triangular hole above the chassis rail into the wheel arch. The streaks of mud seem to suggest that its quite a low pressure area.
This characteristic could be enhanced by a lip on the leading edge of the arch or even wing vents on the vertical faces.
Don't put vents on the tops of the wings... many broken windscreens during development of TVRs attest to the amount of debris that gets thrown onto the screen if they are opened up!
TVR's mostly left the factory with them blanked off, but a few owners have opened them up and then meshed them over.
G Waite

if the number plate is moved up wouldn't it then just obstruct the aperture above the bumper
Nigel Atkins

Hi Lads thanks for all the advice, geting the air out is the next step I'm sure so back to nice looking vents not on the top of the wing of course but at the sides. Nigel the number plate is a problem no matter where it goes it blocks the air, tampering is not permitted but perhaps a little judicious bending of the top and bottom lips will improve its dubious aerodynamic proprerties. Incidently this scoop is made of plastic garden edging, really easy to heat form, a coat of stone chip is next. BTW, the screws and large washers hold the rubber bumper cover on.
R W Bowers

yes I noticed the bend in the number plate

has the testing started/
Nigel Atkins

Testing done last evening ambient 34 celsius, slight improvement say 1 degree drop from running at 90 down to 89 celsius, fan sweitches in at 85. So fan runs all the time, the car is not overheating really its the switch is too low , probably stick in a 90 switch. Next step side vents.
R W Bowers

I've not been following this since I posted, so I missed,

Daniel, -- "Lawrence makes the very point I would make, only he made it first (on this thread...). "

And of course Prop, -- "Any ideas on how to get the hot air OUT of the engine bay and make it look good doing it? ####" -- "NOW bow before me you saxon dogs and worship me "

LOL. And it's not even half way through January yet. :)
Lawrence Slater

how about trying a closer fit to the apertures to see if that gives improvement
Nigel Atkins

Hi Rod,
I fitted this fan switch,.. on at 87, off at 82.
if you look at the catalogue these people have a large selection.
I also added side vents and a bonnet vent and, most effectively i feel, ducting in front of the radiator.
The ducting should do a similar job as you are trying to achieve with your scoop.

Now my engine runs at about 80 degs when on the move, but fan comes on if i slow down from a higher speed and almost immediately when i stop.

I tried an experiment with my number plate, it sits under the grill (frogeye), i tried angling it forwards so that it would act like a scoop and, in theory, direct more air in to the radiator.
I found it had the opposite effect, after maybe 5 miles of driving the engine was definately as much as 5 degs hotter, so i twisted the number plate back so that it faces towards the ground as about 45 degs and the engine temp went down.
I put this down to the extra air scooped up and being forced upwards from the number plate across the grill interfering with the straight-on airflow coming from in front of the grill, the extra turbulance causing a net reduction in airflow.

Another thing worth looking at is your thermostat,
i fitted a 'tropical spec' 79 deg one. If your fan switch and thermostat are too close together (as i suspect mine are) then they might fight against each other with the thermostat reducing the flow at the same time the fan is trying to cool the water...

i also drilled two 3mm holes through my thermostat flange just to make sure there is always some circulation, on my datsun engine there dosent seem to be any bypass as std, but i understand on Austin A series there is a bypass hose that does this function...

Andy Phillips (frankenfrog)

also.... i fitted these vents

i need to do some testing to see how effective they actually are but they allowed me to cut a 4" x 2" hole in each side of my one piece bonnet....

Andy Phillips (frankenfrog)

is it just the photo angle or is it that your windscreen is shorter or perhaps that the black framing gives the look of your car being slightly beefier and higher off the ground
Nigel Atkins

must be the camera angle, though it is slightly higher i think due to the light weight of the all fibreglass body and lighter datsun engine.... another shot below...
Its definitely higher than it should be at the back...maybe the tyres distort it slightly too, 175/70 x 13...

Andy Phillips (frankenfrog)

just re-read my last but one post.....

I said...
"Another thing worth looking at is your thermostat,
i fitted a 'tropical spec' 79 deg one. If your fan switch and thermostat are too close together (as i suspect mine are) then they might fight against each other with the thermostat reducing the flow at the same time the fan is trying to cool the water..."

What i meant was close together in terms of temperature operation rather than being near each other physically....
Andy Phillips (frankenfrog)

just found this diagram, which is another way to look at what you are trying to achieve...

At risk of having to kiss the feet of Prop, Daniel and Lawrence....

Instead of looking at using the air scoop as a scoop to force more air in the front, why not re-engineer it slightly to become a splitter which will reduce the air pressure underneath the car and enable the air to get out from under the bonnet better...

Andy Phillips (frankenfrog)

And yet, the air passing over an airfoil moves faster, creating a low pressure area that keeps airplanes in the air and necessitates all sorts of aero aids on Countachs and such to keep them on the ground... So that diagram is a little confusing, as it seems to depict the opposite.

Back to the topic, I think Andy's fitment of vents high on the wings is closer to a real solution. I think they'd be better yet if they were configured as extractors of some sort, thus providing a more active airflow through the engine bay... Sort of like reversed scoops, so air passing over them would generate a localized low-pressure zone that would serve to draw air from inside.

Gryf Ketcherside

yep it's a complex problem. Another thing is the issue of the radiator itself being unable to transfer enough heat because it is too small, hence the many alloy rads being offered for sale.
Andy have you got an alloy rad? Also the minimum height we are allowed to have above the road surface is 6 inches (150mm) so I'm not sure if a splitter would actually work
Cheers Rod
R W Bowers

Yes, i have a nice alloy rad that i picked up from the breakers, it came with an electric fan and cowling.
Ive never had a proper original radiator so not sure how it compares, but i think this one is bigger as i have had to angle it backwards to get it to fit.
Andy Phillips (frankenfrog)

To follow on gryfs comment

If the vent is flat along the surface of the wing it wont suck out much air from the engine bay... infact the engine bay air will be held in

The vent needs a hump, or a bow... like an airplane wing to create a low pressure depression area over the vent thus alowing the engine bay air to escape at speed.

Prop and the Blackhole Midget

rad, itís about design and size as much as materials used

for the 1500 Iíve seen a wider rad from another classic Triumph suggested (sorry canít remember which) or more modern rads from scrap yard cars

a couple of quotes from a previous thread about alloy rads -

Daniel Thirteen-Twelve, United Kingdom
>>An aluminium radiator isn't necessarily more efficient as a heat exchanger than copper brass and in fact is less so like for like, and any radiator shop should now that. However, most aluminium classic radiators are more efficient than copper brass because of the core design whether more efficient in itself or more rows or thickness or whatever.<<

S Overy, Northamptonshire, United Kingdom
>>Does it need to look period? If not, a lot of the kit car guys use modern plastic and alloy rads from small engined cars. They're dead cheap, as little as £40, widely available and come in a huge range of inlet/outlet configurations.<<

another thing to consider is that perhaps you could have an engine thatís running warmer due to a change of coolant required (I saw that your car stood unused for a couple of years) to renew the anti-corrosion and lubricant elements that go off before the antifreeze element - and/or crud that needs cleaning out of the cooling system particularly the engine block (often not drained at changes/flushes/cleaning Ė engine running warmer due to timing or weaker fuel mixture Ė just thoughts
Nigel Atkins

Hi Nigel, coolant is pure water with a corrosion inhibitor (no glycol) and the system is thoroughly clean, no rust, newish rad, and pump. Timing checked at 10 degrees BTDC (before test run) running 98 octane. Mixture may be an issue. Will post a picture of a plug for you gurus to analyse under a new thread. Cheers
R W Bowers

for the plugs photo do bear in mind the variances you get from digital photos and monitors and monitor settings only extremes really show up well
Nigel Atkins

Re using pure water. I copy pasted this as it says what I was going to compose.

"The boiling point of Clean water(H20) is 100 degrees Celsius or 212f, With all the salts like Magnesium, calcium and chlorine(in tap water) you can have it boil at less than 85 celcius. These salts deposit after after long use of water( same whitish stuff you seee at the bottom of kettles)and the deposits clog your cooling lines and stresses the water pump.
As water boils it expands and also releases gases dissolved in it.Gas expansion due to heat is way more than liquid expansion. Your car cooling system is a close system and this expansion causes pressure build up. At some point some thing has to give way, either the water pump, hose, or radiator.

Coolant is made up of mainly TEG ( Tri ethylene glycol) and silicates. TEG has a boiling point above 320f and low expansion due to heat."

You're better with a mix. It may well cure your overheating problem on it's own.
Lawrence Slater

I did think about putting something about water but Iíve no idea what the water Rod gets is like

plus thereís the info/debate from the MGA forum archives on a thread called ĎCoolant temperatureí

the water that comes out of my taps is hard water and Iíve no idea how much (if any) chloride it contains so there are local differences to be taken into consideration

I would stress the scrapping out the engine block (David Squire is a big fan of it) and the racers even suggest taking the core plugs out for a scraping and clean

some people who don't follow the refill instructions in the Driver's Handbook do seem to be able to get 'hotspots' in the engine
Nigel Atkins


That sounds like BS to me that dissolved minerals can drop the boiling point that much in tap water, I wouldn't want to be drinking it if the levels were that high. Also magnesium and calcium salts in water should increase the boiling point, not sure what form the chlorine is in though.

I've used my local tap water, which is hard, to calibrate a temperature controller by checking the melting and boiling point and checked against another couple of thermocouples and the results were spot on 0C and 100C within a degree which is what I would expect given measuring tolerances. No compensation for altitude was made as I live at maybe 200m or less above sea level.
David Billington

the water came out of my water tanks, no dissolved metal salts, flouride, chlorine etc at all (maybe some bird poo). Didn't we have a debate on gycol's heat transmission being worse than pure water? I think you'll find that, yes it boils at a higher temp but doesn't transmit heat as well. HTH
R W Bowers

I don't know how accurate the stuff is about the salts and crap, but plain water boils at a lower temp than a 50-50 mix antifreeze. And when water boils it becomes gaseous and thus less of a coolant. Or at least that's what I've been thinking for yonks. :).
Lawrence Slater


It depends on the details of the system, have a look at
David Billington

But does a Spridget employ evaporative cooling?

Meanwhile, this is an interesting discussion.

Heat transfer - water vs. 50/50 water/antifreeze.
Lawrence Slater


No it doesn't but it illustrates that a small amount of localised vapourisation is not necessarily a bad thing in a healthy cooling system due to the amount of energy it absorbs.

I found this while looking for the propylene glycol data and posted it on the waterless coolant thread, see page 4,%20PG%20fluids.pdf

Likely that'll have to be copied and pasted into the URL bar.
David Billington

" OK its somewhat agricultural "

Not if you paint it black...

I removed the vertical center column between the holes in the front valence of my 1500. Maybe increased the opening 10% but that 10% is dead-center facing on the oil cooler and radiator.


Richard Reeves

Ok Richard so you maybe have similar heat to us so your experience is valuable. Presently it's 41 degrees C here and is staying there for 4 days straight. drops to 28 at night.
I'm not game to cut metal out of this area until I decide whether or not to put chrome bumpers on in which case the look of the front will be not standard. With the rubber bumpers off I expect greater airflow thru the new ally rad (maybe)
R W Bowers

For what it's worth, of the things I've done to keep the car cool in the summer heat I believe the oil cooler far and away had the greatest positive effect. Radiator is standard.

Trimmed front valence
External carb air supply
Carb jetted a bit rich
Catalyst removed
Oil cooler installed

Once warmed up the thermostat barely wavers, regardless of the heat outside or driving conditions. Problem solved.

Richard Reeves

Hi Richard all this has been done
Oil cooler fitted (with thermostat)
Original air cleaner with external air fed via plastic tubes
No catalyst

Mixture may be a bit lean, and I'm not going to trim the "valance" yet. Too bloody hot to drive anyway. Cheers
R W Bowers

maybe slightly off topic, but have a look at this thread on the mgexp site,2442986

lots of nice pics, but look at the last page with the nice MGB bonnet and the chrome vents... very nice....

Record low temps in Thailand this week, got down to 13 degs C at my house, my car loves the cooler air and definite performance improvement due to 20 degs lower air temp than normal....

Andy Phillips (frankenfrog)

Yep noted and thanks Andy, some cooler air into the carbies couldn't hurt Cheers Rod
R W Bowers

This thread was discussed between 06/01/2014 and 22/01/2014

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.