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Hamish

Bonnet and louvres

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Hi folks. 
thought I would share my next small task of putting louvres in my 3a bonnet. 
it’s a bid to get some heat out of the engine bay. Especially when queuing up for sprint and hillclimb runs. 
also it can’t be a racer without louvres :ph34r:

this is the bonnet after blasting. 
will be primed before louvring hopefully louvres in this bonnet and not a welded in plate. 

3EE318E1-AD09-4508-8299-9F275C3E7DFA.jpeg

7404A6FA-AC5D-4F02-8276-A3EEB746C5ED.jpeg

B7C272F3-A0E7-40EC-A4F0-6AA2C5F2AD0C.jpeg

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Nice bonnet H. Now all you need to do is make sure the louvres are in the right place to work. I have no experience in this but, before you make the decision to cut make sure you know what works and what doesn't. Too  close the the windscreen is a big fail apparently......wheres Mick he will explain? :D

Iain

 

Edited by iain

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Yes, there is a high pressure area in front of the screen that can prevent air escaping from the engine bay. However, the TR2 bonnet had 4 rather than 2 vents towards the screen. But louvres do look good Hamish!

My memory may be playing tricks, but on MGAs I think there were vents in the front wheel arches to aid air flow from the engine bat area when on the move. Any thoughts?

Mick will no do doubt list other venting options on a racing 3A.

Miles

Edited by MilesA

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Hi Hamish,

As Ian says you have to beware of the high pressure area extending forwards from the base of the windscreen, that's why car manufacturers fit heater inlet vents there, they get fed with a pressured air feed into the heater which helps flow out.

The old trick with the sidescreen cars of spacing the bonnet hinge fitments upwards by maybe 1 inch does help when the car is stationary allowing hot air to seep out and the upward tilt of the bonnet at the rear feeds the air rearwards to it. When the car is in use that outward going air is compromised by the high pressure area from the windscreen which battles with it trying to stuff it back in !

If you are racing with aeroscreens (can't remember) that obviously compromises the now missing windscreen high pressures area swinging it across to one side and reducing it's forward spread (lower screen probably at a more aggressive angle) which will help. As regards the louvres I would "eye up" your existing bonnet fitment and have them fitted just inside the pressline with the rear edge of them around 8" from the across car ridge which has your 2 slots in it. I have an excellent 4 slot bonnet for sale if you or anybody else wants it to help the engine compartment cooling.

Underneath the car if you fit an engine compartment undertray from front scuttle rearwards that will help the airflow greatly and if you finish it a couple of inches in front of the rear of engine compartment firewall and shape the end downwards it will cause a low pressure area and help extract the hot engine compartment air out underneath and rearwards.

Mick Richards 

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planning on something like this. (excuse the freehand mouse lines.)

 

according to my wife prime numbers are lucky and a designer friend suggested that even number of Louvres wouldn't be attractive to the eye ?

hence the 7, 5, 7 arrangement

i tend to sprint with Aeroscreens 

Tr bonnet_LI.jpg

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Yeah, that’s something like.
If it was mine I’d be looking to position them maybe a couple of inches forward from your markings, making sure you don’t catch any residue of high pressure. But not a million miles off, the TR7 high pressure stretched forward 15” from the screen !

Mick Richards

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So this set wont be helping then? As fitted to Martin Jays car. No I didnt fit them, the bonnet was already supplied like it, I too have a 4 slot internal bonnet lock bonnet if anyone wants to come and collect it (£50)

Stuart.

 

photo1416.jpg

Edited by stuart

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Yes we used to pack the rear of the hinge up say 10mm for added air flow over the engine. I no longer do this and haven't found any issues.

Just think with a major engine fire the flames would come straight back at you through that larger 1" gap. And with areo's not nice.

My 250 has vents directly over the weber trumpets to aid airflow. if it rains ? well water injection ;)

Roy

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1 hour ago, stuart said:

So this set wont be helping then? As fitted to Martin Jays car. No I didnt fit them, the bonnet was already supplied like it, I too have a 4 slot internal bonnet lock bonnet if anyone wants to come and collect it (£50)

Stuart.

 

photo1416.jpg

Hi Stuart,

Oh yes those slots will be helping.

The slots at the front and into the middle are in a major low pressure area, the air sweeping up from the front apron turbulates (I think I just made that word up :o ) as it changes direction from a 45 degree up to a linear flow along the bonnet extracting the hot area behind the radiator as the air is pushed through. The slots along the bonnet continue and extract heat from the headers before the rear slot section becomes compromised by any high pressure from the screen, but those slots at the rear will help remove heat when the car is standing.

Mick Richards 

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6 hours ago, stuart said:

So this set wont be helping then? As fitted to Martin Jays car. No I didnt fit them, the bonnet was already supplied like it, I too have a 4 slot internal bonnet lock bonnet if anyone wants to come and collect it (£50)

Stuart.

 

photo1416.jpg

I'd love to have a 4 vent bonnet for my short door TR2 which has had a two vent bonnet since I bought it. Unfortunately it is a bit difficult to put it in a suitcase to Australia.

 

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10 hours ago, Hamish said:

According to my wife prime numbers are lucky

Ergo, more prime numbers! :)

Here ya go H . . . just for kicks, some variations on a theme. 

7 - 5 - 7

727462717_TRlouver7_5_7.thumb.jpg.d9483a24140b2de4391cf7027bb54ea9.jpg

11 - 7 - 11

1449963712_TRlouver11_7_11.thumb.jpg.04aebb3e7b359635df06687ad97f4bfe.jpg

13 - 11 - 13

1048326323_TRlouver13_11_13.thumb.jpg.455afd599acb8813aebee82203ea3cb6.jpg

Cheers, Deggers

Edited by Deggers

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Get this is me being a fuddy duddy, but would nt this be more plaesing to the eye

with the longer line in teh centre,

kind of arrow head fashion?

John.

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8 hours ago, Deggers said:

Ergo, more prime numbers! :)

Here ya go H . . . just for kicks, some variations on a theme. 

7 - 5 - 7

727462717_TRlouver7_5_7.thumb.jpg.d9483a24140b2de4391cf7027bb54ea9.jpg

11 - 7 - 11

1449963712_TRlouver11_7_11.thumb.jpg.04aebb3e7b359635df06687ad97f4bfe.jpg

13 - 11 - 13

1048326323_TRlouver13_11_13.thumb.jpg.455afd599acb8813aebee82203ea3cb6.jpg

Cheers, Deggers

Nice work Deggars, the Tin man will hate you when H takes these to show him what he wants! :D

Iain

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Great work deggers thank you:D

 

I took my Louvre ideas from 33DNK at the NEC a while ago. 
I liked the layout

Iain

i thought I’d cut the slits with my dremel then tap out the louvres with hammer and a smooth rounded drift. 
it is winter after all. What else is there to do.

 

CFADF44D-D732-464A-A9F7-34769FD8BE67.jpeg

Edited by Hamish

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11 hours ago, John McCormack said:

I'd love to have a 4 vent bonnet for my short door TR2 which has had a two vent bonnet since I bought it. Unfortunately it is a bit difficult to put it in a suitcase to Australia.

 

There might also be objections to taking it as carry on too! This particular bonnet is for internal locks too.

Stuart.

 

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51 minutes ago, Hamish said:

Great work deggers thank you:D

 

I took my Louvre ideas from 33DNK at the NEC a while ago. 
I liked the layout

Iain

i thought I’d cut the slits with my dremel then tap out the louvres with hammer and a smooth rounded drift. 
it is winter after all. What else is there to do.

 

CFADF44D-D732-464A-A9F7-34769FD8BE67.jpeg

Good luck H ......I think your being very ambitious. 

Iain

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1 hour ago, iain said:

. . . the Tin man will hate you when H takes these to show him what he wants!

:D:D

Curious how they do such things, I've just had a quick squint on Youtube . . . and found this, from Classic Metal Shaping.co.uk. V interesting. 

Deggers

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That makes it look so easy.....I have a flypress if you need to borrow it H :lol:

Iain

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I thought that the original 4-slot bonnet on the TR2 was changed at some point to 2-slot because the inner pair of slots permitted rain to dribble over the battery - certainly did on one of my TR2s.

Ian Cornish

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54 minutes ago, Deggers said:

:D:D

Curious how they do such things, I've just had a quick squint on Youtube . . . and found this, from Classic Metal Shaping.co.uk. V interesting. 

Deggers

  that's just cheating

 

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A few years ago I went around the Morgan factory and there was a guy there punching louvres almost by hand at some speed. Obviously he is working on a standard panel shape and he had some kind of jig to provide a back stop (rather like the above video) but he seemed just eyeball the distance between the louvres.

Rgds Ian

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The 2 inner slots on the 4 slot bonnet were apparently deleted on the later TR2s because they

permitted engine compartment fumes to enter the passenger via the newly introduced scuttle vent.

So they appear to have had some effect on engine compartment venting!

Roger M-E

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